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Review: Making sense of heritability
This is a GREAT book, which goes down to the basics about heritability and the various claims people have made against it. Highly recommended. Best book of the 29 i have read this year.
The denial of genetically based psychological differences is the kind of sophisti-
cated error normally accessible only to persons having Ph.D. degrees.
I was introduced to the nature–nurture debate by reading Ned Block
and Gerald Dworkin’s well-known and widely cited anthology about
the IQ controversy (Block & Dworkin 1976a). This collection of arti-
cles has long been the main source of information about the heredity–
environment problem for a great number of scientists, philosophers, and
other academics. It is not an exaggeration to say that the book has been
the major inﬂuence on thinking about this question for many years. Like
most readers, I also left the book with a feeling that hereditarianism (the
view that IQ differences among individuals or groups are in substantial
part due to genetic differences) is facing insuperable objections that strike
at its very core.
There was something very satisfying, especially to philosophers, about
the way hereditarianism was criticized there. A strong emphasis was on
conceptual and methodological difﬁculties, and the central arguments
against hereditarianism appeared to have full destructive force indepen-
dently of empirical data, which are, as we know, both difﬁcult to evaluate
and inherently unpredictable.
So this looked like a philosopher’s dream come true: a scientiﬁc issue
with potentially dangerous political implications was defused not through
an arduous exploration of themessy empiricalmaterial but by using a dis-
tinctly philosophical method of conceptual analysis and methodological
criticism. It was especially gratifying that the undermined position was
often associated with politically unacceptable views like racism, toler-
ation of social injustice, etc. Besides, the defeat of that doctrine had a
certain air of ﬁnality. It seemed to be the result of very general, a priori
considerations, which, if correct, could not be reversed by “unpleasant”
discoveries in the future.
But very soon I started having second thoughts about Block and
Dworkin’s collection. The reasons are worth explaining in some detail
I think, because the book is still having a considerable impact, especially
on discussions in philosophy of science.
First, some of the arguments against hereditarianism presented there
were just too successful. The refutations looked so utterly simple, elegant,
and conclusive that it made me wonder whether competent scientists
could have really defended a position that was somanifestly indefensible.
Something was very odd about the whole situation.
There is indeed something about this. This book is a premier case of what Weinberg called mentioned with his comment “…a knowledge of philosophy does not seem to be of use to physicists – always with the exception that the work of some philosophers helps us to avoid the errors of other philosophers.”
Of course,Bouchardwould be justiﬁed in notworrying toomuch about
these global methodological criticisms if the only people who made a
fuss over them were philosophers of science. Even with this unfriendly
stance becoming a consensus in philosophy of science, scientists might
still remain unimpressed because many of them would probably be sym-
pathetic to JamesWatson’s claim: “I do not like to suffer at all from what
I call the German disease, an interest in philosophy” (Watson 1986: 19).
Source is: Watson, J. D. 1986, “Biology: A Necessarily Limitless Vista,” in S. Rose and L.
Appignanesi (eds.), Science and Beyond, Oxford, Blackwell.
At this point I am afraid I may lose some of my scientiﬁc readers.
Remembering Steven Weinberg’s statement that the insights of philoso-
phers have occasionally beneﬁted scientists, “but generally in a negative
fashion – by protecting them from the preconceptions of other philoso-
phers” (Weinberg 1993: 107), they might conclude that it is best just to
avoid reading any philosophy (including this book), and that in this way
they will neither contract preconceptions nor need protection fromthem.
But the problemis that the preconceptions discussed here do not originate
from a philosophical armchair. Scientists should be aware that to a great
extent these preconceptions come from some of their own. Philosophers
of science uncritically accepted these seductive but ultimately fallacious
arguments from scientists, repackaged them a little, and then fed them
back to the scientiﬁc community, which often took them very seriously.
Bad science was mistaken for good philosophy.
Sesardic clearly saw the same connection to Weinberg’s comments as i did. :)
It may seem surprising that Jones dismissed the views of the founder
of his own laboratory (Galton Laboratory, University College London)
in such amanner. But then again this should perhaps not be so surprising.
