Evolutionary theory

1
Evolutionary theory Definitions Thoughts on
evolution The evidence for evolution
2
What is evolution? the process by which
characteristics of organisms change over
time Macroevolution-studying the changes that
take place over long periods of time formation
of new species appearance of novel
structures episodes of extinction
3
Microevolution- changes that occur within
populations genetic variation due to natural
selection adaptation- changes that increase
likelihood of survival and reproduc- tion of
that organism in that environment
4
Why is it called evolutionary theory?
A scientific theory is an explanation of natural
events based on a large number of observations
and consistent with scientific principles
Evidence for evolution the fossil
record comparative anatomy/embryology molecular
(biochemical and DNA)
5
History of evolutionary thought
I. Each organism was created at the same time and
remains exactly as it was created. Also, Earth is
approx.4000 years ancient Greeks (Plato,
Aristotle) Judeo-Christian theology
II. Age of exploration many new species
discovered similarities and differences noted
Discovery of fossils
6
Allosaurus (65 mya)
Seed ferns (150 mya)
trilobites
(230 mya)
7
Smith (1700s) certain fossils are always found in
the same layers younger fossils are in higher
layers that older ones older fossils very
different from modern organisms many organisms
were extinct
How did different organisms appear at different
times?
8
Comte de Buffon (1700s) a few founding species
changed over time
Cuvier (early 1800s)- catastrophism catastrophies
killed off many of the founding species
Hutton (1700s) and Lyell (1800s)-geologists among
the first to realize that the earth is very
old Uniformitarianism- forces of wind, water,
earthquakes, volcanic eruptions etc.-lead to
formation of many layers of rock,
repeatedly Potassium-40 dating shows that earth
is approximately 4.5 billion years old K-40 is
found in volcanic rocks Half-life of K-40 is 1.25
billion years (compare to C-14, with half-life
of 5730 years)
9
Biological mechanisms for evolution
Lamarck- inheritance of acquired characteristics
(Giraffes acquired long necks because they
needed them)
Darwin (and Wallace) and natural
selection (Trait was already there selection
acted on it.)
10
Some types of finches observed in the Galapagos
Islands
11
Gradualism or punctuated equilibrium? Eldredge
and Gould, 1970s Not all species evolve at the
same rate The fossil record is not complete
12
Formation of evolutionary theory
13
Evidence for evolution
Fossil record change over time
14
Anatomical record evidence of a common ancestor
15
Homologous structures
16
Vestigial structures signs of common ancestry
17
Embryology embryos of vertebrates have many
features in common (gill slits, tail)
18
Biochemical and genetic evidence
All living organisms have DNA and RNA the
nucleotides are biochemically identical Many
essential molecules are so similar they have been
compared to deduce divergence hemoglobin cytoch
rome c
19
macaque
human
lamprey
bird
dog
frog
Time
differences between human and other
vertebrates (amino acids in hemoglobin)
20
Molecular clocks, p. 239 Why do pseudogenes
evolve more rapidly than genes like histone or
cytochrome C?
Histone a protein that helps stabilize
the structure of DNA in a chromosome Cytochrome
c plays a role in aerobic Respiration Pseudogene
a DNA sequence that resembles a gene but does
not function
21
Darwin (and others) observed artificial selection
Breeding superior livestock and
crops Dogs (some dog species are so
different from each other they cant
mate without assistance)
22
Natural selection and adaptive evolution
Darwin adaptation to environment closely related
to species formation
Example of natural selection antibiotic-resistan
t bacteria
23
(No Transcript)
24
Darwin didnt know about genetics. Evolutionary
biology and genetics came together many years
later Population genetics
Population group of individuals of the same
species living in the same area at the same time
(and tending to breed with each other)
25
Sources of genetic variation
Random processes mutation sexual recombination
Natural selection is nonrandom
26
(No Transcript)
27
Gene pool
All alleles in all individuals making up
a population. Say you have two alleles for a
trait, p and q. pq1 (why?)
Hardy-Weinberg equilibrium applies if gene pool
is unchanged p22pqq21
If p0.8, what is q? (1-p) p2 homozygous
dominants 2pq heterozygotes q2 homozygous
recessives
28

• Hardy-Weinberg applies if
• Population is very large
• Random mating
• No mutation
• No new genetic input
• No natural selection

29
If p0.8, what is q? 0.2 (1-p) p2 homozygous
dominants (0.8)(0.8)0.64 2pq
heterozygotes 2(0.8)(0.2)0.32 q2 homozygous
recessives (0.2)(0.2)0.04
0.640.320.041
But the gene pool is not unchanging. What can
change a gene pool?
30
I. Genetic drift- change of allele frequency in a
small population
Bottleneck effect
Founder effect
31
(No Transcript)
32
(No Transcript)
33
Founder effect Tendency for hereditary
disorders In isolated human populations
34
II. Gene flow- exchange of genes
between populations III. Nonrandom mating IV.
Mutation
V. Natural selection (adaptation)
35
Directional stabilizing diversifying
36
Examples of natural selection
Antibiotic-resistant bacteria
Starvation gene hypothesis
Microevolution is not the whole
story Macroevolution- diversity of
species formation of new species extinctions