1. 4 Human Evolution
After you have finished reading this chapter, you should be able to:
Identify important arboreal adaptations of primates and list the
distinguishing features of prosimians, monkeys, and apes.
Discuss the development of bipedalism in the early hominids.
Compare and contrast the characteristics of fossil hominid species.
Mankind stood up first and got smarter later.
Stephen Jay Gould
Introduction
The theory of evolution is one of the most important ideas in science. It
is also a wonderful example of what science does best: tests ideas against
evidence and observations in the real world to determine if the ideas are
correct. The study of how the human species evolved is a good example
of how science has tested the idea of evolution.
II LOOKING FOR HUMAN ORIGINS
It is only natural that we are extremely curious about human origins.
“Where did I come from?” is a question that occurs to every person at
some point in her or his life. “Where did we come from?” is the question
we ask now.
Two hundred million years ago, dinosaurs populated Earth. Those great
reptiles had come to dominate Earth through the adaptive radiation to
life on land that occurred after the evolution of the watertight egg. Living
alongside the dinosaurs, but close to the ground and very small indeed—
about the size of a mouse—were the first mammals. (See Figure 4-1.) Like
72

2. Chapter 4 / Human Evolution 73
all mammals, these ancestors had hair, nursed
their young, and likely maintained a steady,
high body temperature. The early mammals
lived between 220 million and 65 million years
ago. The most common parts of these animals
to be found are their teeth. Because teeth are
covered with hard enamel, they are frequently
preserved as fossils. Studies of these teeth have Figure 4-1 The first
shown that early mammals probably ate mammals lived alongside
the dinosaurs.
LIVING ENVIRONMENT BIOLOGY, 2e/fig. 4-1 s/s
insects, worms, leaves, and fruits.
For almost 130 million years, reptiles were
the dominant life-forms on Earth. Then suddenly, at least by geologic
time, dinosaurs became extinct. Faced with fewer competitors, an enor-
mous variety of mammals evolved, again by adaptive radiation. These
new groups of mammals included the carnivores (cats, dogs, seals, bears);
hoofed mammals (pigs, deer, cattle); rodents (squirrels, porcupines, mice);
whales; elephants; bats; insectivores (shrews, moles); and primates
(lemurs, monkeys, apes, and humans). (See Figure 4-2.)
Tamarin Coyote
Bighorn
Sheep
Porpoise
Squirrel
Mole
Bat Elephant
Figure 4-2 Representatives of the main groups of mammals.

3. 74 Evolution
II ADAPTATIONS FOR LIFE IN THE TREES
The fossils of the earliest mammals indicate that they had five separate
digits on each of their four feet. As explained in Chapter 2, this was a
primitive feature. Fossil remains of various types of later mammals show
feet and hands that evolved into hooves for running, feet for digging,
wings for flying, or flippers for swimming. Mammals whose feet and
hands had fewer than five digits were said to show advanced features.
However, one group of mammals—the primates—through natural selec-
tion kept five digits on their feet and hands. In fact, these digits became
even more fully developed. Eventually the thumb could bend over and
easily touch the forefinger. This is called an opposable thumb; all pri-
mates have this feature. (See Figure 4-3.) What was the great advantage of
an opposable thumb? How did this kind of thumb contribute to primate
evolution through natural selection? An opposable thumb could hold on
to tree branches. Primate evolution began with adaptations suited to an
arboreal life, that is, a life in the trees. An opposable thumb was a very
important adaptation for an arboreal way of life.
Figure 4-3 The opposable thumb is
a great advantage to tree-dwelling
primates.
The order of primates includes prosimians, known as the “lower pri-
mates,” and monkeys, apes, and humans, known as the anthropoids or
LIVING ENVIRONMENT BIOLOGY, 2e/fig. 4-3 s/s
“higher primates.” Many characteristics of modern primates are related to
their original arboreal way of living. For example, a baseball pitcher uses
an amazing shoulder joint, which first evolved to swing from one tree
branch to another. Primate hands—with their fingernails, opposable
thumbs, and strong, sensitive fingers—helped these animals hang on to
branches, hold food, and groom themselves. Primates’ eyes are positioned
close together on the front of the face. Observe how the eyes of nonpri-
mates, such as horses, are on either side of the head. (See Figure 4-4.)
Because their eyes are positioned closer together, primates have stereo-
scopic (3-D) vision. Knowing how near or far an object is becomes a crit-

