Darwin and Natural Selection

Charles Darwin & Evolution — AP Biology Notes

Evolution

  • Evolution = change in populations over time

  • Defined by Darwin as “descent with modification”

  • All organisms share a common ancestor

Charles Darwin (1809–1882)

  • British naturalist

  • Voyage on H.M.S. Beagle (1831–1836)

  • Observed variation, adaptation, and speciation

  • Published On the Origin of Species (1859)

Galápagos Islands Observations

  • Species similar to mainland species but modified

  • Adaptations matched local environments

  • Key examples:

    • Finches → different beak sizes/shapes

    • Tortoises → different shell shapes

    • Marine iguanas → feeding adaptations

Natural Selection (Mechanism of Evolution)

Five Key Principles

  1. Overproduction: More offspring produced than survive

  2. Competition: Limited resources

  3. Variation: Individuals differ in traits

  4. Differential survival: Better-adapted individuals survive/reproduce

  5. Inheritance: Adaptive traits passed to offspring

➡ Over generations, advantageous traits become more common

Key Definitions

  • Adaptation: Heritable trait increasing survival/reproduction

  • Fitness: Ability to survive and reproduce

  • Species: Organisms that can interbreed

  • Population: Group of same species in one area

Darwin’s Finches

  • Beak variation linked to:

    • Food source

    • Habitat

    • Feeding method

  • Evidence for:

    • Natural selection

    • Adaptive radiation

    • Common ancestry

Speciation

Formation of new species

Steps

  1. Migration

  2. Geographic isolation

  3. Genetic divergence

  4. Reproductive isolation

  5. Natural selection
    ➡ Results in new species

Example: Peppered Moth

  • Two forms: light & dark

  • Industrial soot darkened trees

  • Dark moths survived better

  • Demonstrates:

    • Variation

    • Differential survival

    • Heredity

    • Evolution by natural selection

Influential Scientists Before Darwin

James Hutton (1785)

  • Earth is very old

  • Geological change is slow and continuous

Charles Lyell (1833)

  • Uniformitarianism

  • Earth processes operate today as in the past

Thomas Malthus (1798)

  • Populations overproduce

  • Limited resources → competition

Jean-Baptiste Lamarck (1809)

  • Inheritance of acquired traits

  • Use/disuse of organs

  • Incorrect but influential

Alfred Wallace (1858)

  • Independently proposed natural selection

Darwin vs. Lamarck

Concept

Lamarck

Darwin

Species change over time

Yes

Yes

Adaptation

Yes

Yes

Mechanism

Use/disuse

Natural selection

Inheritance

Acquired traits

Heritable traits

Extinction

No

Yes

➡ Darwin accepted today due to genetics

Why Lamarck Was Disproved

  • Acquired traits are not inherited

  • Only genetic traits are passed on

  • Injuries or body changes are not heritable

Core AP Biology Takeaways

  • Evolution acts on populations, not individuals

  • Natural selection requires:

    • Variation

    • Heritability

    • Differential survival

  • Environment selects, does not cause traits

  • Genetics supports Darwin’s theory