Download Variation in species in nature

Last day… overview of what the course will cover,
started discussing historical development of
evolutionary thinking
- idea of evolution had been debated, but generally rejected
Buffon
Erasmus Darwin
Saint Hilaire
Lamarck
Charles Darwin
- provided evidence that evolution had occurred
- first to develop a theory to explain how & why
evolution happens
- left him last day on voyage of the Beagle (1832-36)
Glyptodon
4 spp. of
mockingbirds
from
Galapagos
What patterns of distribution would be expected if species
are independently created (as opposed to what is expected
if species are related by descent from a common ancestors)?
a) very similar species will be expected in similar habitats
even if on different continents
b) species in very different habitats will be very different,
even if the habitats are geographically close
c) different species will be found on opposite sides of
geographic barriers, even if the habitats are similar
d) endemic species on islands will be closely similar to
those of the nearest continent
e) species will be found in environments that they are well
adapted to
- influence of geological theories
Lyell: Uniformitarianism: geological patterns
created by presently observable forces, ancient
history of the earth
Charles Lyell: 1797-1875
Started notebook (1837) to record ideas
Many facts suggested evolution, but
needed a theory...
- must produce change
- must account for adaptation
- must explain speciation
Inspiration from Thomas Robert Malthus (1798)
- population growth will always tend to
outrun food supply
- immediately suggested natural selection
Darwin’s insight in 1838
- quickly developed this into theory explaining how all
living things evolved into their diverse forms
"is the most powerful and the most comprehensive idea
that has ever arisen on earth. It helps us understand our
origins ... We are part of a total process, made of the
same matter and operating by the same energy as the
rest of the cosmos..." (Sir Julian Huxley)
and then... silence
Delayed publishing - started outline 1842
…until he received a paper in 1858 outlining natural selection
Who mailed the paper to Darwin?
a)
b)
c)
d)
e)
Robert FitzRoy
Thomas Henry Huxley
Alfred Russell Wallace
Sir Charles Lyell
Samuel Wilberforce
Wallace’s paper stunned Darwin…
Friends arranged for joint reading of papers at Linnean Society
- Darwin published ‘The Origin of Species’ in late 1859
Darwin & Wallace disagreed on many issues regarding the
details of HOW natural selection would work, but
both were convinced that it was the primary mechanism
by which evolution occurred
Darwin: 1809-1882
Wallace: 1823-1913
Basic outline of Darwin’s theory:
1. Individuals within a species differ in morphology,
physiology, & behavior
2. Some of this variation is heritable
3. Organisms have a huge capacity for increase in
numbers, but populations tend to remain
+/- constant
4. As a result of competition, some variants will leave
more offspring than others
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 common in the
next generation
(Thus evolutionary change by natural selection)
‘Origin’ controversial
among public
- human descent from
apes stressed
Among many scientists,
concept of evolution
was largely accepted
Much supporting evidence
collected from paleontology,
morphology, etc. to
establish the fact of
evolution
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 offspring?
Is it a problem for Darwin’s theory if inheritance works
by blending (e.g. tall parent & short parent produce
kids of medium height)?
a) yes, it will remove the potential for variation
b) no, it does not affect the potential for natural selection as
best adapted individuals still leave the most offspring
...and doubts about the age of the earth
- Lord Kelvin estimated about 100 million years,
based on cooling of earth
What did Kelvin leave out of his calculations?
Ooops. Didn’t know radioactivity continues to heat earth
Darwin’s arguments for evolution
& natural selection
Variation in domesticated forms: - great variation in
animal breeds & cultivated plants
- deliberate selection to modify varieties
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)
Increase in numbers and competition:
- calculated expected # of offspring if all survive
- gave examples of increase for plants & animals
introduced to new areas
Ox-eye Daisies
Geological succession:
- new species occur at intervals
- ‘modern’ species may be found among extinct forms
- intermediate forms between orders found
- older forms differ more from modern species
- fossils belong to same groups as modern species
in same area
trilobite
Geographical distribution:
- species isolated by strong barriers tend to be distinct,
though physical conditions are similar
Indigo Bunting
Lazuli Bunting
- species in the same area are related, even if occupying
different habitats
Eastern Gray Kangaroo
Lumholtz’s
Tree Kangaroo