4. Chapter 4 / Human Evolution 75
Figure 4-4 A horse’s
eyes are far apart, while a
monkey’s eyes are close
together.
ical piece of information when an animal needs to jump safely from one
LIVING ENVIRONMENT BIOLOGY, 2e/fig. 4-4 s/s (rev. 10/10/03)
tree branch to another. You can observe the advantage of 3-D vision if
you close one of your eyes. Notice how the arrangement of objects in
front of you seems flatter; you lose a sense of “depth” in your field of
view.
A life lived in trees poses many hardships and dangers, especially for
the young who need time to develop their skills. Because they could eas-
ily fall to the ground if left on their own, young primates would have
trouble surviving. To ensure the survival of the young, a period of parental
care is vital. Primates are great parents, caring for their young for a long
time. Although humans no longer live in trees, we share many traits from
our arboreal origins with other primates, including prolonged care of our
young until they are able to live on their own.
II A CLOSER LOOK AT PRIMATES
Prosimians, monkeys, apes, and humans are the main groups of primates
alive today. Current research from molecular biology, combined with fos-
sil evidence, indicates that the oldest common ancestor of today’s pri-
mates lived between 80 and 90 million years ago, long before the
dinosaurs disappeared. Weighing less than 2 pounds, this primate ances-
tor, it is theorized, looked like a very small lemur, lived in tropical forests,
and was nocturnal (that is, active at night).
Prosimians include the lemurs of Madagascar and the lorises, bush
babies, and tarsiers of tropical Africa and southern Asia. They are rela-
tively small arboreal animals that feed on insects, leaves, fruits, and flow-
ers. Like their ancestors, the prosimians are often nocturnal. These

5. 76 Evolution
Figure 4-5 This lemur is a type
of prosimian, one of the four main
groups of primates alive today.
animals existed in great numbers in the huge forests north and south of
the equator 65 to 38 million years ago. Today, because of the destruction
of their forest habitats, many prosimians are in grave danger of becoming
extinct. (See Figure 4-5.)
Monkeys evolved from prosimian ancestors about 50 million years
ago. There are two main groups of monkeys alive today. The New World
monkeys, such as capuchins, spider monkeys, squirrel monkeys, and mar-
mosets, are found in Central and South America. (See Figure 4-6.) The
Old World monkeys, such as baboons, vervets, langurs, and macaques,
live in Africa and Asia.
The higher primates, also known as hominoids, include all apes and
humans. Ape fossils found in East Africa show that these primates evolved
from the monkeys of Africa and Asia. The earliest known ape fossils are
of an organism called Aegyptopithecus, which means “dawn ape”; they are
about 35 million years old. This hominoid lived in trees and was about the
size of a cat. Aegyptopithecus migrated across Asia around 25 million years
ago.
The apes include gibbons, orangutans, chimpanzees, bonobos, and
gorillas. Apes are generally larger than monkeys, have larger brains, and
lack tails. They can hang upright from tree branches and have relatively
long arms and short legs.
Because of the close relationship of apes to humans, we are fascinated
by their behavior. Several long-term scientific studies of the apes have

6. Chapter 4 / Human Evolution 77
Figure 4-6 Some monkeys
have grasping tails, an
adaptation to living in trees.
been completed. It is not only our behavior that is so close to that of the
apes; most of our DNA is the same as that of the African apes, too. (See
Figure 4-7.)
Gorillas live in troops of 8 to 24 individuals with one large male as
the leader. Usually peaceful, male gorillas can appear menacing when they
threaten an enemy with screams, broken tree branches, and chest pound-
ing. Female gorillas nurse their infants from two to four years.
Chimpanzees are thought to be the primates most closely related to
Figure 4-7 Chimpanzees—
intelligent apes closely related to
humans—are known to use tools
in the wild.