One can hardly be expected to study seriously the work of a man whom
one happens to call publicly “Victorian racist swine” – the way Jones
referred to Galton in an interview (Grove 1991). Also, in Jones’s book
Genetics for Beginners (Jones & Van Loon 1993: 169), Galton is pictured
in a Nazi uniform, with a swastika on his sleeve.
The virulent antinazism among these lefties is extraordinary. It targets everybody having the least to do with ideas the nazis also liked. It is a wonder no one attacks vegetarians or people who campaign against smoking for being nazis...
Arthur Jensen once said that “a heritability study may be regarded
as a Geiger counter with which one scans the territory in order to ﬁnd
the spot one can most proﬁtably begin to dig for ore” (Jensen 1972b:
243). That Jensen’s advice as to how to look upon heritability is merely
an application of a standard general procedure in causal reasoning is
conﬁrmed by the following observation from an introduction to causal
analysis: “the decomposition of statistical associations represents a ﬁrst
step. The results indicate which effects are important and which may be
safely ignored, that is, where we ought to start digging in order to uncover
the nature of the causal mechanisms producing association between our
variables” (Hellevik 1984: 149). High heritability of a trait (in a given
population) often signals that it may be worthwhile to dig further, in the
sense that an important geneticmechanismcontrolling differences in this
trait may thus be uncovered.8
Another great Jensen insight.
Citation is to: 1972b, “Discussion,” in L. Ehrman, G. S. Omenn, E. Caspari (eds.), Genetics,
Environment and Behavior, New York, Academic Press.
Second, even if a trait is shared by all organisms in a given population
it can still be heritable – if we take a broader perspective, and compare
that populationwith other populations. The critics of heritability are often
confused, and switch from one perspective to another without noticing it.
Consider the following “problem” for heritability:
the heritability of “walking on two legs” is zero.And yetwalking on two legs
is clearly a fundamental property of being human, and is one of the more
obvious biological differences between humans and other great apes such
as chimpanzees or gorillas. It obviously depends heavily on genes, despite
having a heritability of zero. (Bateson 2001b: 565; cf. Bateson 2001a: 150–
151; 2002: 2212)
When Bateson speaks about the differences between humans and other
great apes, the heritability of walking on two legs in that population
(consisting of humans, chimpanzees, and gorillas) is certainly not zero.
On the other hand, within the human species itself the heritability may
well be zero. So, if it is just made entirely clear which population is
being discussed, no puzzling element remains. In the narrower popula-
tion (humans), the question “Do genetic differences explain why some
people walk on two legs and some don’t?” has a negative answer because
there are no such genetic differences. In the broader population (humans,
chimpanzees, and gorillas) the question “Do genetic differences explain
why some organisms walk on two legs and some don’t?” has an afﬁrma-
tive answer. All this neatly accords with the logic of heritability, and cre-
ates no problem whatsoever. The critics of hereditarianism like to repeat
that heritability is a population-relative statistic, but when they raise this
kind of objection it seems that they themselves forget this important
Things like the number of finger is also heritable within populations. There are rare genetic mutations that cause supernumerary body parts: https://en.wikipedia.org/wiki/Supernumerary_body_part
However, these are very rare, so to spot them, one needs a huge sample size. Surely the heritability of having 6 fingers is high, while the heritability of having 4 fingers is low, but not zero. Of the people who have 4 fingers, most of the casesare probably caused by unique environment (i.e. accidents), but some are caused by genetics.
(4) It is often said that in individual cases it is meaningless to compare
the importance of interacting causes: “If an event is the result of the joint
operation of a number of causative chains and if these causes ‘interact’
in any generally accepted meaning of the word, it becomes conceptually
impossible to assign quantitative values to the causes of that individual
event” (Lewontin 1976a: 181).But this is in fact not true.Take, for example,
the rectangle with width 2 and length 1 (from Figure 2.3). Its area is 2,
which is considerably below the average area for all rectangles (around
100). Why is that particular rectangle smaller than most others? Is its
width or its length more responsible for that? Actually, this question is
not absurd at all. It has a straightforward and perfectlymeaningful answer.
