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Becoming Human:

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Title: Becoming Human:


1
Chapter 4
  • Becoming Human
  • The Origin and Diversity
  • of Our Species

2
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.

3
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.

4
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.

5
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.

6
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.

7
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.

8
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.

9
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 apeschimpanzees, bonobos, gorillas,
    orangutans, and gibbons.

10
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.

11
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

12
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.

13
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.

14
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.

15
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

16
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 animals
    rank in the community, the rank of its mother,
    largely determined through her cooperative social
    behavior also plays a role.

17
Nutrition and Hunting Chimpanzees
  • Jane Goodalls 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.

18
Nutrition and Hunting Bonobos
  • Recent research shows that bonobos in Congos
    rainforest 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.

19
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
    females fertile period.
  • Dominant males do not necessarily father all of
    the off spring in a social group.

20
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.

21
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 others
    genitals.
  • The primary function of most of this sex is to
    reduce tensions and resolve social conflicts.

22
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 individuals 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.

23
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 apeschimpanzees, bonobos, and
    gorillasare our closest living relatives.

24
Common Primate Ancestors
  • Based on molecular similarities and differences,
    a relationship can be established among various
    primate groups.

25
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.

26
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.

27
Australopithecine Fossil Locations
  • Australopithecine fossils have been found in
    South Africa, Malawi, Tanzania, Kenya, Ethiopia,
    and Chad.

28
Skeletons and Locomotion Humans and Chimps
29
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.

30
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.

31
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.

32
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.

33
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.

34
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.

35
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.

36
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.

37
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.

38
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.

39
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 earths 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.

40
H. erectus and the Ice Age
  • Of all the epochs in the earths 4.6 billion-year
    history, the Pleistocene is the period in which
    humansfrom 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.

41
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.

42
Homo Erectus Fossil
  • One of the oldestat 1.6 million yearsand 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.

43
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.

44
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.

45
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.

46
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.

47
Pit of the Bones
48
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.

49
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.

50
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.

51
Anatomically Modern Peoples and the Upper
Paleolithic
  • The Upper Paleolithic was the last part
    (10,00040,000 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.

52
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
    sharp-edged blades.

53
Pressure Flaking
  • Pressure flakingin which a bone, antler, or
    wooden tool is used to press rather than strike
    off small flakesis a technique of tool
    manufacture that became widespread during the
    Upper Paleolithic.

54
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.

55
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.

56
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.

57
Human Biological VariationAnd 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.

58
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.

59
Factors in the Biological Definition of Race
  • It is arbitrary there is no agreement on how
    many differences it takes to make a race.
  • 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.
  • The differences among individuals and within a
    population are generally greater than the
    differences among populations.

60
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.

61
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.
    (18011809).

62
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
    skins outer layer

63
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.
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