Last day brief history of evolutionary ideas,

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Last day brief history of evolutionary ideas,
Darwins development of theory of natural s
election
Led to believe species evolve by observations
made in South America the Galapagos - idea
of natural selection from reading Malthus
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Darwin spurred to publish after receiving paper
from Alfred Russel Wallace - Wallace had also
collected in South American rainforests
a tropical archipelago (Malay instead of
Galapagos), and read Malthus
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• Basic outline of Darwins theory
• Individuals within a species differ in
  morphology,
  
• physiology, behavior

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2. Some of this variation is heritable
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3. Organisms have a huge capacity for increase in
numbers, but populations tend to remain /-
constant
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4. As a result of competition, some variants will
leave
more offspring than others

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5. If reproductive success is due to the varying
trait, and that trait is heritable, it will be
passed on to the offspring and become more comm
on in the next generation (Thus evolution
ary change by natural selection)
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• Origin controversial
• among public
• human descent from
• apes stressed

Among many scientists, concept of evolution

was largely accepted
Much supporting evidence collected from pal
eontology, morphology, etc. to estab
lish the fact of
evolution
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Mechanism of natural selection was not viewed as
favorably - many doubted its power to produce
evolution
Later, more serious objections e.g. about nature
of heredity... do traits blend together in off
spring?
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...and doubts about the age of the earth
- Lord Kelvin estimated about 100 million
years,
based on cooling of earth
Ooops. Didnt know radioactivity continues to
heat earth
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Darwins arguments for evolution
natural selection Variation in domesticated f
orms - great variation in animal breeds cult
ivated plants - deliberate selection to modify va
rieties
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• Variation in species in nature
• pointed to variation in individual traits (even
  in
  
• important organs)
• - difficulty classifying varieties vs. species

Eastern Screech-Owls
barnacles (Semibalanus)
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• Increase in numbers and competition
• - calculated expected of offspring if all
  survive
  
• gave examples of increase for plants animals
• introduced to new areas

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Geological succession - new species occur at in
tervals - modern species may be found among ext
inct forms

• - intermediate forms between orders found
• - older forms differ more from modern species
• fossils belong to same groups as modern species
  
  
• in same area

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• Geographical distribution
• species isolated by strong barriers tend to be
  distinct,
  
• though physical conditions are similar

Lazuli Bunting
Indigo Bunting
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• species in the same area are related, even if
  occupying
  
• different habitats

Eastern Gray Kangaroo
Lumholtzs Tree Kangaroo
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• islands tend to have endemic spp., but related
  to
  
• nearest mainland
• - frogs, mammals, generally absent from oceanic
  islands

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Classification - general pattern of groups withi
n groups

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• homologous organs (mouthparts of insects, bones
  of
  
• vertebrate limbs)

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- close similarity of embryonic stages
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• rudimentary organs (teeth in baleen whales,
• wings of flightless birds beetles)

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These points (and more!) converted most
biologists in England to a belief in evolution (
if not natural selection. ...) in about 10 years

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Problems with natural selection led to increasing
skepticism about Darwins mechanism for evolu
tion - confusion due in part to lack of understan
ding of heredity
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Answer came in 1866 from Austrian monk
- Gregor Mendel
Studied peas, worked out the essentials of
heredity,
published promptly
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How does heredity work?
Mendel succeeded by studying simple characters
like flower color plant height that are inher
ited in
straight-forward manner
Traits he studied did not blend
Only one trait was expressed in first
generation
offspring
Dominance
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In 2nd generation, both traits show
up (in 31 ratio)
1st generation offspring must contain info f
or both traits, although exhibit only
one
Some 2nd generation offspring inherit 2
copies of hidden
trait, exhibit it
Recessive