Massimo Pigliucci
The debate on the relative importance of nature (genetics) and nurture (environment) in determining human traits has been
prolonged and often acrimonious. Great minds have engaged in it over the
last 300 years, including philosophers John Locke and Thomas Hobbes, and
scientists Stephen Gould, Richard Lewontin, and Edward Wilson. The problem
is that most of the debate has proceeded on the basis of either a
simplistically dichotomous view of the question,
or with a dearth of relevant empirical evidence. The controversy has in fact
largely been solved when it comes to plants and non-human animals.
Unfortunately, most philosophers are not aware of such progress, which has taken
place within the arcane discipline of evolutionary ecology. On the other
hand, most scientists keep focusing on the special case of humans which -
while obviously the most interesting - has demonstrated to be the most
recalcitrant to empirical analysis and the most
open to philosophical inquiry.
While it is safe to say that humans have always investigated their own
nature and have certainly done so since the onset of Greek philosophy,
modern positions on the issue of nature/nurture may more or less clearly be traced
to the works of two English philosophers, John Locke and
Thomas Hobbes. Locke (1632-1704) was the founder of the school known as
empiricism, holding that knowledge can be gained only through the use of
the senses, as opposed to rationalism, according to which the mind can
derive knowledge solely on logical grounds. On the question of human
nature, Locke thought of the human mind as a tabula
rasa (literally, a blank slate). On it, experience writes and moulds the
individual throughout her life. Innate thoughts do not enter the picture,
according to this view. Interestingly, Locke's theory of human nature -
like the ones espoused by biologists such as Gould and Lewontin in modern
times - was tightly coupled with his social theories. Locke thought that people are
born
essentially good and with equal rights, and that an ideal society should
reflect these fundamental assumptions.
Thomas Hobbes (1588-1679) espoused a different notion. In his
books, and particularly in the famous
Leviathan he proposed that mechanical
processes control human actions, which are innately fearful and violent.
Consequently, the only hope for humans is to
submit entirely to an organised state (and religious authority), so to be forced to
live in a reasonable way. This is not a far cry from the right-wing politics
implicitly or explicitly adopted by some social
scientists involved in the modern debate, such as Arthur Jensen, R J
Herrnstein, and C Murray.
Of course, modern philosophers and scientists readily acknowledge that
human traits are in fact the result of both nature and nurture, but they are
usually also quick to add that one of these two components takes precedence. For
example, Gould, Lewontin and others think that the environment is the
major determinant of human nature. Their position could hardly be
summarised more concisely than by the title of one of Lewontin's books,
Not in Our Genes. If the causes of intelligence,
aggression, or whatever other aspect of our behaviour are not in our genes, they
must surely be found in the environment. On the other side of the divide,
Jensen, Herrnstein, Murray, Wilson (albeit in a category of his own) and many
others are convinced that genetics and natural selection have shaped the physical as
well as mental characteristics of all living beings, including humans. When
Murray suggests (in the title of one of his articles) that 'IQ will put you in your
place' he is assuming that IQ is written in stone in the DNA of each one of us.
Interestingly from the point of view of the sociology of science, the modern
debate on nature/nurture has often been accompanied by unpleasantness, as in
the case of E O Wilson being treated to a shower of ice cold water during a
conference by somebody who disagreed with his opinions on sociobiology, and
Gould being characterised as someone "whose ideas are so confused as to
be hardly worth bothering with, but as one who should not be publicly criticised
because he is at least on our side against the creationists" by an esteemed
British colleague. Clearly, the emotional stakes are much higher than in your
typical academic debate.
A solution to the nature/nurture problem has been at hand since the
beginning of the 20th century, with the
introduction in evolutionary biology of the concept of 'reaction norm'.
Simply put, a reaction norm is the set of all possible morphologies and
behaviours that a living organism with certain
genes can exhibit whenever exposed to a variety of environmental conditions.
Biologists have quickly come to realise that if one changes
either the genes or the environment, the resulting behaviour can
be dramatically different. The trick then, is not in partitioning causes between
nature and nurture, but in what is technically known as
'genotype-environment interactions', the way genes and
environments interact dialectically to generate an organism's appearance and
behaviour. This dialectical relationship produces different outcomes when
genes or environments change, and the precise shape of a reaction norm can
only be found empirically.
