Adaptation refers to a change in the structure or function of an organism that makes it better suited for its environment. Biologists recognize two types of adaptation: plastic adaptation (plasticity) and evolutionary adaptation. Plasticity is the ability of organisms, including humans, to change biologically or behaviorally in response to environmental change. One example of plasticity is human height. It has been shown that over decades, height averages have increased as quality of life has improved. For instance, in 1850, the average height of men in Holland was 5.4 ft (1.6 m), but today their height averages 5 ft 8 in (1.7 m). The increase is due to healthier living brought about by purified drinking water, sewer systems, food regulation, and health care. Evolutionary adaptation involves inherited traits due to genes that pass from generation to generation. An organism's total adaptation to the environment ultimately depends on the combined effect of plasticity and genetic inheritance...