The rectangleswith thatwidth (2) have on average the area that is identical
to the mean area for all rectangles (100.66), so the explanation why the
area of that particular rectangle deviates so much from the mean value
cannot be in its width. It is its below-average length that is responsible.
Even the usually cautious David Lykken slips here by condemning
the measurement of causal inﬂuences in the individual case as inherently
absurd: “It is meaningless to ask whether Isaac Newton’s genius was due
more to his genes or his environment, as meaningless as asking whether
the area of a rectangle is due more to its length or its width” (Lykken
1998a: 24). Contrary to what he says, however, it makes perfect sense to
inquire whether Newton’s extraordinary contributions were more due to
his above-average inherited intellectual ability or to his being exposed
to an above-average stimulating intellectual environment (or to some
particular combination of the two). The Nufﬁeld Council on Bioethics
makes a similar mistake in its report on genetics and human behavior:
“It is vital to understand that neither concept of heritability [broad or
narrow] allows us to conclude anything about the role of heredity in the
development of a characteristic in an individual” (Nufﬁeld 2002: 40). On
the contrary, if the broad heritability of a trait is high, this does tell us
that any individual’s phenotypic divergence from the mean is probably
more caused by a non-standard genetic inﬂuence than by a non-typical
environment. For a characteristically clear explanation of why gauging
the contributions of heredity and environment is not meaningless even in
an individual case, see Sober 1994: 190–192.
This is a good point. The reason not to talk about the causes of a particular level of g in some person is not that it is a meaningless question, it is that it is difficult to know the answer. But in some cases, it is clearly possible, cf. my number of fingers scenario above.
Nesardic mentions two studies that fysical attractiveness is not correlated with intelligence. That goes against what i believe(d?). He cites:
Feingold, A. 1992, “Good-looking People Are NotWhatWe Think,” Psycholog-
ical Bulletin 111: 304–341.
Langlois, J. H., Kalakanis, L., Rubenstein, A. J., Larson, A., Hallam, M., and
Smoot, M. 2000, “Maxims or Myths of Beauty? A Meta-Analytic and Theo-
retical Review,” Psychological Bulletin 126: 390–423.
But i apparently dont have access to the first one. But the second one i do have. In it one can read:
According to this maxim, there is no necessary correspondence
between external appearance and the behavior or personality of an
individual (Ammer, 1992). Two meta-analyses have examined the
relation between attractiveness and some behaviors and traits
(Feingold, 1992b2; L. A. Jackson, Hunter, & Hodge, 1995). Fein-
gold (1992b) reported significant relations between attractiveness
and measures of mental health, social anxiety, popularity, and
sexual activity but nonsignificant relations between attractiveness
and sociability, internal locus of control, freedom from self-
absorption and manipulativeness, and sexual permissiveness in
adults. Feingold also found a nonsignificant relation between at-
tractiveness and intelligence (r = .04) for adults, whereas L. A.
Jackson et al. found a significant relation for both adults (d = .24
overall, d = .02 once selected studies were removed) and for
children (d = .41).
These meta-analyses suggest that there may be a relation be-
twe^n behavior and attractiveness, but the inconsistencies in re-
sults call for additional attention. Moreover, the vast majority of
dependent variables analyzed by Feingold (1992b) and L. A.
Jackson et al. (1995) assessed traits as defined by psychometric
tests (e.g., IQ) rather than behavior as defined by observations of
behaviors in actual interactions. Thus, to fully understand the
relations among appearance, behaviors, and traits, it is important to
broaden the conception of behavior beyond that used by Feingold
and L. A. Jackson et al. If beauty is only skin-deep, then a
comprehensive meta-analysis of the literature should find no sig-
nificant differences between attractive and unattractive people in
their behaviors, traits, or self-views.
So, maybe. It seems difficult that g and pa (phy. attract.) is NOT associated purely by effect of mating choices, since females prefer males with high SES and males prefer females with have pa. Then comes the mutational load hypothesis, and the fact that smarter people presumably are better at taking care of their bodies, which increases pa. I find it very difficult indeed to believe that they arent correlated.
