The First Function Cogito Ergo

G. Elliot Smith, both as an anatomical mentor of Davidson Black and as a describer of the Longgushan skull himself, promoted a view of the primacy of the brain in the evolutionary transformation of the human skull. Paraphrasing French philosopher René Descartes, we might characterize this hypothetical stance of embracing the human brain as the prime mover of hominid skull evolution as "cogito ergo sum"-— I think therefore I am." Less metaphorically, in this theoretical stance natural selection placed a premium on human intelligence, and the brain increased in size and complexity as the human species evolved through time. Anatomical changes that we can observe in hominid fossils record this evolution.

Hominid brain size, as recorded by the space within the skull, increased substantially through time. The earlier three-quarters of our known cerebral expansion were entirely unknown in the first quarter of the twentieth century. This early part of the hominid fossil record has been discovered primarily in Africa and mostly in the latter part of the twentieth century. It shows an increase in cranial volume beginning from a chimpanzee-sized brain in early Australopithecus, a fossil hominid genus first published in 1925 but roundly ignored by our protagonists Elliot Smith, Black, and Weidenreich.2

The increase in brain size that occurred in Homo erectus explains some of the characteristics of its cranial form, particularly the more globular nature

Characteristic Homo Erectus

Cranial capacity of Homo erectus compared with other hominids and apes. The cranial capacities of early hominids (Australopithecus and Paranthropus) generally fall within the range of the African great apes (Pan and Gorilla). When the genus Homo evolved, brain size began increasing at a much more dramatic pace. The upper range of cranial capacity in Homo erectus overlaps with the lower range documented for Homo sapiens.

Cranial capacity of Homo erectus compared with other hominids and apes. The cranial capacities of early hominids (Australopithecus and Paranthropus) generally fall within the range of the African great apes (Pan and Gorilla). When the genus Homo evolved, brain size began increasing at a much more dramatic pace. The upper range of cranial capacity in Homo erectus overlaps with the lower range documented for Homo sapiens.

of the neurocranium (that part of the skull containing the brain) compared to the viscerocranium (that part of the skull containing the teeth). A larger brain had to have a larger skull to contain it. Homo erectus has larger, broader, and flatter frontal, temporal, and parietal skull bones than its ancestors. But there are evolved features of other parts of its skull that are not primarily related to brain size increase.

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