1. The Living World George B. Johnson Jonathan B. Losos Chapter 27
Fifth Edition
George B. Johnson
Jonathan B. Losos
Chapter 27
How Humans Evolved
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 27.1 The Evolutionary Path to Apes
the story of human evolution begins around 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 the different types of mammals, including
bats, tree shrews, and primates
primates are the order of mammals that includes humans

3. 27.1 The Evolutionary Path to Apes
primates are mammals with two 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. 27.1 The Evolutionary Path to Apes
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
most are diurnal

5. Figure 27.1 Prosimians.

6. Figure 27.2 A primate evolutionary tree.

7. 27.1 The Evolutionary Path to Apes
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

8. Figure 27.3 New and Old World monkeys.

9. 27.2 How the Apes Evolved
hominoids evolved from anthropoid ancestors from the split that formed Old World Monkeys about 25 M.Y.A.
hominoids are comprised by the apes and the hominids (i.e., humans and their direct ancestors)

10. Figure 27.4 The living apes.

11. 27.2 How the Apes Evolved
considerable controversy surrounds the identity of the first hominoid
very few fossils have been recovered from the period 5 to 10 M.Y.A.
past candidate ancestors include Ramapithecus and Proconsul

12. 27.2 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

13. 27.2 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.

14. 27.2 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
apes evolved knuckle-walking

15. Figure 27.5 A comparison of ape and hominid skeletons.

16. 27.3 An Evolutionary Tree with Many Branches
bipedal locomotion is the hallmark of hominid evolution
Australopithecus is an old and small-brained lineage of hominid
a skull specimen of Australopithecus africanus was discovered in 1924
this specimen was dated to be 2.8 million years old

17. 27.3 An Evolutionary Tree with Many Branches
other australopithecine specimens were discovered after A. africanus
in 1938, Australopithecus robustus
in 1959, Australopithecus boisei
in 1974, Australopithecus afarensis
this was the famous “Lucy” skeleton
in the past 10 years, three additional kinds of australopithecines have been reported
an initial radiation of australopithecine seems to have initiated the evolution of hominids

18. Figure 27.6 Nearly human.

19. 27.3 An Evolutionary Tree with Many Branches
hundreds of fossils from australopithecine have been examined
all have been found in Africa only
the structure of these fossils indicates that they walked upright
their dentition was hominid but their cranial capacity was not any larger than that of apes

20. 27.4 The Origins of Bipedalism
the evolution of bipedalism marks the beginning of hominids
which came first, bipedalism or bigger brains?
evidence of bipedalism extended back 4 million years ago
Indications of brain expansion appeared roughly 2 million years ago
the real reason why bipedalism evolved is controversial

21. Figure 27.7 A reconstruction of an early hominid walking upright.

22. Figure 27.8 The Laetoli footprints.

23. 27.5 The Beginning of Hominid Evolution
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

24. 27.5 The Beginning of Hominid Evolution
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

25. Figure 27.9 A hominid evolutionary tree.

26. 27.6 African Origin: Early Homo
the first humans evolved from australopithecine ancestors about 2 million years ago
Homo habilis
this “handy man” was described because fragments of the first skeleton of this species was found in the 1960s interspersed with stone tools
it had a larger brain volume than Australopithecus but was similarly short in stature

27. 27.6 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

28. Figure Early Homo.

29. 27.6 African Origin: Early Homo
too few fossils have been found of early Homo to explain with certainty the evolution of Homo
if three species are accepted, then it would appear Homo underwent an adaptive radiation

30. 27.7 Out of Africa: Homo erectus
Homo erectus is definitely a true human and has been supported by many specimen finds
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
although younger specimens have been found in Asia, the origin of the oldest specimen of H. erectus is Africa

31. Figure 27.11 Brain size increased as hominids evolved.

32. 27.8 The Last Stage of Hominid Evolution
modern humans first appeared in Africa about 600K years ago
there have been three species of modern humans
Homo heidelbergensis
Homo neanderthalensis
Homo sapiens

33. 27.8 The Last Stage of Hominid Evolution
Homo heidelbergensis is the oldest known modern human
an Ethiopian fossil dates back to 600K years old
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 and a thick ridge over the eye sockets
its range included parts of Africa, Europe, and western Asia

34. 27.8 The Last Stage of Hominid Evolution
about 130K years ago, Homo neanderthalensis appeared in Europe
compared to modern humans, Neanderthals were short, stocky, and powerfully built
their skulls were massive

35. Figure Our own genus.

36. 27.8 The Last Stage of Hominid Evolution
the oldest known fossil of Homo sapiens is 130K years old and occurred in Africa
outside of Africa and the Middle East, the earliest known fossils of H. sapiens are no older than 40K years old
did Homo sapiens evolve first in Africa and then migrate to the rest of the world?

37. 27.8 The Last Stage of Hominid Evolution
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

38. 27.8 The Last Stage of Hominid Evolution
studies of human mitochondrial DNA (mtDNA) 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 170K years ago
only 52K 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 taken half a million years before

39. Figure 27.13 Out of Africa— many times.

40. 27.9 Our Own Species: Homo sapiens.
Neanderthals
this species of modern human were common in Europe in Asia around 70K years ago
they did not interbreed with members of Homo sapiens
Cro-Magnons
fossils of these early members of Homo sapiens date back as late as 100K years ago in Europe
they appear to have completely replaced the Neanderthals around 34K years ago

41. Inquiry & Analysis
Is the angle of the premolar tooth in Lucy’s jaw set at a sharp angle to the tooth row, or square to it?
Based on the comparisons, does Lucy’s upper jaw more closely resemble a chimpanzee or a human jaw?
Figure of Jaws of Chimpanzee, Human, and Lucy