Our species separated into two parts 50, 60, or 70 thousand years ago, depending on which paleoanthropologist you ask. One part remained in Africa, the ancestral homeland. The other crossed into Southwest Asia, then split, and re-split, and re-split, until there were human populations living in near-total reproductive isolation from each other in all parts of the world. This went on for hundreds of generations, causing the divergences we see today. Different physical types, as well as differences in behavior, intelligence, and personality, are exactly what one would expect to observe when scrutinizing these divergent populations.
[...]
We see the same differences in traits that we don’t think of as directly physical, what evolutionary psychologists sometimes refer to as the “BIP” traits — behavior, intelligence, and personality. Two of the hardest-to-ignore manifestations here are the extraordinary differentials in criminality between white Americans and African Americans, and the persistent gaps in scores when tests of cognitive ability are given to large population samples.
Via United States of Jamerica.
24 comments:
Disgusting. Why did they want to listen to him? It strikes me as like a Jewish law student group inviting someone like Joseph Sobran or Pat Buchanan to speak.
Hey man, thanks for the link, I appreciate it!
It's not a problem -- I've come across your blog before; it's got good stuff on it. I'll try to make a point of stopping by more often.
You grossly misrepresent Mr.Derbyshire's point. He makes no claim that blacks are inferior. He only claims that they are different, which is true. He merely states the positive truth.
How silly of me. I would have thought a claim that Blacks are biologically predisposed to be dumber and criminal has a normative component to it, connoting inferiority. Apparently, that's a "gross misrepresentation" on my part. How I will ever live with myself in the morning, God only knows.
Nope, you are conflating average measures of intelligence with moral value. It's a truth that can have normative implications, but a truth nonetheless. Does the fact that blacks dominate sports like sprinting and basketball demonstrate their "superiority"?
As a very smart person yourself (judging from your academic credentials), does this "fact" of your high intelligence also mean you are superior to people of lesser intelligence?
I half agree with Rebecca. On the one hand, I am not sure that there is anything immoral, at least per se, in any facts, even disagreeably bothersome facts which could be used, for example, by racists and others to advance a nasty political agenda. I think facts are facts.
On the other hand, I rather doubt that science has solved the most basic problems of what "intelligence" is, how to measure it and how to distinguish innate "intelligence(s)" from other facts, background, upbringing, experiences, etc. that impact on "intelligence(s)." The same problem exists for physical attributes. Some plants do well in sunlight. Others do not. So, the "do well" innate to a plant is, by its very nature, dependent on factors not entirely within the plant. And, knowing which type of plant is better on the "do well" is tied to the same things.
So, I think we have questionable science, all in all. We have people with eugenics interests who want to advance their agenda - call them "positive" Darwinists as opposed to the rest of us who are neutral or "negative" Darwinists - that has been shown by history to have a disgusting, as Rebecca seems to note, history. And, lastly, we do have the facts that, as measured - whatever the measurements really mean, if anything - show one group doing better or worse on a test (i.e. there are different results).
I see nothing wrong with reporting the results. I do see something wrong with politics and morals based on such results, even if the goal is the "perfection" of man.
I think the question of whether "facts" have normative elements is a fascinating one. But it's a question that doesn't need to be gotten into here, because Derbyshire isn't reciting a series of uncomfortable "facts" -- he's reciting pseudo-scientific gibberish that essentially every reputed scientist has rejected for decades.
For Derbyshire's claim to be true, we'd need to accept a couple of ridiculous assumptions:
1) The idea of cohesive biological "races" whose "interracial" differences are more pronounced than intraracial differences. Virtually no scientist believes this is the case.
2) Even granting Derbyshire's historically dubious proposition that the "races" developed in relative reproductive isolation from another, thanks to a mix of intermarriage and good old fashioned slave rape, most Blacks in the US have decidedly mixed-racial heritage. So we'd need to accept some measure of "one-dropism" as a genetic matter where even an ounce of Black blood is enough to taint the body. This proposition's ratio of support from racial supremacism versus science is approximately...100:0.
3) There'd have to exist some "natural" propensity for criminality -- which makes no sense, as criminality is necessarily a social concept (something is only against the law once society is around to pass laws). Likewise, though I'm skeptical of the possibility of a non-socially constructed definition of intelligence, even assuming there is one NF is quite correct that it's pretty unlikely we've managed to nail how to measure it.
