Descent with Modification

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Descent with Modification
http//itc.utk.edu/jklittle/origin/domesticus.htm
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Evolution - biological history from microbes to
modern organismsall the
changes in life forms over the history of the
Earth evolutionary change a genetic change
in a population over time as it adapts the
change in frequency of certain genes in a
population Charles Darwin between 1831 1859
traveled around the world as a naturalist on
the HMS Beagle and wrote The Origin of
Species. Darwin proposed the idea of descent
with modification ( evolution ) and his theory
of how evolution occurs evolution occurs by
natural selection
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Darwins 2 main points

• 1. Species on Earth today have descended from
  ancestral species and this
• happened gradually he predicted there were be
  transition life forms
• 2. The mechanism of evolution is natural
  selection

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A naturalist, biologist
1840 portrait of Charles Darwin, age 31, by
George Richmond
Charles Darwin in the 1870's
Darwin was influenced by other scientists such
as Linnaeus, Lyell and Malthus
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Figure 22.7 Descent with modification
Darwin proposed Descent with modification
Darwin said that all life has come from a common
ancestor through gradual changes over long
periods of time
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Figure 22.5 The Voyage of HMS Beagle
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Phylogeny of Galapagos finches
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Darwins Theory of evolution Natural
Selection Natural Selection is the mechanism
Darwin proposed to explain the theory of
Evolution The Theory of evolution is supported
over and over again by scientific findings ..
Amino acid sequences, homebox genes, common
genetic code, fossils, embryological
development, conserved genes throughout so many
species. homology, vestigial structures,
radiometric age dating, transitional fossils
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Acquired traits are changes you develop in your
lifetime and are not genetic and are not passed
on

• Lamarck believed acquired traits were
  heritable. This is false. If you bleach you
  hair, your kids will not be blondes. Parakeets
  kept in captivity over many generations do not
  produce flightless offspring. Do not use
  Larmarckian explanations when discussing adapting
  and evolving species. Do not say that something
  changed because
• it needed to.

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Darwin observed that a) organisms tend to
over reproduce yet populations remain stable
in size b) resources are limited - compete
c) variations exist between members of each
population d) most variations are heritable
Darwin inferred - ( his idea for the
mechanism of change )
(natural selection) a)
offspring must struggle to survive, some will
die b) survival depends on inherited factors
that best suit them to their
environment c) survivors will more likely
leave more offspring with the
survivor traits d) this will cause a
gradual change in the population with
favorable traits accumulating
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Strata of sedimentary rock at the Grand Canyon
Sedimentary rock strata provide chronological
fossils
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Figure 22.8 Overproduction of offspring
Over reproduction of offspring
Cowbird eggs
spores
All organisms over reproduce
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Figure 23.0 Shells
Variation - shell color is a polymorphism
variation in a specie
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Individuals are selected, but populations
evolve. A population is the smallest unit that
can evolve
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Homologous structures are evidence for common
ancestry
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Homologous bone structure in front limb of whale
scapula
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appendix
appendix
coccyx
Coccx /tail bone
Genes for vestigial body parts leftover from
evolution produce body parts that are reduced in
size and not functional.
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Gill slits
Vestgial, homologous pharyngeal pouches
tail
Human embryo
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Hardcore evidence of evolution
Fossils
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Comparative Embryology
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Similarities in embryos reflect common ( the
same ) ancestry.
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• HOX genes

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Similarities in DNA and proteins show common
ancestry and evolutionary relationships
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evolution
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