Download 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
NGSSS
• SC.912.L.15.13 Describe the conditions
required for natural selection, including:
overproduction of offspring, inherited
variation, and the struggle to survive,
which result in differential reproductive
success. (MODERATE)
10.3 Theory of Natural Selection
Charles Darwin
• Darwin set sail on the H.M.S. Beagle
(1831-1836) to survey the south seas
(mainly South America and the
Galapagos Islands) to collect plants
and animals.
• On the Galapagos Islands, Darwin
observed species that lived no where
else in the world.
• These observations led Darwin to write
a book
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10.3 Theory of Natural Selection
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10.3 Theory of Natural Selection
Giant Tortoises of the Galápagos Islands
Pinta
Pinta Island
Intermediate
shell
Fernandina
Isabela
Tower
Marchena
James
Santa
Cruz
Santa Fe
Hood Island
Floreana
Hood
Saddle-backed
shell
Isabela Island
Dome-shaped shell
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10.3 Theory of Natural Selection
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http://www.galapagosislands.com
10.3 Theory of Natural Selection
Charles Darwin
Wrote in 1859:
“On the Origin of Species by Means of
Natural Selection”
Two main conclusions:
1. Species were not created in their
present form, but evolved from
ancestral species.
2. Proposed a mechanism for evolution:
NATURAL SELECTION
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10.3 Theory of Natural Selection
Darwin’s Observations
1. Most species produce more offspring
than can be supported by the
environment
2. Environmental resources are limited
3. Most populations are stable in size
4. Individuals vary greatly in their
characteristics (phenotypes)
5. Variation is heritable (genotypes)
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10.3
Theory
of
Natural
Selection
Natural Selection
• Individuals with favorable traits are
more likely to leave more offspring
better suited for their environment
Example:
English peppered
moth (Biston betularia)
10.3 Theory of Natural Selection
Animation
Example of directional selection animation.
Click to view
animation.
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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
Selectively Bred Pigeons
10.3 Theory of Natural Selection
• 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.
• Natural selection is a mechanism by which individuals
that have inherited beneficial adaptations produce
more offspring on average than do other individuals
10.3 Theory of Natural Selection
Natural selection explains how evolution can occur.
• There are four main principles to the theory of natural
selection.
– variation
– overproduction
– adaptation
– descent with modification
ADAPTATION
VARIATION
OVERPRODUCTION
DESCENT
with
MODIFICATION
10.3 Theory of Natural Selection
Variations:
• Differences in traits
• Come about by mutations in
genes
• Random
• Occur in sex cells
• Passed on to future generations
10.3 Theory of Natural Selection
Over Production
• Having many offspring increases the chance of survival
but also results in competition for resources
10.3 Theory of Natural Selection
Bird Beak Adaptations:
10.3 Theory of Natural Selection
Adaptations
: a certain variation
suited to a particular environment that allow organisms
to survive
Inuit people, who
live in the extreme
cold of the Arctic,
have short, stout
bodies that conserve
heat.
10.3 Theory of Natural Selection
Masai people,
who live in the
arid lands of
eastern Africa,
have tall, lean
bodies that
disperse heat
well.
10.3 Theory of Natural Selection
Descent with modification
• Heritability of adaptations
• More individuals will have
the trait in every following
generation
• As long as the
environmental conditions
remain beneficial for the
trait
10.3 Theory of Natural Selection
Survival of the Fitness
• Fitness is the measure of survival ability and ability to
produce more offspring.
• Does not mean the strongest!
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