Regularities in brain evolution?

KathieDon (
22 Aug 1995 23:18:03 -0400

Hello. I'm an "amateur" paleoanthropologist with an interest in brain
evolution, esp. human brain evolution. In Science (16 June 1995), Finlay
and Darlington propose a model of brain growth across mammals. They
suggest that the size of any one brain feature correlates more stongly
with overall brain size than with any other feature of the organism. A
suggestion here, then, is that the brain expands as a whole, not
piece-meal. Therefore, I speculate, no one feature of the human brain
(large neocortex, large cerebellum, large limbic system) needs
explanation--what needs explanation is why the entire brain expanded.
I think that something of a "decoupling hypothesis" is called for
here. The decoupling was brain growth from body growth. Under this
picture, a mutation or, more probably, linked series of mutations resulted
in "runaway brain growth," which in turn permitted new functions (i.e.
behaviors and mental processes), which proved to be adaptive in the
environment at that time. I would tentatively use this idea to explain
the divergence of early Homo from Australopithecus, and possibly also the
divergence of Homo sapiens from Homo erectus.
I'd appreciate any comments on this approach to thinking about brain
evolution. For personal replies, please send messages to:

Carl Sachs