Unit 3: Lecture 1-4

Evolution

Biological evolution defined

the descent of modern organisms with modification from preexisting life-forms

Ecology subtopics

species interactions, dispersal, population dynamics, community structure, ecosystem functions, spatial structure

Evolution subtopics

natural selection, sexual selection, gene flow, genetic drift, migration

Structure and function of species, biodiversity, human society

Things evolution explains

Biogeography

Cofounding evidence: similar species often in the same geographic region, different species with similar forms in different regions, specific traits of organisms living in certain environments (thick, waxy leaves in desert plants)

Comparative morphology

Cofounding evidence: study of similarities and differences in body plans of major groups, puzzling patterns (homologous structures, developmental homology, vestigial structures)

Human arm: Dog foreleg: Seal flipper

Homologous structure example

Both chick and human embryos have gill pouches and tails

Developmental homology example

Snake: Human

Vestigial structure example

Geological discoveries

Cofounding evidence: Georges Cuvier, James Hutton & Charles Lyell

Georges Cuvier 1769-1832

Concluded deeper layers contain simpler fossils than shallow layers, some fossils seem to be related to known species, from one layer to the next; some fossils appear or disappear

James Hutton (1726-1796) & Charles Lyell (1797-1875)

Concluded that geology changes gradually over time

Charles Darwin (1831)

Galapagos Finches: observed variety of lifestyles and body forms, correlated variations with environmental challenges

Peter and Rosemary Grant

Long-Term Galápagos Study 1973: provided the first direct, real-time proof that evolution by natural selection happens rapidly in the wild

Alfred Wallace (1850s)

independently developed a theory similar to Darwin’s

Origin of Species (1859)

Book by Darwin theorizing natural selcection and evolution

Darwin’s 6 facts:

1. Any species is capable of increasing size exponentially

2. Populations tend to remain stable in size

3. Resources are limited

4. Individuals in any species vary

5. Some vary in ways that aid survival and reproduction

6. Variation is inherited

Inference from Darwin’s facts 1-3

Few offspring survive to reproduce: “struggle for existence”

Inference from Darwin’s facts 4-6

Certain inherited traits increase probability of survival and reproduction

2 Darwin conclusions

1. Overproduction and struggle for existence

2. Heritable individual variation

Final Darwin conclusion

Differential reproductive success causes evolution: Natural selection

Clauses of Darwin’s theory

1. natural selection acts only on heritable traits

2. traits mayt be more or less beneficial depending on circumstances

3. populations evolve, not individuals

“The Descent of Man and Selection in Relation to Sex”

Published by Darwin 1871: Applies evolution theory to humans, sexual selection

Sexual selection (Darwin definition)

advantage which certain individuals have over others of the same sex and species, solely in respect to reproduction

Sexual Selection

natural selection for mating process, selection for phenotypic differences that increase mating success - within or between sexes

Asymmetrical investment in offspring

females invest directly in offspring, males invest in mating opportunities → inter/intrasexual selection

Non-adaptive choice

Female selects a mate based on a specific trait that does not provide her or her offspring with any direct survival or health benefits: sensory bias, species recognition

Directly adaptive choice

Female selects a mate based on a specific trait that does provide her or her offspring with direct survival or health benefits: phenotypic trait infers higher fitness

Indirectly adaptive choice

Female selects a mate based on a specific trait that signals higher fitness

Intersexual selection

Female reproductive success not limited by access to mates → females will be choosy to maximize quality of offspring, since they have to invest so much in esc

Intrasexual selection

Male reproductive success is limited by access to mates → males will be competitive

Sexual dimorphism

Both intersexual and intrasexual selectionn lead to _______ _______

Precopulatory competition

Male-male competition before sex: fighting

Postcopulatory competition

Male-male competition after sex: sperm competition

Costs to sexual reproduction

Slower population growth, more energetically costly

Benefits to sexual reproduction

Increases genetic variability, greater resistance to disease, greater resistance to changing envrionments

Parthenogenesis

Form of asexual reproduction where an embryo develops from an unfertilized egg

Gene pool

All genes and alleles in a population

Microevolution

Change in frequency of alleles in a population or the gene pool of a population

p

frequency of dominant allele

q

frequency of recessive allele

of copies of allele / sum of all alleles

p or q =

1

p + q = or p² + 2pq + q² =

p²

frequency of homozygous dominants

q²

frequency of homozygous recessives

2pq

frequency of heterozygous dominants

5 Causes of microevolution

1. mutation

2. gene flow

3. genetic drift

4. nonrandom mating

5. natural selection