Nature vs. Nurture Essay

This essay has a total of 2340 words and 13 pages.

Nature vs. Nurture

The dubious history of the heredity environment controversy can be
easily traced as far back as the start of the present century with at least some
historical evidence placing the roots of this dispute in the time of John Locke.
This controversy has continued despite continual reiteration that the critical
question is not how much of a trait is due to heredity and how much is due to
environment, but rather how environment transact to influence development.” (
Wachs , 1983, p. 386).
This paper will focus on the nature/nurture controversy and the extent
to which an individuals intellectual level is determined either by inborn
intelligence or by environmental factors.
The relative powers of nature and nurture have been actively pursed by
psychologists and biologists striving to determine how heredity and environment
influence the development of intelligence.
Before we can go on to discuss the relationships between intelligence
and the controversy that exists between the different schools of thought
regarding inherited or environmental issues we must have an understanding of
what intelligence really is.
Of all the words used in pressed day psychology, intelligence is one of
the most difficult to define and is also one of the most controversial. There
is however, a general agreement that intelligence refers to the overall
faculties of the mind which concern themselves with the sorting of information
in the brain after it has been received by the senses, the perceiving of
relationships between this new data and information which is already in memory,
and the capacity to make rapid and appropriate decisions as a result of the
previous processes.
The intellectual faculties of the brain are dynamic and interactive and
relate to the capacity of the central nervous system to respond speedily and
appropriately in a rapidly changing and potentially threatening environment.
Raymond J. Corsini provides us with a somewhat more simplistic
definition of the term intelligence. According to Corsini (1984) the term
intelligence can be employed to indicate the amount of knowledge available and
the rapidity with which new knowledge is acquired; the ability to adapt to new
situations and to handle concepts, relationships, and abstract symbols.
While the heredity/environment topic continues to be a controversial
issue, a great deal of evidence has been gathered to support both arguments.
In order to investigate the topic of nature/nurture it is important to
consider a variety of research elements. Among these elements are some of the
most relevant issues pertaining to this subject including: twin, adoption,
family, orphanage life, IQ, and race studies. It is to these studies we will
now turn our attention.


The importance of twin studies is evident if we look at the studies
objectively, if intelligence is basically hereditary, identical twins who have
the same genetic legacy, should be concordant for that trait than are fraternal
twins, which are no more alike genetically than other siblings.
Burt's (1958) famous study show that the intelligence test scores of
identical twins, whether reared together or apart , display considerably higher
correlation than the scores of fraternal twins.
Burt's work is currently viewed with caution due to the manner in which
he gathered and interpreted his data (Vernon, 1979). However, Burt's research
provides an important foundation for this research.
Jone's study (1946) shows that there is a modest difference in the
intelligence test scores of twins reared apart, and the more divergent the
environments, the greater the difference.

“While environmental factors are important in raising or lowering a
child's level of intellectual performance, these studies demonstrate that they
only do so within limits set by heredity.” (Mussen, Conger, and Kagon, 1963

The Louisville Twin Study (Wilson, 1983) showed that environmental
considerations such as characteristics of home and the interaction of the mother
with the infant, have a prominent effect upon the infant's mental development.

Vermon (1979) concludes that we may attribute 60 percent of the
determination of IQ status to heredity, 30 percent to environment and 10 percent
tot he combined effects of the two.
David Layzer's (1976) study indicates that the more relevant a given
task is to an individuals specific environmental challenges, the more important
are the efface of this interaction. A child grown up in circumstances that
provide motivation, reward and opportunity for the acquisition of verbal skills
will achieve a higher level of verbal proficiency than his twin reared in an
environment hostile to this id of development.
According to Layer if two egg twins are reared together we cannot assume
the environmental factors are the same for both. If one twin has a greater
verbal aptitude he will devote more time and effort to this kind of learning
than his twin. So test results on verbal proficiency will not reflect genetic
difference, only, but differences between the ways in which the genetic
endowments of the twins have interacted with their common environment.
Longitudinal studies have also found the influence of heredity on
intelligence increases with age. Among 500 pairs of twins, identical twins
became more and more alike in IQ from infancy to adolescence, while fraternal
twins became less alike. The home environment had some impact, but genetic
factors had more (Plomin, Pedersen, McClean, Nesselroade, and Bergman, 1988).
IQ of identical twins are more highly correlated than less closely
related people and IQ's of children growing up in similar circumstances tend to
be more highly correlated than those of children growing up in dissimilar
circumstances. This fact helps to illustrate that IQ is strongly influenced by
both genetic and environmental factors.


Adoption studies are important for us to look at because they provide
one of the few methods available for separating the effects of environment and
heredity in intellectual development.
When adopted children are more like their biological parents and
siblings, we see the influence of heredity; when they resemble their adoptive
families more, we see the influence of environment.
The Texas Adoption Project (Horn, 1983) conducted intelligence tests
from parents and children in 300 adoptive families and compared them with
similar measurers available for the biological mothers of the same adopted
children. The results of this study supported the hypotheses that genetic
variability is an important influence in the development of individual
differences for intelligence.
The study also concluded that adopted children resemble their biological
mothers more than they resemble the adoptive parents who reared them from birth.
In an extensive study dealing with the mental growth of foster children
after they had lived in their new homes found that on the whole, they improved
their mental status, the extent of improvement being contingent upon the quality
of the foster home, the length of residence there, and the age at which the
child entered the new environment. It found, also, that siblings living in
different foster homes resembled one another much less than brothers and sisters
ordinarily do. In general, the results demonstrate that improved environmental
conditions which endure can raise the level of intelligence, if optimal
conditions are provided early in life.
A child born into a poor home often shows an improvement in intelligence
if adopted by a more intelligent and stimulating family, and it has been found
that Negro children born into backward rural families improve steadily if they
move to the city. But the amount of improvement is always limited by the mental
capacity that was there a t birth. Freeman. (1928)
The Minnesota Adoption Studies of 1974 included the Transracial Adoption
Study to test he hypotheses that black and interracial children that are reared
by white parents would perform on IQ tests and school achievement measures as
well as other adopted children.
Results were that black and interracial scored as well as adoptees in
other studies. The high IQ scores of the black and interracial children showed
that genetic racial differences do not account for a moor portion of the IQ
performance difference between racial groups. The study also found that black
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