ABSTRACT
As reviewed in earlier chapters, there is an extensive literature that suggests that physical activity is genetically regulated, even though the mechanisms controlling this genetic influence have not been definitively identified. While there are multiple groups working to understand how genetically linked mechanisms may regulate physical activity, there have been few efforts devoted to understanding how these mechanisms originally developed in humans. Two alternative explanations can be proposed toward this end: 1) the genetic mechanisms that control physical activity were just “built-in” to all mammals as part of the basic set of physiological controllers; or 2) the genetic mechanisms that control physical activity evolved over time due to drift, selection, or mutation (54). The former explanation does not hold if it is assumed that humans evolved from single-celled organisms originally, which is the so-called universal common ancestry (UCA) theory. The UCA theory was initially proposed by Darwin (18) and is currently accepted by most evolutionary biologists with recent quantitative results supporting UCA over a variety of competing, alternative hypotheses (60). If then the genetic mechanisms regulating physical activity evolved over time in mammals, what combination of drift, selection, and mutation resulted in genetic control of activity? Further, if the physical activity regulating genetic mechanisms evolved, which – if any – potential external factors may have contributed to this evolution?
