An understanding of the diversity of genes responsible for individual species' adaptations and responses to their environment (intraspecific diversity) is a foundation for understanding almost all ecological and evolutionary processes. Genetic diversity is the ``raw material'' permitting species to adjust to a changing world, whether these changes are due to natural or human factors. The level of similarity (homogeneity) or difference (heterogeneity) in the genetic makeup (genome) of populations of the same species indicates to what extent genetic material can be exchanged between populations and still maintain a species-specific gene pool.
In turn, understanding gene-exchange phenomena within a species can provide further insight into the role of diverse populations in maintaining a species' genetic diversity, or in leading to the isolation and creation of distinctive new genomes and thus potentially new species. Studies of genetic diversity within a species also has the potential to reveal that a single species may in fact be two or more species. Such findings have important implications for understanding human impacts on marine biodiversity, as discussed in the three examples below.