Steven Pinker
Why nature & nurture
won’t go away
When Richard Mulcaster referred in
1581 to “that treasure . . . bestowed on
them by nature, to be bettered in them
by nurture,” he gave the world a eupho-
nious name for an opposition that has
been debated ever since. People’s beliefs
about the relative importance of heredi-
ty and environment affect their opinions
on an astonishing range of topics. Do
adolescents engage in violence because
of the way their parents treated them
early in life? Are people inherently ag-
gressive and sel½sh, calling for a market
economy and a strong police, or could
they become peaceable and cooperative,
allowing the state to wither and a spon-
taneous socialism to blossom? Is there a
universal aesthetic that allows great art
to transcend time and place, or are peo-
ple’s tastes determined by their era and
cultura? With so much seemingly at
stake in so many ½elds, it is no surprise
Steven Pinker, Johnstone Family Professor in the
department of psychology at Harvard University,
conducts research on language and cognition. A
Fellow of the American Academy since 1998, él
is the author of six books, including “How the
Mind Works” (1997), “The Language Instinct”
(2000), and “The Blank Slate” (2002).
© 2004 por la Academia Americana de las Artes
& Ciencias
that debates over nature and nurture
evoke more rancor than just about any
issue in the world of ideas.
During much of the twentieth century,
a common position in this debate was to
deny that human nature existed at all–
to aver, with José Ortega y Gasset, eso
“Man has no nature; what he has is his-
tory.” The doctrine that the mind is a
blank slate was not only a cornerstone
of behaviorism in psychology and social
constructionism in the social sciences,
but also extended widely into main-
stream intellectual life.1
Part of the blank slate’s appeal came
from the realization that many differ-
ences among people in different classes
and ethnic groups that formerly were
1 Carl N. Degler, In Search of Human Nature:
The Decline and Revival of Darwinism in American
Social Thought (Nueva York: Universidad de Oxford
Prensa, 1991); Steven Pinker, The Blank Slate:
The Modern Denial of Human Nature (Nueva York:
Viking, 2002); Robin Fox, The Search for Soci-
ety: Quest for a Biosocial Science and Morality
(New Brunswick, NUEVA JERSEY.: Rutgers University
Prensa, 1989); Eric M. Gander, On Our Minds:
How Evolutionary Psychology Is Reshaping the
Nature-Versus-Nurture Debate (baltimore:
Johns Hopkins University Press, 2003); John
Tooby and Leda Cosmides, “The Psychological
Foundations of Culture,” in The Adapted Mind:
Evolutionary Psychology and the Generation of
Cultura, ed. Jerome H. Barkow, Leda Cosmides,
and John Tooby (Nueva York: Universidad de Oxford
Prensa, 1992).
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Steven
Pinker
en
humano
naturaleza
thought to reflect innate disparities in
talent or temperament could vanish
through immigration, social mobility,
and cultural change. But another part
of its appeal was political and moral. Si
nothing in the mind is innate, then dif-
ferences among races, sexes, and classes
can never be innate, making the blank
slate the ultimate safeguard against rac-
ismo, sexism, and class prejudice. También,
the doctrine ruled out the possibility
that ignoble traits such as greed, preju-
dice, and aggression spring from human
naturaleza, and thus held out the hope of un-
limited social progress.
Though human nature has been debat-
ed for as long as people have pondered
their condition, it was inevitable that the
debate would be transformed by the re-
cent efflorescence of the sciences of
mente, cerebro, genes, and evolution. Uno
outcome has been to make the doctrine
of the blank slate untenable.2 No one,
por supuesto, can deny the importance of
learning and culture in all aspects of
human life. But cognitive science has
shown that there must be complex in-
nate mechanisms for learning and cul-
ture to be possible in the ½rst place. Evo-
lutionary psychology has documented
hundreds of universals that cut across
the world’s cultures, and has shown that
many psychological traits (such as our
taste for fatty foods, social status, y
risky sexual liaisons) are better adapted
to the evolutionary demands of an an-
cestral environment than to the actual
demands of the current environment.