4) We'd have to reject other, non-biological reasons for differentiation on the relevant axis -- anything from culture, to discrimination, to oppression. Derby doesn't even attempt this. And given that IQ scores amongst all ethnic groupings have risen from generation way too fast for it to be a product of genetics, rather than social conditions, the case for it being biologically determined is extraordinarily weak.
White racism in America has historically been premised on the notion that Blacks were a) hard workers who b) were biologically incapable of being good citizens (intelligent and emotionally mature). They always backed it up with "science", and the "science" was always shit. Derbyshire is heir to a long legacy of White supremacist nonsense.
David,
What you write and what Derbyshire says are only tangentially related. I am not writing to support him. I am merely noting that you are reading into what he writes far more than what is there.
I should add: there is both junk and real science involved in issues relating to intelligence and race. It is not clear at all from what you quote that Derbyshire is relying on junk science. Rather, you are reading things into what he asserts.
Nor is it even rational to suggest - which is the flip side espoused by leftist ideologues - that all attributes are equally distributed across humanity. That proposition is a dubious one, since very few things in this world are equally distributed.
The reality is that we do not have enough information to reach a full opinion, most especially on the question of intelligence because intelligence is hard to define and, with any definition, difficult to measure and, if measured, difficult to determine whether what is measured is wholly innate or mixed with other factors. But, surely, there are innate factors - even if humans turn out to be plants that, depending on how nurtured, develop better or worse.
But, frankly, it is a fact that some groups test higher than other groups. The tests do test something. On such tests, there are measurable differences. So, this is not a situation where there is nothing to say on the issue of intelligence. Rather, given the obvious limitations on the ability to distinguish innate from other factors and to determine what counts as intelligence - which is not to say that problem solving ability (i.e. what Iowa tests and the like are supposed to uncover) is not part of intelligence; it certainly is -, there are few things that one can say with any assurance.
I note your points.
1 & 2. Derbyshire does not claim that there are or were ever cohesive biological races. He made an historical point that he says accounts for some of what is seen today. That is quite different from what you have him say. So, on your first point, you are playing games with what he wrote. I find his point questionable but it is not wholly ridiculous in the way you assert.
Why, David, if your points are so strong, lawyer to death what Derbyshire actually asserts?
3. The criminality question is not, in my view, well taken by Derbyshire. He is reading more into the available evidence than is there. On the other hand, I am not sure I agree with the view that crime and poverty are as directly connected as some leftist ideologues assert, but there is some degree of truth to their point. Opposed thereto: poor Jews in early 20th Century American were not associated with violent crime - in fact, just the opposite. So, we have a group that does not fit the poverty prediction.
4. White racism was not premised on Blacks being hard working. Just the opposite. While I do not advocate Howard Zinn's writings - because he was a terrible historian who put his agenda ahead of the evidence -, he is correct when he writes in his book, A People's History of the United States, that, in fact, notwithstanding what racists pretty universally said about Blacks, Blacks worked hard, just like everyone else. That, after all, was part of the point of their supposedly being inferior.
Here's the speech Derbyshire gave. The highlights (I reproduce quotes rather than summarizing, lest I, like David, be accused of misrepresenting what Derbyshire said):
* "racial disparities in education and employment have their origin in biological differences between the human races. Those differences are facts in the natural world, like the orbits of the planets. They can't be legislated out of existence; nor can they be 'eliminated' by social or political action."
* "Different physical types, as well as differences in behavior, intelligence, and personality, are exactly what one would expect to observe when scrutinizing these divergent populations."
* "We see the same differences in traits that we don't think of as directly physical, what evolutionary psychologists sometimes refer to as the "BIP" traits — behavior, intelligence, and personality. Two of the hardest-to-ignore manifestations here are the extraordinary differentials in criminality between white Americans and African Americans, and the persistent gaps in scores when tests of cognitive ability are given to large population samples."
* "Should you want to say at this point that these so-called tests of so-called cognitive ability measure nothing important, you had better go and argue with the authorities here at the University of Pennsylvania law school. They have carefully recorded, and posted on the internet, that half their student intake, second and third quartiles, falls between LSAT scores 166 and 171."
