Brain Expansion in Early Members of the Homo Genus
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Approximately 5-6 million years ago (MY A) the hominid lineage split from that our closest relative, the chimpanzee. For the next 3-4 million years, the cranial capacity of the hominid brain (which was not much larger than that of a chimpanzee), and hominid technological innovation, both remained relatively static. At the end of the Pliocene Epoch (--2.4 MYA), Africa became significantly more arid, spurring significantly extinction and speciation events, including among several hominid species. By 1.9 MYA the Homo genus had emerged, and with it significant brain expansion began. Based on evidence from the fossil record and comparative studies between the anatomies of modem humans and chimpanzees, this significant brain expansion was possible due to changes in the hominid diet that accompanied the emergence of the Homo genus. These changes involved a shift from a diet primarily based on plant food sources, to a more high quality diet that included meat and fish. This shift was necessary due to the high metabolic and nutritionally costs associated with having a large brain. Changes in the anatomical structure of hominids, such as modifications to the skeletal and muscle structure, large fat deposits in hominid infants, and strengthened mirror neuron networks, as well as technological innovations, such as the emergence of tool use and cooking, all may have enhanced hominids access to energy and nutrient rich foods. In addition, climate change at the end of the Pliocene Epoch, and aquatic environments may also have affected hominids in ways allowing them greater access to high energy and nutrient rich food sources.