Final answer:
Evolution explains how species develop from common ancestors and diversify through natural selection and speciation. Advantageous traits inherited because of genetic variation allow organisms to better survive and reproduce, thus shaping species over time.
Step-by-step explanation:
Evolution most helps explain how species develop from common ancestors and diversify. It is the process through which the characteristics of living things change over time. Evolution happens by natural selection, where those with advantageous traits are more likely to reproduce and pass on these traits. This process leads to species evolving adaptations that help them survive in their environments. Over generations, this can lead to significant changes within a species, and these accumulated changes may eventually result in the formation of new species.
Speciation occurs when populations become reproductively isolated and diverge genetically to the point where they can no longer interbreed. Essential to this process is genetic variation, which allows individuals within a population to have different levels of fitness in response to environmental pressures. Changes in the environment can thus lead to the evolution of traits that are beneficial at one time but may not be in another, showcasing the non-directional nature of evolution.
Natural selection and resulting adaptations explain the diversity and unity found in life, as organisms that are well adapted to their environment are more likely to survive and reproduce, hence spreading those adaptive traits within the population.