Nathan Lents: How Did The Eye Evolve?

[T_aquaticus]

@Michael_Callen

My serious obstacle to this is not any single stepwise change (mutation or other) that can occur along the way, but rather how many stepwise changes can occur, undirected, in concert with so many other physiological changes that must also take place. For eyes, there is not just the myriad disparate cells that have different functions, but their construction order, connections to other kinds of cells, and the like. And then, the eyeball is not an island unto itself, but rather there are muscles that move them, lids that cover them, glands that water them, vessels that feed them, ducts that drain them, lashes that shade them, bones that contain them, and so on and so on.

The first step is in realizing that all of these features you list aren’t needed for a functioning eye, and there are species with eyes that lack many of these features. A great example are the Planarians, a group of flatworms:

All they have is an eye cup. It is a pit with light sensitive cells at the bottom. The indentation allows for very crude directionality, but it doesn’t form a focused image and it certainly doesn’t have bones, ducts, and the other stuff you are talking about.