Natural selection
Previously, the concept of evolution and evidence supporting the theory was covered. This topic focuses on the process of evolution via natural selection.
Natural selection is the process by which an organism that is more adapted to its environment can survive, and so pass on the genes for its adaptation to its offspring. In order for this to occur, two criteria must be met:
- There must be genetic variation within the population that causes different characteristics. These are caused by:
- Mutation - to form new alleles.
- Meiosis - to form new combinations of alleles via crossing over in prophase I or random orientation in prophase II.
- Sexual reproduction - combining alleles from two individuals to form groups of alleles.
- This variation must result in an adaptation. This is defined as a characteristic that make an organism suited to a particular way of life.
Having genetic variation bring about an adaptation in a portion of the population then allows for natural selection to occur:
- At some point, populations will experience overpopulation, increased predation, a loss in habitat, or a loss of resources.
- This will create competition for survival within a population.
- The organisms more adapted to the environment are therefore more likely to survive, and those that are not are more likely to die.
- The organisms that survive can then reproduce and create offspring, whereas those that survive do not.
- The genes for their adaptation is then inherited by these offspring.
- Therefore, over time, there is an increase in the proportion of adapted organisms.
As this is a change in heritable characteristics over time, it is evolution, but it occurs via selection of particular traits due to natural pressures on the population.