Unit 11 - II. Theories of Mechanisms of Evolution

Ideas about how

species change over time

LaMarck believed that evolutionary changes were caused by

organisms actively adapting themselves to environmental conditions (disproven)

Law of Use and Disuse (disproven)

the more a particular structure is used → the more prominent and well-developed it will become (& vice versa)

Inheritance of Acquired Characteristics (disproven)

belief that traits an organism developed can be passed down

No genetic link to explain how

developed traits are heritable

Malthus realized populations tended to increase

geometrically

• limited supply of resources could not keep up (competitive situation)

Darwin had 3 major points in his theory of “descent with

modification” through natural selection

1. Species over-

reproduce

2. Competition for

limited resources occurs

3. Variations exist among individuals -

• some are better at competing for limited resources

  • ultimately reproduce more (offspring skews the gene pool)

  • leads to evolution

Adaptation (favorable genetic variation)

makes an organism more likely to survive & reproduce

Fitness (measure of reproductive success)

how many surviving offspring are produced

Speciation

accumulation of favorable adaptations over time

• result in formation of new species