Unit B

Module 4 ~ Lesson 1

Natural Selection

Organisms best adapted to the environment will survive and pass on their genetic characteristics to the next generation. Those organisms less adapted may not survive or reproduce, making it less likely that their traits will be passed on. In time, the characteristics of the population change due to the surviving traits. Charles Darwin developed his theory of natural selection to explain how populations change or evolve over time. There are key mechanisms in natural selection.
  1. All populations have variation in traits. 
  2. A selective pressure exists in the environment, such as a predator, extreme weather conditions, or limited food resources. If no traits provide benefit over others, there will not be a change in the population.
  3. Not all individuals have the same reproductive advantage. Some individuals are more likely to survive, and therefore mate, due to particular characteristics such as strength, speed, camouflage, or resistance to disease. Individuals may have a better chance of attracting a mate due to particular characteristics.
  4. Traits are inherited. Traits of the offspring generation were passed down from the parent generation.
  5. Over time, the advantageous trait becomes more common in the population.

The desire to mate is strong in all organisms, and it creates a strong selection pressure. In some cases, the mate's selective pressure is oblivious to other environmental selection pressures. Selecting characteristics based on attracting a mate is called sexual selection.


Watch this video to learn about how the decorative peacock tail provides a reproductive advantage.

Abiotic and biotic environmental conditions can exert selective pressure on a population by selecting for certain characteristics. These selected characteristics allow the individual to survive.

In the peppered moth activity, the soot darkening the forest is an example of an abiotic environmental condition, exerting a selective pressure on the population of peppered moths. The soot-darkened forest selected for the dark-coloured moths and against the light-coloured moths. Therefore, the dark-coloured moth population increased and the light-coloured moth population decreased.

Selective pressure can also be exerted by a biotic component in the environment, as was observed with sexual selection. Predators are another example of a biotic component in the environment exerting a selection pressure.

Image by 272447 from Pixabay

Image by Anrita1705 from Pixabay

In the photos above, if the environment of each lizard was to change drastically, and they were no longer camouflaged, the lizards could be in greater danger than those that blend in better.