10.3 Theory of Natural Selection

KEY CONCEPT Darwin proposed natural selection as a mechanism for evolution.

10.3 Theory of Natural Selection

Several key insights led to Darwin’s idea for natural selection.

• Darwin noticed variation in domesticated plants and animals.

• Artificial selection is the process by which humans select traits through breeding.– cabbage, brussel sprouts, kale, cauliflower were all

developed from a wild cabbage plant– all dogs have a common ancestor

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10.3 Theory of Natural Selection

• Natural selection is a process by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.

• Heritability is the ability of a trait to be passed down.• There is a struggle for survival due to overpopulation

and limited resources. • The environment is the selective agent – determines

which traits are advantageous• being dark green may be good in a forest but not so

in a desert• Darwin proposed that adaptations arise over many

generations – descent with modification

10.3 Theory of Natural Selection

• There are four main principles to the theory of natural selection.– variation – in all populations there are slight differences

caused by differences in DNA

Natural selection explains how evolution can occur.

– overproduction – most organisms produce more

offspring than can survive; leads to competition

– adaptation- a certain variation may allow individuals to survive at a greater rate in that particular environment; that trait is passed on to the offspring; – descent with modification- over time there will be more individuals with that trait, and the species will be changing

• Fitness is the measure of survival ability and ability to produce more offspring (reproductive fitness)

10.3 Theory of Natural Selection

• Genes change by random mutations.• It the change is an advantage, then it will be selected for.

– (may be harmful or neutral)• If the environment changes, the adaptation may not be

beneficial anymore

Natural selection acts on existing variation.

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