1. Evolution
Ch 13

2. Historical Theories Anaximander (~2500 yrs ago) Aristotle
Georges Buffon (1700’s)
Jean Baptist Lemark (late 1700’s - early1800’s)
Erasmus Darwin
Many modern views were first expressed or at least alluded to by the ancient Greeks
Anaximander
- proposed that life began in water & that simpler forms led to more complex ones
Aristotle
- postulated that species were fixed
- dominant belief for some time
Questioning the dominant belief began in the 1700’s with Georges Buffon
- viewed fossils and postulated that the earth may be older that 6000 yrs old
Jean Baptiste Lemark (early 1800’s)
- suggested (1800) that organisms evolved, though was wrong about the mechanisms
- thought it was usage or non-usage of body parts that resulted in characteristic changes
+ passed to offspring
+ ex, giraffes which stretched their necks in life would pass on longer necks
Erasmus Darwin, Charles’ grandfather was an evolutionist

3. Charles Darwin
Darwin (1809 -
- English gentleman naturalist
1874
1859

4. Voyage of the HMS Beagle
5 year voyage
- only chance that he got on the ship in the first place
+ Fitzroy wanted an educated companion
+ encouraged Darwin to think and come up with theories
* though he would later deny it.
- Most of the time was spent off the southern tip of South America
+ charting the Tierra del Fuego area
- Only a short time in the Galapagos area off of Ecuador
- collected fossils, specimens of all sorts of plants and animals
Most importantly, made observations about what he saw.

5. On the Origin of Species…
Descent With Modification
By means of Natural Selection
Only published it then because of Alfred Russel Wallace’s correspondence to him
- describing theories very similar to his own
All organisms are related through descent

6. How Did Darwin Come Up With His Ideas?
Scientific Method
Key observations
Traits vary in a population
Most traits are inherited from parent to offspring
More offspring are produced than the environment can support (Thomas Malthus)
What is the mechanism by which organisms become adapted to their environment?
Darwin’s theory were the result of several Key observations
1) Species tend to overproduce offspring (more than can possibly survive).
- Theory proposed by Malthus (economist)
+ thought human suffering (disease, famine, starvation, etc.) resulted from
human populations’ growth faster than food and other resources are produced.
- Darwin proposed that this theory could be applied to all species
- Natural resources are limited, therefore, the production of more individuals than
the environment can support sets up a struggle for existence
- As a result, only a percentage of offspring survive to reproduce in each
generation
2) Individuals in a population vary in their characteristics
3) Varying traits are often passed on from one generation to the next

7. Trait Variation

8. Recap Limited resources Overproduction of offspring
Heritable individual variation
Therefore, survival depends partly on inherited features

9. Darwin’s Theory of Evolution
In a varied population, individuals whose inherited characters best adapt them to the environment are more likely to survive and reproduce.
Therefore, more fit individuals tend to leave more offspring than less fit individuals.
Natural Selection is the mechanism
Reproduction (differential) is Key
Scientific method
- hypothesis phase of method
Put another way:
- heritable variation is a fact of life.
+ In an environ. of finite resources, individuals that are best adapted to the it will
be more “fit”
- Fitness is the contribution to the next generation’s gene pool
- fittest individuals are those that pass the most genes to the next generation
+ not necessarily the longest lived
- And therefore, more likely to pass on their genetic makeup
Came up with theories with no knowledge of genetics
- Mendel’s work came about 20 years later

10. Natural Selection Descent with Modification
Acts on individuals, affects population

11. Artificial Selection Darwin used artificial selection as an argument
= selective breeding of domesticated plants an animals by man
Humans breed animals for desired traits
- achieve results in relatively short amount of time
- Therefore, natural selection should be able to result in great changes

12. Observing natural selection
Camouflage adaptations that evolved in different environments
A flower mantid in Malaysia
A leaf mantid in Costa Rica
Figure 13.5A
Camouflage adaptations that evolved in different environments are examples of the results of natural selection
Ex- Leaf mantid and flower mantid

13. Pestacide Resistance Figure 13.5B
Pesticide application
Survivor
Chromosome with gene conferring resistance to pesticide
Additional applications of the same pesticide will be less effective, and the frequency of resistant insects in the population will grow
Figure 13.5B

14. Antibiotic resistance
The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria
Colorized SEM 5,600
Figure 13.13

15. Natural Selection Experiment
Darwin Finches (Galapagos Finches)
Similar EXCEPT for beaks
Beaks = specialization
Peppered moths- comment on study
Darwin finches- The birds are all about the same size (10–20 cm). The most important differences between species are in the size and shape of their beaks, and the beaks are highly adapted to different food sources. The birds are all dull-colored.
The ancestral finch was a ground-dwelling, seed-eating finch

