Transcript Natural_Selection_2

Natural Selection
Charles Darwin’s “suggestion”
about how species change over
time.
Evolution refers to
changes in a SPECIES,
not an individual
4 Key Features to Charles Darwin’s
theory of Natural Selection:
 Variation
 Competition
 Fitness
 Adaptation
Part 1: Variation
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Individual members of a population have
HERITABLE DIFFERENCES: small
differences in the base sequence of their
DNA
The differences that individuals have in their
DNA gets passed on to their offspring
Happens because of
– Random mutations
– Sexual reproduction: combinations of gametes
Peppered moths
Part 2: Competition
The struggle for survival
 The amount of resources in a habitat is
fixed
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– Food, water, living space, mates,
sunlight, minerals, shelter
MANY more individuals are produced
during reproduction than will survive
 There is a limit to how large a
population can grow for a given area=
carrying capacity
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During spring, oak trees
have FLOWERS, which
produce pollen and egg
cells.
Pollen will fertilize the
egg cells, producing the
oak tree seed= the
ACORN
In one single year, an oak
tree may produce up to
2000 acorns. MOST will
not grow to be mature oak
trees
What eats acorns?
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Blue jays
Pigeons
Ducks
Mice
Squirrels
Chipmunks
Skunks
Raccoons
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Deer
Bears
possums
Crows
Wild pigs
Moth larva
Weevil larva
NOT HORSES:
acorns are toxic to
them!
Mice
A single field mouse can have up to 17
litters of babies each year
 Each litter can have up to 13 babies
 That’s 221 baby mice per year from one
female
 MOST get eaten or die:
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– Hawks, owls, foxes, weasels, snakes
Sunflower
One sunflower plant can produce up to
1000 seeds
 MOST get eaten!!
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Part 3: Fitness
Genetically, some individuals have
traits, either physical or behavioral,
that make them better at surviving and
reproducing
 What determines which traits it is good
to have???
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– THE ENVIRONMENT
Part 4: Adaptation
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Eventually, as more and more time
goes by, and more and more
individuals inherit a particular trait,
ADAPTATION of the population occurs
Neck stretching
Natural selection?