Download Darwin and Natural Selection

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Darwin and Natural Selection
Evolution is a Theory – Just like Einstein's Theory of General Relativity, which
helps to explain gravity!

Evolution is a well-supported explanation of phenomena that have
occurred in the natural world

A theory in science is a well-tested hypothesis, not just a guess

Charles Darwin (___________________________________)
Sailed around the world 1831-1836
What did Darwin’s travels reveal

The diversity of living species was far greater than anyone had previously
known!!

These observations led him to develop the theory of evolution!!
Diversity on the Galapagos

Each island had ____________________________________________
___________________________________________________________
Influences on Darwin’s Theories
Theories of geologic change set the stage for Darwin’s theory:

Fossils: traces of organisms that existed in the past.

Theory of ___________________________ states that natural disasters
like floods and volcanic eruptions have shaped landforms and caused
species to go extinct.

Theory of ___________________________ states that changes in
landforms resulted from slow changes over a long period of time.

Theory of ___________________________ states that the geologic
processes that shape Earth are uniform through time (Charles Lyell’s
theory).

Lyell argued that the earth is many millions of years
o layers of rock take time to form
o processes such as volcanoes and earthquakes shaped the earth and
still occur today

Jean-Baptiste Lamarck:
o ___________________________________________________

Organisms acquired traits by using their bodies in new ways

These new characteristics were passed to offspring

_________________________________________________________!

Thomas Malthus
o If the human population continued to grow unchecked, sooner or
later there would be insufficient living space and food for
everyone.

Artifical Selection: Process in which humans change a species by
breeding it for certain traits.
Darwin’s The Origin of Species (1859)

Other naturalists, like Alfred Wallace, were developing the same theory as
Darwin’s.

Even though Darwin was afraid of the Church’s reaction to his book he
wanted to get credit for his work.
Summary of Darwin’s Theory of Natural Selection
1. Organisms differ; _______________________________________________
2. Organisms produce more offspring than survive
3. Organisms ____________________________________________________
4. Organisms with advantages survive to pass those advantages to their children
(“_________________________________________”)
5. ______________________________________________________________
________________________________________________________________
What is evolution?
o ____________________________________________________
o explains how modern organisms have descended from ancient
organisms
Fitness and Adaptation

Organisms ______________________________________________ and
some organisms are more ______ than others

Fitness – ___________________________________________________
________________________________________________________
________________________________________________________

Adaptation – ________________________________________________
________________________________________________________
________________________________________________________
What determines survival?
o Traits that help individuals survive

survive _____________________

survive _____________________

compete for _________________

compete for _________________
o Traits that help individuals reproduce

attracting a ___________

compete for _____________________

successfully _____________________
Natural Selection

There is ___________________________ (difference in the physical
traits of an individual from those of other individuals in the group) in
traits.
o For example, some beetles are green and some are brown.

There is ___________________ .
o Since the environment can’t support unlimited population growth,
to their full potential. In this example, green beetles tend to get
eaten by birds and survive to reproduce less often than brown
beetles do.

There is___________________________
o The surviving brown beetles have brown baby beetles because this
trait has a genetic basis (trait is passed down from one generation
to the next).

End result: ___________________________
o The more advantageous trait, brown coloration, which allows the
beetle to have more offspring, becomes more common in the
population. If this process continues, eventually, all individuals in
the population will be brown

Over time, ______________________ results in changes in the _______
_____________________________of a population.

These changes __________________________ in its ________________.

Species: Group of organisms so similar to one another that they can
reproduce and have fertile offspring.
Sources of Genetic Variation

Genetic Variation is stored in a populations _________________, which
is the combined alleles of all of the individuals in a population.

Each allele exists at a certain rate in a population. ___________________,
is a measure of how common a certain allele is in the population

Gene flow: movement of __________ from ______________________
(migration)

Mutation: __________________________________________________
o Some mutations can affect an ____________________ while
others have __________________________.

Recombination (occurs during meiosis): __________________________
o Independent ________________
o ________________ over
o _______________ reproduction
Evolution as Genetic Change

Natural selection determines which alleles are passed from one generation
to the next.

As a result, it can change the relative frequencies of alleles in a population
over time.

Evolution is __________________________________ in a population’s
gene pool.

Evolution acts on ____________________, not on _________________.
* Remember: Populations include individuals of the same species living in an
area.
Genetic Drift

Natural selection is not the only source of
evolutionary change.

Genetic drift: _______________________________________________

In __________ populations, individuals that carry a _________________
may leave more descendants than other individuals, just by ___________.

Over time, a series of chance occurrences of this type can cause an allele
to become common in a population.
Bottleneck Effect
 _________________________ of genetic
drift, occurs after an event drastically
_______________________ the size of a
population.
 This causes the population to have _____________________________
variation. The reason for this is that certain alleles have become fixed in
the population and others have been lost.
Founder Effect

Occurs when a
______________ of individuals
_________ a new
____________.

Members of the colony may
carry alleles in different relative frequencies than the larger population
from which they came.

If so, the population that they found will be genetically different from the
parent population.
Sexual Selection
 Certain traits increase mating success, so these traits will be passed down
from generation to generation.
Summary: