Becoming Human:
The Origin and Diversity
of Our Species
To What Group of Animals Do
Humans Belong?
 Biologists classify humans as Homo sapiens, members of
the primates— a subgroup of mammals.
 Biological species are defined by reproductive isolation
and designated by a two part name including genus
(Homo) and species (sapiens).
 Other primates include lemurs, lorises, tarsiers, monkeys,
and apes.
 Studying the anatomy and behavior of other primates helps
us understand how and why early humans developed as
they did.
When and How Did Humans
Evolve?
 Present evidence suggests that humans evolved from small
African apes between 5 and 8 million years ago.
 Bipedalism, or walking on two feet, was the first change to
distinguish the human evolutionary line.
 Several million years after the evolution of bipedalism,
brain size began to expand, along with development of
cultural activities such as making stone tools.
 The earliest stone tools date to between 2.5 and 2.6 million
years ago, coinciding with the appearance of the first
members of the genus Homo in the fossil record.
Is the Biological Concept of Race Useful for
Studying Physical Variation in Humans?
 Biologically defined, race refers to subspecies, and no
subspecies exist within modern Homo sapiens.
 The vast majority of biological variation within our
species occurs within populations rather than among
them.
Paleoanthropologists and
Primatologists
 Paleoanthropologists are anthropologists specializing
in the study of human evolutionary history.
 Primatologists are specialists in the behavior and
biology of living primates and their evolutionary
history.
Evolution Through Adaptation
 Evolution refers to changes in the genetic makeup of a
population over generations.
 Genes are basic physical units of heredity that specify
the biological traits and characteristics of each
organism.
Evolution Through Adaptation
 Evolution takes place through adaptation, a series of
beneficial adjustments of organisms to their environment.
 Adaptation is the cornerstone of the theory of evolution by
natural selection, originally formulated by English
naturalist Charles Darwin in 1859.
 In this theory, individuals with characteristics best suited
to a particular environment survive and reproduce with
greater frequency than individuals without those
characteristics.
Human Adaptations and
Culture
 Humans relied increasingly on culture as an effective
way of adapting to the environment.
 They figured out how to manufacture and utilize tools.
 They organized into social units that made food-
foraging more successful;.
 They learned to preserve and share their traditions and
knowledge through the use of symbols that ultimately
language.
Humans and Other Primates
 Humans are one of 10 million species on earth, 4,000 of
which are fellow mammals.
 Species are populations or groups of populations having
common attributes and the ability to interbreed and
produce live, fertile off spring.
 The human species is a kind of primate, a subgroup of
mammals that also includes lemurs, lorises, tarsiers,
monkeys, and apes.
 Among fellow primates, humans are most closely related to
apes—chimpanzees, bonobos, gorillas, orangutans, and
gibbons.
Classifying Primates
 Early scientific struggles to
classify great apes, and
identify and weigh the
similarities and differences
between them and humans, is
reflected in early European
renderings of apes, including
this 18th-century image of a
chimpanzee portrayed as a
biped equipped with a walking
stick.
Anatomical Adaptations
 Ancient and modern primate groups possess a number
of anatomical characteristics:
 Generalized set of teeth, suited to insect eating but also
fruits and leaves.
 Depth perception
 Intensified sense of touch
 Binocular stereoscopic vision
Anatomical Adaptations
 Brain is large, heavy in proportion to body weight, and
very complex
 Skeleton has adaptations for upright posture and
flexibility of limb movement.
 Fewer offspring born to each female and a longer period
of infant dependency.
Jaws: Reptiles and Mammals
 The jaw of reptiles contains a series of identical teeth. If
a tooth breaks or falls out, a new tooth will emerge.
 Mammals possess precise numbers of specialized teeth,
each with a particular shape characteristic of the group,
as indicated on the chimpanzee jaw.
Primate Vision
 Anthropoid primates possess
binocular stereoscopic vision.
 Binocular vision refers to
overlapping visual fields
associated with forward facing
eyes.
 Three-dimensional vision comes
from binocular vision and the
transmission of information from
each eye to both sides of the
brain.
Behavioral Adaptations
 Primates adapt to their environments not only
anatomically but also through a wide variety of behaviors.
 Young apes spend more time reaching adulthood than
most other mammals.
 During their growth and development, they learn the
behaviors of their social group.
 Two closely related African species of chimpanzee:
common chimpanzees and bonobos, provide models to
reconstruct the behavior of evolving humans
Chimpanzee and Bonobo
Behavior
 Among chimps, the largest social unit is the community,
fifty or more individuals who inhabit a large geographic
area.
 Chimps are usually found ranging singly or in small
subgroups consisting of adult males, or females with their
young, or males and females together with young.
 While strength and size contribute to an animal’s rank in
the community, the rank of its mother, largely determined
through her cooperative social behavior also plays a role.