7. 78 Evolution
humans. In fact, new research has shown that human and chimpanzee
DNA is almost identical. The main difference is that greater quantities of
proteins are produced by human genes, especially within brain cells, than
by chimpanzee genes. Chimpanzee behavior also shows the evolution-
ary closeness. They live in social groups, and the males and females form
temporary bonds to mate. Friends within the group spend long hours
grooming each other. Chimps love to play together and are curious, noisy,
and outgoing. However, they can also be quite aggressive and do fight
with neighboring groups of chimpanzees. Bonobos (sometimes called
pygmy chimps) are also very closely related to humans in their genetic
makeup and behavior. They are considered highly intelligent and tend to
be more peaceful in their social interactions than the chimpanzees.
II HOMINIDS: THE EARLIEST HUMANS
The rising of the Himalayan mountains and drier weather around 20 mil-
lion years ago caused forest areas to diminish in size. At that time, Asian
and African apes became separated from one another. Between 14 and 8
million years ago, from within the African group, the common ancestor
of humans and chimpanzees evolved. This does not mean that our ances-
tors were chimpanzees. We are most closely related to chimpanzees
because we shared an ancestor with chimpanzees more recently than with
any other animal. Very few details are known about this early stage in the
evolution of humans.
One of the most important discoveries in human evolution occurred
in 1924 when a small fossilized skull was found in a mine in Taung, South
Africa. The “Taung child” skull was sent to a skilled neurologist, Raymond
Dart, who recognized that the fossil had humanlike features. (See Figure
4-8.) He concluded that this specimen was the fossilized skull of an early
human, a type of hominid. The appearance of the skull, the size and
shape of the brain case, and the shape of the teeth all showed that this fos-
sil was from an early ancestor on the human family tree. Later fossils con-
firmed that the Taung child walked on two feet. More than any other
feature, walking on two feet is what makes an early human a hominid.
Dart named this 3-million-year-old hominid Australopithecus africanus
(southern ape of Africa). It took 25 years for scientists to accept Dart’s
conclusions. During that time, many australopithecine fossils were found
in different places in Africa. Raymond Dart was indeed correct about the
little skull. Discoveries of more fossils provided additional evidence that
A. africanus walked upright and had hands and teeth similar to ours.

8. Chapter 4 / Human Evolution 79
Figure 4-8 Raymond Dart and the
Taung skull—the fossilized skull of
an early human ancestor.
In 1974, a fossil discovered in Ethiopia became famous worldwide. Sig-
nificant portions of a 3.18-million-year-old skeleton of a female hominid
were unearthed; she was 1 meter tall with a skull about
the size of a softball. This fossil also showed evidence of
upright walking. She was named Lucy after the Beatles
song the scientists were listening to at the time of their
discovery! Donald Johanson, of the Cleveland Museum
of Natural History, led the team of scientists. Further
work showed that Lucy’s species, Australopithecus afaren-
sis, was the ancestor of the A. africanus species identified
by Raymond Dart. Recently, several other more ancient
species have been discovered that bring us ever closer to
the dividing point (about 7 million years ago) between
humans and apes. (See Figure 4-9.)
The most important point about australopithecine
species is that hominids walked on two feet, not four,
for at least 2 million years without much enlargement
of their brain. Bipedalism (walking on two feet) may
have helped hominids gather food and care for their
Figure 4-9 A
young more efficiently by freeing their hands. Tools were drawing of an
not made until much later. That is why evolutionary Australopithecus
LIVING ENVIRONMENT BIOLOGY, 2e/fig. 4-9 s/s
biologist Stephen Jay Gould of Harvard University said afarensis
that “Mankind stood up first and got smarter later.” skeleton.

9. 80 Evolution
Raymond Dart and the Skull of the Taung Child
In the 1920s, large amounts of limestone were being dug from the ground
in Taung, an area of South Africa. Many human fossils were also being dug
up in the limestone quarry. Raymond Dart, an Australian doctor teaching at
the medical school in Johannesburg, heard about the fossils. Dart was an
expert on the anatomy of the human head and was anxious to examine the
fossils—a natural curiosity. Dart contacted the owner of the quarry and, in
time, two large boxes of fossils arrived at his home.
When he examined the material in the boxes, Dart found a dome-shaped
piece of stone and immediately recognized that it was shaped like a brain. In
this fossil, Dart saw the folds of tissue that make up the brain and even the
blood vessels on the surface. Dart realized what had happened many years
before. Long ago, someone had died in the vicinity of this present quarry.
Sand and water that contained minerals had entered the skull; eventually
these materials hardened into rock in the exact shape of the brain.
II WHY DID EARLY HUMANS STAND?
Our earliest ancestors lived in the trees. One of the first big steps on the
path of human evolution occurred when early hominids walked on two
feet on the ground. Where, when, how, and why did this occur?
For more than 100 years, it has been widely believed that the big step
from ape to human occurred the day some apes left the forest. According
to this story, the apes had been spending their lives in the manner of
most forest animals, enjoying the warm, humid days, with plenty of
shade and abundant fruits and berries to eat. For some reason, perhaps
because the forest area was decreasing, they now found themselves out on
the open, where tall grasses, small shrubs, and occasional trees replaced
the forest, in an environment called the savanna. (See Figure 4-10.)
It was drier on the savanna, it took longer to find food, and predators
could see you more easily. Life was harder. To survive, you had to walk
upright on two feet. By being upright you could see approaching danger
more easily. You also had to get smarter. So here are the early hominids
out on the dangerous savanna, while back in the forest the other apes are
still doing what they always did, going about picking fruits and berries in
an environment that was relatively safe.
Interesting story, but does the evidence confirm it? Science is based
on proposing ideas, or hypotheses, that can be tested and then seeing if
the evidence supports or contradicts the idea. The “savanna hypothesis”
is now being thoroughly tested. Evidence against the hypothesis would be

