Submitted by insink2300 t3_11drr8s in askscience
Tiny_Rat t1_jabhwuj wrote
Reply to comment by PatrickKieliszek in Why does temperature determine the sex of certain egg laying animals like crocodiles? by insink2300
>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.
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