Nutrition and Hunting:
Chimpanzees
 Jane Goodall’s fieldwork among chimpanzees revealed they
sometimes kill small invertebrate animals for food, and
also hunt and eat monkeys.
 Hunting is not done purely for dietary purposes, but for
social and sexual reasons as well.
 Fertile females are more successful than others at begging
for meat, and males often share the meat after copulation.
 Males use their catch to reward friends and allies, gaining
status in the process.
Nutrition and Hunting:
Bonobos
 Recent research shows that bonobos in Congo’s rainforest
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supplement their diet by hunting.
Among bonobos hunting is primarily a female activity.
Female hunters regularly share carcasses with other
females, but less often with males.
Even when the most dominant male throws a tantrum
nearby, he may still be denied a share of meat.
Discriminatory sharing among female bonobos is also
evident when it comes to other foods such as fruits.
Sexual Practices: Chimpanzees
 For chimps, sexual activity occurs only when females signal
their fertility through genital swelling.
 Dominant males try to monopolize females, although
cooperation from the female is usually required for this to
succeed.
 An individual female and a lower-ranking male sometimes
form a temporary bond, leaving the group together for a
few private days during the female’s fertile period.
 Dominant males do not necessarily father all of the off
spring in a social group.
Female Chimpanzee Genital
Swelling
 Female chimpanzees
display their fertility
through swelling of the
genitalia at the time of
ovulation.
 In contrast to humans
and bonobos, animals
with time limited
displays are sexually
receptive only during
these times of fertility.
Sexual Practices: Bonobos
 Bonobos do not limit their sexual behavior to times of
female fertility, bonobo female genitals are perpetually
swollen.
 Concealed ovulation in bonobos may play a role in the
separation of sexual activity for social reasons and pleasure
from the biological task of reproduction.
 Primatologists have observed every possible combination
of ages and sexes engaging in an array of sexual activities,
including oral sex, tongue-kissing, and massaging each
other’s genitals.
 The primary function of most of this sex is to reduce
tensions and resolve social conflicts.
Chimpanzee and Bonobo
Childhood Development
 The young chimp or bonobo learns by observation,
imitation, and practice how to interact with others and
manipulate them for his or her own benefit.
 Young primates learn to match their interactive behaviors
according to each individual’s social position and
temperament.
 Anatomical features such as a free upper lip allow varied
facial expression, contributing to greater communication
among individuals.
 Young chimpanzees also learn to how to make and use
tools.
Human Ancestors
 Humans are classified as hominoids, the broad-shouldered
tailless group of primates that includes all living and
extinct apes and humans.
 Humans and their ancestors are distinct among the
hominoids for bipedalism, walking upright on two feet.
 Genetic and biochemical studies have confirmed that the
African apes—chimpanzees, bonobos, and gorillas—are
our closest living relatives.
Common Primate Ancestors
 Based on molecular
similarities and
differences, a
relationship can be
established among
various primate groups.
Human Ancestors
 Between 5 and 8 million years ago, humans,
chimpanzees, and gorillas began to follow separate
evolutionary courses.
 Chimpanzees diverged into two separate species: the
common chimpanzee and the bonobo.
 Early human evolutionary development followed a path
that produced only one surviving bipedal species: Homo
sapiens.
The First Bipeds
 During the early Pliocene, 5 million years ago, the
genus Australopithecus appeared in Africa.
 Australopithecines include a diverse group of bipedal
species with small brains in proportion to body size.
 One of the other australopithecine species appears to
be a direct ancestor of the genus Homo.
Australopithecine Fossil
Locations
 Australopithecine fossils have
been found in South Africa,
Malawi, Tanzania, Kenya,
Ethiopia, and Chad.
Skeletons and Locomotion:
Humans and Chimps
Advantage of Bipedalism
 A way to cope with heat stress.
 Allowed them to gather food and transport it to a place
of safety for consumption.
 Mothers were able to carry their infants safely.
 They could reach food on trees too flimsy to climb.
 Allowed them to travel far without tiring.
Advantages of Bipedalism
 Food and water were easier to spot.
 More likely to spot predators before they got too close
for safety.
 Hands freed from locomotion provided protection by
allowing them to brandish and throw objects at
attackers.
Early Homo
 Increased meat consumption was important for human
evolution.
 Failure to satisfy protein requirements can lead to stunted
growth, malnutrition, starvation, and death.
 Without sharp teeth, our ancestors needed sharp tools for
butchering carcasses.
 The earliest identify able stone tools have been found in
Africa often in the same geological strata as the earliest
Homo fossils.
Early Homo and Tools
 Stone flakes and choppers mark the beginning of the
Lower Paleolithic, the first part of the Old Stone Age, from
about 200,000 to 2.6 million years ago.
 Flakes were obtained from a “core” stone by striking it
with stone or against a large rock.
