Final answer:
Organisms evolve through natural selection, where traits that improve survival and reproductive success become more common over generations. This process is not intentional but is a result of advantageous traits being passed on due to a better fit with the environment.
Step-by-step explanation:
Organisms evolve through a process known as natural selection, which operates on the variations present within a population. These variations arise due to random mutations and can result in traits that offer either an advantage or disadvantage to an organism's chance of survival and reproduction. Organisms with advantageous traits, which we call adaptations, are more likely to survive to reproductive age and pass these traits on to their offspring, leading to more of these advantageous traits in succeeding generations. Over time, a population can evolve significantly, meaning that its characteristics change. This evolutionary process is a response to a changing environment but does not occur as an intentional choice by the organisms. Instead, it is a natural consequence of certain individuals having a genetic makeup that provides a better fit to the current environment, resulting in their increased reproductive success and the perpetuation of those beneficial traits.