Chapter 9 The Evolution of Hominin Behavior

Chapter 9 The Evolution of Hominin Behavior - Chapter 9 The...

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Chapter 9 – The Evolution of Hominin Behavior Hominin Characteristics - Hominins are characterized by a rather distinctive set of evolving traits: 1. habitual bipedalism 2. canine reduction (shortening and blunting) 3. brain enlargement 4. speech and language 5. technology (i.e. tools) Bipedal Locmotion In the Beginning - Hominins diverged from apes sometime between 5 and 7 million years ago - Those ancestral aes were arboreal creatures that engaged in arm-swinging and arm- hanging, as well as quadrupedal climbing - Continuous ground living and bipedalism made survival and reproductive sense, and the transition from tree living to ground living and from quadrupedalism to bipedalism were gradrual Tool Use and Bipedalism - Darwin speculated that bipedalism must have evolved rather quickly among “protohumans” after they began to live on the ground - “The free use of the arms and hands was partly the cause and partly the result of man’s erect posture” - Sherwood Washburn believed that tool use appeared before bipedalism, and that it was the trigger for locomotor change - The connection between the two is still uncertain; modern chimps show that it is possible to use tools and still remain a quadruped - The clear appearance of bipedalism also precedes the appearance of the oldest known stone tools by about 1.7 million years Energy Efficiency and Bipedalism - Bipedalism was favored by selection because it was more energy efficient than the terrestrial quadrupedalism of the latest ape ancestor - The energy efficiency of different locomotor patterns is measured by standardized oxygen consumption (bipedalism is most efficient during moderate walking, but not running) - The earliest hominins had to evolve either energy-efficient locomotor abilities or smaller group sizes (which would have been at a disadvantage for intergroup competition - However, the earliest hominin bipeds did not have particularly energy efficient bipedalism, and wouldn’t have had it until routine bipedalism had been achieved Body Temperature and Bipedalism - The accumulation of heat from direct solar radiation depends on the amount of body surface a creature has exposed and the intensity of the rays
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- The heat buildup of a biped is 60% less than that of a quadruped because of the biped’s minimal surface exposure - Bipeds are also better in their convectional heat loss, which is assisted by the reduction of
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