10. Chapter 4 / Human Evolution 81
On close examination, Dart felt that the fossil brain looked like it had come
from an ape, but he recognized that the fossil also had some similarities to
a human brain. The skull, he thought, might provide some clues to the
brain’s origin. Dart looked again in the box that contained the fossilized
brain. Much to his amazement and delight, he found pieces of the lower
jaw and the skull. However, the front of the fossil skull—the face—was
covered by layers of rock. In a procedure that took several months, Dart
chipped away at the rock layers. What he eventually revealed was the face
of a young creature, later dubbed the “Taung Child,” which Dart believed
was an early ancestor of the human species. His find turned out to be one
of the most important hominid fossil discoveries ever made, adding crucial
details to our understanding of human evolution.
hominid fossils that showed upright walking and the ability to climb trees.
Lucy had curved fingers that might have been adapted for tree climbing
even though she could walk on two feet. To support the savanna hypoth-
esis, fossils of other animals and of plants living at the same time as the
hominids would have to show that the climate had become drier, that
the forests had disappeared, and that the savannas remained as an
exploitable food source. In some places in Africa, such as Tanzania, where
3- to 4-million-year-old footprints of A. afarensis, Lucy’s species, were
found, it was definitely very dry, with no forests. However, in Ethiopia,
Figure 4-10 The savanna has tall grasses, small shrubs, and scattered trees.

11. 82 Evolution
where Lucy lived, there were forests as well as open places. Were our
bipedal hominid ancestors savanna dwellers or neighbors of other pri-
mates that lived in the forests?
The oldest hominid fossils found so far, Ardipithecus ramidus, have been
dated at 5.8 million years old. The fossils of these individuals, who lived
in Ethiopia, show that the skull was balanced at the top of the skeleton
for walking erect. Meanwhile, other animal fossils found nearby indicate
that A. ramidus definitely lived in the forest. If careful studies of the A.
ramidus bones show that it really did walk upright, the savanna hypoth-
esis will be disproved.
If some apes began walking on two feet not because they left the for-
est for the open savanna, what other explanations could there be? Why
did some apes begin walking upright if not to gain a selective advantage
out of the forest and on the open savanna? Perhaps standing up on tree
branches, as chimps sometimes do, makes it easier to feed. (See Figure
4-11.) Standing erect to threaten an enemy, as gorillas are known to do,
may have provided a survival advantage maintained by natural selection.
Another explanation that has been offered is that apes that were born
with a slightly greater ability to stand up were better able to gather food,
even in the forest. Males with this advantage could bring food back to
the females with whom they had mated and to their offspring. In this
story, the offspring most likely to survive were those of apes that could
walk erect. This would be a tremendous evolutionary advantage and could
easily have led to the evolution of walking on two feet.
Figure 4-11 There are many
possible advantages to standing
and walking upright, as this
young chimpanzee is doing.

12. Chapter 4 / Human Evolution 83
Once again, science will put this idea to the test, if it becomes a seri-
ous hypothesis. Eventually, the question of why bipedal hominids
evolved will be answered. By then evolutionary biologists will have new
questions to study that have not yet even been asked.
Check Your Understanding
Why is bipedalism such an important characteristic of hominids?
II OUR OWN GENUS
None of the fossils that have been discussed so far belong to the genus of
modern humans, Homo. To be a hominid, as the australopithecines were,
you had to walk on two feet. However, to be a hominid in the genus Homo
(from the Latin word for “man”), you also need to have the enlarged brain
that sets you apart from the other primates.
Lucy’s species, A. afarensis, remained relatively unchanged for almost
1 million years. Then, about 3 million years ago, an adaptive radiation
resulted in the Taung child species, A. africanus, and several other aus-
tralopithecine species with heavier bones and much wider faces. (See Fig-
ure 4-12.) Known as A. robustus and A. boisei, these robust species were
first discovered by Mary Leakey in Tanzania in 1959 and were dated at
1.8 million years ago, using the potassium-argon radioisotope dating tech-
nique. Mary Leakey, her husband Louis, their son Richard, and his wife
Meave, are among the most important scientists who have studied the
fossil evidence of human origins. Much debate has taken place about how
A. robustus and A. boisei fit into the human family tree. Most researchers
believe these species to be separate branches on the tree, branches that
Figure 4-12 Reconstructed fossils of A. africanus and A. robustus
show the differences in their jaws.

