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Human Evolution


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Title: Human Evolution

Human Evolution
Human Classification
  • Domain Eukarya
  • Kingdom Animalia
  • Phylum Chordata
  • Class Mammalia
  • Order Primate
  • Family Hominidae
  • Genus Homo
  • Species sapiens

  • Animals
  • multicellular eukaryotic organisms that ingest
    other organisms
  • Chordates
  • Animals that at some point during their
    development have
  • a notochord (long flexible rod that runs along
    the dorsal axis of the body in the future
    position of the vertebral column)
  • a dorsal, hollow nerve cord
  • pharyngeal slits or clefts
  • and a muscular, post-anal tail.

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  • Mammals
  • amniotes with mammary glands that produce milk
  • Primates
  • Include lemurs, monkeys, chimpanzees, gorillas
    and humans
  • Main characteristics
  • Opposable thumbs
  • Forward facing eyes
  • Well-developed cerebral cortex
  • Omnivorous

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  • Hominidae
  • The great apes
  • Includes orangutans, gorillas, chimpanzees and
  • Larger than monkeys
  • Relatively long arms, short legs, no tail
  • Larger brain in proportion to body size
  • More flexible behavior than other primates

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  • Homo
  • Genus that includes extinct species such as
    Homo habilis, Homo erectus, and
    Homo neanderthalensis as well as Homo sapiens,
  • Had larger brains than predecessors, such as the
  • Sapiens
  • Modern humans
  • Homo sapiens idaltu extinct lived 160,000
    years ago in Pleistocene Africa slight skull
    differences from
  • Homo sapiens sapiens only extant subspecies of
    Homo sapiens

  • Australopithicus
  • 1974 Lucy
  • discovered

Homo Characterized by Larger Brain Size
Homo sapiens sapiens
Homo sapiens idaltu
Major Physical Features Defining Humans as
  • Grasping limbs, with long fingers and a separated
    opposable thumb
  • Mobile arms, with shoulder joints allowing
    movement in 3 planes, and the bones of the
    shoulder girdle allowing weight to be transferred
    via the arms

Major Physical Features Defining Humans as
Primates, contd.
  1. Stereoscopic vision, with forward facing eyes on
    a flattened face, giving overlapping fields of
    view. Each eye gets a slightly different view of
    the world. The brain fuses the two views to get
    depth information.

Major Physical Features Defining Humans as
  • Skull modified for upright posture

What is the Evidence that Humans are a Species of
Ape that Spread to Colonize New Areas?
  • Closest existing relatives of humans are
    orangutans from Southeast Asia and gorillas and
    chimpanzees of Africa.

Biochemical Evidence that Humans are a Species of
Ape that Spread to Colonize New Areas
  • Study of amino acid differences for proteins and
    mitochondrial DNA show humans are more closely
    related to chimps and gorillas than to

Three phylogenetic trees were reconstructed based
on the DNA sequences of
  1. 4700 bp of mitochondrial DNA
  2. the testis specific protein on the Y chromosome
  3. noncoding regions of the ß-globin gene

All three trees show that human and chimp DNA
sequences are more similar on average than are
human and gibbon or human and orangutan
Biochemical Evidence that Humans are a Species of
Ape that Spread to Colonize New Areas
  • These biochemical data support the theory that
    human ancestors split from ancestors of the
    chimps and gorillas in Africa.
  • The molecular data also allow approximate dating
    of the splits of various groups of humans
  • Between Africans and other humans 140,000 y.a.
  • Between Europeans and Japanese 70,000 y.a.

Ancestors of modern humans migrated out of Africa
less than 500,000 y.a.
  • Older fossil hominids found out of Africa must
    have been the result of earlier migrations, and
    modern humans are not descended from these

Anatomical Evidence that Humans are a Species of
Ape that Spread to Colonize New Areas
  • Neoteny when infant characteristics persist in
    the adult
  • Adult humans show similarities in appearance to
    baby apes, including flat faces, large brain to
    body size ratio, upright heads, and little body
  • This suggests that human evolution may have
    involved a slowing down of development with long
    childhood, delayed puberty, and retention of
    juvenile characteristics into adulthood.

Neoteny and Brain Size
  • The slowing down of development in the genus Homo
    included continued brain growth after birth, as
    opposed to cessation of growth after birth.
  • Consequences of increased brain size include
  • increased capacities for learning, complex
    thought, and memory
  • possibility of language and complex tool
  • increased amount of energy required to use brain

Anatomical Evidence that Humans are a Species of
Ape that Spread to Colonize New Areas Bipedalism
  • Bipedalism is walking on two legs
  • All apes are capable of bipedalism, but are not
    as nearly as adept as humans are

Bipedalism Adaptations Involved
  • Foramen magnum, hole in skull through which brain
    and spinal cord connect, moved forward, allowing
    the head to balance on the backbone
  • Arms became shorter and less powerful
  • Legs became longer and stronger
  • Knee changed to allow the leg to straighten fully
  • Foot became more rigid, with longer heel, shorter
    toes and a non-opposable big toe

Bipedalism Some Consequences
  • Collecting food from bushes may be easier
  • Walking long distances while carrying food,
    water, infants, tools, or weapons is possible
  • Tree climbing is more difficult
  • Go to Evolution Library The Transforming
    Leap, from Four Legs to Two
  • Read the article, "The Transforming Leap, from
    Four Legs to Two."
  • Summarize the different hypotheses offered to
    explain the development of bipedalism and the
    evidence that supports or refutes each.