Title: Human Evolution
1Human Evolution
2The 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
3Primates
- 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
4The 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
5A primate evolutionary tree
6New 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
7How the Apes Evolved
- Hominoids evolved from anthropoid ancestors
- hominoids are comprised of the apes and the
hominids (humans and their direct ancestors)
8How 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
9How 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.
10How 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
11Walking 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
12Fossilized Australopithecus Footprints Laetoli,
East Africa
13The 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
14The 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
15A hominid evolutionary tree
16African 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.
17African 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
18Homo ergaster
19African 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
20Out 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
21Brain size increased as Homo evolved
22Out 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
23Our 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
24Our 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
25Our 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
26Our 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
27Our 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
28Our 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
29Figure 27.9 Out of Africamany times
30The 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
31The 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
32Homo sapiens is still evolving