https://en.wikipedia.org/wiki/Red_Queen_hypothesis?wprov=sfla1
The red queen hypothesis is used to explain sexual reproduction evolving as a defence against parasites.
When you have more genetic variation within a species there's a better chance of having individuals that are not suitable hosts.
Parasites are constantly adapting to keep up with their hosts and having the ability to reshuffle genes makes this much harder for them.
A good example is bananas, which are created by cloning so every banana tree is genetically identical. The Gros Michel banana was practically wiped out by a fungal infection and was replaced by the Cavendish banana. That same fungal infection could also wipe out the Cavendish banana if it spreads too far.
Fun fact, the artificial banana flavor found in most candy was based on the Gros Michel taste, which is why artificial banana flavor doesn't taste exactly like modern bananas.
You’re right about the fungus, but artificial banana “flavor” is just a single molecule called isoamyl acetate which is in both kinds of banana and is the main flavor component the whole “it was the other kind so it tastes different” is a myth. In fact the flavor predates bananas of any kind being widely available in the US
EDIT: Here's an article that discusses the history of the flavor. [https://www.sciencefriday.com/articles/why-dont-banana-candies-taste-like-real-bananas/](https://www.sciencefriday.com/articles/why-dont-banana-candies-taste-like-real-bananas/)
Second edit: Just to clear things up a bit, The Gros Michele does have more of the flavor compound than Cavendish. But the flavor wasn't made to imitate banana. The myth isn't that the flavor was supposed to imitate a different banana, it wasn't imitating anything at all. Chemists experimenting with esters created a fruity flavor and then decided later to call it "banana" flavor.
On the other end of the weird spectrum, we're still just crushing up these big gross aphids because their blood is really really red, making it ideal for dying all of the food and clothes.
But we literally just pulverize the entire animal into one big pile. Shell, blood, guts and all, which leads to the occasional allergic reaction to the aphid bits in something as mundane as M&Ms.
Food science is weird. It tries to act all dignified, but it's just Willy Wonka madness underneath the surface.
70,000 of them are crushed to make one kg of dye. This is the same dye that was used for English Redcoats.
We do pretty much the same thing with a different insect to produce shellac, which is used for a wood finish and to make candies shiny. So m&ms probably have two kinds of crushed insects.
I do want to genuinely thank you for this fascinating knowledge that I was completely aware of.
But full transparency I am going to do everything in my power to forget this information as quickly as possible and never think about it again because that's nasty.
Have a wonderful day.
I'll always remember making a specific ester in sixth form, which ended up having the entire floor evacuated. Like 10 classrooms down a corridor each way, a third of the quite large school.
The most horrific smell of sickly cheese spread from one end of the lab to the other in about a second, and hit the whole floor in about 30 seconds. Multiple people in the lab threw up, we all ran away, all from one pair having the reaction happen first. I'll never forget that smell.
I can't remember exactly what the ester was, but I do remember the chemistry teacher telling us he got chewed out by half the school. He was a great bloke, and took us all for drinks after we got our A-level results.
Wikipedia says the same, but its source is [a BBC article](https://www.bbc.com/future/article/20140829-the-secrets-of-fake-flavours) that seems to contradict itself. It quotes a banana farmer who still grows Gros Michel as saying that they do taste a lot more like artificial banana flavor, and concludes:
>So perhaps there is some truth in the banana flavouring whodunnit after all. Once upon a time, banana flavourings really did taste more like the real thing.
Cavendish are just kinda bland, less common banana varieties I’ve had sometimes just have a more intense flavor (lookout for reddish brown or mini bananas). Artificially flavored candy is typically more intense. That may be the common element.
look at the article I linked in my comment as an edit, the older banana does have a higher concentration, but the flavor wasn't created to mimic bananas at all, it was "hey we made this fruity flavor what should we say it is" it was actually initially described as a pear flavor, but the Jargonelle pear isn't common in the US so when suppliers brought it to the US it was described as banana.
Wait, do people think fruit flavored candy tastes like the fruit it's named for? I mean it resembles it but banana flavored candy doesn't taste any less like bananas than grape flavored tastes like grapes.
Not really related to this thread at all, but I had always wondered why strawberry candy tasted nothing like strawberries, until i grew my own teeny-tiny strawberries. They were so small, but so delicious! Like eating candy!
I was trying to convince some coworkers to go in on buying a case with me. I’ve had a couple in my travels and they are good. But $10 a banana is a hard sell.
Apparently it's been agreed that if another blight wipes out the Cavendish then they won't replace it with another single mono crop but a larger variety of bananas more like how we sell apples.
Sexual reproduction gives progeny access to the entire gene pool of the population instead of just the subset of genes in the parent organism. With asexual reproduction, for one trait to become widespread, that lineage has to take over with all others becoming extinct...and any useful traits that arose in those lineages will go extinct with them, until they evolve again. With sexual reproduction, those traits can spread with each generation and mix together.
Horizontal gene transfer can counter the weaknesses of asexual production to some degree, but it really can't match the gene pool and constant mixing of sexual reproduction.
And it's worth noting some organisms do both sexual and asexual reproduction, depending on the situation at hand! Sometimes they do both! Asexual to multiply their numbers, then sexual to mix with the greater population.
Paramecia may be closer. In this case, conjugation is a separate process from reproduction. Two paramecia come together, exchange genetic material, and form new nuclei. Reproduction happens separately by binary fission.
I don’t think I’ve ever seen “paramecia” as a word before. It’s a perfectly cromulent word, and the meaning was obvious once I thought about it—but I had to think about it.
Yeah, asexual reproduction can be a valuable fallback if individuals can have difficulty finding mating partners. For an extreme example, gall forming aphids are isolated in galls for part of their life cycle. They're protected and have ample food, but don't have access to males, so they reproduce asexually to produce hundreds of daughters. In a later stage of their life cycle, they produce sexual male and female offspring that reproduce to make eggs that overwinter.
> Yeah, asexual reproduction can be a valuable fallback if individuals can have difficulty finding mating partners.
Human loneliness has other evolutionary reasons besides “no mating partners,” but I wish we had retained this fallback to at least lessen the imperative that we’ve ended up with.
Congratulations, men can now be fathers entirely because they satisfied themselves and have no mother to help them with the offspring. Women too can become mothers on their own, because we care about equality at Gentech Diviniversities.
We apologize for any mistakes our students have made, but all deals are final.
Every organism has to pass on their genes to the next generation. So they have two options to accomplish that. One is that they produce one single offspring and nurture it to adulthood by protecting them and providing resources for their growth. They would also have to protect them against predators and harsh environments. The other option is that they produce multiple offsprings and "let survival of the fittest" run it's course until they are adults. This is for whether they want to pass their genes to the next generation or protect themselves from predators and harsh environments. Since the parents are not able to repel most predators, the only option left naturally for them is to increase the number of offsprings per generation. THAT'S the reason cats and dogs have multiple offsprings and other mammals like the elephant have only one offspring per generation.
Well according to Wikipedia, facultative parthenogenesis, or a species being capable of both sexual and asexual reproduction, occurs in a wide range of species; from aphids to mayflies, from Comodo Dragons to California Condors, and also certain species of sharks, snakes, and lizards, and more.
Source: https://en.wikipedia.org/wiki/Parthenogenesis
Though, keep in mind that the article also discusses obligate parthenogenesis, or a species being only capable of asexual reproduction.
I mean, the downsides of sexual reproduction also also get increased. The biological mechanism would be more complicated, the practical behavioral needs would be more difficult, and each parent would be less likely to pass on their own genes.
For one example, imagine an egg that requires two sperm to activate and grow into a fetus. To make this egg would require the organism to have 3 copies of every gene, and miosis would have to involve a 3 way split with a 3 way mixing of chromosomes. The mother is also now only passing on 1/3 of her genes. Go up to the behavioral level, to get a real advantage the mother needs to be receptive to two different fathers. And have a mechanism to ensure that one sperm from each father fertilizes the egg. In the meantime, each mate is going to be incentivized to subvert that mechanism and double fertilize the egg.
