Glenn cites Dean Falk as writing:
"But monkeys don't have language and humans do. Are [141/142] there
morphological manifestations of human brains that (a) correlate with
functional lateralizations including language and (b) are capable of leaving
traces in the hominid fossil record? Indeed there are. Shape asymmetries of
the frontal and occipital lobes, known as petalias, exist in human brains
(and to a lesser degree in brains of monkeys and apes) and are statistically
associated with handedness in humans. Further, a characteristic sulcal
pattern associated with Broca's speech area in left frontal lobes is present
in human but not in ape brains. Both humanlike petalis and the pattern of
sulci associated with Broca's area have been detected on endocranial casts
(endocasts) from the early part of the hominid fossil recordi."
Some comments:
1) Falk says "statistically associated with handedness in humans."
This is jargon for, "most times its associated with handedness, but sometimes
not". If these functions are so variable that we cannot even say for certain
that modern humans will have them in the same place, how can we even begin
to speculate about species that are known only from bone scraps hundreds of
thousands of years old?
2) "Have been detected on endocranial casts from the early part of the
hominid fossil record" sounds suspiciously guarded to me. How certain is it
that these patterns are impressions of a Broca's area structure or homolog?
Are there any dissenters in the evolutionary community?
Falk continues:
"The oldest evidence for Broca's area to date is from KNM-ER 1470, a H.
habilis specimen from Kenya, dated at approximately two million years ago.
From that date forward, brain size 'took off,' i.e., increased
autocatalytically so that it nearly doubled in the genus Homo, reaching its
maximum in Neanderthals. If hominids weren't using and refining language I
would like to know what they were doing with their autocatalytically
increasing brains (getting ready to draw pictures somehow doesn't seem like
enough)."~Dean Falk, Comments, Current Anthropology, 30:2, April, 1989, p.
141-142.
Sarcasm aside, I think the argument from size is extremely weak. What do
elephants do with their brains? They are four times the size of human
brains and I don't think all of it can be attributed to learning how to
trumpet. In fact, the brain size of modern human beings vary by almost a
factor of two!!!
Glenn writes:
>I might point out that "homologous" does not mean that it is capable of
>performing the same function. Unless you have a talking rhesus monkey or
>something, I dare say we have experimental evidence that the "lesser" degree
>of structure in the monkey does not control speech. My right arm is
>homologous to the right wing of a bird, but that does not give me the ability
>to say that birds can not fly. Homologous structures may or may not have the
>same function. Obviously the "lesser" structure in the monkey brain, does
>not have the ability to gives speech.
This is exactly my point, Glenn. Brain functions are so complex we have only
the dimmest notion of what various parts of the brain are used for and that
from brains that are traumatically impaired. The idea that we can infer speech
from the presence of something that might be like the Broca's area in modern
humans is farfetched. These endocasts lend some credibility to the idea of
human evolution, but not much.
Glenn continues:
>Thus there is multiple confirmation that Broca's area is involved in speech
>in many different people. Now I have no doubt that there are other areas of
>the brain which process speech, but as far as I know, no other area is in
>charge of the muscles of the larnyx. Does anyone else have any information
>on this?
Again from the Encyclopedia of Human Evolution:
Brain damage to the primary oral-motor area produces paralysis of
the muscles of sound production. Damage to the adjacent Broca's
area may produce problems in producing the complex sounds
sequences of words, without producing paralysis and may also disrupt
grammar and syntax. Individuals with damage to Broca's area are
often unable to use grammatical information, but can still understand
the meanings of content words, such as nouns and verbs. Their speech
is halting, laboured and telegraphic in style, and often lacks verb
tenses or case markings. (p. 120)
Because Deacon (the author of the above) distinguishes between the primary
oral-motor area and the Broca's area, I assume that they are not the same.