Developmental psychology has shown
2 Pinker, The Blank Slate; Gary F. marco, El
Birth of the Mind: How a Tiny Number of Genes
Creates the Complexities of Human Thought (Nuevo
york: Libros Básicos, 2004); Matt Ridley, Naturaleza
Via Nurture: Genes, Experience, and What Makes
Us Human (Londres: Fourth Estate, 2003);
Robert Plomin, miguel j.. Owen, and Peter
McGuf½n, “The Genetic Basis of Complex Hu-
man Behaviors," Ciencia 264 (1994): 1733–1739.
that infants have a precocious grasp
of objects, intentions, numbers, faces,
herramientas, and language. Behavioral genetics
has shown that temperament emerges
early in life and remains fairly constant
throughout the life span, that much of
the variation among people within a cul-
ture comes from differences in genes,
and that in some cases particular genes
can be tied to aspects of cognition, lan-
guage, and personality. Neurociencia
has shown that the genome contains a
rich tool kit of growth factors, axon
guidance molecules, and cell adhesion
molecules that help structure the brain
during development, as well as mecha-
nisms of plasticity that make learning
posible.
These discoveries not only have shown
that the innate organization of the brain
cannot be ignored, but have also helped
to reframe our very conception of nature
y nutrir.
Nature and nurture, por supuesto, are not
alternatives. Learning itself must be
accomplished by innate circuitry, y
what is innate is not a set of rigid in-
structions for behavior but rather pro-
grams that take in information from the
senses and give rise to new thoughts and
comportamiento. Language is a paradigm case:
though particular languages such as Jap-
anese and Yoruba are not innate, the ca-
pacity to acquire languages is a uniquely
human talent. And once acquired, a lan-
guage is not a ½xed list of sentences, pero
a combinatorial algorithm allowing an
in½nite number of new thoughts to be
expressed.
Además, because the mind is a com-
plex system composed of many inter-
acting parts, it makes no sense to ask
whether humans are sel½sh or generous
or nasty or noble across the board. Rath-
es, they are driven by competing motives
elicited in different circumstances. Y
6
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if genes affect behavior, it is not by tug-
ging on the muscles directly, but by their
intricate effects on the circuitry of a
growing brain.
Finalmente, questions of what people in-
nately have in common must be distin-
guished from questions of how races,
sexes, or individuals innately differ. Evo-
lutionary biology gives reasons to be-
lieve that there are systematic species-
wide universals, circumscribed ways in
which the sexes differ, random quantita-
tive variation among individuals, y
few if any differences among races and
ethnic groups.3
This reframing of human nature also
offers a rational way to address the polit-
ical and moral fears of human nature.4
Political equality, Por ejemplo, does not
hinge on a dogma that people are innate-
ly indistinguishable, but on a commit-
ment to treat them as individuals in
spheres such as education and the crim-
inal justice system. Social progress does
not require that the mind be free of ig-
noble motives, only that it have other
motives (such as the emotion of empa-
thy and cognitive faculties that can
learn from history) that can counteract
a ellos.
By now most scientists reject both the
nineteenth-century doctrine that biolo-
gy is destiny and the twentieth-century
doctrine that the mind is a blank slate.
Al mismo tiempo, many express a dis-
comfort with any attempt to character-
ize the innate organization that the mind
does have (even in service of a better
understanding of learning). En cambio,
3 John Tooby and Leda Cosmides, “On the
Universality of Human Nature and the Unique-
ness of the Individual: The Role of Genetics
and Adaptation,” Journal of Personality 58
(1990): 17–67.
4 Pinker, The Blank Slate.
there is a widespread desire that the
whole issue would somehow just go
away. A common position on nature and
nurture among contemporary scientists
can be summarized as follows:
Why nature
& nurture
won’t go
away
No one today believes that the mind is a
blank slate; to refute such a belief is to tip
over a straw man. All behavior is the prod-
uct of an inextricable interaction between
heredity and environment during develop-
mento, so the answer to all nature-nurture
questions is “some of each.” If people only
recognized this truism, the political re-
criminations could be avoided. Además,
modern biology has made the very dis-
tinction between nature and nurture ob-
solete. Since a given set of genes can have
different effects in different environ-
mentos, there may always be an environ-
ment in which a supposed effect of the
genes can be reversed or canceled; allá-
fore the genes impose no signi½cant con-
straints on behavior. En efecto, genes are
expressed in response to environmental
signals, so it is meaningless to try to dis-
tinguish genes and environments; doing
so only gets in the way of productive re-
buscar.