In my opinion, this kind of deliberate misrepresentation in attacks on
hereditarianism is less frequent than sheer ignorance. But why is it that a
number of peoplewho publicly attack “Jensenism” are so poorly informed
about Jensen’s real views? Given the magnitude of their distortions and
the ease with which these misinterpretations spread, one is alerted to
the possibility that at least some of these anti-hereditarians did not get
their information about hereditarianismﬁrst hand, fromprimary sources,
but only indirectly, from the texts of unsympathetic and sometimes quite
biased critics.8In this connection, it is interesting to note that several
authors who strongly disagree with Jensen (Longino 1990; Bowler 1989;
Allen 1990; Billings et al. 1992; McInerney 1996; Beckwith 1993; Kassim
2002) refer to his classic paper from 1969 by citing the volume of the
Harvard Educational Review incorrectly as “33” (instead of “39”). What
makes this mis-citation noteworthy is that the very same mistake is to
be found in Gould’s Mismeasure of Man (in both editions). Now the
fact that Gould’s idiosyncratic lapsus calami gets repeated in the later
sources is either an extremely unlikely coincidence or else it reveals that
these authors’ references to Jensen’s paper actually originate from their
contact with Gould’s text, not Jensen’s.
Gotcha. A nice illustrating case of the thing map makers used to use to prove plagiarism. https://en.wikipedia.org/wiki/Copyright_trap
Incidentally, in this case it ended up having another use! :)
In December 1986 our newly-born daughter was diagnosed to be suffering
from a genetically caused disease called Dystrophic Epidermolysis Bullosa
(EB). This is a disease in which the skin of the sufferer is lacking in certain
essential ﬁbers. As a result, any contact with her skin caused large blisters
to form, which subsequently burst leaving raw open skin that healed only
slowly and left terrible scarring. As EB is a genetically caused disease it
is incurable and the form that our daughter suffered from usually causes
death within the ﬁrst sixmonths of life . . .Our daughter died after a painful
and short life at the age of only 12 weeks. (quoted in Glover 2001: 431 –
from: Glover, J. 2001, “Future People, Disability, and Screening,” in J. Harris (ed.),
Bioethics, Oxford, Oxford University Press.
Nasty disease indeed. Only eugenics can avoid such atrocities.
On the contrary, empirical evidence suggests that for many important
psychological traits (particularly IQ), the environmental inﬂuences that
account for phenotypic variation among adults largely belong to the non-
shared variety. In particular, adoption studies of genetically unrelated
children raised in the same family show that for many traits the adult
phenotypic correlation among these children is very close to zero (Plomin
et al. 2001: 299–300). This very surprising but consistent result points
to the conclusion that we may have greatly overestimated the impact
of variation in shared environmental inﬂuences.6The fact that variation
within a normal range does not have much effect was dramatized in the
following way by neuroscientist Steve Petersen:
At a minimum, development really wants to happen. It takes very impov-
erished environments to interfere with development because the biological
system has evolved so that the environment alone stimulates development.
What does this mean? Don’t raise your children in a closet, starve them, or
hit them in the head with a frying pan. (Quoted in Bruer 1999: 188)
But if social reforms are mainly directed at eliminating precisely these
between-family inequalities (economic, social, and educational), and if
these differences are not so consequential as we thought, then egalitar-
ianism will ﬁnd a point of resistance not just in genes but also in the
non-heritable domain, i.e., in those uncontrollable and chaotically emerg-
ing environmental differences that by their very nature cannot be an easy
object for social manipulation.
All this shows that it is irresponsible to disregard constraints on mal-
leability and fan false hopes about what social or educational reforms can
do. As David Rowe said:
As social scientists, we should be wary of promisingmore than we are likely
to deliver. Physicists do not greet every new perpetual motion machine,
created by a basement inventor, with shouts of joy and claims of an endless
source of electrical or mechanical power; no, they know the laws of physics
would prevent it. (Rowe 1997: 154)
I will end this chapter with another qualiﬁcation.Although heritability
puts constraints on malleability it is, strictly speaking, incorrect to say
that the heritable part of phenotypic variance cannot be decreased by
environmentalmanipulation. It is true that if heritability is, say, 80 percent
then at most 20 percent of the variation can be eliminated by equalizing
environments. But if we consider redistributing environments, without
necessarily equalizing them, a larger portion of variance than 20 percent
can be removed.
