The human retina is constructed backward: The light-sensitive cells are at the back, and the nerves emerge from the front and go back through the retina into the brain. Hence the blind spot. To a human engineer, this looks simply stupid—and other organisms have independently evolved retinas the right way around.
This isn’t entirely accurate—there are advantages to having the retina at the back, because the nerve improves visual precision. I don’t recall exactly how this works, but I read about it in Life Ascending by Nick Lane if anyone wants to verify it.
The Achilles’ heel of such thinking is that you can find arguments for or against anything. Despite some workarounds that got selected for to make the “darn thing work at all”, the general failure mode is quite evident from a phylogenetic trace, from an engineering standpoint and from the way that evolution on average only selects for neutral or greedily beneficial mutations.
After a certain point there was just no stochastical way for the retina to invert itself back to “sane architecture”, it would have necessitated too many mutations at the same time. Same time, because otherwise the intermediate steps would be at a clear disadvantage and thus would not propagate.
chkno linked an excellent paper in the other response.
This isn’t entirely accurate—there are advantages to having the retina at the back, because the nerve improves visual precision. I don’t recall exactly how this works, but I read about it in Life Ascending by Nick Lane if anyone wants to verify it.
Life Ascending claims that the neurons out in front may act as a “‘waveguide’” to funnel photons more efficiently to the light-sensitive bits.
This topic is treated in much more depth in Live Cells as Optical Fibers in the Vertebrate Retina, which I read as marveling at how the darn thing works at all.
“there are advantages to having the retina at the back”
Such invented reasons are irrelevant because they aren’t why the eye is the way it is.
There are advantages to dying at age 30, too.
The Achilles’ heel of such thinking is that you can find arguments for or against anything. Despite some workarounds that got selected for to make the “darn thing work at all”, the general failure mode is quite evident from a phylogenetic trace, from an engineering standpoint and from the way that evolution on average only selects for neutral or greedily beneficial mutations.
After a certain point there was just no stochastical way for the retina to invert itself back to “sane architecture”, it would have necessitated too many mutations at the same time. Same time, because otherwise the intermediate steps would be at a clear disadvantage and thus would not propagate.
chkno linked an excellent paper in the other response.