Evidence of Evolution

Chapter 8

Historical

• Jean-Baptiste Lamarck

Alfred Wallace

Voyage of the Beagle

Darwin and Natural Selection

A Key Insight – Variation in Traits

Darwin’s observations:• Populations can produce more individuals than

their environment can support• Some versions of a trait might enhance an

individual’s ability to survive and reproduce in its environment

Finches in the Galapagos Islands

Terms

Alleles• Heterozygote• homozygote

Genotype Phenotype Frequency equilibrium

genotypephenotype

At What Level Does Evolution Occur?

Individuals don’t evolve, populations do!

Fig. 18-3b, p. 280

420 Aa butterflies medium-blue wings

490 AA butterflies dark-blue wings

490 AA butterflies dark-blue wings

490 AA butterflies dark-blue wings

420 Aa butterflies medium-blue wings

420 Aa butterflies medium-blue wings

90 aa butterflies white wings

90 aa butterflies white wings

90 aa butterflies white wings

Starting Population Next Generation Next Generation

How can a gene pool change?

• Mutation• Genetic drift• Gene flow

(migration)• Natural selection• Sexual selection• Will the above have

more of an effect on a large population or a small population? Why?

Genetic Drift—The Chance Changes

Genetic drift• A random change in allele frequencies over time• Founder effect• Bottleneck Effect

Genetic drift is pronounced when a few individuals start a new population

Gene Flow (Migration)

Natural Selection

Differential survival and reproduction among individuals of a population that vary in the details of their shared traits

In other words….. Some organisms have a better chance of surviving and reproducing than other organisms depending on their traits

Natural Selection

Natural selection Differential survival and reproduction

among individuals of a population that

vary in details of shared, inherited traits

Adaptive trait Any trait that enhances

an individual’s fitness-

ability to survive and reproduce in a

particular environment)

Not this kind of fitness!

Sexual Selection

With sexual selection, some version of a trait gives an individual an advantage over others in attracting mates

Sexual Selection