Sulcal Skirmishes - The Fossil Chronicles - page 69

tom of the brain in the temporal lobe: “There is present simultaneously
a marked relative widening of the lower portion of the contour, which
corresponds with a relatively increased expansion of the posterior part
of the temporal region, especially in its inferior part.” 37 Interestingly,
Dart attributed the shape of Taung's temporal lobe to an improved
ability for interpreting social sounds and cries: “The process of wid-
ening in the temporal lobe indicates a general improvement beyond
the Chimpanzee in its capacity to recognize the significance of sounds,
and to interpret the significance of the cries emitted by his compan-
ions and the ideas underlying their employment.” 38 However, he did
not think that Taung's temporal lobe was as advanced as the parietal
and prefrontal cortices, because, in his opinion (also expressed in 1925),
Australopithecus had not yet evolved speech.
Dart nevertheless thought that Taung's brain had evolved globally as
a result of bipedalism, rather than in the more piecemeal hind-end-first
manner suggested by others : 39
It would be erroneous to believe that in the assumption of the erect attitude,
the only necessary cerebral development, important as it might be, was a
fine coordination of visual impressions with those streaming into the cor-
tex from the trunk and lower limbs themselves. On the sensory side it also
involved enhanced representation of vestibular sensation [for balance] in the
temporal cortex; in addition to the tactile, [and] muscular . . . delegations
in the parietal cortex. On the motor side the phenomenon was even more
complex; for the ascendancy of the forebrain over the brain stem and the
cerebellum, as a pliable posture-regulating mechanism, is achieved through
descending tracts from the prefrontal, temporal, occipital and probably also
the parietal territories (see Elliot Smith . . . ). The assumption of the erect
posture and the ability to display great muscular skill therefore depends
upon the orderly expansion of all three of the significant cortices. 40
Dart's detailed description of the three advanced regions on Taung's
endocast, combined with the observation that Taung's sulcal pattern
was, in fact, completely apelike, suggests to me that shape changes
associated with cortical expansions preceded changes in sulcal patterns