16. Support for Descent with Modification
Biogeography
Fossil Record
Molecular Biology, Biochemistry, Cell Biology
Comparative Anatomy
Support for the theory comes from all areas of biology
Fossil Record
- shows animals and plants have appeared on earth in a historical sequence
- consistent with other lines of data
Molecular/cell data put prokaryotyes as ancestors of all life
- earliest fossils (~3.5 Billion years old) are prokarotes 16

17. Biogeography Geographic distribution of species
Geographic distribution of species
Galápagos animals resembled species of the South American mainland more than animals on similar but distant islands
Organisms may have common ancestor
Biogeography = geographical distribution of species
- Darwin’s observations of biogeography
+ 1st suggested that all organisms might have common ancestors
- many of the Galapagos species resembled mainland species more than they
resembled species of similar but distant islands 17

18. Fossil Evidence Organisms evolved in a historical sequence
Organisms evolved in a historical sequence
A Skull of Homo erectus
D Dinosaur tracks
B Petrified tree
C Ammonite casts
E Fossilized organic matter of a leaf
G “Ice Man”
F Insect in amber
Figure 13.3A–G

19. Fossil Evidence
Many fossils link early extinct species with species living today
Figure 13.3I
Whales 19

20. Comparative Anatomy Comparison of body structures in different species
Comparison of body structures in different species
Homology- similar characteristics resulting from common ancestry
Homologous structures- features with different functions but structurally similar due to common ancestry
Human
Cat
Whale
Bat
Figure 13.4A
Homology is the similarity in characteristics that result from common ancestry
Homologous structures are features that often have different functions but are structurally similar because of common ancestry 20

21. Comparative Embryology
Post-anal tail
Pharyngeal pouches
Chick embryo
Human embryo
Figure 13.4B
Comparison of early stages of development among different organisms
Many vertebrates have common embryonic structures 21

22. Molecular Biology
Table 13.4
Comparisons of DNA and amino acid sequences between different organisms to reveal evolutionary relationships

23. Unit of Evolution
Evolution acts on individuals, affects whole populations
Populations are the unit of evolution
Group of individuals of the same species living in the same place at the same time
Population genetics = study of genetic change in populations
Modern synthesis
~1940’s, a comprehensive evolutionary theory incorporating genetics emerged
+ Melds population genetics and Natural selection
Species = a group of populations whose individuals have the potential to:
1) interbreed
2) produce fertile offspring

24. Unit of Evolution
Evolution is change in prevalence of heritable traits in population through time
A gene pool
Is the total collection of genes in a population at any one time
Microevolution
Is a change in the relative frequencies of alleles in a gene pool

25. Hardy-Weinberg Equilibrium
Frequency of alleles in a stable population will not change over time
Very large population
Population is isolated
Mutations don’t alter gene pool
Random mating
All individuals are equal in reproductive success
In reality, this never happens
It is often intuitive to think that a dominant allele will force our the recessive one over time
But this is not the case.
Allele frequencies will remain = in a population over time in the presence of 5 conditions
- Very large population
- Population is isolated
+ no migration in or out of population
+ no alleles added or lost
- No mutations
- Mating is random
- all individuals are equal in reproductive success
In reality, this never happens
- restrictive conditions
- allow us to determine the possible agents of change in a pop. by it’s deviation from
H-W equilibrium

26. Agents of Change Genetic Drift Gene Flow Mutation Non Random Mating
Bottle neck affect
Founder affect
Gene Flow
Mutation
Non Random Mating
Natural Selection
Non-Random mating = preferential mating
- quite common in many populations
- non-random assortment
+ tall men with tall women, short men with short women
- Dominant male populations
Natural Selection
- differential reproductive success
- variation results in varied fitness
- THE factor likely to produce adaptive changes in a gene pool

27. Variation Extensive in most populations
Extensive in most populations
Mutation and sexual recombination generate variation and can create new alleles.
Figure 13.11
Many populations exhibit polymorphism or different forms of phenotypic characteristics
Populations may also exhibit geographic variation or variation of an inherited characteristic along a geographic continuum

28. Endangered species often have reduced variation
Endangered species often have reduced variation
Low genetic variability
May reduce the capacity of endangered species to survive as humans continue to alter the environment
Figure 13.10

29. Types of Selection
So, what does the culling affect on the genotypes to at the population level?
3 Types of Selection
1) Stabilizing Selection
- favors intermediate variants over the extremes
- decreases variability
2) Directional Selection
- shifts overall populations makeup by selecting against an extreme and driving the
population in the other direction
- most common during periods of environmental change or after migration
3) Diversifying Selection
- selects for the extremes over the intermediates
- can lead to speciation if the differences become large enough or if there is isolation

30. Sexual Selection Sexual Dimorphism
Sexual Selection- where individuals with certain characteristics are more likely to obtain mates than others.
Intrasexual selection
Intersexual selection

31. Diploidy Balancing selection Heterozygote advantage
Frequency-dependent selection
Neutral Variation

32. Natural Selection is Limited
Only act on existing variation
Historical constraints
Compromise
Chance, selection and the environment