Does anyone want to dispute that John Derbyshire is ignorant enough to believe that the LSAT is a test of "cognitive ability" rather than an exam for which people can and do prepare with resulting boosts in their scores? I scored a 165 when I took my first LSAT practice test. Then I worked once a week for nearly 2 months with a Kaplan tutor, focusing mainly on improving my ability to do logic games. My actual LSAT score was 172. Did my "cognitive ability" improve in 2 months, or did my ability to take a particular test improve in that time?
Sorry, but even on his own terms, Derbyshire doesn't know what he's talking about.
I agree that it sounds Derbyshire is citing junk science. And that's exactly the kind of thing the advocates of the vilest forms of tend to spit out when confronted with their own irrationality.
And you're right to note this, David:
We'd have to reject other, non-biological reasons for differentiation on the relevant axis -- anything from culture, to discrimination, to oppression. Derby doesn't even attempt this. And given that IQ scores amongst all ethnic groupings have risen from generation way too fast for it to be a product of genetics, rather than social conditions, the case for it being biologically determined is extraordinarily weak.
But part of me wonders whether, in the abstract, saying that "differentiation on the relevant axis" is the result of social forces couldn't equally be considered a claim of inferiority from the individual's perspective. After all, both society and biology are something outside the individual's control. Is the only distinction that one claim is true and the other is not?
As I said, I was not writing to defend Derbyshire. The larger segment quoted by PG is very helpful to understanding Derbyshire's view. On that larger basis - if it is a sufficient segment of his writing to get his full point -, I think he goes way beyond the facts and confuses his politics with facts. It is not a very becoming politics either.
I agree that there are serious flaws in LSAT. That was true back when I went to law school - when the LSAT had a different test scale, by the way - and, given what I have seen with Kaplan and my son's friends, with the SAT and other supposed intelligence tests.
On the other hand, I note my earlier point that, with plants, innate characteristics are tied to environment. Which is to say, while it is, I think, true that LSAT/SAT type tests are impacted by environmental factors (e.g. by test prep courses), that does not mean that the test is not a measurement of ability. Like the plant which grows better in indirect light, test preparation may merely allow innate ability better to shine
Neither the LSAT nor the SAT claims to be an intelligence test. The SAT may have done so 20+ years ago, but so long as I have been looking at it (which is since about 1990), it's been very careful not to claim that it measured innate ability. The letters originally stood for "Scholastic Aptitude Test," but again since about 1990 have stood for "Scholastic Achievement Test." And the SAT when I took it in the mid '90s was even more preppable than the LSAT. You do not want to know how much time my parents put into drilling me on vocabulary flash cards, or how many hours I worked with a math tutor. Result: 1590 score (on the old 1600 scale).*
Seriously, it's to my personal advantage that people believe the bullshit about these tests measuring intelligence because then I look pretty damn smart, but the test-prep industry exists because these tests don't do that. Some people are just better at test-taking -- we are good at multiple-choice guessing, we don't suffer from panic or anxiety in testing situations -- but that's a pretty worthless "innate ability" in the real world, where I have encountered precious few multiple- choice questions.
(In case it wasn't obvious, the reason schools post their students' LSAT score range is to give applicants, who have to spend money for each application they submit, an idea of how likely they are to be admitted. Law schools also post the admitted students' undergraduate GPA ranges for the same purpose. It's a very useful service -- it let me know that applying to HLS and YLS would be a waste of time because they almost never take someone with an undergrad GPA below 3.3 -- and it's a pity that Derbyshire is so ignorant whereof he speaks that he misrepresents the reason for it.)
* This would be the moment for superdestroyer to chime in about Asians' manipulating a system that originally worked to measure intelligence until those uncreative grinds showed up and wrecked everything.
PG,
Genius that you are as measured by the SAT's, the test is only subtly different from a traditional IQ test. Some argue, with evidence to support them, that the test is, in fact, a measurement of ability and even of aspects of intelligence. However, that is all controversial for reasons noted on this page, which is why the claim to be an "aptitude" test has been changed as of late.
As the parent of a child just admitted to Vassar - not exactly an easy college to get into (and even harder to get into for 2014) -, I know quite a bit about all of this.
While I do not believe that one can encapsulate all of intelligence by means of a problem solving test, that does not mean the test is invalid. Which is to say, the test does measure something, albeit imperfectly.
