Gene Pool

In a population of sexually reproducing organisms, a gene pool is the sum of that population's genetic material at a given time. In terms more specific to a particular genetic locus on a chromosome, it is the sum of the alleles in a population at that locus.

As is currently posited by the “Out of Africa” hypothesis, the species of homo sapiens, and its gene pool, began as a relatively small group of individuals (roughly in the hundreds) in east Africa. Over some tens of thousands of years, some groups left Africa and increasingly populated the rest of the world. This hypothesis finds wide agreement by modern evolutionary theorists. At the end of the 20th century, it has also found strong confirmation from the molecular genetic and chromosomal studies of population origins that have mapped the specific route taken by different human subgroups or races throughout evolutionary time.

Evolution is the change in composition of a pop-ulation's gene pool. This can occur by a variety of mechanisms, including mutations, natural selection, and genetic drift. As populations left Africa, each faced different environments, different novel diseases, diets, and climates. To the extent that this was the case, over time, the surviving composition of each subpopulation's gene pool was altered to be attuned to the needs of its specific environment. Two well-studied examples are illustrative of this point.

As a population moved away from the equator where the average amount of sunlight (and also the risk of skin cancer) is less, over time pigments in the skin were selected to allow more translucency per sunlight exposure. This allowed a more efficient manifestation of the endogenous synthesis of vitamin D, an absolutely critical vitamin for proper human bone development and therefore proper childbirth. Second, as Europeans domesticated new animals and increasingly relied on such animals for sustenance, they had to evolve the enzymes necessary to digest specific novel nutrients (lactose). It is interesting to note that most of the world is lactose intolerant because the gene for the enzyme to digest lactose originated in Europeans. As populations change or evolve in response to different environments, their gene pools are changing their composition and character.

Evolutionary “fitness” is defined not from the perspective of the human person but from the unconscious perspective of the gene: it is the ability to pass on one's genes, the ability to reproduce. Because populations often face difficult and rapid changes in their environments (e.g., famine, plagues, ice ages as in Eurasia 20,000 years ago, social selection, etc.), the advantages gained in fitness by the adaptive specificity of a gene pool must be balanced by [Page 711]the risks posed to evolutionary fitness by too narrow of a genetic profile. A large and diverse gene pool allows a greater chance for future adaptation to an ever-uncertain environment.