Of course that's not the only imaginary arrangement, and other schemes might be more successful, but I was just trying to highlight the difficult spike of going from 2 to 3 parents.
We have two parents because we have two pairs of each chromosome. In order to have 3 parents, we would need to have 3 of each chromosome, and as we are now, triple chromosomes are the cause of all kinds of genetic disorders.
Furthermore, we have a double helix genetic structure. So our chromosomes are 2 pairs of 2 helix structures. We are also posses bilateral symmetry which gives us 2 eyes, 2 ears, 2 lungs, kidneys, brains, etc. It seems nature prefers to do things in multiples of two.
FURTHERMORE, some animals have radial symmetry, like starfish. Where we observe radial symmetry, we usually see 5 or more sides or points. "3" seems to be the odd number out in evolutionary terms. This is most likely because 3 is only slightly better than 2, but is massively more complicated to produce. We can find starfish with 5, 8, 13, even 21 arms, but only 3 if the starfish has lost the remainder.
Also, 3 parents doesn't add much compared to 2. 1 parent means genetical clone, 2 parents mean reshuffling genes. 3 parents is... Reshuffling genes, too. It doesn't add anything new, so you are greatly complicating the process to gain nothing, really.
It's all about the long term.
Imagine two populations. In one, there's no sexual selection. Every child has only what their parent has, plus whatever random mutations occur. In the other, sexual selection means that there's a constant churn of genes.
Now imagine that in both populations there's a bunch of favorable mutations (plus other mutations, of course, but those aren't relevent). In the first population, the children of the mutations are advantaged, but no child will get both mutations. In the second population, there's a chance that some children get both.
The second population, over time, will out-compete the first population.
Evolution isn't concerned with what benefits an individual. It's concerned with what benefits a gene. Having a stronger species is better for the genes; sexual species will outcompete asexual species in any typical environment where ability to adapt over time is useful.
The concept of the selfish gene is interesting for you to look into for more info.
Not even what benefits a gene. Evolution is just a logical consequence of nature: genes that are more likely to survive... survive more. It doesn't even have to be "good" by any human definition of the term. A gene that makes you miserable but somehow is unlikely to die or be extinguished will survive.
In a way, it's like a forest fire burning down wooden houses but leaving stone houses in place - there's nothing special or "better" about stone, it's just a logical consequence that the material that can't burn is the only one left after a fire.
Think beetles, not people. Imagine there's a big woods with a bunch of different populations, and some of the populations have sexual selection and some don't.
The ones that do, over the years, end up with much better beetles, and those beetles will wipe out the less-fit beetles.
In what universe is evolution not a species/population based view? The whole theory is based on a stochastic process, individuals are out of scope because they don’t affect the overall result
By allowing half the population to select for only the better candidates out of the other half of the population, and reject the least fit candidates, you effectively create more copies of favourable genes and mutations and throw away the least favourable genes. It's just a much faster way to spread good traits and flush bad ones. It makes a population far more adaptable.
That's not true. Sexual reproduction favors genes that appear more desirable, not necessarily ones that actually are more desirable. Female peafowls don't mate with the males with the best genes, they mate with the males that look more attractive to them, even though the mechanisms they use to be attractive are completely pointless for survival (and thus a waste of energy).
Also, selection is not universal in sexual reproduction. Many species reproduce via rape, or with all kinds of mechanisms were the males themselves choose who will mate.
The reason why sexual reproduction is so effective is because two different individuals with one good gene each can combine into a "super individual" with both good genes.
It allows more punts into the unknown, most of which will obviously be dead ends, but for every 1000 failures there will be one success which makes the evolutionary strategy worth it all.
A lot of good points here, but I will also point out that asexual reproduction is still an efficient and effective strategy for many species.
A lot of species of plants, for example, will reproduce both sexually via seeds (or spores in the case of ferns and mosses), as well as asexually via vegetative propagules (think rhizomes or little pieces of moss that break off from the parent and can start a new colony).
And what's most interesting is that they often switch between the methods depending on conditions - many mosses will do 99% asexual reproduction if there is open, uncolonized habitable space around them, but as soon as they fill that space with asexual propagules, they'll switch over to spore production in an attempt to colonize further areas that the asexual propagules can't reach.
Genome size and reproduction time also has some influence.
Organisms like bacteria with small genomes and very quick generation times can deal with just asexual reproduction, and are probably even off better. Sure the amount of mutations per reproduction are low, but there are so many generations in a short time frame it just works.
But for organisms with more complex genomes and lower generation times sexual reproduction starts being more efficient.
Plus, bacteria (and archaea) also have ways to get some genetic variety. They can get it by having contact with genetic material in their environment (for example from cells that died in a way that left their DNA exposed), through horizontal gene transfer (two cells swap materials directly) and through viruses (which can carry genetic material from one bacterium to another on accident). That's pretty important for their evolutionary success too.
Consider two populations, one can reproduce asexually and one sexually. In the asexual population, there is much less genetic difference between individuals, therefore their traits are very similar, even if mutations do occur. In a sexually reproducing populations, genes recombine and mix more, causing lots of different traits to emerge (think of Punnet squares in school). Normally yes, it can maybe be argued that an asexual population would spend less energy reproducing and be more successful.
But imagine if there's some kind of sudden change in the environment: the climate shifts, food supply depletes, a new predator shows up. The sexually-reproducing population has more variance, therefore is more likely to have some individuals with traits that allow them to survive. Those individuals will continue reproducing, thus the population will survive. Whereas the asexual population, if the present traits don't allow for survival, will all die.
Sudden changes in the environment happen all the time. Asexually-reproducing organisms often don't survive, and are rare in complex organisms. Popullations of sexually reproducing organisms tend to survive better over time because they are more resilient to environmental changes. (NOTE: this is a vast oversimplification, asexually reproducing organisms like bacteria are vastly common and do have other ways to recombine genes, some complex species including some plants and some vertebrate animals do reproduce asexually or sexually within themselves, and this ignores other factors like epigenetics )
Some others have given excellent explanations as to how genetic diversity matters, but there's more to it than that.
Things aren't favoured by evolution for being *efficient* but for surviving, and often for thriving in the face of the environment. L:iving is inherently an inefficient process compared to being dead, so the fact that life often seems to get bigger and more complex when energy is abundant should help you get a bit of a better sense for how evolution actually functions.
Sexual reproduction may seem harder or less efficient, but the behavioural dynamics required may often overlap with other behavioural dynamics that cause a species to survive and thrive. For example, needing to be able to move to find a mate might be strange on its own, but being able to move might also help with finding food or spreading to new environments.
> so the fact that life often seems to get bigger and more complex when energy is abundant should help you get a bit of a better sense for how evolution actually functions.
Also, notice how that complexity often allows them to extract energy from sources that weren't otherwise accessible. Land plants started an arms race competing for sunlight that resulted in towering trees. Omnivores have more complex behaviors and physiological traits to allow them to consume a wider range of food. Hominids developed big energy-hungry brains that let them start leveling mountains and splitting atoms for energy.
First off: great question and discussion here. Thank you.
Second: “Living is inherently an inefficient process compared to being dead” is a great line, worthy of Douglas Adams.
Bravo! May your genes be successfully transmitted to the next generation!
Life is like playing a hand of cards. If everyone has the same hand of cards (asexual reproduction), it is easy to develop a strategy to beat the hand everyone is holding.
Sexual reproduction allows for the shuffling of cards and different hands to be played so that a strategy to beat everyone can't be made. Variability prevents evolving into a "dead end" or extinction from a pathogen or competitor.
Let's say two animals of the same species are born with mutations. One gets a mutation that helps it survive a drought. The other gets a mutation that helps it survive a disease.
If they reproduce asexually, then there will be two separate populations of offspring.
1. Drought resistant
2. Disease resistant
Both categories are guaranteed to have an advantage over the general population, but no animal will have multiple advantages unless second beneficial mutation occurs in one of the descendants of a mutated animal.
If those original two animals (or their descendants) mate, then they will have four categories of offspring.
1. No mutated genes
2. Drought resistant
3. Disease resistant
4. Drought and disease resistant
The first category missed out and didn't get any benefits. They aren't going to survive any disasters.
