scientists still have not pinpointed the exact cause of this accelerated growth . Environmental changes such as improvements in public health,nutrition and child care are unquestionably responsible to some degree but there seem to hereditary factors at work, too. For instance,industrial expansion takes relatively inbred country people and transports them to cities; where they intermarry.Apparently the mixing of genetic stocks tends to produce bigger children.Therefore, industrialization and increases in the size of human beings seem to go hand in hand.A full explanation of the long-term trend to greater height, however,will undoubtedly disclose other restricted that are still unknown.