Human Evolution

1
Human Evolution
2
The Evolutionary Path to Humans Begins with Early
Primates

• Human Evolution began 65 M.Y.A.
• This time marks the explosive radiation of a
  group of small, arboreal mammals called the
  Archonta
• they were likely nocturnal and were arboreal and
  insectivorous
• their radiation gave rise to different types of
  mammals, including
• bats, tree shrews, and primates
• primates are the order of mammals that includes
  humans

3
Primates

• Distinctive features that allowed them to succeed
  in the arboreal, insect-eating environment
• grasping fingers and toes
• the first digit in many primates is opposable and
  at least some of the digits have nails
• binocular vision
• this permits the brain to judge distance precisely

4
The Evolutionary Path to Humans Begins with Early
Primates

• About 40 M.Y.A. the earliest primates split into
  two groups
• prosimians
• surviving representatives today include the
  tarsiers, lemurs, and lorises
• most are nocturnal
• anthropoids
• these higher primates included monkeys, apes, and
  humans
• the early anthropoids, now extinct, likely
  evolved in Africa

Prosimians
Anthropoids
5
A primate evolutionary tree
6
New World Monkeys vs. Old World Monkey

• The monkeys are a very successful group of
  primates
• New World monkeys
• South American descendants of African ancestors
• all are arboreal, have flat spreading noses, and
  prehensile tails
• Old World monkeys
• descendants of the ancestral anthropoids that
  remained in Africa
• none have prehensile tails
• include both ground-dwelling and arboreal species

7
How the Apes Evolved

• Hominoids evolved from anthropoid ancestors
• hominoids are comprised of the apes and the
  hominids (humans and their direct ancestors)

8
How the Apes Evolved

• Studies of ape DNA have revealed much about how
  living apes evolved
• Asian apes evolved first
• gibbons diverged from other apes about 15 M.Y.A.
• orangutans split off about 10 M.Y.A.
• neither are closely related to humans
• African apes evolved more recently (between 6 to
  10 M.Y.A.)
• these apes are the closest living relatives to
  humans

9
How the Apes Evolved

• Chimpanzees are more closely related to humans
  than gorillas are
• chimpanzees diverged from the ape line less than
  6 M.Y.A.
• the genes of humans and chimpanzees have not had
  time to evolve many differences
• humans and chimpanzees share 98.6 of their
  nuclear DNA
• gorilla DNA differs from human DNA by about 2.3
• gorillas split off from the ape line around 8
  M.Y.A.

10
How the Apes Evolved

• The common ancestor of apes and hominids is
  thought to have been an arboreal climber
• Much of the subsequent evolution of the hominoids
  differs with respect to locomotion
• hominids evolved bipedal walking
• anatomical features include S-shaped spine,
  bowl-shaped pelvis, lower limbs larger than upper
  limbs
• apes evolved knuckle-walking
• anatomical features include slightly curved
  spine, long pelvis, upper limbs larger than lower
  limbs

11
Walking Upright The Beginning of Hominid
Evolution

• As the worlds climate began to change 510
  million years ago, forests began to be replaced
  by savannas, and bipedal apes began to evolve
• Hominids include species of the genus Homo,
  species of the smaller-brained genus
  Australopithecus, and several older lineages
• Hominids are bipedal
• Bipedalism arose 4 million years ago, before
  brain expansion

T. rex
King penguin
12
Fossilized Australopithecus Footprints Laetoli,
East Africa
13
The Hominid Family Tree

• Recent fossil specimens of early hominids have
  been found that date as far back as 6 to 7
  million years
• these fossils are confusing because they show a
  mixture of primitive and modern traits
• there are too few of these very old fossils to
  make certain their connections to
  australopithecines and humans

14
The Hominid Family Tree

• In 1995, hominid fossils dating 4.2 million years
  old were found in the Rift Valley of Kenya
• they were assigned to the species
  Australopithecus anamensis
• they represent an intermediate form between apes
  and A. afarensis
• this species represents a base of the family tree
  for human evolution

15
A hominid evolutionary tree
16
African Origin Early Homo

• The first humans evolved from australopithecine
  ancestors about 2 million years ago
• Homo habilis
• it had a larger brain volume than
  Australopithecus but was similarly short in
  stature
• called handy man because of its association
  with tools.

