Selective pressure refers to environmental factors that influence the survival and reproductive success of organisms within a population. These pressures can arise from various sources, such as predation, competition for resources, disease, and changes in environmental conditions. Organisms that possess favorable traits that enhance their ability to survive and reproduce under specific selective pressures are more likely to pass those traits on to future generations, thereby shaping the evolutionary trajectory of the species.
For example, in a population of beetles where some individuals are green and others are brown, if the environment is predominantly brown (e.g., brown soil and dead leaves), brown beetles may have a survival advantage because they are better camouflaged from predators. As a result, the brown beetles are more likely to survive and reproduce, leading to an increase in the proportion of brown beetles in subsequent generations.