Biology Reference
In-Depth Information
Putting the lunate sulcus aside for the moment, I find it interesting
to compare my sulcal identifications for the Taung endocast (figure 7)
with Dart's previously unknown identifications, which have just sur-
faced (figure 8). To my surprise and delight, Dart saw and illustrated
every single sulcus that I identified on the Taung endocast, although
our names for some of them difered—particularly at the back end of
perceptions of sulci contrasts with the opinion that “almost none [of the
sulci] can be identified with any certitude. . . . There is simply too much
damage and lack of clarity on the rest of the frontal lobe of the Taung
specimen to attempt such categorical labeling of gyri and sulci.”
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The lunate sulcus has been such a lightning rod for debate because it
is a feature that clearly distinguishes human from ape brains. As shown
in figure 5, apes have a lunate sulcus that is far forward on their brains.
Humans do not, and for over a century scientists have believed this
to be the result of the lunate sulcus's displacement toward the back of
the brain by the enlargement of cortical association areas in front of
been identified toward the back of human brains, which is where Dart
depicted the sulcus when he misidentified the lambdoid suture as the
lunate sulcus on Taung (figure 5). A recent magnetic resonance imaging
(MRI) study on the sulci of 110 living people, however, raises serious
questions about whether or not human brains ever have lunate sulci like
sulci were found near the back of the brain, appearing crescent-shaped
like the lunate sulci of apes, the resemblance proved to be merely
superficial, because, unlike in apes, in people these sulci did not extend
beneath the surface and did not approximate the front border of the
primary visual cortex. It may, thus, be that lunate sulci that once bor-
dered the visual cortex in our ancestors simply disappeared as brains
enlarged and became internally reorganized over time. Lunate sulci
do not reproduce well on endocasts of apes, so it is not surprising that
