A. Bejan et al., Int. Journal of Design & Nature. Vol. 5, No. 0 (2010) 1–13 © 2010 WIT Press, www.witpress.com ISSN: 1755-7437 (paper format), ISSN: 1755-7445 (online), http://journals.witpress.com DOI: 10.2495/DNE-V5-N0-1-13 THE EVOLUTION OF SPEED IN ATHLETICS: WHY THE FASTEST RUNNERS ARE BLACK AND SWIMMERS WHITE ADRIAN BEJAN 1 , EDWARD C. JONES 2 & JORDAN D. CHARLES 1 1 Duke University, Department of Mechanical Engineering and Materials Science, Durham, NC, USA. 2 Howard University, Department of Nutritional Sciences, Washington, DC, USA. ABSTRACT Here we explain a much avoided phenomenon in the evolution of speed sports for men and women: The world records in running tend to be set by black athletes and in swimming by white athletes. We show that this phenomenon is predictable from physics. Locomotion is a ‘falling-forward’ cycle, in which body mass falls forward and then rises again. Mass that falls from a higher altitude falls faster, down and forward. In running, the altitude (L 1 ) is set by the position of the center of mass above the ground. In swimming, the altitude is set by the upper body rising above the water, and it is proportional to H – L 1 , where H is the height of the athlete. The anthropometric literature shows that the center of mass in blacks is 3 percent higher above the ground than in whites. This means that blacks hold a 1.5 percent speed advantage in running, and whites hold a 1.5 percent speed advantage in swimming. Among athletes of the same height Asians are even more favored than whites in swimming but they are not setting records because they are not as tall. Keywords: animal locomotion, constructal, evolution, running, speed sports, swimming. THE PHENOMENON: BLACK VERSUS WHITE IN SPEED SPORTS 1 Speed records increase in time. Figure 1 shows two examples that cover the past century: men’s record speeds in running (100 m dash) and swimming (100 m freestyle). They illustrate the evolution of the speed sports, not the evolution of an individual athlete in training. The evolution of the sport is the morphing of the societal ‘flow system’ in which faster individuals from the large population are recruited and trained in constantly improving institutions and facilities. The few athletes who are remembered for having climbed once on the highest podium are a small sample of how the performance of the population of runners and swimmers is evolving in time. In a recent paper [1] we showed that the steady increases in winning speed are accompanied by increases in body mass and height. We showed that this speed-mass (or speed-height) relation is predictable from the constructal-theory scaling of animal speed versus body size [2]. Examined more closely, the evolution of the speed sports (Fig. 1) reveals a phenomenon that is as obvious as it is obviously not discussed. More and more, the winning runners are black athletes, particu- larly of West African orgin, and the winning swimmers are white. More and more, the world finalists in sprint are black and in swimming are white (Fig. 1). Here, we show that this evolutionary phenomenon too is predictable, and is an integral part of the phenomenon of speed evolution in modern athletics. Our approach is to study phenotypic (somatotypic) differences of human locomotion in different media (terrestrial vs. aquatic), which we consider to have been historically misclassified as racial characteristics. These differences represent consequences of still not well-understood variable envi- ronmental stimuli for survival fitness in different parts of the globe during thousands of years of habitation [3–6]. Our study does not advance the notion of race, now recognized as a social construct, as opposed to a biological construct. We acknowledge the wide phenotypic and genotypic diversity among the so-called racial types.