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 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
Hominids:
•Ardipithcus
•Australopithecus
•Homo habilus
•Homo erectus
•Neanderthals (Homo neanderthalensis)
•Cro-magnons (Homo sapiens)
•Ardipithecus
•Oldest fossil found – 5.8 to 5.2 millionyears-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 precell (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.