Human evolution

Classification of Modern Humans: Kingdom – Animalia

Phylum – Chordata Subphylum – Vertebrata

Class – Mammalia Order – Primates

Family – Hominidae Genus & Species –

Homo sapiens

Primate evolutionary tree

• Primate characteristics: • Front-facing eyes –

• Broader field of view• Depth perception

• Color vision• Grasping hands (prehensile)• Movable fingers & toes with flat nails (not

claws)

There are two suborders of primates:•Prosimians – include lemurs, tarsiers & lorises•Anthropoids – include monkeys, apes & humans

•Anthropoid characteristics:•Flexible shoulders & forelimbs that can rotate•Opposable thumb (and sometimes great toe)•4 pair of incisors•Large brain relative to body size high level of problem-solving

• Hominid: a primate that can stand upright and walk on two feet (bipedalism).

• 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

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•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 - 4.4 MYA; less apelike than the older fossil.

•In general: •Earliest known hominids•Ape-like teeth•Some bipedal features – probably not fully bipedal

•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?

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• 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 – 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.

Origin of Life• Earth formed 4.5 billion years ago – initially a

frigid ball of ice• Decay of radioactive elements inside earth release

energy, rock layers move releasing molten lava, and meteor crashes into Pacific converts planet into blazing scene of molten lava, black ashen skies, and towering infernos

• No life existed in these conditions

•3.8 billion years ago, earth begins to cool – atmosphere consists of methane, hydrogen, and ammonia

•Experiments by Stanley Miller in 1953 tested the hypothesis that small organic molecules were formed at the ocean’s surface when hit by lightning.

•The first atmospheric gases (methane, ammonia, and hydrogen) were placed into a closed system, heated, and circulated past an electric spark to simulate lightning.

•A variety of amino acids and organic acids formed.

Miller’s experiment

• Once a plasma membrane formed, a pre-cell (proto-cell) could have come into existence (1st life would have appeared in the oceans).

• Energy for the chemical reactions could have come from ultraviolet radiation, volcanoes, comets, or from oceanic hydrothermal vents.

• The early atmosphere lacked oxygen and also a shield of ozone

Origin of the first cell(s)

•1st cells were heterotrophs – got food from environment•Cells who evolved ability to take in energy from environment and use it to make their own food had advantage – photosynthesis added oxygen to atmosphere.•Eukaryotic cells (cells with a nucleus) evolve.•Multicellular organisms begin to appear in the ocean – land not yet suitable for life.

•UV light converts some of this oxygen into ozone layer, which once developed will protect the earth from harmful UV rays – will make life on land possible.•Abundance of oxygen in atmosphere leads to evolution of complex life.•Cambrian explosion – burst of simple animal life – mollusks, crustaceans, starfish.