Transcript Sexual selection

The Theory of
Natural Selection
Artificial Selection
• Humans created diversity choosing specific traits to breed
– Dogs, Crops, Livestock
• Humans selected (not naturally) traits thought to be
advantageous
• Only inheritable traits can be passed down
• Importance: Shows life can change over a period of time
Dog traits have
been selected by
breeders for
centuries to
produce various
breeds.
Plants have been
bred to produce
certain traits for
human use also!
These kittens
have variations
Not all these
wildebeest will
survive
• Four factors:
1) Overpopulation: more offspring are born than can survive
2) Variation: individuals of a population have differences
3) Adaptation: Some variations allow a better chance of
survival
4) Descent w/ modification: Those with advantages will
reproduce  more of the population will have the
advantage
The Myth
• 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
Which rabbit is best adapted to this environment?
Over time, those not adapted most likely die…that’s
natural selection!
Which rabbit is best adapted?
Do the dark rabbits turn white? No! They get eaten.
(survival of the fittest)
Struggle for Survival
• Populations do not grow unchecked
– Limiting Factors: food, water, shelter, disease, predators
• Fitness: measure of the ability to survive & produce
more offspring
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.
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
• There are two types of sexual selection.
– intrasexual selection: competition among males
– intersexual selection: males display certain traits
to females
Natural Selection in Action:
The Peppered Moth Analysis
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.
Natural Selection in Action:
The Peppered Moth Analysis
As the Industrial Revolution progressed, the trees became covered with sulfur
dioxide, turning the trunks dark.