Natural selection. Darwin hypothesized that there requisites for natural selection to occur and that there are definite steps to natural selection. Note the two models seen here. Both of the models illustrate an important requisite for natural selection. That is: A) sexual reproduction must occur. B) there is survival of the fittest. C) variation in the population exists. D) genetic sameness reduces the chances of natural selection.

The important requisite for natural selection illustrated in both models is: C) Variation in the population exists.

Natural selection is one of the key mechanisms of evolution, described by Charles Darwin. For natural selection to occur, there must be variation within the population. This variation is what allows some individuals to have characteristics that give them an advantage in surviving and reproducing in their environment. Those individuals are more likely to pass their advantageous traits to their offspring. Over time, these traits become more common within the population, leading to evolutionary change.

The steps of natural selection generally include:

1. Genetic Variation: Individuals in a population have natural variations in their genetic makeup.

2. Overproduction of Offspring: Organisms typically produce more offspring than the environment can support.

3. Struggle for Existence: Individuals compete for resources, and not all survive to reproduce.

4. Differential Survival and Reproduction: Individuals with traits better suited to the environment tend to survive and reproduce more than others.

5. Inheritance of Favorable Traits: The traits that confer an advantage are more likely to be passed on to the next generation.

Over time, these steps can lead to populations changing and, eventually, to the development of new species.