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Nature versus nurture is a popular phrase used to describe debates over the relative degrees to which one's
genetic makeup ("nature") and one's life experiences ("nurture") influence one's traits and behavior. A wide variety of
characteristics have been considered in such debates, including personality,
sexual orientation, gender identity, political orientation, intelligence, and propensity for violence or criminality.
Although "nurture" may have historically referred mainly to the care given to children by their parents, any environmental
(not genetic) factor also would count as "nurture" in a contemporary nature versus nurture debate, including one's
childhood friends, one's early experiences with television, and one's experience in the womb. Indeed, a substantial source of
environmental input to human nature may arise from stochastic variations in prenatal development. Additionally, although
childhood experience (especially early childhood experience) is often regarded as more influential in who one becomes
than post-childhood experience, a liberal interpretation of "nurture" might count all life experience as "nurture".
Uncomplicated cases
In a few clear-cut cases, it makes sense to say that a trait is due almost entirely to nature, or almost entirely to nurture.
In the case of highly penetrant genetic diseases, such as Huntington's disease, nature seems to be the right answer; basically, you will get the disease if and
only if you have the corresponding disease-causing allele (gene variant). In the case of which particular language you speak,
nurture seems to be the right answer; linguists have found that any "normal" child can learn any human language. With most
interesting traits, however, there is probably an intermediate mix of nature and nurture, and people may disagree wildly about
the relative importance of each.
How to compare the effects of nature and nurture, and why this is hard
Current thinking in biology discredits the notion that genes alone can determine a trait because genes are never sufficient in
isolation. Rather, particular genes influence the development of a trait in the context of a particular environment. Thus,
measurements of the degree to which a trait is influenced by genes versus environment will depend on the particular environment
and genes examined. In many cases it has been found that genes may have a substantial contribution to psychological traits, such
as intelligence and personality; yet these traits may be largely influenced by environment in other circumstances.
A researcher seeking to quantify the influence of genes or environment on a trait needs to be able to separate the effects of
one factor away from that of another. Often this reduces to calculating the heritability of a trait.
In many cases the difficulty of creating situations suitable for testing environmental and genetic influence on traits has
been compensated for by finding existing populations that reflect the experimental setting the researcher wishes to create. One
way to do this is the study of twins. Some studies compare identical twins to
fraternal twins, while others study identical twins reared apart.
For example, many twin studies have made use of identical twins (who have the same genetic makeup) who were raised in
differing environments in order to control for genetic effects: that is, any variation between twins is clearly attributable to
the environment, allowing the researcher to quantify the effects of the environment by measuring variance of a trait between
twins. Identical twins raised separately may have experienced quite different environments; yet many studies have often been
found that they live similar lives, have similar personalities and similar levels of intelligence. On the other hand, even
identical twins who are raised together often differ in significant ways.
Some have rightly pointed out that environmental inputs affect the expression of genes. This is one explanation of how
environment can influence the extent to which a genetic disposition will actually manifest. Even using experiments like those
described above, it can be very difficult to determine convincingly the relative contribution of genes and environment.
Twin studies have highlighted another complication to the nature versus nurture debate. The effects of nurture can be further
divided into shared and non-shared. Shared environmental factors are those experienced by siblings raised together. Non-shared
environmental factors are not shared by siblings (i.e. unique experiences). In many cases non-shared environmental effects have
been found to out-weigh shared environmental effects. That is, environmental effects that are typically thought to be
life-shaping (such as family life) have less of an impact than non-shared effects, which are harder to identify. One possible
source of non-shared effects is the environment of pre-natal development. Random variations in the genetic program of development
may be a substantial source of non-shared environment.
Moral difficulties: eugenics, etc..
Modern science, however, tends to frown upon giving too much weight to the nature side of the argument, in part because of
social consciousness. Historically, much of this debate has
had undertones of racist, and eugenicist
policies - the notion of race as a scientific validity has often been assumed as a prerequisite in various incarnations of the
nature versus nurture debate. Genetics, long having been used as "scientific" justification for genocide, or race-based discrimination.
...Steven Pinker: moral ideals directing science?
Philosophical difficulties: are the traits real?
It is sometimes a question whether the "trait" being measured is even a real thing. Much energy has been devoted to
calculating the heritability of intelligence (usually the I.Q., or intelligence quotient), but there is still some disagreement as to what exactly 'intelligence' is.
Philosophical difficulties: Biological determinism
If genes do contribute substantially to the development of personal characteristics such as intelligence and personality, then
many wonder if this implies that genes determine who we are. Biological determinism is the thesis that genes determine who we are. Few if any scientists would
make such a claim; however, many are accused of doing so.
Others have pointed out that the premise of the "nature versus nuture" debate seems to negate the significance of free will. More specifically, if all our traits are determined by our genes, by our
environment, by chance, or by some combination of these acting together, then there
seems to be little room for free will. In any case, this line of reasoning suggests that the "nature versus nurture" debate tends
to exaggerate the degree to which individual human behavior can be predicted based on knowledge of genetics and the
environment.
Myths and mysteries
Within the debates surrounding cloning, for example, is the far-fetched contention that a Jesus or a Hitler could be "re-created" through genetic cloning. Current
thinking finds this largely preposterous, and discounts the possibility that the clone of
anyone would grow up to be the same individual.
Misc
The concurrent development phenomenon: why do identical twins, separated at birth, grow to look and act so
similarly?
A number of social issues exist, especially in education and in law with regards to culpability.
See also
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