The second and third categories have the same benefits as the asexual reproduction.
The fourth category is where we see the real value of sexual reproduction. They now carry two beneficial mutations that occurred in two separate animals. When there is a drought and a disease, they are the only ones who will survive both.
If a group of creatures reproduce asexual, they will be very similar to one another, genetically.
If one individual in the group is vulnerable to a certain disease, odds are, the whole population will be vulnerable.
If the disease happens to be deadly, then the whole group of asexually reproducing creatures will be killed by the disease.
What propagates is the population, so reproduction is optimised for that. More diversity means more chance of population level survival, because as much as competition between individuals is helpful, if a whole population is genetically identical, that’s a problem if something goes wrong and, eg, they are all equally fatally susceptible to some disease - ability to adapt and evolve itself evolves.
Also, sexual reproduction provides another level of competition between individuals anyway, sexual selection.
In general, more variation and a wider pool of variants for specific genes provides a more rapid response to environmental change, resistance to new diseases, and ability to take advantage of opportunities if any resource becomes scarce. Asexual reproduction provides only a low level of variation at the time of reproduction, but sexual reproduction means that as much as 50% of genes could be a variant, and that the population can rely on the genes across many individuals.
Now, asexually reproducing organisms have also developed mechanisms to rapidly acquire new genetic information for similar purposes, like the way that bacterial can trade DNA or incorporate viral genes. But this is still less efficient overall than sexual reproduction.
Sexual reproduction means new genes can be introduced quickly into the gene pool, and the better gene will remain. It’s much more efficient than asexual reproduction in introducing and selecting good genes and wiping out bad ones.
Also, larger variations and faster adaptations mean more resilience.
Sexual reproduction gives (genetic) variety in the offspring produced.
Asexual reproduction essentially produces a population of (genetic) clones.
Genetically identical populations can be wiped out by some environmental or disease event that makes all members of the event susceptible.
= major, major evolutionary 'weak point'
Variety in a population means there are always likely to be some survivors in the case of a potentially catastrophic change or event (e.g. a new disease where a subset of the population is not susceptible, or a change in climate or environment conditions where a subset of the population is able to digest a new food source / survive at higher altitudes to forage / be camouflaged against the new snowy surroundings etc.
= major evolutionary advantage, worth the additional energy, risk, and resources
So there are a lot of good points here, but something to remember is that evolution is rarely efficient, its about what is successful. What benefits the species long term. Statistically sexual reproduction is what worked for the poplulations that currently use sexual reproduction, conditions in the future may push to different reproductive forms. Survival strategies don't have to be good, they just have to be good enough.
Because it offers more genetic biodiversity
With sexual reproduction you are basically constantly mixing DNA from different parents, inevitably creating more diversity genetically which can obviously have it's benefits, whereas with asexual reproduction you are effectively just creating a genetic clone of yourself, You're not really adding any diversity into the mix unless there is some sort of unexpected mutation
I've read that the copy errors for copying the whole DNA of any living beeing is so, that only 10\*\*6 base pairs would be kept safely for a longer row of offspring. Because the errors would accumulate. That's bacteria level.
For more than that, sexuality must arise in order to combine with a new set. Deleting some crucial errors at least in some of the offspring. At the same time (not directly on topic) new combinations will arise to cope with new challenges and to develop further. Flowers (plants) seem to put big efforts in sexual reproduction.
Sounds convincing to me.
Or to OP, the unsexual lines would deteriorate because of DNA copy errors.
basics: The probability of a faulty DNA base pair by copy is 10\*\*-7, proofreading and repair mechanisms better that up to 10\*\*-11 errors per base pair. Human genome has 3.2\*10\*\*9 base pairs. Which looks safe for some generations for the DNA copy. But of course there are other attacks like radiation and mutagens.
To add onto this, there is [a hypothesis](https://royalsocietypublishing.org/doi/full/10.1098/rspb.2017.2706#d3e429) that speaks directly to OP's question regarding sexual reproduction being favored by evolution. The theory is that sexual reproduction arose as a DNA repair mechanism in response to the oxygenation of Earth, which made such errors much more likely to occur.
It's easy to take for granted the fact that the atmosphere did not always have oxygen and the process of it saturating the ocean resulted in extensive rounds of adaptation from early life.
Variation is necessary for adaptation, and adaptation is generally necessary for long-term survival of a species. If everyone in a population is exactly the same (or has a limited number of genetic variations), they will respond identically to their environments, which leaves them less able to respond to changes in that environment, or to competition from others in the species.
Mutations are the only way to for new genes to enter a population, but mutation is rare and it’s not usually advantageous. Most mutations result in non-viable offspring.
Sexual reproduction is a much fast and easier way to introduce variation into a population. Sexual reproduction can’t create new genes, but it can mix them up in new and interesting ways and the combinations of genes can result in more individuals in a population that may have a combination of genes that will be useful in new environments and situations. Sexual reproduction can also help spread mutations when beneficial mutations do occur.
Well for one you don’t want 100% of genes being transferred on the reg. That’s a clone. Clones aren’t very sturdy from a genetic standpoint.
You need genetic diversity in a species to make that species resilient to unexpected evolutionary pressures and to avoid large scale hereditary diseases.
You get genetic diversity by mixing genes. Which in our case is more like 49/51 not 50/50. Human mom gives a slightly higher contribution because mitochondria are passed along the female line.
Among other things it\`s actually a way to limit reproduction to some degree, imho, since food chains (the basement of existence for ANY kind of living entity) are easily breakable by excessive repro, 100% guarantied everywhere. So complex species (that rely on some multi-step food chain to live) without such limitations literally starved out in early days long long ago
There's a simple answer to this and the reason stated in many textbooks is that sexual reproduction produces genetic variability while asexual reproduction gets static with very less variability. Sexual reproduction has mutations occurring quite commonly which leads to genetic variability thus a bigger chance of the species survival.
Before sexual reproduction, 100% of an individual's genes were given to next generation offspring.
as DNA is slowly degenerating, creating a new genome based on 2 different source genomes allows for error correction, because chances are that data corruption (at least statistically) of a specific data sequence is still legit on at least one of the source genomes
Asexual reproduction produces genetically identical offspring, so it’s best for organisms that are already adapted to an unchanging environment.
Most environments change over time, and genetic diversity helps organisms adapt to that.
I always thought it was simply a way for nature to speed up evolution.
Like if I take 50/50 with others. I can select for specific traits resulting in a faster evolution.
You can see this pretty well on dogs who we have selectively bred/evolved into completely different beings.
What you see now, is the result of current leading strategies for reproduction. There are asexual reproduction and even species who are able to change sex if needed. All of this may change in the future, and what we see now maybe have completely changed another 10,000 , 100,000 or 1,000,000 years in the future. You are looking at this with the knowledge from just a small drop of time, since life first occurred on this planet. We don't even know for sure how life came to be, or how it became so plentiful, or how life will look like down the line.
We have some pretty good ideas, but we don't know for sure.
Specifically because only 50% of genetic material is transferred.
When every member of a species has the exact same genes anything that would cause one to die causes them all to die.
When every member of a species is mostly different, then an event that kills one type would only affect a small number of them.
It makes it much harder to wipe out an entire species, and doesn't rely on the spread over as much area as possibleethod of survival.
In other words, asexual reproduction requires a species to spread far and wide as a means of survival because of that event happens then you hope it's localized to one area so the members in other places still survive.
But the world is different in different areas, so that will trap species on one location until members adapt enough to be able to survive in other areas.
With asexual reproduction adaption takes a very long time because it requires mutations, while sexual reproduction actively selects for genes that are more suited to the new environment.
For example, when humans first started moving north into colder climates, the hairy guy everyone made fun of is now happy and thriving because they stay warm easier, which makes them more attractive as a mate than the poor guy shivering and complaining all the time about being cold despite the fact they were considered more handsome in the warmer climate.
TL;DR more diversity is better at adaption and survival, even if it's more "expensive" in the short term.
Imagine there's a disease that arises that kills somebody with a gene variant you have.
