Re: Holloway/Morgan ...the BAH....
Lloyd Jacobs (snoop@r-node.io.org)
31 Jul 1995 23:52:06 GMT
Ralph L Holloway (rlh2@columbia.edu) wrote:
: serious the loss is to intelligent social behavior. Most of the fossil
: hominids had fairly short lives, with a few exceptions, and thus their
: brain sizes were largest in their living days, before aging would have
: wiped them out, so to speak. I think it is easier to look at the larger
: size as something coming out of embryological development that allowed
: for early learning to be efficient and adaptive, rather than as a buffer
: against aging. It is not clear that the regulator genes responsible for
Probably most hominids did die young, but perhaps there were a few that
survived as elders who would function as an invaluable repository of
cultural and technical knowledge. (Speculation here of course)
Undoubtedly though, the health of primitive hominid brains was affected
more by things such as disease, famine and trauma than mere natural
aging, thus a critical loss of cells in ancient brains (up to and
including 19th century homo sapiens sapiens) coming into play earlier
relative to present day humans. As well, the brain must have a
considerable ability to repair itself on a continuing basis in order to
maintain existing high performance in humans.
: hypertrphy and hyperplasia of the nerve cells (neurons and neuroglia)
: operate very differently between ourselves and chimpanzees. Noone has
: idetified any such genes yet, that i know of. But the hyperplastic
: aspect seems to commence early in humans, perhaps lasting somewhat longer
: than in chimps, and then is followed by a longer period of hypertrophy,
: during which as the cell size increases, and the perikarya enlarge, there
: is more material available to increase the amount of dendritic branching
: in the nerve cells, and thus synaptic connectivity, and thus too,
: neuroglia ratios, as these are important for metabolic sustenance and
: exchange.
Demanding newsgroup. Couldn't the increased dendritc branching
facilitate improved collateral regeneration (the process by which damaged
nerve pathways in the central nervous system are repaired by surrounding
cells rather than the cells directly involved, if I interpret the
Encyclopedia Brittanica correctly)?
: The recent announcement, by the way, by Witelson et al, regarding an
: increased neural density in female brains should mean LESS, not MORE,
: synaptic connectivity, if the neural geometrics are the same between
: males and females.
If synaptic connectivity has something to do with neuronal redundancy it
may imply females have less of a need for a tough brain (better immune
system, more fat reserves to tolerate famine, they aren't clobbered over
the head as often etc.).
Lloyd
--
There's a Fundamentalist reborn every minute!
|