Human Brain and Race Notes

4 03 mya stedman et al 2004 nature 428 415418

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Unformatted text preview: a of attachment of masticatory (chewing) muscles o Gracilization and increase in cranial size were facilitated by inactivation of the MYH gene that encodes the myosin heavy chain MYH: active gene in chimps and orangutan MYH: inactive in humans • Results in reduced size of muscle fibers individually and the muscle overall Molecular clock estimate for time of gene activation: 2.4 +/ ­ 0.3 Mya (Stedman et al. 2004 Nature 428: 415 ­418) Comparative Neurology o Human brain not simply quantitatively different (bigger) o Qualitative differences are crucial! o Terrence Deacon: searching for special ‘language’ part of human brain Relative Brain Sizes o Rat’s cortex = postage stamp o Monkey’s = post card o Human’s = four pages o Chimp’s = page of printer paper o OR…the neocortex is about the size of two large pizzas Brain Areas that Grew o Frontal lobe, associated with synthesizing information from other areas and inhibiting action o Volume of white matter, brain interconnections, grows faster than neocortex, eventually constituting 34% of human brain o Differentiation of tissue (but only through development) Hypotheses: Why Hominins Evolved Larger Brains o Radiator Hypothesis • • • • ...
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