All traits depend both on genetic and environmental factors. Heredity and environment interact to produce their effects. This means that the way genes act depends on the environment in which they act. In the same way, the effects of environment depend on the genes with which they work. For example, people vary in height. Although height is highly heritable, environmental variables can have a large impact. For example, Japanese-Americans are on the average taller and heavier than their second cousins who grew up in Japan, reflecting the effect of environmental variables, especially dietary differences.