13. 84 Evolution
ended long ago. These species did not adapt successfully to changing envi-
ronmental conditions. As a result, they became extinct.
The adaptive radiation that led to the robust, now extinct, australo-
pithecine species also led to hominids with larger brain capacities. The
size of the Taung child’s brain was about 500 cubic centimeters (cc). These
larger hominid skulls, sometimes found along with simple stone tools,
were about 650 cc. Great arguments arose when Louis Leakey first stated
in 1962 that his 1.75-million-year-old fossils from Kenya with the larger
brains belonged to the genus Homo. He named the species Homo habilis,
meaning “handy man.” Most scientists now accept Leakey’s interpreta-
tion. Homo habilis is placed on the human family tree. Although there is
little agreement on how the Australopithecus species are related to Homo
habilis, it is generally accepted that H. habilis led toward modern humans,
evolving first into Homo erectus, which later evolved into Homo sapiens
(modern humans).
All of the early hominid fossils discussed so far have been found only
in Africa. Homo erectus was the first hominid to migrate from Africa to
Asia and into Europe. Fossils of this species were found in Java in 1896
(Java Man), in Beijing, China, in 1929 (Peking Man), and in northern
Kenya in 1984, where the skeleton of a 12-year-old-boy of this species
who died 1.6 million years ago was found in 1984.
Homo erectus had a body skeleton much like that of modern humans.
The 12-year-old boy was 1.7 meters tall and walked like modern humans.
Differences are found in the size of the skull. Their brains, 700 to 1200 cc,
were much larger than those of earlier species and almost as large as those
of modern humans. (See Figure 4-13.) However, their jaws and teeth were
much larger than those of modern humans. Homo erectus skulls had thick,
low foreheads and sloping chins.
1,400
Range
1,200
Brain volume (cm3)
1,000
800
600
400
Australopithecus Homo Homo Homo sapiens Homo sapiens
habilis erectus neanderthalensis sapiens
Figure 4-13 A comparison of the brain volume of several important hominids.
LIVING ENVIRONMENT BIOLOGY, 2e/fig. 4-13 s/s

14. Chapter 4 / Human Evolution 85
By this time, the larger brains of our
hominid ancestors showed that they were
definitely becoming more intelligent.
Much more efficient tools, such as the
hand ax (a stone that has a surface for grip-
ping and several cutting edges), are often
found with H. erectus fossils. (See Figure
4-14.) These are the first hominids known
to build fires, live in caves, and clothe
themselves. With these skills they were
able to migrate to colder northern climates Figure 4-14 A hand ax; such
found outside Africa. H. erectus existed for tools were made and used by
a long time on Earth, from 1.8 million Homo erectus.
years ago to about 300,000 years ago.
There is much debate about recent human evolution. In 1997,
researchers in northern Spain announced the discovery of yet another
ancestor of modern humans, Homo antecessor. They think that the
800,000-year-old fossils from Spain belong to the common ancestor of
modern humans and other extinct hominids. Today, there are two main
views of human evolution. One group of scientists sees it as a ladder, with
one species at a time leading to the next species. The other group sees
human evolution as a tree, with several branches. One branch leads to
modern humans; the other branches lead to extinct hominid species.
II THE HUMAN SPECIES
The migration of humans from one place to another on Earth occurred
long before travel by ship and plane. These early travelers went over land
on foot. Helping them and perhaps encouraging them to move on were
the Ice Ages. These were periods when Earth’s climate cooled, causing
great sheets of ice to move over the land. The levels of the oceans dropped
as water remained on land frozen as ice. Thus humans could walk on
places once covered by oceans, traveling to the island of Java, to the island
continent of Australia, and eventually walking east across the land bridge
in the northern Pacific Ocean to North America. The last Ice Age began
about 1 million years ago and included several periods of deep cold.
Extensive ice sheets covered much of North America and Europe.
Hominids living after Homo erectus colonized a variety of places with
varying climates, including Africa, Asia, Europe, and Australia. As Earth’s
climate warmed, and the ice sheets melted and retreated, early humans
extended their range. These individuals included the Neanderthals, whose

