Answer: Genetics and Pressures
Step-by-step explanation:
For natural selection to occur, a population must have a wide variety of individuals with different traits. For example, natural selection would not influence fish body color if all individuals in a population were exactly the same color. Variation of scale color can help a fish species have a higher chance of survival by confusing predators as to what species they are.
Reproductive strategies represent a set of behavioral, morphological, and physiological adaptations that facilitate access to potential mates, improve the chances of mating and fertilization, and enhance infant survival. Male peacocks have bright, big tail feathers, for example, to attract females. If an organism has a high appeal, this will make them more likely to be able to meet and continue the survival of the species.
Environmental pressures, such as plant death, could influence the survival of herbivorous organisms. Say a small land creature consisted off grass, and an epidemic killed all the grass in their region. They would either die off, or they would evolve to find different types of food. The former could reduce population, while the latter could increase it.