Nature versus nurture
Nature versus nurture is a popular term 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 or attributes. A wide variety of traits have been considered in such debates, including personality, sexual orientation, political orientation, intelligence, and propensity for violence or criminality.
A few points are worth clarifying about "nature" and "nurture". First, "nature" does not reduce to anything as simple as "present at birth". Height is thought to depend very extensively on genetics, for example, but one is not born adult-sized; one must slowly grow up.
Second, although "nurture" may have historically referred mainly to the care given to children by their parents, a number of other environmental factors probably also would count as "nurture" in a contemporary nature versus nurture debate, including one's childhood friends, one's early experiences with television, or even one's experience in the womb. 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".
Finally, some nature versus nurture debates might be criticized for leaving little role for free will; if "nature" and "nurture" together have so much influence on who I am, then where do my individual choices come in?
Some contemporary ideas
Much of current thinking tends to discount the notion of genetics as valid in determining subjectively qualified traits, such as intelligence or personality. The caveat to this is the apperance of peculiar evidence which seems to point to the contrary, as in separately raised identical twins who have lived similar lives.
Modern science 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.
Over the course of scientific development, the nature versus nurture debate has long been a bellweather indicator of the validity of the scientific method at the time, and as might be expected, the history of science and sociology have long been intertwined.
After a long, contentious, maturing, what can be said scientifically, is that for valid categorical attributes, there can be probabilities assigned to genetic triggers. This is the limit of what genetics can scientifically "predict" about human psychological development.
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.
Anotheer incarnation is the forementioned twins phenomenon, called the concurrent development phenomenon. How is it possible that identical twins, separated at birth, have grown to look and act so similarly? The possibility of genetics as being a common influence cannot be immediately ruled out.
Another is the question of intelligence - was Einstein genetically predestined to become a revolutionary thinker? The subject is highly contentious, as many questions raised seem unlikey to be answerable scientifically. With so many variables to contend with, it seems impossible to isolate the effects that either genes or the environment have on a subject in experiments.
Difficulties in Testing
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. 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.
Contemporary researchers have pointed out the likelihood that the individual, to some extent, shapes their own environment in ways that are presumably influenced by their genes. In addition, environment may trigger the expression of genes, that is, determine whether and to what extent a genetic predisposition will actually manifest itself. Hence, untangling nature and nurture, even with experiments like the above, can be almost impossible.
Additional problems with the question include the creation of a dichotomy, where the influence of genes and environment is all-encompassing (that is, either something is caused by genes, or by environment). This is made difficult by the blurry boundary between the two for such questions as maternal effect (i.e., the influence of the mother's womb on the development of the child).
Finally, it is often 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 far from any agreement on whether 'intelligence' exists, and how one should define it.
A number of social issues exist, especially in education and in law with regards to culpability.