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
• Primate characteristics:
• Front-facing eyes - stereoscopic vision (depth
perception)
• Cone cells give greater visual acuity – many have
color vision (in those active during the day)
• Flexible bodies
• Opposable thumb (and sometimes great toe)
• Well-developed brain
• Movable fingers & toes; nails (not claws)
• Single birth - extended period of parental care
(Emphasis on learned behavior)
Two sub-groups of Primates:
Strepsirrhines and Haplorhines
• Strepsirrhines (wet-nosed primates)
• Large eyes and ears; rely on smell
for hunting and social interactions
• E.g. lemurs, loris, aye-aye, &
galago
• Haplorhines (dry-nosed primates)
• E.g. tarsiers, monkeys & apes (which
include gibbons, orangutans, gorillas,
chimpanzees, & humans)
• Larger than strepsirrhines, mostly
diurnal, more complex social
behaviors, longer life spans
• Divided into 2 groups – tarsiers, and
anthropoids (New and Old World
monkeys, lesser and greater apes)
• Hominins – preferred term for
humans and our close relatives,
such as Neanderthals
• Bipedal – walk on 2 legs
• Hominids – now used to refer to
hominins as well as orangutans,
gorillas and chimpanzees
• The primate evolutionary tree shows that
all primates share one common ancestor
and that the other lines of descent diverged
from the human lineage over time.
• Humans and great apes shared a common
ancestor.
• Molecular data indicate we are most
closely related to the African apes, whose
ancestry split from ours between 6 and 8
MYA.
Hominins
• To be a hominin, an organism must have an
anatomy enabling it to stand erect and walk
on two feet (bipedalism).
• What makes bipedalism possible?
• Pelvis: grew broader; developed hip
joint and muscles to stabilize pelvis
• Spine: lengthens; becomes more sshaped, 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
Hominins:
•Ardipithcus
•Australopithecus
•Homo habilus
•Homo ergaster
•Homo erectus
•Neanderthals (Homo neanderthalensis)
•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
• First with aligned big toe and arch in
foot
•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
Evolution of Genus Homo
• Classified into the genus Homo if the
following conditions exist:
• Brain size is 600 cc or greater
• Jaw and teeth resemble those of humans
• Tool use is evident.
• We believe the following in this genus are
significant to us: Homo habilus, Homo
erectus, Homo neanderthalensis
(Neanderthals’ relatedness to us is
debatable)
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
•First tool maker - made stone tools – cut marks
on animal bones found nearby indicate tools used
to get meat - scavengers
•Speech areas of the brain enlarged and
contributed to the beginning of society and
culture.
Homo ergaster
• Present between 1.8 and 1.3 MYA
• Taller and lighter than H. Habilus; longer legs,
shorter arms
• Brain average 1000 cm3; rounded skull, reduced
teeth, may have shown first human nose (nostrils
facing downward)
• Hand axes and other tools suggest they may have
been hunters; others think they were still scavengers
• First to migrate in large numbers to Asia and Europe
• Later Eurasian forms of H. ergaster called H.
erectus – an ancestor of humans
Homo erectus
• Present between 1.8 and 0.4 MYA
• Brain capacity of 900-1100 cm3, human-like
teeth; longer skull, lower forehead, and thicker
facial bones; prominent brow ridge
• Same height as modern humans – longer legs
and shorter arms; striding gait like modern
humans
• Adapted to a variety of environments;
sometimes lived in caves
• 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
• 300,000 – 30,000 ya in Europe & Asia
• The Neanderthals had a thick skull, large nose,
had massive brow ridges
• Lived in Europe and Asia during the last Ice
Age – 5 ft. tall; heavy, stocky build for cold
• Some Neanderthals had a brain larger than that
of modern humans – possibly to control larger
muscles; might have been organized differently
• Hunted, skinned animals; may have spoken
• Neanderthals built complex shelters, used fire,
made stone tools & clothing, cared for their sick
& buried their dead with flowers.
Neanderthals
Homo sapiens
• Appeared about 195,000 ya in present-day Ethiopia
• Moved into Australia & North America
• Bigger brain (ave. 1350 cm3); high forehead, no
sagittal crest or brow ridge, rounder skull, smaller
face, prominent chin; thinner skeletons
• Advanced tools: stone tools, with wooden handles;
some handles from 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
• Language and culture
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.
Are Homo sapiens related to Neanderthals?
•Neanderthals and modern human
overlapped for about 10,000 yrs. In the
Middle East and southern Europe
•Some studies suggest they interbred; some
studies suggest they were a distinct species
and did not contribute to the modern gene
pool
•Two theories – Out of Africa hypothesis
and multiregional evolution hypothesis
• The multiregional evolution hypothesis suggests
that modern humans originated from H. erectus
separately in Asia, Europe, and Africa; through
gene flow (migration), all populations
eventually evolved into the one species of
humans seen today
• 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