The lateral brain-tail connection

This is too weird:


That's from a NY Times article by Sandra Blakeslee. The whole article's about this dog tail-wagging emotional asymmetry.

And then there is all this:


Now that's one messed-up experiment. Chicks raised in the dark, suddenly put out in the open where hawks are circling overhead.



The article ends with a bunch of adaptive-sounding explanations for asymmetry and lateralization of "approach and withdrawal" traits, but nothing very convincing. Personally, I would guess the mechanism is essentially like gene duplication: you get two copies of something, and one of them may mutate to take on new functions. Lateralization should be favored as a pathway above functionally redundant brain structures.

But then, there seems to be incredible plasticity to much of brain development, including lateralization in humans. Maybe lateralization in humans has high plasticity because enlarged human brain sizes are comparatively recent -- there hasn't been a lot of time for the evolution of functional lateralization in the new volume of the neocortex. As it becomes clearer what is new and what is old in the human brain, there will be the chance to test hypotheses about the origins of lateralized functions.