Ecological genetics is concerned with the genetics of ecologically important traits, that is, those traits related to fitness such a survival and reproduction. The study of the process of phenotypic evolution occurring in present-day natural populations. Ecologically important traits: those traits that are closely tied to fitness or, in other words, are important in determining an organisms adaptation to its natural environment, both biotic and abiotic. Phenotypic evolution can be defined as a change in the mean or variance of a trait across generations due to changes in allele frequencies. The four processes that cause evolution are mutation, genetic drift, migration, and natural selection. Adaptation is the central theme of ecological genetics. An adaptation is a phenotypic trait that has evolved to help an organism deal with something in its environment. Natural selection is the only evolutionary process which leads to adaptation.