The modernist philosopher John Locke argued that human behavior is determined almost entirely by nurture or environment. He argued that humans are born a tabula rasa (Latin for blank slate), and that all knowledge is acquired through experience. In short, an individual's environments-the home he or she grows up in, the education that he or she receives, and so forth-determine who that individual becomes.
On the other end of the spectrum is genetic determinism-the belief that personality and behavioral traits are formed chiefly by an individual's DNA, and that environment has very little influence. Studies involving identical twins seem to support the claim that genetics play a large role in behavior because identical twins are usually found to be more similar than fraternal twins or regular siblings.

1. Most scientists agree that human personality and behavioral traits are shaped by both genetics and environment; but, if you had to choose between genetics and environment, which one do you think plays the largest role?