 The flakes that broke off had sharp edges, effective for
cutting meat and scraping hides.
 Leftover cores were made into choppers, used to break
open bones.
Early Stone Tools
 The earliest stone tools dated to the beginning of the Lower
Paleolithic between 2.5 and 2.6 million years ago were discovered
by Ethiopian paleoanthropologist Sileshi Semaw at Gona, in the
west-central Afar region of Ethiopia. The 2.6 million-year-old Gona
flake is a cutting tool with sharp edges.
Homo habilis
 “Handy man.”
 The first fossil members of the genus Homo appearing
2.5 million years ago, with larger brains and smaller
faces than australopithecines.
Tools, Food and Brain
Expansion
 Scenarios about behavioral adaptation in early Homo, such
as the relationship among tools, food, and brain expansion,
propose a feedback loop between brain size and behavior.
 Over time, large-brained individuals contribute to
successive generations, so the population evolves to a
larger-brained form.
Tools, Food and Brain
Expansion
 Natural selection for increases in learning ability has
led to the evolution of larger and more complex brains
over about 2 million years.
 Bipedalism set the stage for the evolution of large
brains and human culture by freeing the hands for tool
making and carrying of resources or infants.
Homo erectus and the Spread
of the Genus Homo
 Shortly after 2 million years ago, at a time that Homo
habilis and Oldowan tools had become widespread in
Africa, a new species, Homo erectus, appeared on that
continent.
 Evidence of H. erectus fossils almost as old as those
discovered in Africa have been found in the Caucasus
Mountains of Georgia, South Asia, China, the island of
Java, and western Europe.
 Fossil evidence suggests some differences within and
among populations of H. erectus inhabiting regions of
Africa, Asia, and Europe.
Homo erectus Sites
 Sites, with dates, at which Homo erectus remains have
been found. Arrows indicate the proposed routes by
which Homo spread from Africa to Eurasia.
H. erectus and the Ice Age
 Emergence of H. erectus coincided with the beginning of
the Pleistocene epoch (Ice Age), which spanned from
10,000 to almost 2 million years ago.
 During this period, Arctic cold conditions and snowfall in
the earth’s northern hemisphere created ice sheets that
covered much of Eurasia and North America.
 These periods often lasted tens of thousands of years,
separated by intervening warm periods.
 During much of this time sea levels were much lower than
today, exposing large surfaces now under water.
H. erectus and the Ice Age
 Of all the epochs in the earth’s 4.6 billion-year history, the
Pleistocene is the period in which humans—from H.
erectus to H. sapiens— evolved and spread all across the
globe.
 Our early human ancestors were challenged to make
biological and cultural adaptations in order to survive and
reproduce.
 The principle of natural selection was at work on humans
favoring the perpetuation of certain characteristics within
particular environmental conditions.
H. Erectus
 H. erectus had a body size and proportions similar to
modern humans, though with heavier musculature.
 Differences in body size between the sexes diminished
compared to earlier bipeds, perhaps to facilitate successful
childbirth.
 H. erectus’ average brain size fell within the higher range of
H. habilis and within the lower range of modern human
brain size.
 The dentition was fully human, though relatively large by
modern standards.
Homo Erectus Fossil
 One of the oldest—at 1.6
million years—and most
complete fossils of Homo
erectus is the “strapping
youth” from Lake
Turkana, Kenya: a tall
and muscular boy who
was already 5 feet 3
inches tall when he died
at about age 13.
H. erectus Tools
 The Oldowan chopper was replaced by the more
sophisticated hand axe.
 The hand axes, shaped by regular blows giving them a
larger and finer cutting edge than chopper tools, were
probably all purpose implements for food
procurement and processing, and defense.
 H. erectus also developed cleavers and scrapers to
process animal hides for bedding and clothing.
Use of Fire
 Fire allowed our human ancestors to continue activities
after dark and provided a means to frighten away predators.
 It supplied them with the warmth and light needed for cave
dwelling, and it enabled them to cook food.
 Cooking detoxifies poisonous plants and allows important
vitamins, minerals, and proteins to be absorbed from the
gut rather than passing unused through the intestines.
 When our human ancestors learned to use fire they
dramatically increased their geographic range and
nutritional options.
The Beginnings of Homo
sapiens
 At various sites in Africa, Asia, and Europe, a number of
fossils have been found that date between roughly 200,000
and 400,000 years ago.
 The best population sample, bones of about thirty
individuals of both sexes and all ages comes from
Atapuerca, a 400,000-year-old site in Spain.
 These bones show a mixture of characteristics of Homo
erectus with those of early Homo sapiens.
“Pit of the Bones”
 In a cave beneath a hillside in Atapuerca, Spain, lies the
Sima de los Huesos (“Pit of the Bones”).
 The bottom of the pit is crammed with animal bones,
including cave bears, lions, foxes, and wolves.
