Customarily we say that disease is not inherited by people, but that the body constitution which makes people susceptible is inherited. Structural disturbances may be inherited. Red-green color blindness affects males, who transmit the condition only to their daughters-who do not have it-but transmit it to their sons in about half the births. The response of our bodies to any infection or other trauma or stress depends to a large extent on the nature of our constitution.
Many disease conditions seem to occur more often in some families than in others. Hardening of the arteries, diabetes, rheumatic diseases, and some forms of cancer are conspicuous examples. Tuberculosis, goiter, ulcers of the stomach, and even appendicitis seem to be related to body structure in ways that make a hereditary factor a possibility.
In addition to red-green color blindness, hemophilia-the tendency to bleed-is passed from males through females. Baldness is another condition which is related to the genes that determine characteristics. Strangely the experts in genetics are now convinced that a large amount of head hair is not correlated with virility. Instead, once the baldness gene is present, the excess of male hormone associated with virility is the likely additional factor for baldness. Degrees of baldness and the pattern of distribution are also regulated by hereditary factors.
Absence of certain teeth, deformities in the growth of the jaws, sweat gland deficiencies, albinism-or lack of pigment in the eyes, skin and hair-and extra breasts or nipples as well as extra fingers and toes may also be inherited. Difficulties of vision, and of hearing, taste, and smell occur in families. Finally, heredity also plays a part in determining intelligence or the lack of it.