The issue of how a biological trait manifests itself is extremely complex. Some traits are held back, waiting for appropriate environmental factors to allow them to manifest themselves. In the case of testing intelligence (or testing anything else), the big issue I have seen with kids is that they do not always understand how a test is structured. That issue alone can account for hundreds of points on the test. So, to say that attending something like Kaplan is enough to show the test to be BS is simply contrary to fact.
Again, PG. I am not claiming the test measures IQ. I am claiming that it measures something. I do think it unfair that some students have the benefit of test preparation by which they are better able to take the tests. But, I do not think that such fact, taken alone, shows the test to be invalid as a measure of certain aspects of intelligence.
The test is, however, invalid as a means to rank students who had different preparation for the test. Which is to say, not everyone is taking the test under the same conditions and, on that ground, it is bad science. As such, it is unfair as a means to rank students because, those students aware of how the test works do better.
You are too modest about your abilities. No doubt you are a really bright guy and the testing confirms as much.
Very bright gal.
Like PG, I too have an incentive to trumpet the awesomeness of standardized tests. If the LSAT was all there was, I'd be at Yale Law right now. And perhaps unlike PG, I would feel comfortable saying I have a natural aptitude for taking such tests, in that a) I tend to score far higher on them than I do in class work in the same field and b) I can do very well without substantial preparation. The SAT I don't recall what my practice scores were, so I can't speak to that. But while I took a Kaplan LSAT course, it didn't change my score than much (173 on the diagnostic to 177 for real). The GREs I took essentially cold and got a 790 Math/720 Verbal/6 writing. I got a 4 on the AP Calculus exam despite being a C calc student, and a 5 on every other AP test I took save English Composition (that was embittering).
So these were typically the strong suit in my application. And I do think these tests measure something -- in fact, I'd be surprised if anyone thinks they measure nothing. I just think it's a big stretch to say they measure something like "biological intelligence".
David,
My only problem here is the flippant dismissal by some here - not you, in this case - of such tests. We both agree that the tests measure something. I suspect we both agree that superior problem solving ability is a component of intelligence.
Whether such tests really measure something that is actually helpful to colleges and law schools in predicting the ability to do school work or in otherwise choosing one applicant over another, I have no idea. Clearly, most colleges and law school admission departments either think such tests are valuable in some way or are trapped by inertia (or, I suppose, have some other reason for continuing to use such tests).
My problem with the use of such tests is that a ranking test must be taken, to be valid, under identical circumstances by all persons being tested. If one person or group of people learns the structure of the test and/or can bone up on what questions that are likely to be on the test, that group or person cannot be validly compared to a group or person without that advantage.
That strikes me as an inherent problem for which there is no solution, unless all kids are to be provided, as part of the cost of the test, with the same test preparation.
Now, I have said here before, intelligence is a complex thing about which there is no agreement and no way, thus far, to measure it in a manner that factors out environmental factors. And, in that environmental factors are part of what makes a person "intelligent," factoring out environmental aspects would not necessarily result in finding out about a person's intelligence. So, we have something very complex going on.
I nonetheless find it smug that people dismiss these tests with the wave of a hand without a thought. This, notwithstanding the fact that colleges and law schools use the tests.
My only problem here is the flippant dismissal by some here - not you, in this case - of such tests. We both agree that the tests measure something. I suspect we both agree that superior problem solving ability is a component of intelligence.
My "flippant dismissal" is of the claim that the SAT or LSAT tests something "innate." Obviously they are good measures of how well one can take those particular tests and answer those particular problems. Your prior comments were not just about specific abilities -- abilities can be acquired; e.g. once I was unable to drive a car, and now I can, and maybe someday I'll also be able to parallel park in less than 5 minutes -- but about something beyond particularized skills that might be called "intelligence." I had excellent abilities (now somewhat atrophied) at taking the PSAT, SAT, SAT IIs and LSAT; these are not accurate measures of my overall intelligence or even overall problem-solving ability. (Ask me to solve a problem that involves spatial manipulation, for example, and you'll think I'm a moron.)
Schools use these exams because grading metrics are not standardized across all teachers, and thus the national exams provide a metric by which students can be compared to each other. I personally think that AP tests are much better metrics, because my scores on them were more reflective of my true abilities in the subjects rather than just on the exams (5s in language and literature; 4 in history and government; 3 in calculus AB), but I don't run things.
I had forgotten to respond to the Asian of Reason before now, but I am curious as to whether s/he thinks there is a moral component to criminality, which Derbyshire claims to be a manifestation of African Americans' different "behavior, intelligent and personality." I do consider the person who commits rape, for example, to be inferior to myself.
