[FRIAM] bilateria

[glen]

On 7/13/25 7:46 AM, Prof David West wrote:
> *Initial Question/Answer*: Why to so many species, including human beings, have brains with two distinct lobes? Because they must be capable of two simultaneous activities. Using a bird to illustrate; one activity is to locate and consume food, the other is to watch the sky for predators. Tentative conclusion, one lobe of the brain specializes in "manipulating the World," the other in "attending to the World."

I don't think it's unreasonable to suggest that symmetry is exploitable. So when asking why do so many species have a bicameral brain, we might first ask why so many species are bilateral. There is good correlation between a bilateral body and bicameral brain. The octopus is a familiar exception.

And if we talk about the prevalence of bilateral body types, we might also ask about the prevalence of other symmetries (radial, biradial, etc.). I think the consensus is bilateralism comes from directionality, gradient following. E.g. we might propose that animals with heads have lots of sensors up front because it's better to drive looking out the front window than looking in the rear view mirror. And it makes some sense for a land-walking creature that the horizontal axis is more free than the vertical axis. (Sea or air creatures? Not so much maybe.)

But again, does this exploitation of symmetry (and all the little control muscles required) compose to TWO simultaneous activities? No, not by a long shot. A more general description is that of a bushy coupling of feedback oscillators across many scales. In, for example, a crab or spider ... or a basketball player, you still have a mostly 1 dimensional movement space. But you also have the ability to dance from front to back and maybe even *jump*. Asserting that a bicameral brain is tightly coupled to forward movement just because bilateral body types are so coupled is a fallacy of composition.

Now, I'm sensitive to the argument that all this falls under parallax, even radially symmetric body types and the 9 octopus ganglia. And bi- vision, hearing, etc. is a simple form of parallax: triangulation. But the parallax we engage in when, say, composing a piece of music need NOT be bi-. It seems kinda silly to assert that it is only bi-. We love ... love, love, love, love (false) dichotomies. There are only 2 kinds of people in the world, those who believe in dichotomies and those who do not. >8^D

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