15. 86 Evolution
Figure 4-15 A drawing of how a
Neanderthal might have looked.
fossils have been found throughout Europe1andifthe,YGOLOIB EastMNORwho GNIVIL
s/s 5 -4 .g /e2 Middle TNE and IVNE
had much larger brain sizes than H. erectus—brains about the size of mod-
ern human brains. Some scientists consider them to be members of our
species, Homo sapiens. Others think they made up a separate species, Homo
neanderthalensis. Their bodies were similar to those of modern humans.
However, their faces looked different, with heavier ridges over the eyes, a
long, low skull, and small cheekbones. (See Figure 4-15.) Because of these
differences, these humans, living from about 400,000 to 35,000 years ago,
are usually called early or “archaic” Homo sapiens. They may have been
descendants of the newly discovered species Homo antecessor, representing
one branch of the human tree that has ended.
Neanderthals wore animal skins, made better and more varied tools
than H. erectus did, and buried their dead. We know that they purposely
left weapons and flowers with their dead. These were individuals who
thought about things, including life after death.
All fossils of hominids that lived during the past 30,000 years are like
modern humans both in body and skull size and shape. Modern humans
have an average brain size of about 1350 cc. One of the best-known
groups of these “modern” Homo sapiens is the Cro-Magnons, named for
the place in France where their fossils were first found. Other modern
Homo sapiens fossils, up to 100,000 years old, have been found in Israel
and throughout Africa. Cro-Magnons are well known for their advanced
tools made of stone, bone, and ivory. These tools included spears, fishing
hooks, and needles. In addition, the magnificent cave paintings of these

16. Chapter 4 / Human Evolution 87
Figure 4-16 Cro-Magnon
drawings show the beautiful
forms of many different
kinds of animals, and the
skill of the early human
artists.
humans, which show the beautiful forms of many different kinds of ani-
mals, give us a sense that we are seeing humans like ourselves. Cro-
Magnon fossils are the remains of people like modern humans who
looked and wondered at the world around them, sometimes symbolizing
their thoughts and feelings, for whatever reasons, in the form of art. (See
Figure 4-16.)
II MORE QUESTIONS AND SOME ANSWERS
The study of the history of human evolution is full of controversies, none
being debated more intensely than the question of where modern Homo
sapiens first evolved. This question is considered to be a valid scientific
question because it is assumed that it can be put to the test. It is thought
that evidence will eventually be found to answer the question. Then it
will no longer be just a matter of opinion. This process is an important
part of the scientific method. One hypothesis is that the populations of
H. erectus that had migrated from Africa to a variety of places on Earth
each gave rise to archaic and then modern H. sapiens independently. In
this “multiregional model,” human races in each of these areas arose from
different populations. Breeding between the various populations would
have allowed for gene flow and prevented speciation from occurring.
Today, all human races on Earth belong to one species.
The other hypothesis is that modern H. sapiens evolved from H. erec-
tus in just one place, Africa. According to this “Out of Africa” model, mod-
ern H. sapiens, moving out from Africa, replaced the archaic H. sapiens in
the various places where they met. This is a very different proposal. It
would mean that the varieties or races in the world’s human population
arose in just the last 100,000 years since H. sapiens left Africa, not more

17. 88 Evolution
than 1 million years ago when H. erectus began migrating. Anthropologists
throughout the world strongly support one or the other of the possibili-
ties. Each opposing side claims that the evidence supports its theory. This
scientific question continues to be studied.
Another fascinating question about human evolution concerns lan-
guage. When did humans begin to speak? The answer to this question
remains a mystery. Charles Darwin suggested that human speech evolved
from animal cries. Critics at the time, who were opposed to Darwin’s
views, called this the ”bow-wow” theory. Noam Chomsky, a famous pro-
fessor from the Massachusetts Institute of Technology (MIT), has for more
than 40 years claimed that the rules of human language are built-in, not
learned. How these innate rules could have evolved is difficult to explain.
In 1994, another MIT professor, Steven Pinker, defended the idea that lan-
guage evolved by natural selection, but said he could only guess that it
may have begun with primate calls. Other more recent suggestions are
that language evolved from primate grooming. Apes and monkeys use
physical contact with each other through grooming to establish social
connections. Making sounds might have become a more efficient way of
doing this. In 2002, a New Zealand psychologist, Michael Corbollis, pro-
posed the idea that human language began with hand and face gestures.
He said that the earliest hominid, some 6 million years ago, could not yet
have spoken, but would have had the ability to make voluntary hand and
face movements. A kind of sign language could have developed, eventu-
ally switching from gestures to true speech about 50,000 years ago, after
modern humans had evolved.
In spite of these fascinating theories, the question of where language
comes from may simply be unanswerable. If that is the case, then this
mystery cannot be considered a valid scientific question. Nevertheless,
despite the questions that remain unanswered, we have been richly
rewarded to date in learning so much about the fascinating story of where
we came from.

