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3A BIO HUMAN EVOLUTION (knicked from Hamish) Slide 2 Where we fit Slide 3 Primate family tree Slide 4 Hominoids Slide 5 Primate features Slide 6 Ape features Slide 7 Ape vs. Human - skeletal Slide 8 Ape vs. Human – skull Slide 9 Ape vs. Human – brain Slide 10 Ape vs. Human – other Slide 11 Selection Pressures Slide 12 Bipedalism Main Menu WHERE HUMANS FIT IN To find our place it’s worth studying our taxonomic position… Kingdom: Animalia Phylum: Chordata Class: Mammalia Fur wearin’, warm blooded, young bearin’, milk sucklers. Order: Primates Adapted to arboreal life (living in the trees). Family: Hominidae Man-like. Let’s include our ancestors and great apes. Genus: Homo Man Species: sapiens The thinking man! Main Menu PRIMATE FAMILY TREE Evolutionary speaking… Apes branch off here Main Menu Hominoid refers to human-like species (all apes and humans). HOMINOIDS Hominid refers to humans, recent ancestors and great apes. Hominin is used to differentiate man’s ancestors from all else. With recent DNA analysis allowing a more detailed comparison the views of family/subfamily classifications are changing: Chimps Gorillas Orangutans Gibbons siamangs Old Hominidae classification Pongidae/ Paninae Pongidae/ Ponginae Hylobatidae Hominidae/ New Homininae classification Hominidae/ Hominidae/ Hominidae Ponginae Humans Hylobatidae As our DNA is 98.6% the same as chimps, it has also been suggested that chimps be placed in our Genus, Homo. Manual pg 343 Main Menu What are the adaptations for arboreal life that set primates apart? PRIMATE FEATURES • Dexterous hands – for clutching branches (maybe opposable thumb) • Sensitive fingertips with skin ridges with nails, not claws • Eyes front – need to be good at judging distances • Colour vision – recognise ripe fruit Manual pg 360 • Poorer sense of smell, but emphasis on fine vision • Single offspring and extended parental periods - importance of learned behaviour • Mobile hip and shoulder joints • Unspecialised dentition – omnivorous diet • Big bwain we got • Strong social organisation Main Menu APE FEATURES Features of apes: • No tail • Rib cage is flattened • Molars have 5 cusps (monkeys have 4) • Locomotion is brachiating, knuckle-walking, or bipedalism. • Posture partly (or fully) erect… leaving the hands free The Y5 molar pattern Main Menu APES vs HUMANS 1 Major skeletal differences • S –shaped spine • Pelvis is wide and femur comes in (valgus angle); centre of mass is mid-line of body and above the hips • knee joint bigger, big toe not opposable (much), foot arched – all for walking • Great thumb and fingers are less curved – for tool use rather than brachiating Main Menu APES vs HUMANS 2 Manual pg 360 Skull differences Foramen Magnum position is vertical – balanced bipedalism and therefore no nuchal crest (muscle attachment point) Forehead slope Brow ridge Protruding muzzle Nose width Sagittal crest (jaw muscle attachment) Nuchal crest (neck muscle attachment) Cranial capacity (as a proportion of body size) Canine Molars Zygomatic arch (jaw size Diastema (indicates diet) muscle passes through) Main Menu APES vs HUMANS 3 Brain developments • Human have a large brain (1400cm3 vs. ~ 450cm3) Broca’s area Wernicke’s area • Brain includes well-developed cerebral cortex (the folded surface) - memory - speech (Broca’s area) - understanding of language (Wernicke’s area) Cerebellum • Cerebellum (balance and coordination) more developed – bipedal locomotion and tool use Manual pg 364 Main Menu APES vs HUMANS 4 Other things • More sweat glands • Finer, and shorter, hair • Larynx is lower and pharynx longer – for complex sounds • Smaller teeth – ‘cos we used tools instead, as well as having a more refined diet • Rounded jaw – not rectangular Main Menu SELECTION PRESSURES Environment: In Africa around 6 m.y.a. forests were receding, replaced by grassland. This reduced arboreal habitat driving primates onto the ground. Bipedalism: is more energy efficient than knuckle walking – these species can travel further for scarce food. It allows tool use and carrying of young. The body is also kept cooler (less surface area hit by the sun and greater airflow around the body). Height advantage: gained by being upright and being more able to see food and predators. Dentition: due to the nutty and vegetable diet canines reduced and molars enlarged. Hairlessness: reduces parasites, assists cooling. Brain size: increases correlate to tool use 2.5 m.y.a. and more recent developments are thought to be parallel to communication improvements. See manual pg 360 Main Menu BIPEDALISM The change to bipedalism is thought to have been explosive – within 2 million years or less. What could cause such a rapid evolution? Infant held more by mothers arms More time standing and walking Increased air currents over body Infant less able to grasp mother More forwardly directed big toe More sweat glands beneficial Less body hair beneficial Infant less able to grasp mother Manual pg 361, 362