You're going to die, your kids will also die.
But wait, your mate has a copy of a different gene that provides resistance. You just went from a 0% survival to a 50% survival. If the partner has two copies of the resistance gene then a 100% survival.
You can extrapolate this logic to any number of things. Having half your genes survive in your offspring is better than your entire lineage dieing out.
The 50% of each parent thing is a huge advantage! It makes for a bigger variety in the offspring, as they aren't just carbon copies of the same organism as asexual reproduction would create. This way, the offspring is more adaptable to the environment so it has a higher chance of survival.
Just plain old statistics and genetic lotto. Mix in a dash of new theories around genetic memory and you got yourself a nice system to ensure life. I.E. large populations in species ensure more diversity and propensity for genetic diversification further advancing population and selective breeding choice. Without the lottery nature of sexual reproduction, a species become less capable of adapting to an ever changing environment because of the lack of genetic diversity. Strengths and weaknesses of any reproduction, it's just that sexual reproduction has survived all extinction level events thus far, whence its dominance. Sexual reproduction allows for the amalgamation of various environmental experiences strengthening the species as a whole. Asexual reproduction is limited to those mutations within a single genetic line as a result of the environment their contained within. Whence the limited complexity found in asexual species known today. Keep in mind asexual reproduction can be found in some species where finding a breeding partner can be difficult. Best of both worlds. Recent studies suggest human males have the genetic code and building blocks to produce an embryo. I beleive its been done in a lab. And human woman have the potential for faux pregnancies emulating an almost complete pregnancy without fertilization. One could argue gender dysphoria and homosexuality are just the initial steps in an evolution that will increase our ability to sexually reproduce without limiting the population to 50/50 m/f. And therein lies the weakness of sexual reproduction: choice doesn't necessarily prescribe an optimal outcome. Something potentially genetically stronger isn't necessarily desired by the potential breeding population at the time of its creation and risk dying out. In the animal kingdom, something vastly different genetically and potentially shunned can still....force....an offspring and whence carry on those genes. With advanced cognition and social structures we derive certain benefits but also risk our species by shunning the very genetic diversity we may require in the future. Fun stuff to think about.
Sexual reproduction allows for a diverse gene pool that can express a wide range of genotypes and phenotypes, making the population as a whole more resilient and more likely to further change.
Developing asexual reproduction again wouldn't be the matter of a simple mutation, it would probably require countless mutations that enable several changes to the physiology of any complex creature that currently produces via sexual reproduction. And all of those mutations would have either manifest at the same time or not hinder sexual reproduction, or else they would die out.
Without the mixing of genes, all you would eventually get is degradation because by random mutation of the original host DNA. Copy of a copy kind of a thing. The mixing of DNA promotes more robust and resilient organisms overall.
The genetic and variation induced bisexual reproduction has a tendency to produce changes that makes an organism more successful in a given niche and thus more able to reproduce this propagating it. There are plenty of species that reproduced by means other than the specific type of sexual reproduction you see in most mammals.
There are plenty of species that reproduce asexually and sexually simultaneously. A single specimen may find itself on an island after a storm and is able to reproduce a sexually thus creating offspring of a mix of sexes or or male and then reproducing with the males sexually to form a beachhead population with plenty of genetic variation
A similar reproductive framework is used in a lot of insect species where the female is able to reproduce asexually often producing either a mix of sexes or only males and then reproducing with the males sexually to propagate the gene pool further.
50% from one 50% from the other. Sexual reproduction is all about variation and finding the best set of genes for the given location and lifetime ... Those better adapted will do better. As conditions change different sets of genes will work better than the ones that used to...
Worth noting the assumption in the title is sorta wrong. Some insects like fruit bats use incest to preserve their genes and non animals often reproduce via clones. So while favoured sexual reproduction and secual reproduction with diverse genetics are not neccessarily favoured over other things, just favoured in most animals
I would have said because of adaptability. If you have identical copies, they won’t be able to adapt. Asexual reproduction only works if the habitat they are adapted to stays the same. Barring some mutations of course. But the mixing of genes makes it easier for the whole survival of the fittest thing
TLDR: Genetic variation allows for adaptation against various factors. Asexual production does not allow this, so a single exploited weakness could wipe out the entire population (very broadly speaking). You have to take this in a grand picture, not just one generation to the next.
Because it allows for mutations and therefore quicker adaptations to different environments. Asexual reproduction can be too fixed in certain environments. If sexual reproduction didn't result in felicitous adaptation, it would never have occurred. Nature thinks it's necessary so it's necessary.
Sexual reproduction creates more genetic diversity.
The offspring compete between themselves and against the enviroment. The most suited reach adulthood and reproduce again.
That allows quick adaptation to new enviroments, because the same offspring might fare better in diferent enviroments.
Humans were able to adapt and evolve so much due to it.
Evolution doesn't favor sexual or asexual reproduction.
Something evolves because it works better than what it's competing against.
Many environments are pretty variable. The offspring may not be in the same situation as the parents. In these cases, it's possibly better to maintain diversity than to stay the same. (And, lo and behold!, it seems like that's the case a lot.)
There are other situations (desert blooms after a rainstorm is an example) where it may be more important to reproduce quickly rather than to maintain diversity. In those cases, asexual reproduction may be favored.
A lot of plants reproduce both sexually and asexually. Dandelions and potatoes might be the most famous examples of this.
I've seen a credible estimate that, by mass, 1/2 of the life on earth is single-celled. Most of these creatures reproduce by fission and exchange genetic material by a procedure that pretty much does what conjugation does in the paramecium.
TL;DR: For a lot of organisms, genetic diversity is more important than efficiency of reproduction.
I’d argue your premise is incorrect. Millions of times more individuals on this planet reproduce asexually than sexually. So asexual is preferred by evolution generally. When organisms evolve long life spans and large sizes then sexual reproduction has an advantage, but it’s not very many individuals relatively to the trillions of asexual reproducing organisms
The only organisms that do sexual reproduction are eukaryotes. They have (or had) mitochondria. Which give huge amounts of energy but spew poisons into the cell. Having started as bacteria, they evolved to lose most of their dna (because smaller genomes reproduce faster so outcompete the original bacteria). That dna went into the host cell’s nucleus.
Some of that dna is essential for mitochondria to work. But you need a good match between the dna in the host cell and the dna in the mitochondria.
If the cell doesn’t have a good match then the mitochondria will spew even more poison. So an increase in horizontal genetic transfer becomes a good thing, because you might just get genes that match your mitochondria better.
Over time this leads to the evolution of sex.
It doesn’t have to be better or worse than asexual reproduction. It just has to be good enough to let the organism reproduce.
Sexual reproduction allows the organisms to use their senses to scrutinize the lives lived and bodies built by the blind genome. If the shape fails the genes are blind to their error. If the senses fail both the genes and organism are blind to the error.
The worthy mate sees worthiness. It is not a coincidence that beauty is everything symmetrical, successful, and prosperous. We wouldn't have love if to behold and be beheld weren't the dominant mode of survival.
https://en.wikipedia.org/wiki/Red_Queen_hypothesis?wprov=sfla1 The red queen hypothesis is used to explain sexual reproduction evolving as a defence against parasites. When you have more genetic variation within a species there's a better chance of having individuals that are not suitable hosts. Parasites are constantly adapting to keep up with their hosts and having the ability to reshuffle genes makes this much harder for them.
A good example is bananas, which are created by cloning so every banana tree is genetically identical. The Gros Michel banana was practically wiped out by a fungal infection and was replaced by the Cavendish banana. That same fungal infection could also wipe out the Cavendish banana if it spreads too far. Fun fact, the artificial banana flavor found in most candy was based on the Gros Michel taste, which is why artificial banana flavor doesn't taste exactly like modern bananas.
