Human Evolution

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Chapter 24

• Human Evolution

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Outline

• Biological Evolution
• Common Descent
• Natural Selection
• Primates
• Human Evolution
• Evolution of Modern Humans

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Biological Evolution

• change in life forms that has taken place in the
  past and will take place in the future
• First true cells were prokaryotic
• Eukaryotic cells evolved later
• Multicellularity evolved from eukaryotic cells

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Adaptation

• a characteristic that improves an organisms
  ability to survive and reproduce in an
  environment
• adaptation was recognized by some scientists
  before Darwin
• Darwin was the first to understand how it came
  about

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Common Descent

• Charles Darwin first formulated the theory of
  evolution and gathered several lines of evidence
  that life forms change over time and distance
• Geological Evidence
• Fossil evidence
• Biogeographical evidence
• Anatomical evidence
• Homology vs. Analogy
• Biochemical evidence unknown to Darwin

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Geological Evidence

• Time!
• uplift of sea beds to the top of tall mountain
  chains
• fossil layers showed oldest strata had simplest
  life forms
• Principle of Uniformitarianism earth must be
  billions of years old!

Charles Lyell
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Fossil Evidence

• Extinct species were replaced by new species
• gradual change could often been seen from the
  oldest to youngest fossils
• oldest fossils were simpler life forms

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Biogeograghical Evidence

• Darwins Finches Why were there so many
  different species on one small Island
  Archipelago?
• most islands had similar habitats

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Anatomical Evidence

• Homology same structure evolves to serve
  different functions

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Anatomical Structure

• vestigial structures and other imperfections
• some whales and some snakes have remnants of rear
  legs
• If creation was embodiment of perfection, then
  why were these imperfections present?

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Missing Links Transitional Forms
Ambulocetus The Walking Whale
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Natural Selection

• the process by which species become adapted to
  their environment
• nature selected those individuals that were best
  adapted
• not the first mechanism of evolution proposed
• Lamarcks teleological explanation
• individuals acquired characteristics through use

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Critical elements of natural selection

• Variation occurred among individuals in
  populations of a species
• Struggle for existence occurred because more
  offspring were produced than the environment
  could support
• Survival of the fittest occurred because those
  individuals with the best adaptations survived
  and reproduced
• Adaptation was passed on to the offspring

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Classification of Primates

• Characteristics of primates
• Opposable thumb
• Well-developed brain
• Nails
• Single birth
• Extended parental care
• Emphasis on learned behavior

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Humans Are Apes

• Molecular data have been used to determine the
  date of the split between hominids and apes
• When two lines of descent first split, the genes
  and proteins of the two lineages are nearly
  identical
• As time goes by each lineage accumulates genetic
  changes
• humans share 98 of the same genes with
  chimpanzees

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Hominids Walk Upright

• Many genetic changes can be used as a molecular
  clock to indicate relatedness of two groups
• Evolution of bipedalism is believed to be the
  distinctive feature that separates hominids from
  apes

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Hominids Evolved from Australopithecines

• Evolved and diversified in Africa
• It is unknown which australopithecine is
  ancestral to early Homo
• Lucy, at right, is A. afarensis
• 3.18 MYA

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Several Australopithecine Fossils Found

• A. afarensis may be oldest
• footprints of bipeds in Laetoli volcanic ash from
  3.7 MYA are probably Australopithecine
• A. africanus (gracile) and A. boisei (robust) may
  both have descended from afarensis

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Evolution of Humans

• Homo habilis (handy man) dates between 2.0 and
  1.9 MYA and may be ancestral to modern humans
• Teeth indicate omnivory
• Animal bones indicate use of tools to strip meat
• Skull suggests parts of brain associated with
  speech were enlarged

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Human Evolution
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Homo erectus

• fossils are found in Africa, Asia, and Europe,
  and date between 1.9 and 0.3 MYA
• larger brain and flatter face than H. habilis
• first hominid to use fire, fashioned more
  advanced tools than earlier Homo

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Evolution of Modern Humans

• Multiregional continuity hypothesis holds that
  Homo sapiens evolved in several different
  locations
• Out-of-Africa hypothesis holds that Homo sapiens
  evolved in, and migrated out of, Africa

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Multiregional continuity hypothesis
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Out-of-Africa Hypothesis
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Homo Neanderthalensis

• First discovered in Germanys Neander Valley, and
  date back 200,000 YBP
• Evidence of cultural advancement
• Out-of-Africa hypothesis Neanderthals were
  eventually supplanted by modern humans
• Multiregional Continuity hypothesis Neanderthals
  were assimilated by interbreeding

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Cro-Magnons (Homo sapiens)

• Cro-Magnons are the oldest fossils to be
  designated Homo sapiens
• Named after fossil location in France
• Hunted cooperatively, and may have been first to
  have language
• Advanced culture included art

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We Are One Species

• Human beings are all classified as Homo sapiens
• DNA variation between races is the same level as
  DNA variation within the same race
• Differences in body shape represent adaptations
  to temperature and environmental conditions

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Review

• Biological Evolution
• Common Descent
• Natural Selection
• Primates
• Human Evolution
• Evolution of Modern Humans

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