Of course I believe there is a moral component in criminality. People who commit rape are in a utilitarian sense, "bad". But the genetic tendency for African-Americans to be criminals is morally neutral to me, because after all, I believe human beings have free will, and blacks, are, without a doubt, humans. The decisions that you make in life are what ultimately determine your personal morality. Just because you are born with a complex genetic chain that predisposes you to rape, doesn't mean you can't tell that instinct within you, NO.
And to respond to David, criminal behavior is a social construct, and African-Americans, for what I believe to be genetic reasons, are more likely to be criminals, as evidenced by the large number of African-Americans who are or have been part of the American prison system. And no, the evidence suggests that this over-representation is not due to the prominence of racist police officers.
But I believe that environmental solutions can help alleviate the problem of black crime. Bigger sticks, two-parent households, and strong religious communities, are a few of the tactics that may be used to curb criminality.
Everyone, including blacks, must be subject to the law.
Okay, I've spent enough time playing with the racists.
I think I've pretty conclusively demonstrated that this notion of biologically cohesive "races" (mixed with a one-drop principle) is essentially incoherent, and there is zero evidence of criminality being biological ("as evidenced by the large number of African-Americans who are or have been part of the American prison system" -- this is logic that should be laughed out of a middle school class, and "the [uncited] evidence" regarding the lack of racist police officers, even if true, doesn't even get you a hundredth of the way there) -- even if such a statement was coherent, which it isn't given the disconnect between "biological predisposition" and "social construct".
Go back and play with your Stormfront buddies.
***My "flippant dismissal" is of the claim that the SAT or LSAT tests something "innate." ***
Just as you can't measure height without considering the influence of nutrition, you should consider influences on education which stimulate cognitive development.
Nonetheless, behavioural genetics studies of twins reared apart, adoptees and siblings show that the variation between individuals is largely due to differences in their genes.
Steven Pinker writes:
"To study something scientifically, you first have to measure it, and psychologists have developed tests for many mental traits. And contrary to popular opinion, the tests work pretty well: they give a similar measurement of a person every time they are administered, and they statistically predict life outcomes like school and job performance, psychiatric diagnoses and marital stability. Tests for intelligence might ask people to recite a string of digits backward, define a word like “predicament,” identify what an egg and a seed have in common or assemble four triangles into a square. Personality tests ask people to agree or disagree with statements like “Often I cross the street in order not to meet someone I know,” “I often was in trouble in school,” “Before I do something I try to consider how my friends will react to it” and “People say insulting and vulgar things about me.” People’s answers to a large set of these questions tend to vary in five major ways: openness to experience, conscientiousness, extraversion, agreeableness (as opposed to antagonism) and neuroticism. The scores can then be compared with those of relatives who vary in relatedness and family backgrounds.
The most prominent finding of behavioral genetics has been summarized by the psychologist Eric Turkheimer: “The nature-nurture debate is over. . . . All human behavioral traits are heritable.” By this he meant that a substantial fraction of the variation among individuals within a culture can be linked to variation in their genes. Whether you measure intelligence or personality, religiosity or political orientation, television watching or cigarette smoking, the outcome is the same. Identical twins (who share all their genes) are more similar than fraternal twins (who share half their genes that vary among people). Biological siblings (who share half those genes too) are more similar than adopted siblings (who share no more genes than do strangers). And identical twins separated at birth and raised in different adoptive homes (who share their genes but not their environments) are uncannily similar."
http://www.nytimes.com/2009/01/11/magazine/11Genome-t.html?_r=1&pagewanted=2
""Multivariate genetic analyses indicate that general intelligence is highly heritable, and that the overlap in the cognitive processes is twice as great as the overall phenotypic overlap, with genetic correlations averaging around .80."
Plomin et al (2004) "A functional polymorphism in the succinate-semialdehyde dehydrogenase genes is associated with cognitive ability,"
Molecular Psychology 9, 582-586.
"Data from more than 8000 parent-offspring pairs, 25,000 sibling pairs, 10,000 twin pairs and adoption studies provide evidence that genetic factors play a substantial role in the variation of general intelligence, with heritability estimates ranging from 40 to 80%"
--Burdick et al, Cognitive variation in DTNBP1 influence general cognitive ability. Human Molecular Genetics, 2006, Vol 15, No. 10.
