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I can determine why
natural selection is a
key part of
1. Natural Selection
and Darwin’s ideas
2. Evolution Activity
3. Start Pre-lab
How would you define POPULATION?
• _________________________
What is Evolution?
• Change in the genetic makeup of a population
over time.
• Fitness –
– Populations can evolve, not individuals.
• Diverse gene pool good for long-term survival
of a species. ________________are
• How do genetic variations occur?
Where does Variation come from?
• Mutation
– random changes to DNA
• ____________________
• environmental damage
• Sexual reproduction
– _________________
• genetic recombination
– new arrangements of alleles in every offspring
• __________________________________
“The Origin of Species”
• Documented the occurrence of
• Suggested that the mechanism for evolution
was ______________.
Observation 1 –
Observation 2
• Traits are inherited from _________________.
Observation 3
All species are
capable of
producing more
their environment
can support.
Observation 4
• Owing to lack of food or other resources,
Inference 1
• Individuals _______________________
higher probability of surviving and reproducing
in a given environment tend to leave more
offspring than other individuals.
Inference 2
• This unequal ability of individuals to survive
and reproduce will lead to the accumulation
of favorable traits in the population over
• Determines which characteristics are
• _______________________.
• Result - “Natural Selection”
Artificial Selection
• When man determines the characteristics that
survive and reproduce.
• Result - the various breeds of animals and
plants we’ve developed.
Evolution Success Measured By
• ______________
• ______________
• Whoever lives long enough and has kids is the
“winner” in evolution.
• In order for Natural Selection to work, you
must have:
– _____________________.
– Long periods of time (according to Darwin).
Natural Selection
1. Populations are the units of Evolution.
2. __________________________________.
• Acquired characteristics may allow a species
to evolve "outside" of Natural Selection.
• _______________
Essence of Darwin’s ideas
• Natural selection
– heritable variation exists in populations
– ______________________
• more offspring than the environment can support
– _____________
• for food, mates, nesting sites, escape predators
– differential survival
• successful traits = _____________
– differential reproduction
• adaptations become more
common in population
Lamarckian vs. Darwinian view
• LaMarck
– in reaching higher
vegetation giraffes
stretch their necks &
transmits the acquired longer
neck to offspring
• Darwin
– giraffes born with longer
necks survive better & leave
more offspring who inherit
their long necks
Effects of Selection
• Changes in the average trait of a population
giraffe neck
horse size
human birth weight
rock pocket mice
In addition to natural selection,
evolutionary change is also
driven by random processes…
• The smaller the population, the less genetic
variety it has.
• In a very small population, alleles can be lost
from one generation to the next, simply by
random chance.
• When a population evolves only because of
this type of random sampling error,
_____________is taking place.
Genetic Drift
• Chance events changing frequency of traits in
a population
– not adaptation to environmental conditions
• not selection
– ____________
• small group splinters off & starts a new colony
• it’s random who joins the group
– ___________
• a disaster reduces population to
small number & then population
recovers & expands again but
from a limited gene pool
• who survives disaster may be random
Ex: Cheetahs
 All cheetahs share a small number of alleles
less than 1% diversity
 2 bottlenecks
10,000 years ago
 Ice Age
last 100 years
 poaching & loss of habitat
Conservation issues
Peregrine Falcon
• Bottlenecking is an important
concept in conservation biology
of endangered species
– loss of alleles from gene pool
– __________________
– __________________
Breeding programs must
consciously outcross
Golden Lion
Human Impact on variation
• How do we affect variation in other
– Artificial selection/Inbreeding
• Animal breeds
– ___________________
• Insecticide usage
– ___________________
• resistant bacterial strains