How do populations of organisms evolve according to biological principles?

Populations of organisms evolve gradually over time primarily through changes that occur from one generation to the next. This process is driven by mechanisms such as natural selection, genetic drift, mutations, and gene flow. Each generation has the potential to exhibit variations in traits, which can be influenced by environmental pressures. Over successive generations, advantageous traits become more common in the population, leading to evolutionary change.

In contrast to other options, individual effort and adaptation refer to changes that occur within an organism's lifetime rather than heritable changes in a population. Changes in environmental factors can influence the process of evolution by applying selective pressure, but they do not directly cause evolutionary change in themselves. Genetic engineering and manipulation, while capable of changing organisms at a genetic level, do not reflect the natural evolutionary processes that occur within populations over time.