Submitted by insink2300 t3_11drr8s in askscience
PatrickKieliszek t1_jabbvo8 wrote
Reply to comment by Ieatadapoopoo in Why does temperature determine the sex of certain egg laying animals like crocodiles? by insink2300
One thing about adaptations is that one mutation away from the parent needs to be at least as good if not better than other siblings.
If it's going to take three generations of mutations to get to an advantage, they probably won't make it.
Tiny_Rat t1_jabhwuj wrote
>needs to be at least as good if not better than other siblings.
>If it's going to take three generations of mutations to get to an advantage, they probably won't make it.
This is largely up to chance, unless the mutation is both dominant and a significant disadvantage early in life. Many mutations that are recessive, neutral, or only slightly disadvantageous spread through populations just through chance. For example, just look at human traits like hair color or clinodactyly.
aartadventure t1_jabnb5b wrote
Even recessive traits are selected for in the natural environment over time. However, they remain recessive for various reasons. This could include the recessive trait being advantageous in certain circumstances, but not others. Or that is only an advantage if other traits are also expressed at the same time. Many times a recessive trait can be an advantage but exacts a biological cost as well. If these traits remain recessive, evolutionary pressures cause them to become more common in the "required" circumstances, while allowing them to swiftly become less common when the environment is not suitable for that trait.
Tiny_Rat t1_jadhudx wrote
>However, they remain recessive for various reasons. This could include the recessive trait being advantageous in certain circumstances, but not others. Or that is only an advantage if other traits are also expressed at the same time
This makes no sense. "Recessive" described how an allele intersects with other alleles, and this is largely determined by the molecular mechanisms the protein produced by that allele is part of. A trait cannot change from recessive to dominant, no matter how advantageous or disadvantageous that would be. And while recessive traits are acted upon by evolution, that only happens in homozygous individuals that have two copies of that gene and thus show that trait. A newly-arising recessive mutation could spread through quite a few generations of heterozygous individuals, being passed on but not expressed, until two heterozygous individuals met and bred to make a homozygote. In the meantime, that allele could pick up new mutations that would change it's function without significant selection pressure.
mywan t1_jabvko2 wrote
You can also have a later mutation that randomly takes advantage of a past mutation that was neutral or even somewhat detrimental to confer a significant advantage that wouldn't happen alone.
platoprime t1_jabkv8x wrote
Even neutral mutations are working against entropy if there isn't a pressure keeping it around. Sure you could have a three generation neutral->advantageous or even a twenty generation disadvantageous->advantageous. In the same sense you could phase through a wall if your electrons all randomly lined up.
owiseone23 t1_jac0yw0 wrote
it's not uncommon for traits to evolve across "fitness valleys". That is, a trait with positive fitness that requires multiple generations to evolve with intermediate generations having negative fitness.
With a large population and a lot of time, random variation makes it possible to evolve across fitness valleys.
frogjg2003 t1_jabitib wrote
As long as it's not so much worse that the individual dies before mating, the gene will spread through a population. Over a long enough period, if it is less productive at surviving, it may eventually die out, but that takes many generations.
platoprime t1_jabl4vs wrote
No all genes are working against the force of entropy to exist. If there isn't a pressure keeping something from mutating like it being adaptive or changing it being maladaptive then it will eventually be replaced.
frogjg2003 t1_jabmzb7 wrote
Mutations are random. You can't make a gene mutate in the wild.
When a gene mutation does occur, it is still largely unrelated random factors that will determine if the individual with that mutation survives to pass on the gene. Only once that mutation has spread to a large enough portion of the population, will statistical tends become significant.
If an established gene is not harmful enough to survival and mating, then diffusion will sustain it in the population. Random mating means that any sufficiently established gene will reach an equilibrium between selective pressure reducing its prevalence and diffusion bringing all alleles into equality.
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owiseone23 t1_jac0w3l wrote
That's not quite true. I work on mathematical models of evolutionary processes and it's not uncommon for traits to evolve across "fitness valleys". That is, a trait with positive fitness that requires multiple generations to evolve with intermediate generations having negative fitness.
With a large population and a lot of time, random variation makes it possible to evolve across fitness valleys.
7LeagueBoots t1_jac0s19 wrote
No, it needs to be not worse than. Better is nice, but it's not necessary.
The selection process is often not about gaining an advantage, it's about not having a disadvantage. 'As good as' is usually just fine for evolution.
owiseone23 t1_jac139q wrote
it's not uncommon for traits to evolve across "fitness valleys". That is, a trait with positive fitness that requires multiple generations to evolve with intermediate generations having negative fitness.
With a large population and a lot of time, random variation makes it possible to evolve across fitness valleys.
atred t1_jabiwni wrote
I doubt that's true, that's like saying it's unlikely to get 3 head coin flips in a row.
aartadventure t1_jabnn6o wrote
Most mutations are not good, or downright lethal, leading to miscarriage, cancer and other awful outcomes. Especially in multicellular organisms, advantageous mutations occur quite rarely. That organism also has to be lucky enough to survive long enough to reproduce (you might have an incredibly advantageous mutation but just be unlucky and get struck by lightning before you reproduce for example). It may be something more akin to flipping 50 or 100 heads in a row.
zakabog t1_jabpr91 wrote
> Most mutations are not good...
Based on what exactly? A single mutation isn't likely going to do much unless it happens in the correct place.
> It may be something more akin to flipping 50 or 100 heads in a row.
Which is rather easy if you've got millions of years to do it.
aartadventure t1_jac3zfp wrote
It could be that most mutations do nothing bad, or that they end up being harmful in time, such as cancer. Here is one paper on the topic:
https://www.sciencedaily.com/releases/2022/06/220608112504.htm
And yes, that was my point. Evolution tends to work slowly, over millions of years, due to the low chance of a beneficial mutation occurring, and then also being selected for in a given environment. And, since environments change, what was once beneficial, may end up becoming harmful over time.
owiseone23 t1_jac29v1 wrote
it's not uncommon for traits to evolve across "fitness valleys". That is, a trait with positive fitness that requires multiple generations to evolve with intermediate generations having negative fitness.
With a large population and a lot of time, random variation makes it possible to evolve across fitness valleys.
atred t1_jacj4vp wrote
> It may be something more akin to flipping 50 or 100 heads in a row.
50 heads in a row has a chance of 1 in a quintillion. Are you sure that's the chance to get an advantageous mutation?
platoprime t1_jabl87a wrote
The chances of a random mutation being adaptive is far far lower than 50%. It's more like getting heads ten times in a row.
atred t1_jacjb4c wrote
10 heads in a row is not a big deal given enough trials... that's what happens.
platoprime t1_jada7qj wrote
Did I say it couldn't happen somewhere? If it could not evolution would not work. What a strange interpretation.
Centoaph t1_jacy5fa wrote
It’s unlikely to get heads on your next 10 coin flips. You’re almost guaranteed to get 10 heads in a row if you flip coins all week though.
platoprime t1_jadam8r wrote
Did I say it couldn't happen and forgot about it?
Centoaph t1_jadgtvx wrote
No, but you're saying the odds are low, but in reality the odds are almost guaranteed. It's rare for an individual. Its certain for a species
platoprime t1_jadhh22 wrote
No I am saying the odds are lower than they stated which is true.
I am talking about the odds of any given mutation being advantageous not the odds of any member of a species eventually getting a beneficial mutation. I have no idea where you got that idea.
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