The attitude is often marked by words
like ‘interactionist,’ ‘developmentalist,'
‘dialectic,’ ‘constructivist,’ and ‘epige-
netic,’ and is typically accompanied
by a diagram with the labels ‘genes,'
‘behavior,’ ‘prenatal environment,’ ‘bio-
chemical environment,’ ‘family environ-
mento,’ ‘school environment,’ ‘cultural
ambiente,’ and ‘socioeconomic envi-
ambiente,’ and arrows pointing from
every label to every other label.
This doctrine, which I will call holistic
interactionism, has considerable appeal.
It is based on some unexceptionable
puntos, such as that nature and nurture
are not mutually exclusive, that genes
cannot cause behavior directly, y eso
the direction of causation can go both
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Steven
Pinker
en
humano
naturaleza
maneras (Por ejemplo, school can make you
smarter, and smart people are most en-
gaged by schooling). It has a veneer of
moderation, of conceptual sophistica-
ción, and of biological up-to-dateness.
And as John Tooby and Leda Cosmides
have put it, it promises “safe conduct
across the politicized mine½eld of mod-
ern academic life.”5
But the very things that make holistic
interactionism so appealing should also
make us wary of it. No matter how com-
plex an interaction is, it can be under-
stood only by identifying the compo-
nents and how they interact. Holistic
interactionism can stand in the way of
such understanding by dismissing any
attempt to disentangle heredity and en-
vironment as uncouth. As Dan Dennett
has satirized the attitude: “Surely ‘every-
one knows’ that the nature-nurture de-
bate was resolved long ago, and neither
side wins since everything-is-a-mixture-
of-both-and-it’s-all-very-complicated,
so let’s think of something else, bien?"
In the following pages I will analyze
the tenets of holistic interactionism and
show that they are not as reasonable or
as obvious as they ½rst appear.
No one believes in the extreme nurture
position that the mind is a blank slate.”
Whether or not this is true among scien-
tistas, it is far from true in the rest of in-
tellectual life. The prominent anthropol-
ogist Ashley Montagu, summing up a
common understanding in twentieth-
century social science, wrote in 1973 eso
“With the exception of the instinctoid
reactions in infants to sudden with-
drawals of support and to sudden loud
noises, the human being is entirely in-
stinctless . . . .Man is man because he has
no instincts, because everything he is
and has become he has learned . . . de
“
5 Tooby and Cosmides, “The Psychological
Foundations of Culture.”
8
La caída de Dédalo 2004
his culture, from the man-made part
of the environment, from other human
beings.”6 Postmodernism and social
constructionism, which dominate many
of the humanities, vigorously assert that
human emotions, conceptual categories,
and patterns of behavior (such as those
characterizing men and women or ho-
mosexuals and heterosexuals) are social
constructions. Even many humanists
who are not postmodernists insist bio-
logy can provide no insight into human
mind and behavior. The critic Louis
Menand, por ejemplo, recently wrote
that “every aspect of life has a biological
foundation in exactly the same sense,
which is that unless it was biologically
possible it wouldn’t exist. Después, it’s
up for grabs.”7
Nor is a belief in the blank slate absent
among prominent scientists. Ricardo
Lewontin, Leon Kamin, and Steven
Rose, in a book entitled Not in Our Genes,
asserted that “the only sensible thing to
say about human nature is that it is ‘in’
that nature to construct its own his-
tory.”8 Stephen Jay Gould wrote that
the “brain [es] capable of a full range of
behaviors and predisposed to none.”9
Anne Fausto-Sterling expressed a com-
mon view of the origin of sex differ-
ences: “The key biological fact is that
boys and girls have different genitalia,
6 Ashley Montagu, ed., Man and Aggression, 2nd
ed. (Nueva York: prensa de la Universidad de Oxford, 1973).
7 Louis Menand, “What Comes Naturally,” The
New Yorker, 25 Noviembre 2002.
8 R. C. Lewontin, Steven Rose, and Leon J.
Kamin, Not in Our Genes: Biología, Ideology, y
Human Nature (Nueva York: Pantheon Books,
1984).
9 Stephen Jay Gould, “Biological Potential vs.
Biological Determinism,” in Ever Since Darwin:
Reflections in Natural History, ed. Stephen Jay
Gould (Nueva York: norton, 1977).
