Coevolution is – at a glance – a remarkable thing. But upon reflection earlier today I feel like it probably should not be so. The reality that eyes were naturally selected in multiple locations of the planet separately should not be all that marvelous. The eyes themselves certainly, the amount of complexity you can add to something with small tweaks and millions of years is pretty neat.
But the appearance of eyes in different places at different times is not all that interesting. I’ll tell you why. Which is good because if I didn’t you’d be wondering why I mentioned it. The reason that eyes coevolving do not impress me is because the variable that gives them power is “universal”. Light shines on every inch of the surface of the planet (I’m exaggerating slightly), it is plentiful in ways that few other resources are.
It is only natural that something this plentiful that has a positive impact on survival and reproduction would be found being selected in different places at different times. To help extrapolate on this I’m going to make up a scenario that helps describe it a little simpler.
Imagine if you will a seed. This seed will cause anything that eats it to be twice as fertile as animals that don’t eat this seed. However the seed requires a strong bite to crack it. Randomly in a population of squirrels some of them have stronger jaws. Just like you and those in your family tree might be taller than I and those in my family tree, this strain of squirrels has strong jaws.
They begin cracking these seeds and reproducing at a rate of 2 to 1. For every 1 “non-jaw” squirrel you have 2 “jaw” squirrels. Naturally these jaw squirrels are also eating regular food, fighting for land, and so forth. As these numbers are stressed further the “non-jaw” squirrels will begin to die out because they cannot maintain against the growing horde of strong jawed squirrels.
You’d have to be nuts to go up against us!
Additionally predators would be likely equally consuming both parties but the increased reproduction rates of the “jaws” would lessen the blows of predation. But this wouldn’t only be the case for squirrels! Anything that could have a strong enough jaw to eat these seeds would also be seeing this result! So those animals would begin to see less and less weak jaws and more and more strong ones!
Imagine then if these seeds were plentiful in both Africa and Europe. None of the species involved need ever meet, need ever breed, and need ever split from one another. In both locations completely independently the animals will naturally select towards animals that can eat the seed. Because the alternative is less babies and less genetic influence.
The same is true for the sun. The sun is this magical food source. Most animals and most plants receive numerous benefits from the sun that they would die without. The alternative to the sun in most cases is less efficient and results in weaker offspring, less offspring, and less physical prowess.
It is for this reason that things like hands, feet, eyes, and other organs “evolve” in completely separate places at completely separate times. Because the things that influence those changes are found in equally copious amounts in both locations!
Not magical, not marvelous, really quite obvious once you think about it. Coevolution is still neat but only because it reminds us about how little you need to get something pretty darn fascinating (like a squirrel).