Recorded history informs us that as long as human beings have had free time to contemplate
matters beyond those of basic survival, they have been acutely interested in understanding
the nature of their own behavior. Early writers from Greece, for example, were
impressed by numerous redundancies among people of the same and different cultures, but
they also noted specific abnormalities as well as systematic differences between groups
and individuals. In trying to grasp the nature of these similarities, differences, and abnormalities,
early personologists (e.g., Heraclitus, Socrates, Hippocrates, Aristotle, Galen)
created theories that explained human behavior as a function of ethereal manipulation, social
pressures, personal choices, and physical characteristics such as the quantity of fluids
or “humors” in the body (Durant, 1939; Hergenhahn, 1992; Russell, 1945).
Progress in understanding human behavior from a scientific perspective took a giant
leap forward following Darwin’s (1859) work on the evolution of species. Although Darwin
did not elaborate on the origin of group and individual differences at the phenotypic
level, his contemporaries and followers (e.g., Galton, Helmholtz, Wundt, James) helped
create the fledgling science of psychology from philosophy as the study of human behavior.
In the late nineteenth and early twentieth centuries, scientific and technological advances
helped psychologists develop complex explanations for behavior as stemming from
a mixture of evolutionary, biological, social, and personal variables (Goodwin, 1998;
Koch & Leary, 1992).