Final answer:
Variation among individuals and populations is widespread, with genetic variation being a key factor for natural selection and evolution. Differences in alleles create significant genetic variation, essential for populations to respond to evolutionary pressures.
Step-by-step explanation:
DNA and protein studies reveal that variation among individuals and populations is ubiquitous, meaning that variation is widespread within species and among different populations. An example of population variation is the different fur colors and patterns in domestic dogs, which is a reflection of the distribution of phenotypes within a population. Similarly, the majority of human genes have multiple versions or alleles, leading to significant genetic variation among individuals. Most human genetic variation stems from differences in individual DNA base pairs within alleles, and this variation is crucial for enabling natural selection and driving evolution. Populations that display multiple variations of particular traits, known as polymorphisms, can evolve in response to evolutionary pressures influenced by genetic structure and environmental factors. Without such genetic variation, processes like natural selection would not be possible.