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.