Download Natural Selection 03.25.04

Evidence for Evolution
(Chapter 18)
The real fossil bones of the walking and swimming whale, Ambulocetus natans, are spread
out in this picture with a sledgehammer for scale. The skeleton was about 12 feet long and
is about 49 million years old. It was found in Pakistan.
Evidence for Evolution
1. Remains of living organisms can be trapped
and preserved in…
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Resins that turn to amber
Frozen in ice or snow
In acid peat that prevents decay
In sediments that produce fossils (most important)
– Date rocks and fossils using radioactive isotopes
• Half life is the time it takes for the
radioactivity to fall to ½ of its original level
• 14C – half life is 5730 years so useful for
dating samples 1,000-100,000 years old
• 40K – half life is 1,250 million years so use
for samples >100,000 years old
– Scientists look for paleontological evidence–
specifically transitional fossils
• example: Archaeopteryx -- transitional form
between birds and reptiles
• microraptor
• Ambulocetus natans
This is the "classic" picture of the archaeopteryx fossil. It was not the first
found, but is the most complete. The fossil was found in a limestone quarry in
southern Germany (Bavaria) in 1877 (first one was actually found in 1861)
The latest Nature reveals a new primitive mammal fossil collected in the
Mesozoic strata of the Yan mountains of China. It's small and
unprepossessing, but it has at least two noteworthy novelties, and first
among them is that it represents another step in the transition from the
reptilian to the mammalian jaw and ear.
2. Biography/Geographical Distribution
• The study of the distribution of living things over
the earth
• Why are some species absent from environments
that would suit them?
• Why are there closer relationships between
species that are geographically near each other
than between species that inhabit similar
environments?
– In Asia, find many types of placental animals and very
few marsupials
– In Australia, find mostly marsupials and very few
placental animals
- Polar bears live in the Arctic, but not the
Antarctic. For penguins, the picture is reversed.
3. Comparative Embryology/Anatomy
• Embryos of vertebrates look
similar
• Useful when don’t have much
of a fossil record
• Almost all mammals have
seven cervical (neck) vertebrae
and gill arches
• Ontogeny recapitulates
phylogeny
– The idea that the development
of individuals is a progression
through adult ancestral form
German biologist, naturalist, philosopher, physician, professor and artist who discovered, described and named thousands of new
species (see below), mapped a genealogical tree relating all life forms, and coined many terms in biology, including phylum,
phylogeny, ecology and the kingdom Protista (details below). Haeckel promoted Charles Darwin's work in Germany and developed
the controversial "recapitulation theory" claiming that an individual organism's biological development, or ontogeny, parallels and
summarizes its species' entire evolutionary development, or phylogeny: "ontogeny recapitulates phylogeny" (see below).
• Homologous structures
– have a common evolutionary origin, but can
look quite different and have different functions
– ex. Forelimbs/pentadactyl limb of birds, bat,
horse, humans...
• Analogous structures
– have similar functions, may appear similar,
yet presumed to have different evolutionary
origins
– ex. Wings of an insect and bird
wings of bat, bird (though the BONES are
homologous!), insect:
4. Biochemistry
• All living organisms use DNA/RNA as
genetic material
• All use the same 20 amino acids to make
their proteins
– Differences of a.a. sequences accumulate
(mutations) at a constant rate and therefore
can be used as an evolutionary clock
– The more differences in proteins, the less
likely organisms are “related”
4. Selective Breeding of Domesticated
Animals
• artificial selection
When selective breeding goes too far
The government has confirmed that it will use a report on the
selective breeding of freak pets - including fancy goldfish - to shape
the Animal Welfare Bill.
Evolving Ideas: How Do We
Know Evolution Happens?
http://www.pbs.org/wgbh/evolution/library/11/2/e_s_3.html