Blue eyes, light and Octopuses

Some remarkable facts about the eye:

1. until 10 000 years ago there almost certainly was no blue-eyed person on the face of the earth.

This blows my mind a bit..Language and culture are both dated back to something like 100 000 or 50 000 years ago (See J. Diamond's excellent book). So for tens of thousands of years, all these people were doing what humans are known for doing so well, which is mostly having sex, fighting and talking (not necessarily in that order), fighting again, drinking, eating, talking again, making tools and art, playing chance games and having sex - and all of them had brown eyes. Mr check-this-out-chicks-I've-got-blue-eyes must have had an incredible success. No doubt he was perceived as marked by the gods. But did it make him more, or less popular? Well you say, we know the genes have spread, so after all the pooh-pooh couldn't have been that bad.

Now it turns out that I have blue eyes, and so has a friend of mine. That's not uncommon, but since we have evidence that all blue-eyed people can be traced back to Mr check-this-out who lived 10 000 years ago next to the black sea, it follows that our common ancester cannot be older than him. And we're not more than 700 generations appart (to pick an upper bound).

2. The human eye (the so-called "camera eye") has evolved between 50 to 100 times independently in other species..

Combined with a demonstration of how it has evolved in humans, this is a wonderfully simple rebuttal of creationists' "look how complex this is, how could it have possibly evolved?" favourite sentence. Well, it evolved in small steps, that were selected because they provided small advantages, and we're nothing exceptional it happened not one but many times. Another hit in the long series of demotions being forced upon the human race.

But there is still a sense in which we are exceptional. Turns out we humans, like all vertebrates, have our optic fibers wired in the wrong direction. Imagine you just came home, and you turn the lights on. But your light switch has its electric wires coming out of the switch, rather than being hidden behind the switch and running inside the wall like in any other reasonable place.

"Thanks for your work, yes, we will call you back. Thank you."

Well the appartment is still ok, I mean the lights work, you can stil hit the switch on and off, but all these wires coming out and dangling down - it's a little bit peculiar. The guy who did this job, well you probaby won't call him back. Unless, of course you're the eccentric who did it.

As a matter of fact, let's assume even more eccentricity: for some reason let us imagine that all your light switches must be packed on the same wall with their wires dangling out, and the wires must somehow find a way to run behind the wall (I know, who would do that, but bear with me. Imagine you're some kind of a contemporary artist, you know, like in another room you have a painting entirely blue that you call art.). Well I guess you would have no choice: there's one place on the wall where you cannot put any light switch because you must drill a big hole there and feed in all the wires from all the light switches.

That's our blind spot: at this place the human eye cannot see anything because there's no retinal cell, only optic fibers bundling and running to the cortex. So what the cortex does is that it interpolates the stimlus that was likely to be there given the surrounding. If the surrounding region was white, the blind spot is filled with white.

Blind spot demo. Click on the image to make it full size. Close the left eye and fixate the cross. If you're not an octopus and if you slowly move the screen back, or forth, at some point the cow will disappear.

Octopuses did it better - their optic fibers are wired ouside-in, not inside-out-and-in-again.. These guys don't have any blind spot, in addition to being awesome at hiding (i would pay big money for this camo trick, but I don't think we have any real idea how they can do that).

3. Until the 19th century, nobody (who lived to tell) had ever travelled at more than 100 km/h.

For this reason, it is unclear to me why quantum mechanics should be less intuitive than special relativity (where thinking about light speed is critical). After all these are speed regimes and space scales that are both entirely alien to us - we did not evolve for them. So should they not be equally unintuitive? Yet I find it possible to grasp the Lorentz transform, I mean that's not completely beyond me with some practice, but after years the double slit experiment still baffles me (see lecture 6).

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