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Chapter 15
Main Ideas:
1. Charles Darwin developed the theory of evolution based on natural selection.
2. Multiple lines of evidence support the theory of evolution.
3. The theory of evolution continues to be refined as scientists learn new
information.
I. The Theory of Evolution
A. Natural Selection & Evidence for Evolution
1. what is evolution?-->
2. what is a population?-->
3. how did people know evolution was taking place?
4. is there evidence of evolution?-->fossils
B. Charles Darwin
1.
2. Darwin’s journey began in 1831; 22 yrs old
a. naturalist onboard the HMS Beagle5 yr scientific journey
b.
c. the Galapagos Islands had a profound effect on Darwin
d.
e.
f. Darwin returned to England & spent the next 20 yrs studying,
experimenting, & refining his hypotheses
g. Darwin drew upon a theory proposed by Thomas Malthusthe human
population grows faster than the Earth’s food supply
C. Darwin performed an experiment by breeding pigeons
1-observed that traits varied within a population & showed up in future
generations
2-because variations appear in future generations, they must be inherited
3-bred pigeons with desirable variations, resulting in offspring with these
variations
4-led to his theory of artificial selection
5. Darwin believed that there was a similar force in nature
D. Theory of natural selection
1. Darwin wanted to know why do only certain individuals survive & produce
offspring?
a. what is the mechanism/reason for survival?
2. Darwin from his travels knew:
a-
b-
c-
d-
e-
f-
What do they compete for?
3. Natural selection
a. Russell Wallaceanother British naturalist who reached similar conclusions
b. 1859 Darwin published “On the Origin of Species by Means on Natural
Selection”
E. Is Darwin’s Theory valid?
1. Is it easier to observe/examine evolution in plants/animals or humans?
Why/why not?
a. the older the species the easier it is to observe evolution; remember
evolution takes a long time
II. Evidence of Evolution
A. Fossils also provide evidence of evolution
B. Downside is that fossils are often incomplete, but fossils are still important for
examining changes in structure
C. 2 major classes of traits
1. derived traits
2. ancestral traits
D. Comparative anatomy
1. whenever organisms have similar structures it suggests a common ancestor/
shared ancestry
2. Homologous structures
a. evolution predicts that an organism’s body parts are more likely to be
modifications of ancestral body parts than they are to be entirely new
structures
b. forelimbs of birds are used for flight, but forelimbs of reptiles are used
for walkingboth sets of forelimbs are similar in structuresuggests
they were inherited from a common ancestor
3. Vestigial structures
a. the structure is still inherited, even though it has no use (eyes in mole
rats/cave fish)
4. Analogous structures
a. structures are constructed in diff ways & from diff materials
b. do not indicate close evolutionary relationships, however do show that
functionally similar structures can evolve indep. in similar ENVRs
E. Comparative embryology
1. Embryo
2. Embryos of different species are strikingly similar in the early stages
3. Look at figure 15.9 on pg 426notice how similar the embryos are
4. In each embryo there are pharyngeal pouches, BUT they will become
different structures in each organism
5. When features are shared in embryossuggests they evolved from a
distant common ancestor
F. Comparative biochemistry
1. most organisms contain DNA, ATP, & many other biochemical molecules
2. the enzyme, cytochrome c is very common in many different organisms
3. cytochrome cenzyme that’s essential for respiration & is highly conserved
in animals
4. therefore cytochrome c has changed very little over time
5. scientists compare the difference AA sequences of cytochrome c
6. organisms that are biologically similar have fewer differences in their AA
sequences of cytochrome c
7. scientists have also found shared patterns in proteins, DNA, & RNA among
organisms
G. Geographic distribution
1. distribution of plants & animals in South America suggested that evolution
does occur
2. Darwin observed that animals in South America were more similar to other
organisms living in South America than they were to animals living in similar
ENVRs in Europe
3. migration patterns are also imp when explaining evolutionary relationships
4. biogeography
H. Adaptation
1. adaptation
2. fitness is a means to determine how effectively a trait contributes to
reproductive success
3. fitness
a.
b.
c. explains why the finches on the Galapagos Islands have diff beak shapes &
sizesENVR differed in ea island
4. camouflage
a. allows more of the camouflaged inds to survive & reproduce
5. mimicry
a. resultpredators avoid them
6. antimicrobial resistanceresult of physiological evolution
7. some adaptations might be the consequences of other evolved characteristics
III. Shaping Evolutionary Theory
A. Mechanisms of Evolution
1.
2.
3. the organism may move to another location in response to an environmental
change, but that is not evolution
4.
5. gene pool
6. allelic frequency
a.
b. If a population is in genetic equilibrium is it evolving?-----no b/c allelic
frequencies are remaining the same, therefore there is no change
7. natural selection explains how organisms adapt to their environment & how
variations can give rise to adaptations w/I a species
8. we now know that natural selection is not the only mechanism of evolution
9. population geneticsHardy-Weinberg principle
a.
b.
c.
d. for a pop. to be in genetic equilibrium 5 conditions must be met: no
genetic drift; no gene flow; no mutation; no natural selection; & mating
must be randomunlikely
10. genetic drift
a. founder effect
1. this sub-pop. may have alleles that were uncommon in the original pop.
a. increases the chance of rare genetic disorders occurring
2. common in pops. that rarely marry o/s their communitiesAmish
b. bottleneck
1. us. the result of something catastrophic
2. members of a pop are eliminated w/o regard to their genetic make up
3.
11. gene flow
12. mutations can cause changes in the genetic equilibrium
a.
B. Natural selection
1. the Hardy-Weinberg principle req that all inds in a pop. be equally
adapted to their ENVR & contribute equally to the next generation
2.
3.
4. stabilizing selection
5. directional selection
6. disruptive selection
7. sexual selection
a. often occurs in pops in which the males & females differ significantly in
appearance
C. Reproductive isolation
1. prezygotic isolating mechanisms
a. prevents reproduction by making fertilization unlikely
b. diff species use diff mating songs & do not breed
c. diff species mate at diff times of the yr.
2. postzygotic isolating mechanisms
a. lion & tiger=ligersterile
D. Speciation
1.
2. allopatric speciation
a. the separate pops. eventually will contain organisms that if given enough
time will no longer be able to breed successfully w/1 another
3. sympatric speciation
F. Patterns of evolution
1. adaptive radiation
a.
b. can happen in a short time
c. 1 species gives rise to many species in response to a change in the ENVR
d. Hawaiian honeycreepers
2. coevolution
a. mutualism is a form of coevolution
b. another form is called the coevolutionary arms race
1. 1 organism develops a defense against its predator
2. the predator in response develops a means to negate the defense
3. the organism develops another defense & then the predator develops
another response
4. the cycle continuessuggests 1000s of yrs of evolutionary interaction
3. convergent evolution
a. since they have the same environment, they have similar forms of natural
selection
G. speciation rates
1. scientists disagree over how long evolution takes
a. gradualism
b. punctuated equilibrium
c. it’s believed that environmental changes cause a species to evolve more
quickly in response to the change
d. both ideas are supported by fossil evidence