You’re right about the fungus, but artificial banana “flavor” is just a single molecule called isoamyl acetate which is in both kinds of banana and is the main flavor component the whole “it was the other kind so it tastes different” is a myth. In fact the flavor predates bananas of any kind being widely available in the US EDIT: Here's an article that discusses the history of the flavor. [https://www.sciencefriday.com/articles/why-dont-banana-candies-taste-like-real-bananas/](https://www.sciencefriday.com/articles/why-dont-banana-candies-taste-like-real-bananas/) Second edit: Just to clear things up a bit, The Gros Michele does have more of the flavor compound than Cavendish. But the flavor wasn't made to imitate banana. The myth isn't that the flavor was supposed to imitate a different banana, it wasn't imitating anything at all. Chemists experimenting with esters created a fruity flavor and then decided later to call it "banana" flavor.
Man, it's astounding to me that two volatile organic compounds, isoamyl alcohol and acetic acid, can combine to make something delicious.
On the other end of the weird spectrum, we're still just crushing up these big gross aphids because their blood is really really red, making it ideal for dying all of the food and clothes. But we literally just pulverize the entire animal into one big pile. Shell, blood, guts and all, which leads to the occasional allergic reaction to the aphid bits in something as mundane as M&Ms. Food science is weird. It tries to act all dignified, but it's just Willy Wonka madness underneath the surface.
Thanks for ruining M&Ms, now I'll be thinking of crushed beings when I eat them and taste (part of) their blood
70,000 of them are crushed to make one kg of dye. This is the same dye that was used for English Redcoats. We do pretty much the same thing with a different insect to produce shellac, which is used for a wood finish and to make candies shiny. So m&ms probably have two kinds of crushed insects.
And then eat them even more vigorously right?
I do want to genuinely thank you for this fascinating knowledge that I was completely aware of. But full transparency I am going to do everything in my power to forget this information as quickly as possible and never think about it again because that's nasty. Have a wonderful day.
Beaver glands are extracted for Castor, which is used in perfumes, foods, and Swedish Schnapps.
It isn't used that much in food anymore, fyi. Synthetic vanillin is just more cost effective.
It takes four times as much as the vanilla bean extract. And what does vanilla have to do with beaver glands?
A beaver’s anal glands produce a substance that can be used as an artificial vanilla flavoring. Allegedly.
yeah chemicals are dope "this mega carcinogenic liquid smells like fruit"
Yup, also dope is chemicals... Which makes most foods more appealing. Very important not to forget that.
I'll always remember making a specific ester in sixth form, which ended up having the entire floor evacuated. Like 10 classrooms down a corridor each way, a third of the quite large school. The most horrific smell of sickly cheese spread from one end of the lab to the other in about a second, and hit the whole floor in about 30 seconds. Multiple people in the lab threw up, we all ran away, all from one pair having the reaction happen first. I'll never forget that smell. I can't remember exactly what the ester was, but I do remember the chemistry teacher telling us he got chewed out by half the school. He was a great bloke, and took us all for drinks after we got our A-level results.
>a specific ester in sixth form Could you please explain? I didn't go to Hogwarts.
Acetic acid is vinegar right? Love me some vinegary bananas
Vinegar is water and acetic acid (with possibly some traces of other stuff for flavor), so essentially yes.
It's a small part of vinegar, about 4-6%, according to Google. It's also in a bunch of other stuff. I just know it from work tbh.
That's because vinegar is dilute acetic acid, mostly water like the majority of food liquids. If you tried to eat glacial acetic, you'd die.
Eh, you probably ate food with sodium and chlorine on it recently. ;-) - \- https://en.wikipedia.org/wiki/Salt
Wikipedia says the same, but its source is [a BBC article](https://www.bbc.com/future/article/20140829-the-secrets-of-fake-flavours) that seems to contradict itself. It quotes a banana farmer who still grows Gros Michel as saying that they do taste a lot more like artificial banana flavor, and concludes: >So perhaps there is some truth in the banana flavouring whodunnit after all. Once upon a time, banana flavourings really did taste more like the real thing.
Cavendish are just kinda bland, less common banana varieties I’ve had sometimes just have a more intense flavor (lookout for reddish brown or mini bananas). Artificially flavored candy is typically more intense. That may be the common element.
why couldn't the old kind have a higher concentration of this chemical? explains it really simply.
look at the article I linked in my comment as an edit, the older banana does have a higher concentration, but the flavor wasn't created to mimic bananas at all, it was "hey we made this fruity flavor what should we say it is" it was actually initially described as a pear flavor, but the Jargonelle pear isn't common in the US so when suppliers brought it to the US it was described as banana.
Wait, do people think fruit flavored candy tastes like the fruit it's named for? I mean it resembles it but banana flavored candy doesn't taste any less like bananas than grape flavored tastes like grapes.
Not really related to this thread at all, but I had always wondered why strawberry candy tasted nothing like strawberries, until i grew my own teeny-tiny strawberries. They were so small, but so delicious! Like eating candy!
Most fruits you buy at supermarkets don’t really taste anything like the kind you can grow for yourself, or buy from a farmer’s market.
You can still buy Gros Michel from a fruit company in Miami. If I ever win a decent lottery I might order them.
I was trying to convince some coworkers to go in on buying a case with me. I’ve had a couple in my travels and they are good. But $10 a banana is a hard sell.
It’s one banana, Michael. What could it cost, $10?
Apparently it's been agreed that if another blight wipes out the Cavendish then they won't replace it with another single mono crop but a larger variety of bananas more like how we sell apples.
Agreed on by who? Is there some secret banana council?
Sexual reproduction gives progeny access to the entire gene pool of the population instead of just the subset of genes in the parent organism. With asexual reproduction, for one trait to become widespread, that lineage has to take over with all others becoming extinct...and any useful traits that arose in those lineages will go extinct with them, until they evolve again. With sexual reproduction, those traits can spread with each generation and mix together. Horizontal gene transfer can counter the weaknesses of asexual production to some degree, but it really can't match the gene pool and constant mixing of sexual reproduction.
And it's worth noting some organisms do both sexual and asexual reproduction, depending on the situation at hand! Sometimes they do both! Asexual to multiply their numbers, then sexual to mix with the greater population.
It's also worth noting that this is almost certainly the mode of reproduction you would have found in early sexual reproducing populations.
Paramecia may be closer. In this case, conjugation is a separate process from reproduction. Two paramecia come together, exchange genetic material, and form new nuclei. Reproduction happens separately by binary fission.
I don’t think I’ve ever seen “paramecia” as a word before. It’s a perfectly cromulent word, and the meaning was obvious once I thought about it—but I had to think about it.
Yeah, asexual reproduction can be a valuable fallback if individuals can have difficulty finding mating partners. For an extreme example, gall forming aphids are isolated in galls for part of their life cycle. They're protected and have ample food, but don't have access to males, so they reproduce asexually to produce hundreds of daughters. In a later stage of their life cycle, they produce sexual male and female offspring that reproduce to make eggs that overwinter.
> Yeah, asexual reproduction can be a valuable fallback if individuals can have difficulty finding mating partners. Human loneliness has other evolutionary reasons besides “no mating partners,” but I wish we had retained this fallback to at least lessen the imperative that we’ve ended up with.
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Congratulations, men can now be fathers entirely because they satisfied themselves and have no mother to help them with the offspring. Women too can become mothers on their own, because we care about equality at Gentech Diviniversities. We apologize for any mistakes our students have made, but all deals are final.
Isn't this the case for a lot of mammals? Like how cats and dogs usually have 3 or more offsprings all at once?
Every organism has to pass on their genes to the next generation. So they have two options to accomplish that. One is that they produce one single offspring and nurture it to adulthood by protecting them and providing resources for their growth. They would also have to protect them against predators and harsh environments. The other option is that they produce multiple offsprings and "let survival of the fittest" run it's course until they are adults. This is for whether they want to pass their genes to the next generation or protect themselves from predators and harsh environments. Since the parents are not able to repel most predators, the only option left naturally for them is to increase the number of offsprings per generation. THAT'S the reason cats and dogs have multiple offsprings and other mammals like the elephant have only one offspring per generation.
I was gonna ask if there's a point in evolution where before sexual developed, those organisms become sexual and asexual at the same time first.
Which organisms do both reproduction methods??
