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 - 4.4 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 palmwalking 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.