This familiar expression indicates a division between those who offer biological explanations for some human behaviors and those who insist on environmental explanations. The root of the problem is a basic uncertainty about the causes of human physical and psychological traits. Some traits are obviously inherited in a biological sense, such as having a four-chambered heart or the ability to learn to talk. Such characteristics are said to belong to humans by nature, from a root word meaning birth. Other traits are not inherited, but are a result of environmental influences. A person can inherit a parent's hair color, but not his or her tattoo; and a person must learn the French language in order to speak it. Acquired traits are said to be due to nurture, which in this context indicates any influence other than biological inheritance.

Distinguishing in Specific Cases

In analyzing...