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and it is this biological difference that
leads adults to interact differently with
different babies whom we conveniently
color-code in pink or blue to make it
unnecessary to go peering into their dia-
pers for information about gender.”10
These opinions spill into research and
política. Much of the scienti½c consensus
on parenting, Por ejemplo, is based on
studies that ½nd a correlation between
the behavior of parents and the behavior
of children. Parents who spank have
children who are more violent; authori-
tative parents (neither too permissive
nor too punitive) have well-behaved
niños; parents who talk more to their
children have children with better lan-
guage skills. Virtually everyone con-
cludes that the behavior of the parent
causes the outcomes in the child. El
possibility that the correlations may
arise from shared genes is usually not
even mentioned, let alone tested.11
Other examples abound. Many scien-
ti½c organizations have endorsed the
slogan “violence is learned behavior,"
and even biologically oriented scientists
tend to treat violence as a public health
problem like malnutrition or infectious
enfermedad. Unmentioned is the possibility
that the strategic use of violence could
have been selected for in human evolu-
ción, as it has been in the evolution of
other primate species.12 Gender differ-
ences in the professions, such as that the
proportion of mechanical engineers who
10 Anne Fausto-Sterling, Myths of Gender: Bio-
logical Theories About Women and Men (Nuevo
york: Libros Básicos, 1985).
11 David C.. Rowe, The Limits of Family Influ-
ence: Genes, Experience, and Behavior (Nueva York:
Guilford Press, 1994); Judith Rich Harris, El
Nurture Assumption: Why Children Turn Out the
Way They Do (Nueva York: Free Press, 1998).
12 Martin Daly and Margo Wilson, Homicide
(Nueva York: A. de Gruyter, 1988).
“
are women is less than 50 por ciento, son
attributed entirely to prejudice and hid-
den barriers. The possibility that, en
promedio, women might be less interested
than men in people-free pursuits is simi-
larly unspeakable.13 The point is not that
we know that evolution or genetics are
relevant to explaining these phenomena,
but that the very possibility is often
treated as an unmentionable taboo rath-
er than as a testable hypothesis.
For every question about nature and
nurture, the correct answer is ‘some of
each.’” Not true. Why do people in Eng-
land speak English and people in Japan
speak Japanese? The ‘reasonable com-
promise’ would be that the people in
England have genes that make it easier
to learn English and the people in Japan
have genes that make it easier to learn
Japanese, but that both groups must be
exposed to a language to acquire it at all.
This compromise is, por supuesto, not rea-
sonable but false, as we see when chil-
dren exposed to a given language acquire
it equally quickly regardless of their ra-
cial ancestry. Though people may be ge-
netically predisposed to learn language,
they are not genetically predisposed,
even in part, to learn a particular lan-
guage; the explanation for why people in
different countries speak differently is
100 percent environmental.
Sometimes the opposite extreme turns
out to be correct. Psychiatrists common-
ly used to blame psychopathology on
mothers. Autism was caused by ‘refrig-
erator mothers’ who did not emotionally
engage their children, schizophrenia by
mothers who put their children in dou-
ble binds. Today we know that autism
13 David Lubinski and Camilla Benbow, “Gen-
der Differences in Abilities and Preferences
Among the Gifted: Implications for the Math-
Science Pipeline,” Current Directions in Psycho-
logical Science 1 (1992): 61–66.
Why nature
& nurture
won’t go
away
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La caída de Dédalo 2004
9
Steven
Pinker
en
humano
naturaleza
and schizophrenia are highly heritable,
and though they are not completely de-
termined by genes, the other plausible
contributors (such as toxins, pathogens,
and developmental accidents) tener
nothing to do with how parents treat
their children. Mothers don’t deserve
some of the blame if their children have
these disorders, as a nature-nurture
compromise would imply. They de-
serve none of it.
“
“
If people recognized that every aspect
of behavior involves a combination
of nature and nurture, the political dis-
putes would evaporate.” Certainly
many psychologists strive for an in-
nocuous middle ground. Consider this
quotation:
If the reader is now convinced that either
the genetic or environmental explanation
has won out to the exclusion of the other,
we have not done a suf½ciently good job of
presenting one side or the other. It seems
highly likely to us that both genes and en-
vironment have something to do with this
issue.
