CH 6antb19.doc

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Michael Schillaci

CH 6- THE FIRST HOMININS What’s a Hominin? • A phylogenetic species is one encompassing the smallest set of organisms that share a common ancestor and that can be distinguished from other such set of organisms that share a common ancestor and that can be distinguished from other such sets of organisms. • Gibbons genus (Hylobatidae)& Humans (Hominindae)& Orangutans ( Pongo) • Hominini: Tribe within the Homininae comprising humans (Homo), chimpanzees (pan) and our most recent common ancestors. Morphological Trends In Hominin Evolution • Reviewing morphological trends in homini evolution is important for two reasons 1) Understand what features contributed to an adaptive radiation of hominins at a time when contemporaneous fossil apes were disappearing, 2) Understand that there is no singular feature that resulted in the biological evolution of human beings. Rather, modern humans are the result of millions of years if mosaic evolution. Mosaic Evolution: this evolution is ongoing meaning that our species continue to be subject to natural selection. We will change and eventually go instinct. The evolution at different rates of various related or unrelated features or unrelated features within a lineage or clade. • Bipedalism: Habitual upright locomotion on two feet. Dental & Cranial Morphologies • Robust: physically strong, durable • Gracile: slight, slender • Increased Brain Size Why Did Humans Evolve Bigger Brains? 1) Ecological- early hominins evolved larger brains to improve their ability to hunt or forage for unpredictable food sources. A hominin would presumably need to improve its mental map of a large area in order to assure access to food, particularly during periods of resource scarcity. 2) Epiphenomenal- an increase in hominin body size resulted in a concomitant increase in brain size. Epiphenomenal ( refers to a secondary by-product of some process)-ex pain is an epiphenomenal result of damage to parts of our body) 3) Socialization-hominins evolved larger brains to deal with the increasing complexity of an increased ability to network and scheme in large, complex societies. Bipedalism • How to know its hominin bipedalism? -adducted or valgus knee characterizes bipedal hominins? Adducted: Toward the midline of the body. This means that the top of the femur is naturally farther away from the middle of the femur. • How Did Humans became bipedal? - 1) Feeding Postures: this hypothesis holds that early hominins were pre-adapted to an upright posture due to their evolving from an ape-like primate that maintained an upright body posture in the trees. As early hominins transitioned from an arboreal to a more terrestrial lifestyle thy maintained their upright feeding patterns, which led eventually to habitual bipedalism. - 2) Behavior- this hypothesis holds that bipedalism evolved to improve the ability of males to carry food resources to their mates and offspring. In this theory male provisioning was a necessary outcome of the monogamous, bipedal hominins enjoyed increase fitness because they could invest more care and protection into a few offspring. This theory implies a sexual division of roles in infant caregiving, with a female looking after the immediate physical needs of the offspring and a male undertaking much of the foraging needed to feed the female, offspring and himself. - 3) Thermoregulation: this theory holds that bipedalism evolved to improve the heat- dissipating abilities of early hominins. The earliest hominins evolved in equatorial Africa, which has intense solar radiation and heat, particularly in open environments. A vertical body pos
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