1. The change in species by the process of natural selection
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, and 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. Isn’t it just a “theory”?
Yes, it is. Unfortunately opponents to the teaching of evolution prey on the average American’s 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.
Remember…Gravity 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 individual’s 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 variation—the 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.