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10.3 Theory of Natural Selection
Darwin proposed natural selection as a mechanism for
10.3 Theory of Natural Selection
Several key insights led to Darwin’s idea for natural
• Darwin noticed a lot of variation in domesticated plants
and animals.
• Artificial selection is the process by which humans
select traits through breeding.
• Silver Fox Clip
neck feathers
tail feathers
10.3 Theory of Natural Selection
• Natural selection is a mechanism 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.
• Malthus-said populations will grow exponentially if
• Darwin reasoned similar struggle in nature and
proposed that adaptations arose over many
10.3 Theory of Natural Selection
Natural selection explains how evolution can occur.
• There are four main principles to the theory of natural
– Variation-heritable differences among individuals
– overproduction-producing more offspring than can survive
– adaptation-trait that helps individual survive
– descent with modification-results in new trait in population
• Fitness
is with
the measure of survival ability and ability to
produce more offspring.
10.3 Theory of Natural Selection
• Survival of the fittest: measure of organisms ability to
survive and produce more offspring.
• Key point about Natural Selection:
– 1) Natural Selection acts directly on phenotypes, and
indirectly on genotypes
– 2) New traits are not made by natural selection-they
occur by mutations
– 3) Natural selection can only act on traits that already
10.3 Theory of Natural Selection
Natural selection acts on existing variation.
• Structures take on new functions in addition to their
original function.
• Panda’s Thumb
five digits
wrist bone