Table 5.5 gives an illustration how this might work.
In this examplewith just two genotypes and two environments (equally
distributed in the population), themain effect of the genotype on the vari-
ation in the trait (say, IQ) is obviously stronger than the environmental
effect. Going from G2 to G1 increases IQ 20 points, while going from the
less favorable environment (E2) to the more favorable one (E1) leads
to an increase of only 10 points. Heritability is 80 percent, the genetic
variance being 100 and the environmental variance being 25. Now if we
expose everyone to the more favorable environment (E1) we will com-
pletely remove the environmental variance (25), and the variance in the
new population will be 100. The genetic variance survives environmental
But there is a way to make an incursion into the “genetic territory.”
Suppose we expose all those endowed with G1 to the less favorable
environment (E2) and those with G2 to the more favorable environment
(E1). In this way we would get rid of the highest and lowest score, and
we would be left only with scores of 95 and 105. In terms of variance, we
would have succeeded in eliminating 80 percent of variance by manipu-
lating environment, despite heritability being 80 percent.
How is this possible? The answer is in the formula for calculating vari-
ance in chapter 1 (see p. 21). One component of variance is genotype–
environment correlation, which can have a negative numerical value.
This is what has happened in our example. The phenotype-increasing
genotype was paired with the phenotype-decreasing environment, and
the phenotype-decreasing genotype was paired with the phenotype-
increasing environment. This move introduced the negative G–E corre-
lation and neutralized the main effects, bringing about a drastic drop in
The strategy calls to mind the famous Kurt Vonnegut story “Harrison
Bergeron,” where the society intervenes very early and suppresses the
mere expression of superior innate abilities by imposing artiﬁcial obsta-
cles on gifted individuals. Here is just one short passage from Vonnegut:
And George, while his intelligence was way above normal, had a little
mental-handicap radio in his ear – he was required by law to wear it at all
times. It was tuned to a government transmitter and, every twenty seconds
or so, the transmitter would send out some sharp noise to keep people like
George from taking unfair advantage of their brains. (Vonnegut 1970: 7)
We all get a chill from the nightmare world of “Harrison Bergeron.” But
in its milder forms the idea that if the less talented cannot be brought
up to the level of those better endowed, the latter should then be held
back in their development for the sake of equality, is not entirely with-
out adherents. In one of the most carefully argued sociological studies
on inequality there is an interesting proposal in that direction, about
how to reduce differences in cognitive abilities that are caused by genetic
Asociety committed to achieving full cognitive equality would, for example,
probably have to exclude genetically advantaged children from school. It
might also have to impose other handicaps on them, like denying them
access to books and television. Virtually no one thinks cognitive equality
worth such a price.Certainlywe do not.But if our goalwere simply to reduce
cognitive inequality to, say, half its present level, instead of eliminating it
entirely, the pricemight bemuch lower. (Jencks et al. 1972: 75–76 – emphasis
So although Jencks and his associates concede that excluding geneti-
cally advantaged children from school and denying them access to books
may be too drastic, they appear to think that the price of equality could
become acceptable if the goalwas lowered andmeasuresmademoremod-
erate. Are they suggesting that George keeps the little mental-handicap
radio in his ear but that the noise volume should be set only at half
I wonder if someone cud make a good video based on this... Oh that's right...
David Lykken had a good comment on this tendency of some
Darwinians (he had John Tooby and Leda Cosmides in mind) to pub-
licly dissociate themselves from behavior genetics, in the hope that this
move would make their own research less vulnerable to political criti-
cisms: “Are these folks just being politic, just claiming only the minimum
they need to pursue their own agenda while leaving the behavior geneti-
cists to contend with the main armies of political correctness?” (Lykken
There are some obvious, and other less obvious, consequences of polit-
ically inspired, vituperative attacks on a given hypothesisH.On the obvi-
ous side, many scientists who believe that H is true will be reluctant to
say so, many will publicly condemn it in order to eliminate suspicion that
they might support it, anonymous polls of scientists’ opinions will give
a different picture from the most vocal and most frequent public pro-
nouncements (Snyderman & Rothman 1988), it will be difﬁcult to get
funding for research on “sensitive” topics,19the whole research area will
be avoided by many because one could not be sure to end up with the
“right” conclusion,20texts insufﬁciently critical of “condemned” views
will not be accepted for publication,21etc.