18. LABORATORY INVESTIGATION 4
How Can We Determine the
Sequence of Hominid Evolution?
INTRODUCTION
In spite of the very incomplete fossil record, scientists who study human
evolution have been able to draw some remarkable pictures of what the
different hominid species might have looked like. Studying these pictures
helps us develop a deeper understanding of human evolution.
One misconception that must be avoided, as the pictures are studied, is
the idea that human evolution is like a ladder with a series of steps lead-
ing from the most ancient hominid species directly to our own species,
Homo sapiens. This misconception often has been illustrated as a parade
of fossil hominids, with the specimens in the parade becoming more
modern as they march across the page.
The more accurate understanding of human evolution is that different
hominid species often existed together at the same time and in the same
place. Also, many of these species evolved along certain pathways that
eventually led to dead ends. Rather than a ladder, a better diagram of
hominid evolution would be more like a bush having many branches,
with our species being at the end of the only branch that still survives.
MATERIALS
“Hominid Species A–H” and “Hominid Data Sheet” handouts (from the
Teacher’s Manual), scissors, glue or tape, unlined paper
PROCEDURE
1. Examine the drawings A–H. These are artistic impressions based on
fossil evidence of different hominid species. Examine them closely.
Identify three characteristics that seem to differ and three characteris-
tics that seem to be similar from one figure to another. Share your list
of observed characteristics with your group.
2. Determine which figure you think represents the earliest hominid.
Determine which figure you think represents the most recent hominid.
Give reasons for your choices. Share your choices with the group, dis-
cuss all opinions, and then reach a consensus.
Chapter 4 / Human Evolution 89

19. 3. Cut out the figures and, as a group, arrange them in a sequence from
earliest to most recent. Glue or tape the hominid drawings to the
unlined paper in the order in which you have arranged them. Make a
list of the criteria that guided your choices. Compare your sequence
with those of the other groups. Discuss any differences.
4. Compare your time sequence to the one determined by scientists,
shown in the Chronology of Hominid Evolution table on the Hominid
Data Sheet. Based on this set of data, would you change your sequence?
Explain.
INTERPRETIVE QUESTIONS
1. Draw a horizontal timeline that is 15 cm long. Let 3 cm equal 1 mil-
lion years, going from 5 million years ago (mya) to the present. Place
the letter for each hominid species listed in the Chronology of
Hominid Evolution table at the correct place on your timeline.
2. Study Diagram A and Diagram B on the Hominid Data Sheet. These
diagrams represent alternate ideas of the evolutionary route from
ancient hominids to modern humans. Write a comparison of these
two different interpretations of human origins.
3. Explain why you think the three different characteristics and three
similar characteristics you observed may be important for determining
the sequence of hominid evolution.
90 Evolution

20. Chapter 4 / Human Evolution 91
II CHAPTER 4 REVIEW
Answer these questions on a separate sheet of paper.
VOCABULARY
The following list contains all of the boldfaced terms in this chapter. Define
each of these terms in your own words.
arboreal, bipedalism, hominid, hominoids, mammals, opposable,
robust
PART A—MULTIPLE CHOICE
Choose the response that best completes the sentence or answers the question.
1. Humans belong to the class of animals known as a. mammals
b. carnivores c. rodents d. invertebrates.
2. Which is not considered an adaptation for arboreal life?
a. opposable thumb b. five digits on each foot c. stereoscopic
vision d. prolonged period of parental care
3. The famous fossil known as Lucy belongs to the species
a. Homo antecessor b. Homo erectus c. Australopithecus afarensis
d. Australopithecus africanus.
4. Primates include a. porcupines, squirrels, and mice
b. pigs, sheep, and deer c. humans, lemurs, and chimpanzees
d. shrews, moles, and hedgehogs.
5. The “Taung child” skull is significant because it a. was the first
fossil of Homo habilis to be discovered b. belongs to one of the
earliest types of hominids c. showed that the earliest primates in
the human line walked on all fours d. indicated that members of
its species made tools.
6. The earliest mammals a. first appeared 65 million years ago
b. varied greatly in size, appearance, and lifestyle c. had five
digits on their front feet and four on their back feet d. are known
primarily from fossil teeth.
7. The earliest hominoid fossils are of a. Australopithecus
b. Aegyptopithecus c. Ardipithecus d. Homo.
8. Chimpanzees are classified as a. prosimians b. monkeys
c. hominoids d. hominids.
9. The oldest hominid fossils found so far are about a. 35 million
years old b. 5.8 million years old c. 1.75 million years old
d. 400,000 years old.