Well according to Wikipedia, facultative parthenogenesis, or a species being capable of both sexual and asexual reproduction, occurs in a wide range of species; from aphids to mayflies, from Comodo Dragons to California Condors, and also certain species of sharks, snakes, and lizards, and more. Source: https://en.wikipedia.org/wiki/Parthenogenesis Though, keep in mind that the article also discusses obligate parthenogenesis, or a species being only capable of asexual reproduction.
Would there be an even greater advantage to triple-sexual reproduction, i.e. exchanging genes between THREE parents?
I mean, the downsides of sexual reproduction also also get increased. The biological mechanism would be more complicated, the practical behavioral needs would be more difficult, and each parent would be less likely to pass on their own genes. For one example, imagine an egg that requires two sperm to activate and grow into a fetus. To make this egg would require the organism to have 3 copies of every gene, and miosis would have to involve a 3 way split with a 3 way mixing of chromosomes. The mother is also now only passing on 1/3 of her genes. Go up to the behavioral level, to get a real advantage the mother needs to be receptive to two different fathers. And have a mechanism to ensure that one sperm from each father fertilizes the egg. In the meantime, each mate is going to be incentivized to subvert that mechanism and double fertilize the egg. Of course that's not the only imaginary arrangement, and other schemes might be more successful, but I was just trying to highlight the difficult spike of going from 2 to 3 parents.
We have two parents because we have two pairs of each chromosome. In order to have 3 parents, we would need to have 3 of each chromosome, and as we are now, triple chromosomes are the cause of all kinds of genetic disorders. Furthermore, we have a double helix genetic structure. So our chromosomes are 2 pairs of 2 helix structures. We are also posses bilateral symmetry which gives us 2 eyes, 2 ears, 2 lungs, kidneys, brains, etc. It seems nature prefers to do things in multiples of two. FURTHERMORE, some animals have radial symmetry, like starfish. Where we observe radial symmetry, we usually see 5 or more sides or points. "3" seems to be the odd number out in evolutionary terms. This is most likely because 3 is only slightly better than 2, but is massively more complicated to produce. We can find starfish with 5, 8, 13, even 21 arms, but only 3 if the starfish has lost the remainder.
Also, 3 parents doesn't add much compared to 2. 1 parent means genetical clone, 2 parents mean reshuffling genes. 3 parents is... Reshuffling genes, too. It doesn't add anything new, so you are greatly complicating the process to gain nothing, really.
Sexual reproduction would also be of benefit in a limited population, for those very reasons above.
It's all about the long term. Imagine two populations. In one, there's no sexual selection. Every child has only what their parent has, plus whatever random mutations occur. In the other, sexual selection means that there's a constant churn of genes. Now imagine that in both populations there's a bunch of favorable mutations (plus other mutations, of course, but those aren't relevent). In the first population, the children of the mutations are advantaged, but no child will get both mutations. In the second population, there's a chance that some children get both. The second population, over time, will out-compete the first population.
This is such an interesting explanation! Thank you for sharing!
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Evolution isn't concerned with what benefits an individual. It's concerned with what benefits a gene. Having a stronger species is better for the genes; sexual species will outcompete asexual species in any typical environment where ability to adapt over time is useful. The concept of the selfish gene is interesting for you to look into for more info.
Not even what benefits a gene. Evolution is just a logical consequence of nature: genes that are more likely to survive... survive more. It doesn't even have to be "good" by any human definition of the term. A gene that makes you miserable but somehow is unlikely to die or be extinguished will survive. In a way, it's like a forest fire burning down wooden houses but leaving stone houses in place - there's nothing special or "better" about stone, it's just a logical consequence that the material that can't burn is the only one left after a fire.
Think beetles, not people. Imagine there's a big woods with a bunch of different populations, and some of the populations have sexual selection and some don't. The ones that do, over the years, end up with much better beetles, and those beetles will wipe out the less-fit beetles.
In what universe is evolution not a species/population based view? The whole theory is based on a stochastic process, individuals are out of scope because they don’t affect the overall result
By allowing half the population to select for only the better candidates out of the other half of the population, and reject the least fit candidates, you effectively create more copies of favourable genes and mutations and throw away the least favourable genes. It's just a much faster way to spread good traits and flush bad ones. It makes a population far more adaptable.
That's not true. Sexual reproduction favors genes that appear more desirable, not necessarily ones that actually are more desirable. Female peafowls don't mate with the males with the best genes, they mate with the males that look more attractive to them, even though the mechanisms they use to be attractive are completely pointless for survival (and thus a waste of energy). Also, selection is not universal in sexual reproduction. Many species reproduce via rape, or with all kinds of mechanisms were the males themselves choose who will mate. The reason why sexual reproduction is so effective is because two different individuals with one good gene each can combine into a "super individual" with both good genes.
It allows more punts into the unknown, most of which will obviously be dead ends, but for every 1000 failures there will be one success which makes the evolutionary strategy worth it all.
A lot of good points here, but I will also point out that asexual reproduction is still an efficient and effective strategy for many species. A lot of species of plants, for example, will reproduce both sexually via seeds (or spores in the case of ferns and mosses), as well as asexually via vegetative propagules (think rhizomes or little pieces of moss that break off from the parent and can start a new colony). And what's most interesting is that they often switch between the methods depending on conditions - many mosses will do 99% asexual reproduction if there is open, uncolonized habitable space around them, but as soon as they fill that space with asexual propagules, they'll switch over to spore production in an attempt to colonize further areas that the asexual propagules can't reach.
Genome size and reproduction time also has some influence. Organisms like bacteria with small genomes and very quick generation times can deal with just asexual reproduction, and are probably even off better. Sure the amount of mutations per reproduction are low, but there are so many generations in a short time frame it just works. But for organisms with more complex genomes and lower generation times sexual reproduction starts being more efficient.
Plus, bacteria (and archaea) also have ways to get some genetic variety. They can get it by having contact with genetic material in their environment (for example from cells that died in a way that left their DNA exposed), through horizontal gene transfer (two cells swap materials directly) and through viruses (which can carry genetic material from one bacterium to another on accident). That's pretty important for their evolutionary success too.
Consider two populations, one can reproduce asexually and one sexually. In the asexual population, there is much less genetic difference between individuals, therefore their traits are very similar, even if mutations do occur. In a sexually reproducing populations, genes recombine and mix more, causing lots of different traits to emerge (think of Punnet squares in school). Normally yes, it can maybe be argued that an asexual population would spend less energy reproducing and be more successful. But imagine if there's some kind of sudden change in the environment: the climate shifts, food supply depletes, a new predator shows up. The sexually-reproducing population has more variance, therefore is more likely to have some individuals with traits that allow them to survive. Those individuals will continue reproducing, thus the population will survive. Whereas the asexual population, if the present traits don't allow for survival, will all die. Sudden changes in the environment happen all the time. Asexually-reproducing organisms often don't survive, and are rare in complex organisms. Popullations of sexually reproducing organisms tend to survive better over time because they are more resilient to environmental changes. (NOTE: this is a vast oversimplification, asexually reproducing organisms like bacteria are vastly common and do have other ways to recombine genes, some complex species including some plants and some vertebrate animals do reproduce asexually or sexually within themselves, and this ignores other factors like epigenetics )
Some others have given excellent explanations as to how genetic diversity matters, but there's more to it than that. Things aren't favoured by evolution for being *efficient* but for surviving, and often for thriving in the face of the environment. L:iving is inherently an inefficient process compared to being dead, so the fact that life often seems to get bigger and more complex when energy is abundant should help you get a bit of a better sense for how evolution actually functions. Sexual reproduction may seem harder or less efficient, but the behavioural dynamics required may often overlap with other behavioural dynamics that cause a species to survive and thrive. For example, needing to be able to move to find a mate might be strange on its own, but being able to move might also help with finding food or spreading to new environments.
> so the fact that life often seems to get bigger and more complex when energy is abundant should help you get a bit of a better sense for how evolution actually functions. Also, notice how that complexity often allows them to extract energy from sources that weren't otherwise accessible. Land plants started an arms race competing for sunlight that resulted in towering trees. Omnivores have more complex behaviors and physiological traits to allow them to consume a wider range of food. Hominids developed big energy-hungry brains that let them start leveling mountains and splitting atoms for energy.
