The field of behavioral genetics aims at under-
standing the observable differences in a wide variety
of human characteristics, typically by analyzing the
contributions made by heredity and environment in
the development of the characteristics in question. Al-
though the research in behavioral genetics is
ideologically and methodologically diverse, it is fair
to state that it often helps one theorize how much he-
redity and environment contribute to an observed
outcome, and how various factors may interact with
each other to create a particular outcome. At the root
of such research endeavors lies what is called the na-
ture-nurture controversy.
The Nature-Nurture Controversy
What are the roles of heredity and environment
in the development of various human characteristics?
The nature-nurture controversy deals with this peren-
nial question. The works by several early philosophers
are often viewed as marking the beginning of this
controversy. As early as the seventeenth and the eigh-
teenth centuries, philosophers such as René Des-
cartes and Immanuel Kant argued that human
cognition is largely reflective of genetically deter-
mined predispositions, since environmental factors
do not adequately explain the variations in our cogni-
tive capabilities. They therefore took the nativist per-
spective that humans are born with certain cognitive
tendencies. By contrast, the clean slate view, pro-
posed in 1690 by the British philosopher John Locke,
focuses instead on the role of the surrounding envi-
ronment in describing human thoughts. Locke com-
pared the human mind to a piece of blank paper
without any ideas written on it, and he suggested that
only from experience do humans draw reason and
knowledge. Following these diametrically opposed
ideas, scientists have since extensively explored the
roles of heredity and environment. Before describing
such efforts in detail, it is useful to define relevant
concepts.
Nature and Nurture Defined
Nature refers to heredity: the genetic makeup or
‘‘genotypes’’ (i.e., information encoded in DNA) an
individual carries from the time of conception to the
time of death. Heredity may range from genetic pre-
dispositions that are specific to each individual and
that therefore potentially explain differences in indi-
vidual characteristics (e.g., temperament), to those
supposedly specific to certain groups and that there-
fore account for group differences in related charac-
teristics (e.g., gender and height), and to those that
are theorized to be shared by all humans and are gen-
erally thought to set humans apart from other species
(e.g., the language acquisition device in humans).
The notion of nature, therefore, refers to the biologi-
cally prescribed tendencies and capabilities individu-
als possess, which may unfold themselves throughout
the course of life.
Nurture, by contrast, refers to various external or
environmental factors to which an individual is ex-
posed from conception to death. These environmen-
tal factors involve several dimensions. For example,
they include both physical environments (e.g., sec-
ondhand smoking and prenatal nutrition) and social
environments (e.g., the media and peer pressure).
Also, environmental factors vary in their immediacy
to the individual; they involve multiple layers of
forces, ranging from most immediate (e.g., families,
friends, and neighborhoods) to larger contexts (e.g.,
school systems and local governments) to macro fac-
tors (e.g., international politics and global warming).
To complicate matters even further, the factors in
each of these layers influence and are influenced by
elements within and outside of these layers. For ex-
ample, the kind of peers a child is exposed to may de-
pend on his or her parents’ view of what ideal
playmates are like, the local government’s housing
policies, and the history of race relations.What Is the Controversy?
Despite its nomenclature, the nature-nurture
controversy in its current state is less dichotomous
than commonly believed. In other words, the term
‘‘nature-nurture controversy’’ suggests a polarization
of nature and nurture; continuity and interaction,
however, more aptly describe the central processes in-
volved in this controversy. Therefore, it is not about
whether either heredity or environment is solely re-
sponsible for observed outcomes. Rather, it is more
about the extent to which these factors influence
human development and the ways in which various
factors influence each other.
For example, following the fifteen-person massa-
cre committed by two boys at Columbine High School
in Colorado in April 1999, the media were flooded
with people offering their interpretations of what
drove these high school students to commit this hei-
nous and violent act. Some were quick to attribute the
boys’ actions to such environmental factors as inade-
quate parenting practices in their families and the vi-
olence prevalent and even glorified in the American
media. Others, by contrast, were convinced that these
boys were mentally ill as defined in the American Psy-
chiatric Association’s Diagnostic and Statistical Manual
of Mental Disorders and that their ability to make re-
sponsible judgments had been impaired, perhaps due
to a chemical imbalance to which they were genetical-
ly predisposed. Which argument is ‘‘correct,’’ accord-
ing to most researchers? Probably neither. Most
theorists agree that both nature and nurture are in-182 HEREDITY VERSUS ENVIRONMENT