Some researchers in sports attribute elite performance to genetic talent. However, they do not offer complete genetic accounts that specify the causal processes involved in the activation and expression of the dormant genes in DNA during practice in the athletes’ development that lead to the emergence of the distinctive physiological and anatomical attributes (innate talent). This article argues that it is possible to account for the development of elite performance among healthy children without recourse to unique talent (genetic endowment) – excepting the innate determinants of body size. This account based on the expert-performance approach shows that the distinctive characteristics of elite performers are adaptations to extended and intense practice activities that selectively activate dormant genes that all healthy children’s DNA contain. The expert-performance approach has provided accounts for elite performance in several domains of expertise, such as music, ballet, chess, and medicine. This article shows how the superior performance of athletes can be captured and reproduced under laboratory conditions to discover the mechanisms mediating superior performance. The discovered mechanisms have, so far, been shown to reflect predominantly complex skills and physiological adaptations acquired over years and decades as a result of high daily levels of activities, which were specially designed to improve performance (deliberate practice). The second part of this article describes the development of expert performance in sports as an extended series of stable states of adaptation with associated physiological mechanisms that mediate performance. One section describes how frequent intense engagement in certain types of practice activities is shown to induce physiological strain which cause biochemical changes that stimulate growth and transformation of cells, which in turn leads to associated improved adaptations of physiological systems and the brain. A careful review of the published evidence on the heritability of acquisition of elite sports achievement failed to reveal reproducible evidence for any genetic constraints for attaining elite levels by healthy individuals (excluding, of course, the evidence on body size). The theoretical framework of expert performance explains individual differences in attained performance by the factors that influence the engagement in sustained extended deliberate practice, such as motivation, parental support, and access to the best training environments and teachers. Consequently, the development of expert performance will be primarily constrained by individuals’ engagement in deliberate practice and the quality of the available training resources.

Quantitative genetics using the twin model offers a unique and powerful method of disentangling the relative power of Nature and Nurture, genes and environment, in the variation observed in phenotypes related to sport performance. The model makes use of monozygotic (MZ) twins who have identical heredity and dizygotic (DZ) twins who share half of their genes. From comparisons of intrapair differences between MZ & DZ twins we derive heritability (h2) estimates, which signify the extent to which heredity affects the variation of a given phenotype. There is accumulating evidence to show that individual differences in most functional abilities, morphological characteristics, motor attributes, personality and cognitive traits linked to superior sport performance are substantially influenced by genetic factors. H2 reported by twin studies suggest that genetic influence is so ubiquitous and persuasive that we ask not what is heritable but what is not heritable. However, a high h2 of a given phenotype does not exclude environmental influence. Nature and Nurture are indeed inseparable and phenotypes reflect the effects of genes as well as those of epigenetic influences, the most potent of which is training. Training can produce results within the variability allowed by the genotype, but cannot erase individual differences which are due to innate ability. Deliberate effortful practice is a prerequisite for the actualization of an athlete’s genetic potential. If the environmental forces were optimized, the only decisive factor to peak sport performance would be the gentoype. Yet, though genes and training may set the biophysical limits to human performance, there is evidence that it is behavioral features which determine the ultimate frontiers of sport performance. The postulate that in addition to superior genotypes athletes of olympic caliber have also inherited genes which mediate a high response to training, is not tenable. To unravel the complex etiology of individual differences in sport performance we need to continue using techniques from quantitative genetics for the selection of candidate genes and tools from molecular genetics, now available, for identification of genes of performance phenotypes. Although there is a long way to go before we have a clear picture of the human gene map for sport performance traits, a number of laboratories and scientists concerned by the role of genes and DNA sequence variation in sport performance is rising.