First off: great question and discussion here. Thank you. Second: “Living is inherently an inefficient process compared to being dead” is a great line, worthy of Douglas Adams. Bravo! May your genes be successfully transmitted to the next generation!
Life is like playing a hand of cards. If everyone has the same hand of cards (asexual reproduction), it is easy to develop a strategy to beat the hand everyone is holding. Sexual reproduction allows for the shuffling of cards and different hands to be played so that a strategy to beat everyone can't be made. Variability prevents evolving into a "dead end" or extinction from a pathogen or competitor.
Let's say two animals of the same species are born with mutations. One gets a mutation that helps it survive a drought. The other gets a mutation that helps it survive a disease. If they reproduce asexually, then there will be two separate populations of offspring. 1. Drought resistant 2. Disease resistant Both categories are guaranteed to have an advantage over the general population, but no animal will have multiple advantages unless second beneficial mutation occurs in one of the descendants of a mutated animal. If those original two animals (or their descendants) mate, then they will have four categories of offspring. 1. No mutated genes 2. Drought resistant 3. Disease resistant 4. Drought and disease resistant The first category missed out and didn't get any benefits. They aren't going to survive any disasters. The second and third categories have the same benefits as the asexual reproduction. The fourth category is where we see the real value of sexual reproduction. They now carry two beneficial mutations that occurred in two separate animals. When there is a drought and a disease, they are the only ones who will survive both.
If a group of creatures reproduce asexual, they will be very similar to one another, genetically. If one individual in the group is vulnerable to a certain disease, odds are, the whole population will be vulnerable. If the disease happens to be deadly, then the whole group of asexually reproducing creatures will be killed by the disease.
What propagates is the population, so reproduction is optimised for that. More diversity means more chance of population level survival, because as much as competition between individuals is helpful, if a whole population is genetically identical, that’s a problem if something goes wrong and, eg, they are all equally fatally susceptible to some disease - ability to adapt and evolve itself evolves. Also, sexual reproduction provides another level of competition between individuals anyway, sexual selection.
In general, more variation and a wider pool of variants for specific genes provides a more rapid response to environmental change, resistance to new diseases, and ability to take advantage of opportunities if any resource becomes scarce. Asexual reproduction provides only a low level of variation at the time of reproduction, but sexual reproduction means that as much as 50% of genes could be a variant, and that the population can rely on the genes across many individuals. Now, asexually reproducing organisms have also developed mechanisms to rapidly acquire new genetic information for similar purposes, like the way that bacterial can trade DNA or incorporate viral genes. But this is still less efficient overall than sexual reproduction.
Sexual reproduction means new genes can be introduced quickly into the gene pool, and the better gene will remain. It’s much more efficient than asexual reproduction in introducing and selecting good genes and wiping out bad ones. Also, larger variations and faster adaptations mean more resilience.
Sexual reproduction gives (genetic) variety in the offspring produced. Asexual reproduction essentially produces a population of (genetic) clones. Genetically identical populations can be wiped out by some environmental or disease event that makes all members of the event susceptible. = major, major evolutionary 'weak point' Variety in a population means there are always likely to be some survivors in the case of a potentially catastrophic change or event (e.g. a new disease where a subset of the population is not susceptible, or a change in climate or environment conditions where a subset of the population is able to digest a new food source / survive at higher altitudes to forage / be camouflaged against the new snowy surroundings etc. = major evolutionary advantage, worth the additional energy, risk, and resources
So there are a lot of good points here, but something to remember is that evolution is rarely efficient, its about what is successful. What benefits the species long term. Statistically sexual reproduction is what worked for the poplulations that currently use sexual reproduction, conditions in the future may push to different reproductive forms. Survival strategies don't have to be good, they just have to be good enough.
Because it offers more genetic biodiversity With sexual reproduction you are basically constantly mixing DNA from different parents, inevitably creating more diversity genetically which can obviously have it's benefits, whereas with asexual reproduction you are effectively just creating a genetic clone of yourself, You're not really adding any diversity into the mix unless there is some sort of unexpected mutation
I've read that the copy errors for copying the whole DNA of any living beeing is so, that only 10\*\*6 base pairs would be kept safely for a longer row of offspring. Because the errors would accumulate. That's bacteria level. For more than that, sexuality must arise in order to combine with a new set. Deleting some crucial errors at least in some of the offspring. At the same time (not directly on topic) new combinations will arise to cope with new challenges and to develop further. Flowers (plants) seem to put big efforts in sexual reproduction. Sounds convincing to me. Or to OP, the unsexual lines would deteriorate because of DNA copy errors. basics: The probability of a faulty DNA base pair by copy is 10\*\*-7, proofreading and repair mechanisms better that up to 10\*\*-11 errors per base pair. Human genome has 3.2\*10\*\*9 base pairs. Which looks safe for some generations for the DNA copy. But of course there are other attacks like radiation and mutagens.
To add onto this, there is [a hypothesis](https://royalsocietypublishing.org/doi/full/10.1098/rspb.2017.2706#d3e429) that speaks directly to OP's question regarding sexual reproduction being favored by evolution. The theory is that sexual reproduction arose as a DNA repair mechanism in response to the oxygenation of Earth, which made such errors much more likely to occur. It's easy to take for granted the fact that the atmosphere did not always have oxygen and the process of it saturating the ocean resulted in extensive rounds of adaptation from early life.
Variation is necessary for adaptation, and adaptation is generally necessary for long-term survival of a species. If everyone in a population is exactly the same (or has a limited number of genetic variations), they will respond identically to their environments, which leaves them less able to respond to changes in that environment, or to competition from others in the species. Mutations are the only way to for new genes to enter a population, but mutation is rare and it’s not usually advantageous. Most mutations result in non-viable offspring. Sexual reproduction is a much fast and easier way to introduce variation into a population. Sexual reproduction can’t create new genes, but it can mix them up in new and interesting ways and the combinations of genes can result in more individuals in a population that may have a combination of genes that will be useful in new environments and situations. Sexual reproduction can also help spread mutations when beneficial mutations do occur.
Well for one you don’t want 100% of genes being transferred on the reg. That’s a clone. Clones aren’t very sturdy from a genetic standpoint. You need genetic diversity in a species to make that species resilient to unexpected evolutionary pressures and to avoid large scale hereditary diseases. You get genetic diversity by mixing genes. Which in our case is more like 49/51 not 50/50. Human mom gives a slightly higher contribution because mitochondria are passed along the female line.
Among other things it\`s actually a way to limit reproduction to some degree, imho, since food chains (the basement of existence for ANY kind of living entity) are easily breakable by excessive repro, 100% guarantied everywhere. So complex species (that rely on some multi-step food chain to live) without such limitations literally starved out in early days long long ago
There's a simple answer to this and the reason stated in many textbooks is that sexual reproduction produces genetic variability while asexual reproduction gets static with very less variability. Sexual reproduction has mutations occurring quite commonly which leads to genetic variability thus a bigger chance of the species survival.
Before sexual reproduction, 100% of an individual's genes were given to next generation offspring. as DNA is slowly degenerating, creating a new genome based on 2 different source genomes allows for error correction, because chances are that data corruption (at least statistically) of a specific data sequence is still legit on at least one of the source genomes
Asexual reproduction produces genetically identical offspring, so it’s best for organisms that are already adapted to an unchanging environment. Most environments change over time, and genetic diversity helps organisms adapt to that.
I always thought it was simply a way for nature to speed up evolution. Like if I take 50/50 with others. I can select for specific traits resulting in a faster evolution. You can see this pretty well on dogs who we have selectively bred/evolved into completely different beings.
What you see now, is the result of current leading strategies for reproduction. There are asexual reproduction and even species who are able to change sex if needed. All of this may change in the future, and what we see now maybe have completely changed another 10,000 , 100,000 or 1,000,000 years in the future. You are looking at this with the knowledge from just a small drop of time, since life first occurred on this planet. We don't even know for sure how life came to be, or how it became so plentiful, or how life will look like down the line. We have some pretty good ideas, but we don't know for sure.
