Biology Marking Period 3 Practice Test

Selective pressure is any factor in the environment that causes individuals with certain traits to have a higher chance of surviving and reproducing than others. This differential success changes how common those traits are over generations, driving evolution. It’s not a mutation itself, and it doesn’t mean the environment has no effect or that everyone is equally affected. Instead, it acts on existing variation, favoring traits that confer a survival or reproductive advantage. For example, predators may more often catch less camouflaged prey, so better-camouflaged individuals are more likely to survive and pass on their genes. Antibiotics can favor bacteria that carry resistance genes, increasing their frequency. Therefore, a selective pressure is best described as something that gives certain traits an advantage, shaping the population over time.