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Apparently, some 530 million years ago (give or take) in the #Cambrian age, after about 2.5 billion years of rather plodding #evolution, bi-lateral symmetry appeared in animals (after some dabbling in tri-lateral and penta-lateral symmetry) and when brains showed up they were bi-lateral. #Vertebrate, but still #jawless, fishes were swimming after each other for lunch. #Eyes, which had already existed for a long while, started showing up in pairs, at the head end of the fishes. (1/3)
At first right next to each other, like motorcycle head lamps* and later they separated, making space for a nose. Brain bilateralism took off then. What I’m wondering is, given that bilateral is the way of the world, what was it about 2 eyes, for example, that was better than 3? (Except, of course, in the outflow of the Springfield nuclear plant.) (2/3)
Evolutionary pressures seem to have favored having 2 eyes. 2 eyes let you see and act in 3 dimensions, so maybe 3 eyes just doesn’t give that much of an advantage over 2, when the added cost of maintaining a 3rd eye and a 3rd brain lobe is in the equation?
* A (Very) Short History of Life on Earth, 4.6 Billion Years in 12 Pithy Chapters; Henry Gee, p38.
#science (3/3)
@qurlyjoe Yeah, my thought is why pay for three if you can make do(due?) with two.
@innuendo
Right. No advantage great enough to justify the cost. A pity, really.