Evolution:Natural Selection & Adaptation

Chapters 15 and 16

I. Evolution is the Unifying Principle of all BiologyA. forms foundation for all other concepts

1. answers all “why” questions

2. explains context of boil. phenomena

B. two major aspects:1. descent from a common ancestor why org. have similar characteristics

2. adaptation to environment explains diversity of life

II. Charles DarwinA. developed theory of evolution

• 1859: The Origin of Species

B. descent with modification • “change through time”

C. evol. occurs through natural selection1. env. determines which ind. will survive and reproduce

• are fittest ind. possess best adaptations

2. adaptations• characteristics that increase chance of survival and reproduction

III. Natural SelectionA. mechanism of evol.

B. based on five key points:1. ind. vary within pops.

2. some variation is inherited and affects survival

3. more offspring are produced than env. can support

4. offspring with most adaptive traits will survive better and produce more of their own offspring

• offspring will also have the adaptive traits

5. over time, the pop. changes• more adaptive traits become more prevalent

C. environmental forces affect an individual’s phenotype1. to survive, an org’s. phenotype must become adapted to env.

• but, genotype determines phenotype

2. orgs. with most adaptive genotypes survive better and pass their genes onto their offspring

• their genotypes produce a more fit and adaptive phenotypeo such organisms are “selected for”

3. variation in pop. small genetic changes produce new genotypes lead to new, better adapted phenotypes

4. continued phenotypic change development of new species

D. variation1. occurs in pops. in many different traits

a. behavioral, biochemical, physical

b. must be genetically based

c. two primary sources

i. mutation• source of new variations

ii. crossing over• source of new combinations of traits

d. is very beneficial to a pop. evol. cannot occur without it

2. maintained through a wide variety of mechanisms

a. dispersal of young

b. masking recessive alleles

c. heterozygote advantage

d. others

Fig. 15.7 Variation in a human population

Fig. 16.16 An example of heterozygote advantage

E. Modern Synthesis – Today’s Theory of Evolution• incorporates genetics into evolution

F. nat. sel. causes populations to change, not individuals

G. selection is not a random process

H. evol. is not based on the needs of organisms• mutations acted on by nat. sel. adaptation to local env. conditions

I. selection has been tested and confirmed many times in many organisms

J. fittest ind. are those more likely to survive, based on adaptations1. evolution is not “survival of the fittest”

2. survival not as important as reproduction

Fig. 16.3 Natural selection in peppered moths

IV. Evidence and Examples of EvolutionA. fossil record

1. radioactive dating

2. hard-bodied vs. soft-bodied organisms

3. phylogenetic trees

Fig. 17.17 Evolutionary history of Equus

Fig. 30.7 Human evolution

B. biogeography1. study of where organisms are found on earth

2. provides evidence of past evol. history

3. isolated regions have their own types of plants and animals

4. similarity of unrelated species in similar environments

Page 274 Biogeographical regions

Fig. 15.5 An example of evidence through biogeography – the European hare and the Patagonian (S.A.) hare

Fig. 15.14 Biogeography. Some mammals of Australia and their North and South American counterparts.

C. comparative anatomy1. homologous vs. analogous structures

2. adult and embryological evidence

3. transitional organisms

4. vestigial structures

Fig. 15.15 Homologous structures

Fig. 15.16 Developmental homologies

Fig. 15.12 Transitional fossils - Archaeopteryx

Fig. 15.13 Ambulocetus – an ancestor of whales and a transitional fossil

Fig. 17.1 Whale evolution, showing transitional organisms

Some vestigial structures

D. molecular biology 1. genetic code and cellular structure

2. DNA and amino acid similarities

3. number of mutations

4. phylogenetic trees

Fig. 15.17 Biochemical differences – evidence from molecular biology

E. artificial selection• selective breeding

Fig. 15.8 Artificial selection in animals

Fig. 15.9 Artificial selection in plants