21. 92 Evolution
10. Which of these is not a general characteristic of mammals?
a. complex life cycle with alternation of generations b. nursing
their young with milk c. maintaining a high, steady body
temperature d. body covered in hair
11. An opposable thumb a. can bend and easily touch the forefinger
b. is an adaptation for arboreal life c. is a major characteristic of
primates d. all of these.
12. Animals that live in the trees are a. nocturnal b. arboreal
c. diurnal d. neanderthal.
13. Which of the following statements is true? a. Hominoids include
lemurs, lorises, and tarsiers. b. Prosimians are higher primates.
c. Monkeys include orangutans and gorillas. d. Prosimians,
monkeys, and apes are all primates.
14. Homo erectus a. could build fires b. probably did not make tools
c. lived in Africa only d. is a side branch on the human family
tree and not a direct ancestor of modern humans.
15. The “Out of Africa” model of human evolution a. is not
supported by mitochondrial DNA evidence b. states that modern
Homo sapiens evolved in Africa only c. is supported by DNA
evidence from Neanderthal fossils d. states that breeding among
populations of archaic Homo sapiens allowed for gene flow and
prevented speciation.
PART B—CONSTRUCTED RESPONSE
Use the information in the chapter to respond to these items.
Australopithecus
robustus
A Australopithecus B C Homo sapiens D
africanus (archaic)
Australopithecus Homo Homo
boisei antecessor neanderthalensis
16. The diagram shows one possible pathway of human evolution.
What hominid names should appear in boxes A, B, C, and D in the
diagram?
17. What do you think the discoverers of Homo antecessor might think
LIVING ENVIRONMENT BIOLOGY, 2e/fig. 4-Q16 s/s
about the view of human evolution expressed in the diagram?
18. What is the “savanna hypothesis”? What sort of evidence will
prove or disprove it?

22. Chapter 4 / Human Evolution 93
19. How do australopithecine fossils support the hypothesis that
hominids “stood up first and got smarter later”?
20. Why are Neanderthals considered archaic Homo sapiens and Cro-
Magnons considered modern Homo sapiens?
PART C—READING COMPREHENSION
Base your answers to questions 21 through 23 on the information below and
on your knowledge of biology. Source: Science News (May 10, 2003): vol.
157, p. 302.
New Fossil Weighs in on Primate Origins
Excavations in Wyoming have yielded the partial skeleton of a 55-
million-year-old primate that probably was a close relative of the ances-
tor of modern monkeys, apes, and people. The creature was built for
hanging tightly onto tree branches, not for leaping from tree to tree, as
some scientists had speculated, based on earlier fragmentary finds. Also,
despite expectations, the ancient primate didn’t have eyes specialized for
spotting insects and other prey.
Jonathan I. Bloch and Doug M. Boyer, both of the University of Michi-
gan in Ann Arbor, unearthed the new specimen. It belonged to a group
of small, long-tailed primates that lived just before the evolution of crea-
tures with traits characteristic of modern primates—relatively large
brains, grasping hands and feet with nails instead of claws, forward-
facing eyes to enhance vision, and limbs capable of prodigious leaping.
The new find, in the genus Carpolestes, had long hands and feet with
opposable digits, Bloch and Boyer report in the Nov. 22 Science. The
animal grew nails on its opposable digits, and claws on its other fingers
and toes. Unlike later primates, Carpolestes had side-facing eyes and
lacked hind limbs designed for leaping.
21. State two characteristics of the 55-million-year-old Wyoming
primate (fossil) that are different from what scientists had expected.
22. Explain what characteristics are considered to be those of modern
primates.
23. State two characteristics of the ancient Wyoming primate that
indicate it was not a member of the group of modern primates.