Evolution and entropy

A fair explanation via reddit:

I just had an epiphany on evolution - and understanding where I used to falter. It may help you when you explain it to other people formerly like me.

When most people think of evolution and "survival of the fittest" we tend to think that positive mutations are what makes a species change. Therefore any change that takes place must be positive or it won't take, right?

For example, if a human has no body hair, we must have been aquatic apes at one point and the lack of hair must have been a positive force on our survival for the change to take place?

Possibly for this specific example, but this understanding overlooks one crucial piece of information that can be summed up in one word: Entropy.

This word is missing from many, many people's understanding of exactly how and why evolution (through natural selection) occurs. Simply put, all things in the universe, including the DNA in organisms, have a fundamental tendency to break down over time (or in the case of organisms, over generations through copying errors).

An organisms' makeup, given enough lineal generations, will tend to move down to the bare minimum needed for a survival advantage. This means if a bird does not need to fly to have a survival advantage, after enough generations it will no longer be able to fly (even if the lack of flight does not confer any kind of benefit on it either).

Richard Dawkins explains this example well in The Greatest Show on Earth using the phenomenon we see in cave dwelling animals that are born blind. They obviously have no benefit in being blind. Their eyes do not lose functionality because it helps their survival, since it obviously doesn't. So what gives?

The answer is that their eyes lose their functionality because they have no bearing on their survival at all. Natural mutations pile up and without a force in the environment to make eyes useful, there will not be any difference in the survival rates of the organisms that lose their sight to genetic error and those whose eyes do still work. Natural selection (survival of the fittest) being removed from the equation means that entropy will prevail and the functionality will simply disappear over time. Sooner or later the mistaken code, not being pruned against by environmental factors, will be prevalent in a gene pool.

This is why modern birds lost visible claws on their hands, whales and snakes lost their legs, and why humans lost their body hair. Once we adopted wearing clothing, there was no survival advantage conferred in the form of body hair and it was free to mutate away into oblivion over time.

I hope this made sense. It helped me to write it.