Descent with Modification A Darwinian View of Life

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Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection.

Darwin then described four observations of nature and from these drew two inferences.

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Observation #1: Members of a population often vary greatly in their traits.

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Observation #2: Traits are inherited from parents to offspring.

Observation #3: All species are capable of producing more offspring than the environment can support.

Observation #4: Overproduction leads to competition for food or other resources.

The individuals best adapted to their environment will survive and reproduce.

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Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals.

Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Descent With Modification:

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Darwin was influenced by Thomas Malthus who noted the potential for human population to increase faster than food supplies and other resources.

If some heritable traits are advantageous, these will accumulate in the population, and this will increase the frequency of individuals with those adaptations.

This process explains the match between organisms and their environment.

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Natural Selection: A Summary

Survival of the Fittest: Individuals with certain heritable adaptive characteristics survive and reproduce at a higher rate than other individuals.

Natural selection increases the adaptation of organisms to their environment over time.

Speciation: If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species.

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Predation and Coloration in Guppies : Scientific Inquiry in Natural Selection

John Endler has studied the effects of predators on wild guppy populations.

Brightly colored males are more attractive to females.

However, brightly colored males are more vulnerable to predation.

Guppy populations in pools with fewer predators had more brightly colored males.

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Natural Selection

Predator: Killifish; preys