Positive Selection in Human Populations: Practical Aspects and Current Knowledge

Natural selection targets a heritable trait that provides greater or lower chances for an organism to reproduce, and/or to survive, in a given environment. This evolutionary process is therefore directional: while an advantageous trait will be selected for and, thus, increase in frequency in the population, a prejudicial phenotype will be selected against and purged from the population. This concept, introduced in 1858 simultaneously by Charles R. Darwin and Alfred Wallace ((Darwin and Wallace J Proc Linnean Soc London 3:46–50, 1858); (Darwin On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. John Murray, London, 1859)), has been at the core of the study of evolution and biological research. However, since then there has been passionate debate concerning its relative importance among other evolutionary processes, the prevalence of adaptive traits, and how they are originated in natural populations.