 Thousands of early human fossils dating back 400,000
years have been found here.
 The well-preserved remains come from at least 28
individuals and comprise the greatest single cache of
ancient Homo erectus fossils in the world.
“Pit of the Bones”
Neandertals
 An extremely muscular people living from approximately 30,000 to
125,000 years ago in Europe and southwestern Asia.
 With brains of modern size, Neandertals possessed faces distinctively
different from modern humans.
 Their large noses and teeth projected forward.
 They had bony brow ridges over their eyes.
 On the back of their skull, there was a bunlike bony mass for
attachment of powerful neck muscles.
Mousterian Tradition
 Tool-making tradition of the Neandertals and their
contemporaries of Europe, western Asia, and northern
Africa.
 Named after the Neandertal site of Le Moustier, France.
 Tools included hand axes, flakes, scrapers, borers, wood
shavers, and spears.
 Mousterian peoples buried their dead, cared for the
disabled, and made objects for symbolic purposes.
Neandertals
 As this face-off between paleoanthropologist Milford
Wolpoff and his reconstruction of a Neandertal shows,
the latter did not differ all that much from modern
humans of European descent.
Anatomically Modern Peoples
and the Upper Paleolithic
 The Upper Paleolithic was the last part (10,000–40,000
years ago) of the Old Stone Age, featuring tool
industries characterized by long slim blades and an
explosion of creative symbolic forms.
 Upper Paleolithic tool kits include “blade” tools: long,
thin, precisely shaped pieces of stone demonstrating
the considerable skill of their creators.
Blade Technique
 During the Upper
Paleolithic, a new
technique was used to
manufacture blades.
 The stone is worked to
create a striking
platform; long almost
parallel-sided flakes then
are struck around the
sides, providing sharpedged blades.
Pressure Flaking
 Pressure flaking—in
which a bone, antler, or
wooden tool is used to
press rather than strike
off small flakes—is a
technique of tool
manufacture that
became widespread
during the Upper
Paleolithic.
Solutrean Bifaces
 The techniques of the
Upper Paleolithic
allowed for the
manufacture of a variety
of tool types.
 The finely wrought
Solutrean bifaces of
Europe, made using a
pressure flaking method
are shaped like plant
leaves.
Hypotheses on the Origins of
Modern Humans
 Multiregional Hypothesis - all populations of
archaic H. sapiens are easily derivable from earlier
populations of H. erectus from the same regions.
 “Eve” Hypothesis - transition from archaic to
anatomically modern H. sapiens took place in one
population, probably in Africa.
Spear Throwers
 Spear-throwers (atlatls) allowed Upper Paleolithic people to throw spears
from a safe distance while maintaining accuracy.
 Upper Paleolithic artists combined artistic expression with function,
ornamenting spear-throwers with animal figures.
Human Biological Variation
And The Problem Of Race
 “Race” refers to subspecies, and no subspecies exist
within modern Homo sapiens.
 The majority of biological variation within our species
occurs within rather than among populations.
 Anthropologists have worked to expose the fallacy of
race as a biological concept while recognizing the
existence of race as a social construct.
Defining Anatomical
Modernity
 This indigenous Australian
does not meet the definition
of anatomical modernity
according to skull shape
proposed in the African
origins model.
 Some paleoanthropologists
suggest this narrow definition
is ethnocentric, because all
living people are clearly
members of the species Homo
sapiens.
Factors in the Biological
Definition of Race
It is arbitrary; there is no agreement on how many
differences it takes to make a race.
2. Any one race does not have exclusive possession of any
particular variant of any gene or genes.
 Populations are genetically “open,” meaning that
genes flow between them and no fixed racial groups
exist.
3. The differences among individuals and within a
population are generally greater than the differences
among populations.
1.
The Concept of Human Races
 Many people have become accustomed to viewing racial
groups as natural divisions based on physical differences.
 However, these groups differ from one another in only 6%
of their genes.
 For thousands of years, individuals belonging to different
human social groups have been in sexual contact.
 They maintained the human species and prevented the
development of distinctive subspecies.
Genetic Mixing
 Genetic mixing is illustrated by the photo of distant relatives, all
descendents of Sally Hemings, an African American slave, and
Thomas Jefferson, Euramerican, who had 150 slaves at his
plantation and was third president of the U.S. (1801–1809).
Skin Color: A Case Study in
Adaptation
 Skin color is subject to great variation and is attributed
to several key factors:
 the transparency or thickness of the skin
 a copper-colored pigment called carotene
 reflected color from the blood vessels
 the amount of melanin , a dark pigment, in the skin’s
outer layer
Factors in Variation of Skin
Color
 Exposure to sunlight increases the amount of melanin,
darkening the skin.
 Selective mating, as well as geographic location, plays a
part in skin color distribution.