Evolution

1
Evolution

• The change in species by the process of natural
  selection

2
What is evolution

• Evolution Evolution is a process that results
  in heritable changes in a population spread over
  many generations.
• Evolution can also be defined as any change in
  the frequency of alleles within a gene pool from
  one generation to the next.

3
How does evolution occur?

• For a long time, scientists have observed that
  species of organism changed over time.
• Several ideas were put forward, but none of them
  withstood the test of time and were rejected.
• Charles Darwin, an English Naturalist, developed
  a theory called natural selection to explain the
  change in species over time.

4
What is natural selection?

• When Darwin saw the great variety of different
  species in his travels he thought the mechanism
  for evolution was like the process of artificial
  selection.
• Artificial selection is the process by which
  breeders of plants and animals produce organisms
  possessing desirable traits.

5
Natural selection cont.

• In natural selection it is not the breeder that
  determines which members of the population
  successfully breed, but the environment.
• Individuals that survive and are able to breed
  pass their genetic information to the next
  generation. Those that are not as successful in
  the environment often die without leaving any
  offspring.
• In this manner those traits that best allow
  individuals in a population to survive will
  increase in frequency while those that do not
  will become more and more uncommon.

6
Isnt it just a theory?

• Yes, it is. Unfortunately opponents to the
  teaching of evolution prey on the average
  Americans misconception of the term theory to
  further their own agendas.
• In reality the term theory refers to a concept
  that has been tested and confirmed in many
  different ways and can be used by scientists to
  make predictions about the world.
• RememberGravity is only a theory, too.

7
Interactions and evolution

• The driving force behind evolution is the
  interaction between individual organisms and
  their environment.
• Certain conditions are vital to the process of
  evolution.
• These conditions are overproduction, the struggle
  for survival, variation within the population and
  selection by the environment.

8
1. Overproduction

• Overproduction refers to the fact that in each
  generation, a species has the potential to
  produce more offspring than can possibly survive.
• Organisms such as bacteria, insects and rats all
  reproduce in great numbers. If all were to
  survive they would soon over run the earth.
• This of course, does not happen, and in fact,
  most natural populations remain relatively stable
  year after year.
• Most offspring do not survive to adulthood.

9
2. The struggle for survival

• Overproduction leads to competition within a
  species.
• In many cases, chance determines which members of
  a species survive.
• Chance alone in not the only factor which
  determines an individuals survival.
• Changing environmental conditions, disease,
  parasites and predators all remove individuals
  from the competition.
• Those members of the population that do survive
  then must complete for a finite number of
  resources, such as food, shelter and water.

10
3. Variation

• New traits which can lead to evolution come from
  normal variation within species.
• All the individuals in a species are not exactly
  alike.
• These differences arise from genetic
  variationthe unique combination of traits each
  organism inherits from its parents.

11
Variation cont.

• Some variations give individuals an advantage
  over others in their struggle for survival.
• Any trait that helps an organism survive and
  reproduce under a given set of environmental
  conditions is said to have adaptive value.
• For example, a deer that can run just a little
  bit faster than another will have a greater
  chance of escaping a predator. This would be
  especially advantageous in areas where there is a
  high density of predators.

12
4. Selection by the Environment

• Traits with an adaptive value in a specific
  environment give individuals in that environment
  a competitive advantage.
• If the beneficial trait is passed on to the
  offspring, they, too, are more likely to survive
  and reproduce.
• Over time the proportion of the population
  possessing this trait will increase.
• This change in the characteristics present in the
  population over time is called evolution.

13
Selection by the environment cont.

• Although some evolution may occur without much
  change in the environment, it is usually the
  adaptation of a species to changes in its
  environment that brings about evolution.
• Therefore, a changing environment is often the
  driving force for evolutionary change.
• Selection by the environment has the same meaning
  as Survival of the fittest.