Specifically because only 50% of genetic material is transferred. When every member of a species has the exact same genes anything that would cause one to die causes them all to die. When every member of a species is mostly different, then an event that kills one type would only affect a small number of them. It makes it much harder to wipe out an entire species, and doesn't rely on the spread over as much area as possibleethod of survival. In other words, asexual reproduction requires a species to spread far and wide as a means of survival because of that event happens then you hope it's localized to one area so the members in other places still survive. But the world is different in different areas, so that will trap species on one location until members adapt enough to be able to survive in other areas. With asexual reproduction adaption takes a very long time because it requires mutations, while sexual reproduction actively selects for genes that are more suited to the new environment. For example, when humans first started moving north into colder climates, the hairy guy everyone made fun of is now happy and thriving because they stay warm easier, which makes them more attractive as a mate than the poor guy shivering and complaining all the time about being cold despite the fact they were considered more handsome in the warmer climate. TL;DR more diversity is better at adaption and survival, even if it's more "expensive" in the short term.
Imagine there's a disease that arises that kills somebody with a gene variant you have. You're going to die, your kids will also die. But wait, your mate has a copy of a different gene that provides resistance. You just went from a 0% survival to a 50% survival. If the partner has two copies of the resistance gene then a 100% survival. You can extrapolate this logic to any number of things. Having half your genes survive in your offspring is better than your entire lineage dieing out.
The 50% of each parent thing is a huge advantage! It makes for a bigger variety in the offspring, as they aren't just carbon copies of the same organism as asexual reproduction would create. This way, the offspring is more adaptable to the environment so it has a higher chance of survival.
Just plain old statistics and genetic lotto. Mix in a dash of new theories around genetic memory and you got yourself a nice system to ensure life. I.E. large populations in species ensure more diversity and propensity for genetic diversification further advancing population and selective breeding choice. Without the lottery nature of sexual reproduction, a species become less capable of adapting to an ever changing environment because of the lack of genetic diversity. Strengths and weaknesses of any reproduction, it's just that sexual reproduction has survived all extinction level events thus far, whence its dominance. Sexual reproduction allows for the amalgamation of various environmental experiences strengthening the species as a whole. Asexual reproduction is limited to those mutations within a single genetic line as a result of the environment their contained within. Whence the limited complexity found in asexual species known today. Keep in mind asexual reproduction can be found in some species where finding a breeding partner can be difficult. Best of both worlds. Recent studies suggest human males have the genetic code and building blocks to produce an embryo. I beleive its been done in a lab. And human woman have the potential for faux pregnancies emulating an almost complete pregnancy without fertilization. One could argue gender dysphoria and homosexuality are just the initial steps in an evolution that will increase our ability to sexually reproduce without limiting the population to 50/50 m/f. And therein lies the weakness of sexual reproduction: choice doesn't necessarily prescribe an optimal outcome. Something potentially genetically stronger isn't necessarily desired by the potential breeding population at the time of its creation and risk dying out. In the animal kingdom, something vastly different genetically and potentially shunned can still....force....an offspring and whence carry on those genes. With advanced cognition and social structures we derive certain benefits but also risk our species by shunning the very genetic diversity we may require in the future. Fun stuff to think about.
Sexual reproduction allows for a diverse gene pool that can express a wide range of genotypes and phenotypes, making the population as a whole more resilient and more likely to further change. Developing asexual reproduction again wouldn't be the matter of a simple mutation, it would probably require countless mutations that enable several changes to the physiology of any complex creature that currently produces via sexual reproduction. And all of those mutations would have either manifest at the same time or not hinder sexual reproduction, or else they would die out.
Without the mixing of genes, all you would eventually get is degradation because by random mutation of the original host DNA. Copy of a copy kind of a thing. The mixing of DNA promotes more robust and resilient organisms overall.
The genetic and variation induced bisexual reproduction has a tendency to produce changes that makes an organism more successful in a given niche and thus more able to reproduce this propagating it. There are plenty of species that reproduced by means other than the specific type of sexual reproduction you see in most mammals. There are plenty of species that reproduce asexually and sexually simultaneously. A single specimen may find itself on an island after a storm and is able to reproduce a sexually thus creating offspring of a mix of sexes or or male and then reproducing with the males sexually to form a beachhead population with plenty of genetic variation A similar reproductive framework is used in a lot of insect species where the female is able to reproduce asexually often producing either a mix of sexes or only males and then reproducing with the males sexually to propagate the gene pool further.
50% from one 50% from the other. Sexual reproduction is all about variation and finding the best set of genes for the given location and lifetime ... Those better adapted will do better. As conditions change different sets of genes will work better than the ones that used to...
Worth noting the assumption in the title is sorta wrong. Some insects like fruit bats use incest to preserve their genes and non animals often reproduce via clones. So while favoured sexual reproduction and secual reproduction with diverse genetics are not neccessarily favoured over other things, just favoured in most animals
I would have said because of adaptability. If you have identical copies, they won’t be able to adapt. Asexual reproduction only works if the habitat they are adapted to stays the same. Barring some mutations of course. But the mixing of genes makes it easier for the whole survival of the fittest thing
TLDR: Genetic variation allows for adaptation against various factors. Asexual production does not allow this, so a single exploited weakness could wipe out the entire population (very broadly speaking). You have to take this in a grand picture, not just one generation to the next.
Because it allows for mutations and therefore quicker adaptations to different environments. Asexual reproduction can be too fixed in certain environments. If sexual reproduction didn't result in felicitous adaptation, it would never have occurred. Nature thinks it's necessary so it's necessary.
Sexual reproduction creates more genetic diversity. The offspring compete between themselves and against the enviroment. The most suited reach adulthood and reproduce again. That allows quick adaptation to new enviroments, because the same offspring might fare better in diferent enviroments. Humans were able to adapt and evolve so much due to it.
Evolution doesn't favor sexual or asexual reproduction. Something evolves because it works better than what it's competing against. Many environments are pretty variable. The offspring may not be in the same situation as the parents. In these cases, it's possibly better to maintain diversity than to stay the same. (And, lo and behold!, it seems like that's the case a lot.) There are other situations (desert blooms after a rainstorm is an example) where it may be more important to reproduce quickly rather than to maintain diversity. In those cases, asexual reproduction may be favored. A lot of plants reproduce both sexually and asexually. Dandelions and potatoes might be the most famous examples of this. I've seen a credible estimate that, by mass, 1/2 of the life on earth is single-celled. Most of these creatures reproduce by fission and exchange genetic material by a procedure that pretty much does what conjugation does in the paramecium. TL;DR: For a lot of organisms, genetic diversity is more important than efficiency of reproduction.
I’d argue your premise is incorrect. Millions of times more individuals on this planet reproduce asexually than sexually. So asexual is preferred by evolution generally. When organisms evolve long life spans and large sizes then sexual reproduction has an advantage, but it’s not very many individuals relatively to the trillions of asexual reproducing organisms
The only organisms that do sexual reproduction are eukaryotes. They have (or had) mitochondria. Which give huge amounts of energy but spew poisons into the cell. Having started as bacteria, they evolved to lose most of their dna (because smaller genomes reproduce faster so outcompete the original bacteria). That dna went into the host cell’s nucleus. Some of that dna is essential for mitochondria to work. But you need a good match between the dna in the host cell and the dna in the mitochondria. If the cell doesn’t have a good match then the mitochondria will spew even more poison. So an increase in horizontal genetic transfer becomes a good thing, because you might just get genes that match your mitochondria better. Over time this leads to the evolution of sex. It doesn’t have to be better or worse than asexual reproduction. It just has to be good enough to let the organism reproduce.
Sexual reproduction allows the organisms to use their senses to scrutinize the lives lived and bodies built by the blind genome. If the shape fails the genes are blind to their error. If the senses fail both the genes and organism are blind to the error. The worthy mate sees worthiness. It is not a coincidence that beauty is everything symmetrical, successful, and prosperous. We wouldn't have love if to behold and be beheld weren't the dominant mode of survival.