On the less obvious side, a nasty campaign against H could have the
unintended effect of strengthening H epistemically, and making the criti-
cism of H look less convincing. Simply, if you happen to believe that H is
true and if you also know that opponents of H will be strongly tempted
to “play dirty,” that they will be eager to seize upon your smallest mis-
take, blow it out of all proportion, and label you with Dennett’s “good
epithets,” with a number of personal attacks thrown in for good measure,
then if you still want to advocate H, you will surely take extreme care to
present your argument in the strongest possible form. In the inhospitable
environment for your views, you will be aware that any major error is a
liability that you can hardly afford, because it willmore likely be regarded
as a reﬂection of your sinister political intentions than as a sign of your
fallibility. The last thing onewants in this situation is the disastrous combi-
nation of being politically denounced (say, as a “racist”) and being proved
to be seriously wrong about science. Therefore, in the attempt to make
themselves as little vulnerable as possible to attacks they can expect from
their uncharitable and strident critics, those who defendHwill tread very
cautiously and try to build a very solid case before committing themselves
publicly. As a result, the quality of their argument will tend to rise, if the
subject matter allows it.22
Interesting effects of the unpopularity of the views.
First of all, the issue about heritability is obviously a purely empirical
and factual one. So there is a strong case for denying that it can affect
our normative beliefs. But it is worth noting that the idea that a certain
heritability value could have political implications was not only criticized
for violatingHume’s law, but also for being politically dangerous. Bluntly,
if the high heritability of IQ differences between races really has racist
implications then it would seem that, after all, science could actually dis-
cover that racism is true.
The dangerwas clearly recognized byDavidHorowitz in his comments
on a statement on race that the Genetics Society of America (GSA)
wanted to issue in 1975. A committee preparing the statement took the
line that racism is best fought by demonstrating that racists’ belief in the
heritability of the black–white difference in IQ is disproved by science.
The proposed statement is weak morally, for the following reason: Racists
assert that blacks are genetically inferior in I.Q. and therefore need not
be treated as equals. The proposed statement disputes the premise of the
assertion, but not the logic of the conclusion. It does not perceive that the
premise, while it may be mistaken, is not by itself racist: it is the conclusion
drawn (wrongly) from it that is racist. Even if the premise were correct, the
conclusion would not be justiﬁed ...Yetthe proposed statement directs its
main ﬁre at the premise, and by so doing seems to accept the racist logic.
It places itself in a morally vulnerable position, for if, at some future time,
that the premise is correct, then the whole GSA case collapses, together
with its case for equal opportunity. (Quoted in Provine 1986: 880)
The same argument was made by others:
To rest the case for equal treatment of national or racial minorities on
the assertion that they do not differ from other men is implicitly to admit
that factual inequality would justify unequal treatment. (Hayek 1960:
But to fear research on genetic racial differences, or the possible existence
of a biological basis for differences in abilities, is, in a sense, to grant the
racist’s assumption: that if it should be established beyond reasonable doubt
that there are biological or genetically conditioned differences in mental
abilities among individuals or groups, then we are justiﬁed in oppressing
or exploiting those who are most limited in genetic endowment. This is, of
course, a complete non sequitur. (Jensen 1972a: 329)
If someone defends racial discrimination on the grounds of genetic differ-
ences between races, it is more prudent to attack the logic of his argument
than to accept the argument and deny any differences. The latter stance can
leave one in an extremely awkward position if such a difference is subse-
quently shown to exist. (Loehlin et al. 1975: 240)
But it is a dangerousmistake to premise themoral equality of human beings
on biological similarity because dissimilarity, once revealed, then becomes
an argument for moral inequality. (Edwards 2003: 801)
Good point indeed.