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The nature and nurture of human performance

The focus of this review is on the role of genes in human phenotypic variation. Early twin studies amply demonstrated that the variation observed in several physiological responses to maximal muscular effort is largely genotype-dependent, while in VO2max variation is almost entirely due to the variety of genotypes that exist in individuals. More recent studies have applied the path genetic analysis to twin and nuclear family data, and found genetic influence to be mainly additive and environmental influence to be non-shared, with no evidence for a major impact of genetic dominance of shared environment. Taken together, twin studies converge on the conclusion that not only are genetic influences significant, they are also substantial, accounting for the greatest part of individual differences in most phenotypes related to human performance. However, genetic dependence does not exclude environmental influences. A highly heritable phenotype does not mean that it is predetermined, but training can exert its profound effect only within the fixed limits of heredity. Though genes and training may set the physiologic limit, it is behavioral and other factors that determine the ultimate frontiers of human performance. (Note: This article is based on an invited lecture presented at the Vth Annual Congress of the European College of Sport Science, Jyvaskyla, July 19–23, 2000, and supported by the Hellenic Ministry of Research and Technology and by the Special Account for Research Grants of the National and Kapodistrian University of Athens.)