This appears to be a reasonable interac-
tionist compromise that could not pos-
sibly incite controversy. But in fact it
comes from one of the most incendiary
books of the 1990s, Herrnstein and
Murray’s The Bell Curve. In this passage,
Herrnstein and Murray summed up their
argument that the difference in average
iq scores between American blacks and
American whites has both genetic and
environmental causes. A “some-of-
each” position did not protect them
from accusations of racism and compar-
isons to Nazis. Ni, por supuesto, did it
establish their position was correct: como
with the language a person speaks, el
black-white average iq gap could be 100
percent environmental. The point is that
in this and many other domains of psy-
10
La caída de Dédalo 2004
chology, the possibility that heredity has
any explanatory role at all is still inflam-
matory.
The effects of genes depend crucially
on the environment, so heredity imposes
no constraints on behavior.” Two exam-
ples are commonly used to illustrate the
punto: different strains of corn may grow
to different heights when equally irrigat-
ed, but a plant from the taller strain
might end up shorter if it is deprived of
agua; and children with phenylke-
tonuria (pku), an inherited disorder
resulting in retardation, can end up nor-
mal if given a diet low in the amino acid
phenylalanine.
There is an aspect of this statement
that indeed is worth stressing. Genes do
not determine behavior like the roll of a
player piano. Environmental interven-
tions–from education and psychothera-
py to historical changes in attitudes and
political systems–can signi½cantly af-
fect human affairs. Also worth stressing
is that genes and environments may in-
teract in the statistician’s sense, a saber,
that the effects of one can be exposed,
multiplied, or reversed by the effects of
the other, rather than merely summed
with them. Two recent studies have
identi½ed single genes that are respec-
tively associated with violence and de-
presion, but have also shown that their
effects are manifested only with particu-
lar histories of stressful experience.14
Al mismo tiempo, it is misleading to
invoke environment dependence to deny
14 Avshalom Caspi, Karen Sugden, Terrie E.
Mof½tt, Alan Taylor, and Ian W. Craig, “Influ-
ence of Life Stress on Depression: Moderation
by a Polymorphism in the 5-htt Gene," Ciencia
(2003): 386–389; Avshalom Caspi, Joseph
McClay, Terrie E. Mof½tt, Jonathan Mill, Judy
Martín, and Ian W. Craig, “Evidence that the
Cycle of Violence in Maltreated Children De-
pends on Genotype," Ciencia 297 (2002): 727–
742.
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the importance of understanding the
effects of genes. To begin with, it is sim-
ply not true that any gene can have any
effect in some environment, con el
implication that we can always design an
environment to produce whatever out-
come we value. Though some genetic
effects may be nulli½ed in certain envi-
ambientes, not all of them are: estudios
that measure both genetic and environ-
mental similarity (such as adoption
designs, where correlations with adop-
tive and biological parents can be com-
pared) show numerous main effects of
personality, intelligence, and behavior
across a range of environmental varia-
ción. This is true even for the poster
child of environmental mitigation, pku.
Though a low-phenylalanine diet does
prevent severe mental retardation, él
does not, as is ubiquitously claimed, ren-
der the person ‘perfectly normal.’ pku
children have mean iqs in the 80s and
90s and are impaired in tasks that de-
pend on the prefrontal region of the
cerebral cortex.15
También, the mere existence of some envi-
ronment that can reverse the expected
effects of genes is almost meaningless.
Just because extreme environments can
disrupt a trait does not mean that the
ordinary range of environments will
modulate that trait, nor does it mean
that the environment can explain the
nature of the trait. Though unirrigated
corn plants may shrivel, they won’t grow
arbitrarily high when given ever-increas-
ing amounts of water. Nor does their
dependence on water explain why they
bear ears of corn as opposed to to-
15 Adele Diamond, “A Model System for Study-
ing the Role of Dopamine in the Prefrontal Cor-
tex During Early Development in Humans: Ear-
ly and Continuously Treated Phenylketonuria,"
in Handbook of Developmental Cognitive Neuro-
ciencia, ed. Charles A. Nelson and Monica
Luciana (Cambridge, Masa.: con prensa, 2001).
