What is the primary mechanism by which evolution occurs according to natural selection?

The primary mechanism by which evolution occurs according to natural selection is inherited variation. This concept is foundational to the theory of evolution, which asserts that individuals within a species exhibit variations in their traits, such as color, size, or behavior. These variations are often genetic and can be passed down from one generation to the next.

In the context of natural selection, individuals that possess traits that confer a survival or reproductive advantage in a given environment are more likely to thrive and reproduce. Over time, these advantageous traits become more common in the population, gradually leading to evolutionary change. Therefore, inherited variation is essential because it provides the raw material upon which natural selection acts, allowing for the adaptation of species to their environments.

The other choices do not fundamentally represent the mechanism of natural selection:

• Random genetic drift refers to changes in allele frequencies that occur by chance and is not a directed process like natural selection.

• Environmental resistance encompasses factors that limit population growth but does not explain how traits are selected over generations.

• Co-evolution involves the influence of species on each other’s evolution, which is a type of interaction but not the direct mechanism of evolution by natural selection itself.

Hence, inherited variation is key to understanding how natural selection drives evolutionary change.