Outline 21:
Human/Hominid Evolution
Primate Classification
Order Primates
Suborder Prosimii
Suborder Anthropoidea
Superfamily Hominoidea
Family Pongidae: apes
Family Hominidae: hominids
Prosimians
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Tarsiers
Galagos
Lorises
Lemurs
Tarsiers, a primitive
Primate (Prosimian)
from Southeast Asia.
A Galago or bush
baby, a primitive
Primate
(Prosimian) from
Africa.
A Slow Loris, a
primitive Primate
(Prosimian) from
Southeast Asia.
Check out the
fingers.
Lemurs, primitive Primates (Prosimians)
from Madagascar.
Anthropoids
• Old World Monkeys
• New World Monkeys
• Hominoids
Monkeys, such as baboons, have tails and
are not hominoids.
Hominoids
• gibbons, orangutans, chimps,
gorillas, humans
• Pongidae: orangs, chimps, gorillas
• Hominidae: the hominids
Ardipethecus, Australopithecus,
Paranthropus, Homo
Hominoids
A lesser ape, the Gibbon from
Southeast Asia.
The Orangutan, a Great Ape from
Southeast Asia.
Dogs: Hominoids
best friend?
Gorillas, Great
Apes from Africa.
And
Hollywood!
Bipedal Gorilla!
Yeah, right.
Chimp
Gorilla
Posture of humans vs. gorillas
Chimpanzees, Great
Apes from Africa.
I’m cool
Chimps are simple tool users
Chimp
Human
Oldest Hominoid
Proconsul africanus, 18 MY old
from Kenya. Looked like a
gibbon.
Proconsul, the oldest hominoid, 18 MY
The Gibbon is a living hominoid
similar to Proconsul.
Timing of Lineage Splitting on
the way to Humans
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Based on DNA studies
Old World monkeys: 33 MY
gibbons: 22 MY
orangs: 16 MY
gorillas: 8 MY
chimps: 7 MY
Genetic Differences
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humans - chimps: 1.2%
humans - gorillas: 1.4%
chimps - gorillas: 1.2%
humans - orangs: 2.2%
Origin of Hominids
• What differentiates hominids from
apes? This is what evolved first.
• Large brain?
• Bipedalism?
Origin of Hominids
• Early hominid brains were the same
size as modern chimps.
• Bipedalism evolved before large
brains. In fact, it was bipedalism that
allowed the evolution of large brains
by freeing the hands for tool use.
Origin of Bipedalism
• Thought to be associated with climatic
change 5 MY ago as spreading glaciers
caused global cooling.
• Global cooling created a drier Africa
with fewer rain forests and more
savannahs.
Origin of Bipedalism
• Earliest hominids were forced to travel
between isolated forests if food was in
short supply.
• This produced selection pressure for
upright walking.
Origin of Large Brains
• Associated with selection pressure for
tool use. Tools to find more food or
defend against predators.
• Bipedalism freed the hands for
extensive tool use, and for carrying
helpless babies.
Origin of Large Brains: Neoteny
• Neoteny: an evolutionary/genetic
process
• A slowing of developmental rates
while growth continues normally.
• Developmental stages are reached at a
later stage or not at all.
Neoteny in Human Evolution. Humans
resemble baby apes more than adult apes.
Humans are said to be paedomorphic.
Chimp
Gorilla
Chimp
Human
Chimp skull on the left, human skull on the right
Chimp
Homo sapiens
Consequences of Neoteny
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Helpless babies
Walk later
Extended juvenile period
Prolonged period of learning
Later puberty
Longer life span
Human babies are weaker and more
helpless than newborn apes.
Consequences of Neoteny
• large brain and cranium
• small face, jaws, and teeth: impacted
wisdom teeth
• naked skin, hair mostly on head
• form of external ear
Consequences of Neoteny
Mosaic Evolution
Neoteny does not affect all parts of the
body equally. Some parts are like
juveniles, others like adult apes. We
have retained some juvenile features
yet have reached sexual maturity.
Hominid Brain Sizes
Chimps: 350 cc
Australopithecus afarensis: 400 cc
Australopithecus africanus: 450 cc
Homo habilis: 800 cc
Homo erectus: 1000 cc average
Homo sapiens: 1400 cc average