Variation and Natural Selection

Section 1: Principles of Variation

Variation refers to the differences that can be observed within a species.
Variation can be genetic or environmental, or a result of both.
Genetic variations are caused by differences in an organism’s genes or mutations.
Environmental variations (also known as acquired characteristics) are features or traits determined by an individual’s environment or experiences.
Inherited characteristics are passed from parent to offspring through genes.

Section 2: Genetic Variation and Mutation

Genetic variation is important for evolution to occur.
Mutations are accidental changes to genes and chromosomes, and they provide a source of new genetic variation.
Some mutations may be beneficial and increase an organism’s chance of survival.
There are two broad types of genetic variation: discontinuous and continuous. Discontinuous variation shows distinct categories and is controlled by a single gene. Continuous variation shows a range of characteristics and is usually controlled by several genes.

Section 3: Natural Selection and Survival of the Fittest

Natural selection, also known as survival of the fittest, is a key mechanism of evolution.
It describes the process where organisms best suited to their environment are more likely to survive and reproduce, passing on their beneficial traits to their offspring.
This selective pressure encourages the spread of beneficial traits in successive generations, leading to evolution.
Traits which decrease an organism’s chance of survival will tend to become less common over time due to natural selection.
Both selective breeding (artificial selection) and natural selection can cause changes in a species over time.

Section 4: Evolution as a Result of Natural Selection

Evolution is a process that leads to changes in the inherited characteristics of a species over many generations.
Evolution doesn’t occur in individuals but across populations.
It results from natural selection acting upon genetic variation within a population.
Evidence supporting the theory of evolution includes: the fossil record, DNA sequencing, and observation of change in species over time due to selective pressures.

Section 5: Adaptation and Speciation

Adaptation refers to the process by which a species becomes better suited to its environment, often over many generations.
The process of natural selection encourages adaptations that increase an organism’s chance of survival and reproduction.
Speciation is the formation of a new species. It often occurs when a part of a population becomes separated, making interbreeding impossible.
Over time, genetic variants accumulate in the separated population, leading to new adaptations and, eventually, a new species.