Chapter 15.1 Natural Selection and the Evidence for

Evolution

• Studied to become a clergyman and a doctor before becoming a naturalist.

• 5-year voyage around the world on HMS Beagle (1831-1836).

• Published The Origin of Species in 1859.

• Not the first person to propose that species evolve.

Charles DarwinCharles Darwin

Darwin’s InfluencesDarwin’s Influences• From Thomas Malthus – not all

offspring survive to reproduce. Some are better at competing for limited resources and are therefore more likely to reproduce and pass on their traits to offspring.

• From Charles Lyell – the earth is very old and geologic change occurs very slowly.

Darwin’s InfluencesDarwin’s Influences

• Darwin bred pigeons so he was familiar with the principle of artificial selection.

• Artificial selection – selection of specific traits in domestic animals by breeders.

Selection and EvolutionSelection and Evolution• Natural selection –

not all members of a population are equally likely to survive and reproduce. Why?

• Evolution – heritable change in organisms over time.

Evidence: structural adaptations Evidence: structural adaptations • Mimicry – one species

resembles another species.

1. A harmless species imitates a harmful one. What do you think the ratio of harmful to harmless species must be and why?

2. Two or more harmful species look like each other. How does this benefit both species?

• Warning coloration - bold, distinctive pattern of color characteristic of a poisonous or unpalatable organism,

• Yellow jacket hornets, honeybees, and many other species of wasps all have harmful stings and similar coloration and behavior.

Structural adaptationsStructural adaptations

Structural adaptationsStructural adaptations

• Camouflage – adaptation that allows species to blend with their surroundings.

• Because well-camouflaged organisms are not easily found by predators, they survive to reproduce.

The peppered moth

English peppered moth, Biston betularia

Non-resistant bacterium

Resistant bacterium

Antibiotic

When the population is exposed to an antibiotic, only the resistant bacteria survive.

The bacteria in a population vary in their ability to resist antibiotics.

The resistant bacteria live and produce more resistant bacteria.

Direct evidence of evolutionary changeDirect evidence of evolutionary change

Indirect Evidence for EvolutionIndirect Evidence for Evolution

• Fossils

• Comparative anatomy

• Comparative biochemistry

• Comparative embryology

AnatomyAnatomy• Homologous structures - features with a

common evolutionary history.

Whale forelimb

Crocodileforelimb

Birdwing

AnatomyAnatomy• Analogous structures do not

have a common evolutionary origin but are similar in function.

• Analogous structures don’t shed light on evolutionary relationships, but they do provide evidence of evolution. How?

• Vestigial structure –no longer serves its original purpose in present-day organism.

• Was probably useful to an ancestor.

• Vestigial structures, such as pelvic bones in the baleen whale, are evidence of evolution because they show structural change over time.

AnatomyAnatomy

• Nearly all organisms share DNA, ATP, and many enzymes, such as cytochrome c.

Biochemical Similarities of Organisms

Comparison of OrganismsPercent Substitutions

of Amino Acids in Cytochrome c Residues

Two orders of mammals

Birds vs. mammals

Amphibians vs. birds

Fish vs. land vertebrates

Insects vs. vertebrates

Algae vs. animals

5 and 10

8-12

14-18

18-22

27-34

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BiochemistryBiochemistry

1. More offspring are produced than will survive to adulthood.

2. There is phenotypic variation among offspring (due in large part to differences in genotypes)

3. “Fittest” individuals will be more likely to reach adulthood and reproduce (pass on genes to offspring).

Darwin’s Theory in a NutshellDarwin’s Theory in a Nutshell