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EVOLUTION
A bit of history on the
theory of evolution
Early theories (pre-1700’s)
 nature is seen as not changing and having
originated through spontaneous
generation
 Carolus Linnaeus was the first one to try to
classify life (1735, placed us with
primates)
1700’s
 an understanding of the age of the Earth
develops through geology
 inheritance
of acquired traits (use and
disuse)
ex. Baby giraffes are born with long necks
because their parents stretched their
necks to reach leaves (Jean-Baptiste
Lamarck, 1801)
Darwin and the Voyage of the
Beagle
 in
December, 1831’ Charles Darwin, a
naturalist in his 20’s began a 5-year
journey around the world on a ship called
HMS Beagle
 Darwin’s
role was to
observe, record, and
collect specimens of
rocks, minerals, plants, and animals
Darwin: PBS

Darwin collected 1000’s of specimens and
shipped them to England, mainly from South
America and a chain of volcanic islands called
Galapagos

he collected them but did not realize what he
was seeing until years later (ex. didn’t catalogue
the finches very well, ate turtles that would later
support his theories, etc.)

Darwin spent the next 20 yrs analyzing his
findings in light of artificial selection (ex.
breeding of pigeons, breeding of dogs, etc.)
Darwin’s Finches
 Arrival
 Success
 Competition
 Diversity
&
Opportunity
 Radiation
How does evolution really work?
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
 Hawaiian
honeycreeper
Natural Selection defined:
 The
process in nature by which, according
to Darwin's theory of evolution, only the
organisms best adapted to their
environment tend to survive and transmit
their genetic characteristics in increasing
numbers to succeeding generations while
those less adapted tend to be eliminated.
What is evolution?
A
theory that explains the origin of species
 At
the genetic level, it is the theory of
change in the inherited traits of a
population of organisms through
successive generations
 Or
as Darwin would have put it: descent
with modification from a common ancestor
 This
modification or change through
successive generations come from
variation in a population
 Variation
comes from mutations and
genetic recombination (e.g. crossing
over).; both can be passed on to the next
generation
 Mutation
refers to changes in a genomic
sequence.
 E.g.
For example, two chromosomes in
the Homo genus fused to produce human
chromosome 2; this fusion did not occur in
the lineage of the other apes, and they
retain these separate chromosomes.
How do traits due to genetic variation
become more common or rare?
 Two
main processes are responsible:
 Natural
selection and genetic drift
Natural Selection as the Cause of Evolution
-
called “natural selection” because it happens on
its own
1. Genetic Variation
- there are many varieties of alleles
- caused by random mutations
- can be passed onto offspring (inherited variation)
2. Overproduction of Offspring
- organisms make too many offspring
3. Struggle for existence
- competition for limited resources
4. Differential survival and reproduction
- only organisms that have certain
characteristics will survive to reproduce
- non-random, caused by the environment:
amount of food, competition (ex. Darwin’s
finches)
Most of the beetles in the population (say 90%)
have the genes for bright green coloration and a
few of them (10%) have a gene that makes them
more brown. Some number of generations later,
things have changed: brown beetles are more
common than they used to be and make up 70%
of the population.
Genetic drift
 In
each generation, some individuals may,
just by chance, leave behind a few more
descendents (and genes, of course!) than
other individuals. The genes of the next
generation will be the genes of the “lucky”
individuals, not necessarily the healthier or
“better” individuals. It happens to ALL
populations—there’s no avoiding the
vagaries of chance.
Genetic drift is random – no
adaptation