***1) The idea of cohesive biological "races" whose "interracial" differences are more pronounced than intraracial differences. Virtually no scientist believes this is the case.***
We know now there are enough genetic differences between people from different parts of the world that you can classify people in groups that correspond to popular notions of race. See recent studies by population geneticists Noah Rosenberg, or Neil Risch & Hua Tang:
“we found that individuals could be partitioned into six main genetic clusters, five of which corresponded to Africa, Europe and the part of Asia south and west of the Himalayas, East Asia, Oceania, and the Americas”
http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.0010070
***And given that IQ scores amongst all ethnic groupings have risen from generation way too fast for it to be a product of genetics, rather than social conditions, the case for it being biologically determined is extraordinarily weak.***
Note that researchers like Wicherts (2004) have found that the Flynn effect gains seem qualitatively different to the ‘g’ loaded differences that make up the gaps between groups.
The Flynn effect seems to reflect gains on domain specific items, but not necessarily overall ability. A test’s g loading is the best predictor, not just of school grades and workplace performance, but also of all the other indicators and correlates of intelligence—including biological variables, reaction times, and heritability estimates.
***The idea of cohesive biological "races" whose "interracial" differences are more pronounced than intraracial differences.***
Just to clarify this point, what is being referred to are statistical differences. For instance, no can argue that men and women have different distributions of height. But the male distribution goes from Yao Ming to Mini-me, a spread which is far larger than the difference between male and female averages.
Yet despite this, no one argues against men and women having different height distributions.
Professor Steve Hsu explains the point here:
"On the other hand, for most phenotypes (examples: height or IQ, which are both fairly heritable, except in cases of extreme environmental deprivation), there is significant overlap between different population distributions. That is, Swedes might be taller than Vietnamese on average, but the range of heights within each group is larger than the difference in the averages. Nevertheless, at the tails of the distribution one would find very large discrepancies: for example the percentage of the Swedish population that is over 2 meters tall (6"7) might be 5 or 10 times as large as the percentage of the Vietnamese population."
http://infoproc.blogspot.com/2008/01/no-scientific-basis-for-race.html
***there is zero evidence of criminality being biological ***
It's not a case of criminality being biological per se, but environmental factors being mediated by biological factors. These include testosterone (males commit more crime than females) and MAO-A variants.
For instance, a large study of caucasian males in NZ (Moffit 2002) showed that those who had a low activity variant of MAO-A in combination with a poor childhood environment were at greater risk of crime and anti-social behaviour. The MAO-A finding has been replicated in subsequent studies.
""Previous research has linked low-activity MAOA variants to a wide range of antisocial, even violent, behavior, but our study confirms that these variants can predict gang membership," he said. "Moreover, we found that variants of this gene could distinguish gang members who were markedly more likely to behave violently and use weapons from members who were less likely to do either...
What's interesting about the MAOA gene is its location on the X-chromosome," Beaver said. "As a result, males, who have one X-chromosome and one Y-chromosome, possess only one copy of this gene, while females, who have two X-chromosomes, carry two. Thus, if a male has an allele (variant) for the MAOA gene that is linked to violence, there isn't another copy to counteract it. Females, in contrast, have two copies, so even if they have one risk allele, they have another that could compensate for it."
http://www.sciencedaily.com/releases/2009/06/090605123237.htm
***pseudo-scientific gibberish that essentially every reputed scientist has rejected for decades.***
Well, that's what people may say in public but when surveyed anonymously peoples views are quite different (note people have been assaulted, protested, threatened etc not exactly a way to get honest discourse).
Consider the findings of the Snyderman & Rothman survey of 661 members of the American Education Research Association, the National Council on Measurement in Education, the American Psychological Association, the American Sociological Association, the Behavior Genetics Association, and the Cognitive Science Society:
"Respondents were asked to express their opinion of the role of genetic differences in the black-white IQ differential. Forty-five percent believe the difference to be a product of both genetic and environmental variation, compared to only 15% who feel the difference is entirely due to environmental variation. Twenty-four percent of experts do not believe there are sufficient data to support any reasonable opinion, and 14% did not respond to the question. Eight experts (1%) indicate a belief in an entirely genetic determination.[4]"
http://en.wikipedia.org/wiki/Snyderman_and_Rothman_(study)
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