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Darwin himself actually discusses the evolution of eyes; if you're interested you should consider reading it. Eyes are a very, very important part of the history of animal life on this planet.
Here's a very brief summary. Certain creatures can gain a benefit by having light-sensitive cells on the surface of their bodies. If those cells are collected in one spot, they can gain an additional benefit. If those cells have a ridge around them, they gain additional benefit. If that ridge is more pronounced, so is the benefit. If that ridge almost covered the recessed eyespot, there is additional benefit. If that eyespot is covered by transparent cells, further benefit. If the eyespot is filled with transparent fluid, further benefit. If muscles under the eye can cause it to move relative to the body, further benefit.
We have examples, both living today and fossils, of animals at EACH of these stages of the development of the eye - and there's a clear pathway to get from each stage to the next.
In lighted environments, creatures that see survive better than creatures that don't. That, combined with a viable mechanism for sight to develop in some creatures, is enough for evolution to cause sight to dominate most of the multicellular animal world.
The reverse is also true - in dark environment, eyes don't do much. Hence we find cave lizards who have what were clearly at one point millions of years ago functional eyes, but are now completely overgrown by opaque skin because the eyes are vestigial. I don't see any purpose at all for God to design the lizards that way, but from an evolutionary perspective it makes sense - the lizards are descended from sighted ancestors.
Many mammals developed exterior testes because the ideal temperature for sperm to develop is lower than the animals' body temperature. And actually, your argument is more true in reverse - if you were designing a human from scratch you would never put the testicles there, but as an adaptation of reproductive systems over millions of years it's perfectly reasonable than they'd end up there. Evolution doesn't necessarily end up with perfect designs, just configurations that survive to reproduce.
Here's a very brief summary. Certain creatures can gain a benefit by having light-sensitive cells on the surface of their bodies. If those cells are collected in one spot, they can gain an additional benefit. If those cells have a ridge around them, they gain additional benefit. If that ridge is more pronounced, so is the benefit. If that ridge almost covered the recessed eyespot, there is additional benefit. If that eyespot is covered by transparent cells, further benefit. If the eyespot is filled with transparent fluid, further benefit. If muscles under the eye can cause it to move relative to the body, further benefit.
We have examples, both living today and fossils, of animals at EACH of these stages of the development of the eye - and there's a clear pathway to get from each stage to the next.
In lighted environments, creatures that see survive better than creatures that don't. That, combined with a viable mechanism for sight to develop in some creatures, is enough for evolution to cause sight to dominate most of the multicellular animal world.
The reverse is also true - in dark environment, eyes don't do much. Hence we find cave lizards who have what were clearly at one point millions of years ago functional eyes, but are now completely overgrown by opaque skin because the eyes are vestigial. I don't see any purpose at all for God to design the lizards that way, but from an evolutionary perspective it makes sense - the lizards are descended from sighted ancestors.
Many mammals developed exterior testes because the ideal temperature for sperm to develop is lower than the animals' body temperature. And actually, your argument is more true in reverse - if you were designing a human from scratch you would never put the testicles there, but as an adaptation of reproductive systems over millions of years it's perfectly reasonable than they'd end up there. Evolution doesn't necessarily end up with perfect designs, just configurations that survive to reproduce.