Nature versus nurture
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Nature versus nurture is a shorthand expression for debates about the relative importance of an individual's innate nature and experiences ("nurture") in determining or causing physical and behavioral traits.
These debates arose from problems associated with reconciling the formalist definitions of classical science and philosophy, with emerging theories and new data. While classical theory was primarily concerned with the line between that which was voluntary (the ego, the self, and the personal will) and the involuntary (of Nature, God, etc.), this view was self-centric, which is to say deferential to authorities over the personal concepts; i.e. religious teaching and doctrine.
As science developed an understanding of life's elemental nature (like molecules, genes, atoms, gravity, time) the apparent lines that classical formalism defined became blurred, and the trend of science since has been to stray from the human-centered view to a more general and elemental view. Science culture to this day functions within a social boundary that contains the impact of any discoveries or observations from having an immediate effect or bearing on matters of human society. It is in this social context where attempts to fit new ideas and developments into the old formalist and self-based mold, that the nature versus nurture debates occur. Where science may be at the forefront of this transition, popular culture have tended to lag behind, and this gap is reflected as popular science.
This confusion can be seen in the logical paradoxes that theories regarding these issues present. For example, advocates of a formalist view may in some cases disregard the influence of nature, in deference to the idea of personal will. On the other hand, newer ideas may dictate that certain traits fall under the context of nature. Indeed, Western-based tradition (and early science) has had the problem wherein its criteria for defining 'nature and nurture,' or 'God and person,' and hence tended to coincide with the attribution of positive traits as belonging to oneself, and negative traits belonging to others. A great deal of these conflicts deal with the reconciliation by discipline toward mitigating the perceptions of superior self that manifest as wider gaps between societies.
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Various contexts and issues
A wide variety of human behavioural characteristics may find their way into these types of debates and frame the scope of particular debates. These include personality, sexual orientation, gender identity, political orientation, intelligence, and propensity for violence or criminality.
These various types of nature versus nurture debates tend to be viewed as sensationalistic or oversimplifications of legitimate scientific research, and a misuse of that research for political reasons. Controversial public issues often arise from over-generalisations of specific and incomplete scientific research. Science journalism, the medium for popular science, has always been problematic with scientists when it attempts to make the news of small, incomplete, and perhaps even insignificant developments into headlines which draw public attention.
Definitions of nature and nurture
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 most diseases now strictly identified as genetic, such as Huntington's disease, there is a better than 99.9% correlation between having the identified gene and the disease -- and, contrastively, not having either. On the other hand, such traits as one's native language are entirely environmentally determined: linguists have found that any child (if capable of learning a language at all) can learn any human language with equal facility. With many traits, however, there is an intermediate mix of nature and nurture, and opinions about the relative importance of each will often vary widely.
How to compare the effects of nature and nurture, and why this is difficult
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..
Some observers believe that modern science tends to give 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 truth has often been assumed as a prerequisite in various incarnations of the nature versus nurture debate. In the past, heredity was often used as "scientific" justification for various forms of discrimination and oppression along racial and class lines. Works published in the United States since the 1960s which argue for the primacy of "nature" over "nurture" in determining certain characteristics, such as The Bell Curve, have been greeted with considerable controversy and scorn.
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 due to environmental variation.Yet because of the nature and nurture theory this is still considered a posibility by those who favor herediterianism. Studies show a significantly higher academic correlation between children and their birth parents in comparison to adopted children and their adoptive parents, becoming more pronounced as they grow older...
Misc
The concurrent development phenomenon: why do identical twins who are raised together grow to behave differently?
A number of social issues exist, especially in education and in law with regards to culpability.