Transcript 10.3 Theory of Natural Selection

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 a lot of variation in domesticated plants
and animals.
• Artificial selection is the process by which humans
select traits through breeding.
neck feathers
crop
tail feathers
10.3 Theory of Natural Selection
• Natural selection: individuals that have inherited
beneficial adaptations produce more offspring on
average than others.
• Heritability is the ability of a trait to be passed down.
• There is a struggle for survival due to overpopulation
and limited resources.
• Darwin proposed that adaptations arose over many
generations.
10.3 Theory of Natural Selection
Natural selection explains how evolution can occur.
• There are four main principles to the theory of natural
selection.
• Fitness is the measure of
– variation
survival ability and ability
to produce more offspring.
– overproduction
– adaptation
– descent with modification
ADAPTATION
VARIATION
OVERPRODUCTION
10.3
Theory
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Which
rabbitof
is Natural
best adapted?
10.3
Theory
Selection
Which
rabbitof
is Natural
best adapted?
10.3 Theory of Natural Selection
Natural selection acts on existing variation.
• Natural selection can act only on traits that already exist.
• Structures take on new functions in addition to their
original function.
five digits
wrist bone
10.3 Theory of Natural Selection
Natural and artificial selection are not the only factors in
evolution.
• We’ve learned about natural selection and artificial
selection, but what about sexual selection?
– Mating can have an important effect on the evolution
of a population.
10.3 Theory of Natural Selection
Sexual selection occurs when certain traits increase
mating success.
• Sexual selection occurs
due to higher cost of
reproduction for females.
– males produce many
sperm continuously
– females are more
limited in potential
offspring each cycle
10.3 Theory of Natural Selection
• There are two types of sexual selection.
– intrasexual selection: competition among males
– intersexual selection: males display certain traits
to females
10.3
ofMoth
Natural
Selection
TheTheory
Peppered
Mini-Lab
• Before the industrial revolution, the trees in the forest around Manchester,
England were a light grey/green due to the color of lichens (fungus) on their
trunks. Peppered moths, or Biston betularia, which lived in the area, were
mostly lightly colored with dark spots. However, there was some color
variation between the moths. The most common moth color was light with
dark spots and the least common were dark with light spots. Because there
were not enough resources to support the entire population, the members of
this species had to compete for survival. Their coloring, when against a
similar background, served as camouflage against predators such as birds
and lizards, thus increasing chances of survival. As the Industrial Revolution
progressed, the trees became covered with sulfur dioxide, turning the trunks
dark.
10.3 Theory of Natural Selection