The concept of reaction norms has dealt a fatal blow to a staple of nature/nurture
discussions throughout the last century: the much vaunted (or criticised, depending
on the author) measure of 'heritability' of a trait. When we hear (or read in
newspapers, textbooks, and even technical papers) that the heritability
of, say, intelligence (or homosexuality, or what have you) is 70% we tend to
conclude that that is a major reason to believe that genes have a lot to do
with determining the trait in question. Yet, biologists working on plants and
animals have shown over and again that heritability changes dramatically (sometimes
between 0 and 100%!) if one studies a different population of the same species,
or even the same population raised in a different environment. Furthermore,
we now understand that genetic influences do not imply rigid determinism: studies
of reaction norms in a variety of organisms have shown that the genes only set
the limits of what an organism can do, but that within such limits the degree
of 'plasticity' of the organism - its ability to respond to different environmental
challenges - can be very high.
Perhaps one of the best examples of the true relationship between nature and
nurture is found in classic experiments performed by Cooper and Zubek in the
late 1950s. They compared 'intelligence', as measured by the ability to avoid
mistakes in running through a maze, in two genetically distinct lines of rats.
One line had been selected for high performance in the maze ('bright' rats),
the other for particularly low performance ('dull' rats). When reared under
a standard environment, comparable to the one in which the selection process
occurred, the two lines showed a highly significant difference in their abilities
(i.e., a high 'heritability' of the trait). Cooper and Zubek, however, also
reared individuals of the two lines in two other environments: a situation in
which the cage was entirely devoid of visual and tactile stimuli ('poor' environment),
and one in which the developing animals were exposed to brightly coloured walls
and toys ('enriched' environment). The results were simply stunning: under the
poor conditions, the bright rats performed as badly as the dull ones, while
under the enriched environment the dull rats did as well as the bright ones
(and the heritability of intelligence plummeted to zero in both cases)! The
inescapable conclusion is that maze-running ability in rats is very plastic,
and that different genes may lead to similar behaviours depending on environmental
conditions.
So, why is there still such an acrimonious debate among philosophers
and scientists about nature and nurture in humans? Because for both technical
and ethical reasons we simply cannot perform on ourselves the sort of
clear-cut experiments that Cooper and Zubek carried out on rats. Not only do
humans have a very long life span and encounter very complex environments during
their typical lifetime, but it is obviously unacceptable to experimentally breed
human beings and control their environment for the sole purpose of scientific
or philosophical investigation (or for any purpose, most would argue).
Unfortunately, this means that we are left with no sensible answer to a crucial
question. Our educational policies, for example, may be more or less fruitful
depending on the precise shape of human reaction norms. The same can be said
for policies concerned with curbing crime, or for a host of other fundamental
and difficult decisions we have to make in our societies. Regrettably, it should
be clear by now that this is where the line must be drawn and that the only
honest answer a philosopher or a scientist can give is 'I do not know'. There
is of course a strong temptation to keep guessing anyway. Sociologists, psychologists,
and philosophers of science have long pointed out that personal egos, social
prestige, financial rewards (personal or for research) all play into this tendency
in a remarkably complex fashion. The fact remains, however, that there are -
and always will be - some questions that science cannot answer (either at the
moment, or in general). As Richard Lewontin himself put it in a similar context:
"I must say that the best lesson our readers can learn is to give up the
childish notion that everything that is interesting about nature can be understood.
... It might be interesting to know how cognition (whatever that is) arose and
spread and changed, but we cannot know. Tough luck."
Learning to live with this conclusion actually empowers the scientist,
because by not pretending to be omniscient she can enjoy the fruits of the most
effective tool humans have devised so far to understand the world around us.
Ironically, this leaves ample space to philosophers in crucial areas such as public
policy and its ethical consequences, since when science must be silent on a given
subject matter we are obliged to focus more on how the world ought to be rather
than on how it currently is.
Massimo Pigliucci (www.rationallyspeaking.org)
is Associate Professor of ecology & evolutionary biology at the University
of Tennessee.
Suggested reading
Not in Our Genes, R C Lewontin, S Rose & L J Kamin (Pantheon)
Phenotypic Plasticity: Beyond Nature and Nurture, M Pigliucci (Johns
Hopkins University Press)
On Human Nature, E O Wilson (Harvard University Press)
