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8_1 Explaining Hominin Adaptations_lecture script.pdf

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Simon Fraser University
ARCH 131
Dennis Sandgathe

UNIT 8EARLY HOMININ ADAPTATIONS Slide 1 Title slide Slide 2 There are several characteristics of hominins that tend to make us unique from other mammals and most other primates and Human Origins researchers have been grappling for many years trying to develop hypotheses that might explain why hominin evolution and adaptation followed these specific trendsSlide 3 Three of the more prominent ones arelarge brainswhy have primates in general and hominins more specifically developed such a high degree of Encephalizationbipedalismwhyand how did our early hominin ancestors become bipedalreduced haircoverwhy have humans become essentially hairless In the world of mammals we are almost entirely unique in this respectA fourth characteristichunting and meat eatingis certainly not unique to us among mammals and not unique among primates even but has traditionally been seen as a defining characteristic of humans The main question here is how important was hunting and meat eating to our ancestors and our evolutionary development And if it was important then why did it become so important when the evidence seems to indicate that prior to the emergence of apes and hominins most primate species were likely predominantly vegetarian or ate insects Slide 4 Lets begin by examining hypotheses associated with our trend towards ever increasing Encephalization Increasing brain size has been an ongoing trend throughout primate evolution and especially in the line that lead to modern humans Since the evolutionary split with our common homininape ancestor sometime between 6 and 8 million years ago brain size has increased perhaps 3 or even 4 fold This is a very rapid increase in size over a relatively short period Slide 5 However as we briefly discussed earlier we need to express brain size as a function of body size since among most animals simple raw brain size seems to be more a product of body size and less of an accurate reflection of intellectThe ratio of brain size to body size is what we call Encephalization quotient or EQ and EQ seems to be far more informative about intelligence than simple raw brain size although detail of brain structure is also very important Slide 6 This table presents the Encephalization Quotients of a range of living primates including us There are different EQ formulas used by different researchers and therefore you will see slightly different EQ values given in different textbooks for the same species of primate but they all express the same concept An EQ value suggests that that species brain is that many times what it should be relative to its body weight compared to an average for the whole of the class mammalia For example the EQ value for the average chimpanzee given here 20 suggests that its brain is 2x larger than we would expect it to be for an average mammal of comparable body size as expressed using the same EQ formula Slide 7 This table presents some estimated EQs for some of the more important species in the hominin line While not exactly in the order of when they first appeared along that line you can still see in the righthand column and starting at the bottom of the chart that increasing
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