Here's why:
* Variation: Individuals within a population have different traits. This could be anything from differences in physical characteristics (like fur color, height, or beak shape) to differences in behavior or resistance to diseases.
* Heritability: These variations are at least partially heritable, meaning they can be passed down from parents to offspring.
* Differential Survival and Reproduction: Some variations give individuals an advantage in their environment. This could mean they are better at finding food, escaping predators, or resisting disease. These individuals are more likely to survive and reproduce, passing on their advantageous traits to their offspring.
* Evolutionary Change: Over time, the frequency of advantageous traits will increase in the population, while less advantageous traits will decrease. This leads to a gradual change in the population's characteristics, known as evolution.
In short, natural selection acts on the existing variation within a population, favoring individuals with traits that make them better suited to their environment. This leads to the gradual evolution of populations over time.
