3 ms·
In his 1986 book, The Blind Watchmaker, Dawkins comments: Any engineer would naturally assume that the photocells would point towards the light, with their wir
by joubert 17y ago
In his 1986 book, The Blind Watchmaker, Dawkins comments:
Any engineer would naturally assume that the photocells would point towards the light, with their wires leading backwards towards the brain. He would laugh at any suggestion that the photocells might point away, from the light, with their wires departing on the side nearest the light.
Yet this is exactly what happens in all vertebrate retinas. Each photocell is, in effect, wired in backwards, with its wire sticking out on the side nearest the light. The wire has to travel over the surface of the retina to a point where it dives through a hole in the retina (the so-called "blind spot") to join the optic nerve.
This means that the light, instead of being granted an unrestricted passage to the photocells, has to pass through a forest of connecting wires, presumably suffering at least some attenuation and distortion (actually, probably not much but, still, it is the principle of the thing that would offend any tidy-minded engineer). I don't know the exact explanation for this strange state of affairs. The relevant period of evolution is so long ago.
- gaius 17y agoYou often come across odd stuff like this in machinery. The usual reason is that it made fabrication (or access for repair) easier. Engineering is all about tradeoffs, the "right" design is just one of them.
- wensing 17y agoThat's really fascinating--thanks for elaborating. That said, this isn't, for me, a strong refutation of design. Perhaps the designer's purpose was to create creatures with imperfections such as these, with the higher purpose of communicating something deeper. Or, is there any way of knowing that we won't some day discover there is a very good reason for this?