17
African Origin Early Homo

• Homo rudolfensis
• described from a specimen discovered in 1972 with
  a larger brain capacity than H. habilis
• Homo ergaster
• a species used to describe specimens that have a
  larger brain capacity than H. rudolfensis and a
  skeleton more like modern humans and less like
  australopithecines

18
Homo ergaster
19
African Origin Early Homo

• Too few fossils have been found of early Homo to
  explain with certainty the evolution of Homo
• if two species are accepted, then it would appear
  Homo underwent an adaptive radiation
• because of its modern skeleton, Homo ergaster is
  thought to be the most likely ancestor to later
  species of Homo and is often lumped with Homo
  erectus

20
Out of Africa Homo erectus

• Homo erectus is definitely a true human and has
  been supported by many specimen finds, including
  those of Java Man and Peking Man
• Homo erectus was taller and had a larger brain
  than H. habilis
• the shape of the skull interior suggests that it
  was able to talk
• it was a social species

21
Brain size increased as Homo evolved
22
Out of Africa Homo erectus

• The oldest specimen of H. erectus is from Africa,
  indicating that H. erectus arose in Africa
• Homo erectus survived for over a million years,
  longer than any other species of human
• Homo erectus disappeared about 500,000 years ago
  in Africa, but the species survived even longer
  in Asia

23
Our Own Species also Evolved in Africa

• Modern humans first appeared in Africa about
  600,000 years ago
• According to some scientists, there have been
  three species of modern humans
• Homo heidelbergensis
• Homo neanderthalensis
• Homo sapiens

24
Our Own Species also Evolved in Africa

• Homo heidelbergensis is the oldest known modern
  human
• an Ethiopian fossil dates back to 600,000 years
  ago
• it co-existed with H. erectus in Africa but had
  more advanced features
• it had a bony keel running along the midline of
  the skull, a thick ridge over the eye sockets,
  and a large brain
• its range included parts of Africa, Europe, and
  western Asia

25
Our Own Species also Evolved in Africa

• About 130,000 years ago, Homo neanderthalensis
  appeared in Europe
• compared to modern humans, Neanderthals were
  short, stocky, and powerfully built
• their skulls were massive

26
Our Own Species also Evolved in Africa

• The oldest known fossil of Homo sapiens is
  130,000 years old and occurred in Africa
• Outside of Africa and the Middle East, the
  earliest known fossils of H. sapiens are no older
  than 40,000 years old
• This implies that Homo sapiens first evolved in
  Africa and then migrated to the rest of the world

27
Our Own Species also Evolved in Africa

• Recently-Out-of-Africa model
• this view of Homo evolution states that Homo
  sapiens evolved in Africa and then migrated to
  Europe and Asia
• Multiregional hypothesis
• this view of Homo evolution states that the human
  races evolved independently from Homo erectus in
  different parts of the world

28
Our Own Species also Evolved in Africa

• Studies of human mitochondrial DNA (mtDNA) and
  chromosomal nuclear DNA have helped to clarify
  the controversy over the origin of Homo sapiens
• because DNA accumulates mutations over time, the
  oldest populations should show the greatest
  genetic diversity
• all modern humans of different ethnic backgrounds
  share common ancestor dating back 170,000 years
  ago
• only 52,000 years ago do Africans separate from
  non-Africans
• essentially the migration of Homo sapiens out of
  Africa followed the same paths taken by Homo
  erectus half a million years before

29
Figure 27.9 Out of Africamany times
30
The Only Surviving Hominid

• Neanderthals
• this species of modern human were common in
  Europe in Asia around 70,000 years ago
• they made diverse tools and lived in huts or
  caves
• they did not interbreed with members of Homo
  sapiens
• Cro-Magnons
• fossils of these early members of Homo sapiens
  date back as late as 100,000 years ago in Europe
• they appear to have completely replaced the
  Neanderthals around 34,000 years ago
• they used sophisticated tools and likely had full
  language capabilities

31
The Only Surviving Hominid

• Modern Homo sapiens
• humans eventually spread across Siberia to North
  America about 13,000 years ago
• a recent genomic survey provides clear evidence
• human evolution has been characterized by an
  increase in brain size and the ability for
  conceptual thought

32
Homo sapiens is still evolving