Chapter 32 Section 3: Human evolution

Classification of Modern Humans: Domain - Eukarya Kingdom – Animalia Phylum – Chordata Subphylum – Vertebrata Class – Mammalia Order – Primates Family – Hominidae Genus & Species – Homo sapiens

Primate evolutionary tree

Primates: Examples – humans, monkeys, apes, lemurs and tarsiers Adapted for the trees Characteristics: Forward-facing eyes – Broader field of view Binocular vision = Depth perception Grasping hands (prehensile) (Most also have grasping feet)

There are two groups of primates: Prosimians – include lemurs, tarsiers & lorises Anthropoids – include monkeys, apes & humans Anthropoid characteristics: Active during the day Opposable thumb (and sometimes great toe) Large brain relative to body size  high level of problem-solving

Hominid: a primate that can walk on two legs Bipedalism – walking on two legs Characteristics of hominids: Bipedal S-shaped spine Short arms (relatively) Bowl-shaped pelvis Thighs angle in under body Spinal cord exits at bottom of the skull Canine teeth are smaller than other primates

What makes bipedalism possible? Pelvis: grew wider; developed hip joint and muscles to stabilize pelvis Spine: lengthens; becomes more s-shaped, moving center of gravity forward to help with balance

Femur/thighbone: angles inward to allow for support under torso Knee joint: groove in femur keeps knee joint from sliding off Big toe: loss of opposable toe; muscles associated with opposable toe realign under foot Foot: muscles from opposable toe realign to become arch; arch acts as shock absorber

Why can’t gorillas walk on 2 legs?

But what about the gorilla in the news recently who walked upright?

Possible advantages to bipedalism: Easier to get food – for reaching up into trees to get food or collect food when foraging on the ground Allows males to carry food to females – may have mated more often Easier to keep cool in hot sun – les surface area exposed to sun, more to cooling wind Able to see further over horizon – protection from predators

Hominids: Ardipithcus Australopithecus Paranthropus Homo habilus Homo erectus Neanderthals (Homo neanderthalensis) Cro-magnons (Homo sapiens)

Ardipithecus Oldest fossil found – 5.8 to 5.2 million-years-ago (MYA); found in Ethiopia More recent find MYA; less apelike than the older fossil. In general: Bipedal – upper pelvis, leg bones & feet – still retained ability to climb trees Didn’t climb like modern apes, but used palm- walking like extinct apes Opposable big toes on foot – less flexible than apes; no arch in foot

Hands more flexible than chimps; capable of catching things on ground while walking on 2 legs 47 inches tall; weighed 110 lb. Environment grassy woodland with denser portions of forest and freshwater springs Smaller canines – suggests pair-bonding among males and females – omnivorous diet Social system where males helped females and offspring forage for food – carrying food in wooded environment easier if bipedal – may explain why bipedalism evolved

Australopithecus Around from 4 – 1.4 MYA Location – E. Africa Diet – fruit, plants, eggs, insects Posture – bipedal Height – 3.5 female, 4.5 male Skull – crest & ridge present, protruding jaw Brain – chimp-sized Long arms, short legs  tree dwellers?

Two forms – Gracile & Robust; many species Gracile Australopithecines – Petite body frame Most likely fed on fruits & leaves Robust Australopithecines (formerly referred to as Paranthropus) – Strong upper bodies Massive jaws with chewing muscles anchored to brow ridge Fibrous diet including hard nuts

Australopithecus afarensis

Human evolution

Homo habilis – “Handy man” Present at about 2 MYA in S. & E. Africa Brain bigger than Lucy; rounder skull, less prominent ridges 3.7 – 4.2 feet tall Cheek teeth smaller - omnivorous diet Made stone tools – cut marks on animal bones found nearby indicate tools used to get meat Speech areas of the brain enlarged and contributed to the beginning of society and culture.

Homo erectus (called Homo ergaster now by some) Present between 1.9 and 0.3 MYA Bigger brain, flatter face, nose projected – adapted for hot, dry climate Striding gait like modern humans First to move out of Africa into Asia and Europe about 1 MYA. Males were about 6 feet tall and females approaching 5 feet, much taller than earlier hominids – arms & legs in human proportions. H. erectus was the first hominid to use fire (charred bones found nearby) and tools of this time were advanced axes and cleavers.

Homo erectus

Neanderthals - Homo neanderthalensis 230,000 – 30,000 ya in Europe & Asia The Neanderthals lacked a high forehead and a significant chin; had massive brow ridges Lived in Europe and Asia during the last Ice Age – 5 ft. tall; heavy, stocky build for cold Neanderthals had a brain larger than that of modern humans – possibly to control larger muscles; less well-developed Neanderthals lived in caves, made stone tools & clothing, cared for their sick & buried their dead with flowers.

Neanderthals

Cro-Magnons – early modern Homo sapiens Evolved about 100,000 ya Moved into Australia & North America High forehead, no sagittal crest or brow ridge First to have a thoroughly modern appearance. Advanced tools - stone tools with handles of wood or tar; some made tools from bone, antler, & ivory; bows & arrows, animal traps Efficient hunters & home builders. Art - paintings on cave walls, animal carvings, flutes Domesticated animals First calendar – lunar phases

Cro-Magnons

Evolution of Modern Humans Two contradicting hypotheses have been suggested about the origin of modern humans, Homo sapiens, from H. erectus. The multiregionalism hypothesis suggests that modern humans originated from H. erectus separately in Asia, Europe, and Africa. The out-of-Africa hypothesis states that modern humans originated in Africa and, after migrating into Europe and Asia, replaced the archaic Homo species found there.

Multiregional continuity hypothesis

Evidence for multiregional hypothesis: Bones with a mix of Neanderthal and modern traits found “Modern” tools found with Neanderthal bones No evidence of warfare between the groups 60,000 years together in Middle East – culture indistinguishable

Out-of-Africa hypothesis

Evidence for Out of Africa hypothesis: Mitochondrial DNA (mtDNA) Fossil evidence of hominid migration Any interbreeding that occurred was evolutionarily insignificant Modern Homo sapiens would have been intolerant of competition

Trends in Human Evolution: Location – Africa to all over world Brain size – increased Face area of skull – decreased Jaw – smaller, less protruding; U  V shaped Teeth – smaller (especially canines) Sagittal crest & brow ridge – disappeared Posture – bipedal Wider pelvis, s-shaped spine, angled femur, toes aligned, addition of arch, knee joint

Advantages of bipedalism: free hands to gather food, use tools, stay cooler in hot sun, scan horizon for predators Intestines – smaller Diet – less vegetation, more meat Hands – longer thumb, shorter fingers  allowed for tool use Arm/leg length – longer legs, shorter arms  life out of the trees Height - taller

Link between brain size, tool use, and meat-eating: Bigger brain – more intelligent More intelligent – make tools Make tools – hunt & eat meat Eat meat – more protein – helps brain grow Also due to brain size – development of art, music, language, family, rituals, etc.