matoes or pinecones. Chinese foot-bind-
ing is an environmental manipulation
that can radically affect the shape of the
foot, but it would be misleading to deny
that the anatomy of the human foot is
in an important sense speci½ed by the
genes, or to attribute it in equal parts to
heredity and environment. The point is
not merely rhetorical. The fact that kit-
tens’ visual systems show abnormalities
when their eyelids are sewn shut in a
critical period of development does not
imply (as was believed in the 1990s) eso
playing Mozart to babies or hanging col-
orful mobiles in their cribs will increase
their intelligence.16
En breve, the existence of environmen-
tal mitigations doesn’t make the effects
of the genes inconsequential. Sobre el
contrary, the genes specify what kinds
of environmental manipulations will
have what kinds of effects and with what
costos. This is true at every level, desde el
expression of the genes themselves (como
I will discuss below) to large-scale at-
tempts at social change. The totalitarian
Marxist states of the twentieth century
often succeeded at modifying behavior,
but at the cost of massive coercion, ow-
ing in part to mistaken assumptions
about how easily human motives
would respond to changed circum-
stances.17
En cambio, many kinds of genuine
social progress succeeded by engaging
speci½c aspects of human nature. Peter
Singer observes that normal humans in
16 Juan T.. Bruer, The Myth of the First Three
Años: A New Understanding of Early Brain Devel-
opment and Lifelong Learning (Nueva York: Free
Prensa, 1999).
17 Jonathan Glover, Humanity: A Moral His-
tory of the Twentieth Century (Londres: j. Cabo,
1999); Peter Singer, A Darwinian Left: Política,
Evolución, and Cooperation (Londres: Weidenfeld
& Nicolson, 1999).
Why nature
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La caída de Dédalo 2004
11
Steven
Pinker
en
humano
naturaleza
all societies manifest a sense of sympa-
thy: an ability to treat the interests of
others as comparable to their own.18
Desafortunadamente, the size of the moral cir-
cle in which sympathy is extended is a
free parameter. By default, people sym-
pathize only with members of their own
familia, clan, or village, and treat anyone
outside this circle as less than human.
But under certain circumstances the cir-
cle can expand to other clans, tribes,
races, or even species. An important way
to understand moral progress, entonces, is to
specify the triggers that prompt people
to expand or contract their moral circles.
It has been argued that the circle may be
expanded to include people to whom
one is bound by networks of reciprocal
trade and interdependence,19 y eso
it may be contracted to exclude people
who are seen in degrading circum-
stances.20 In each case, an understand-
ing of nonobvious aspects of human na-
ture reveals possible levers for humane
social change.
Genes are affected by their environ-
“
mentos, and learning requires the expres-
sion of genes, so the nature-nurture dis-
tinction is meaningless.” It is, por supuesto,
in the very nature of genes that they are
not turned on all the time but are ex-
pressed and regulated by a variety of sig-
nal. These signals in turn may be trig-
gered by a variety of inputs, incluido
18 Peter Singer, The Expanding Circle: Ethics
and Sociobiology (Nueva York: Farrar, Straus &
Giroux, 1981).
19 Robert Wright, NonZero: The Logic of Human
Destiny (Nueva York: Pantheon Books, 2000).
20 guantero, Humanity; Philip G. Zimbardo,
Christina Maslach, and Craig Haney, “Reflec-
tions on the Stanford Prison Experiment: generación-
esis, Transformations, Consequences,” in Obe-
dience to Authority: Current Perspectives on the
Milgram Paradigm, ed. Thomas Blass (Mahwah,
NUEVA JERSEY.: Lawrence Erlbaum Associates, 2000).
temperatura, hormones, the molecular
ambiente, and neural activity.21
Among the environmentally sensitive
gene-expression effects are those that
make learning itself possible. Skills and
memories are stored as physical changes
at the synapse, and these changes re-
quire the expression of genes in response
to patterns of neural activity.
These causal chains do not, sin embargo,
render the nature-nurture distinction
obsolete. What they do is force us to
rethink the casual equation of ‘nature’
with genes and of ‘nurture’ with every-
thing beyond the genes. Biologists have
noted that the word ‘gene’ accumulated
several meanings during the twentieth
century.22 These include a unit of hered-
idad, a speci½cation of a part, a cause of a
enfermedad, a template for protein synthesis,
a trigger of development, and a target of
natural selection.
It is misleading, entonces, to equate the
prescienti½c concept of human nature
with ‘the genes’ and leave it at that,
with the implication that environment-
dependent gene activity proves that hu-
man nature is inde½nitely modi½able by
experiencia. Human nature is related to
genes in terms of units of heredity, de-
velopment, and evolution, particularly
those units that exert a systematic and
lasting effect on the wiring and chem-
istry of the brain. This is distinct from
the most common use of the term ‘gene’
in molecular biology, a saber, in refer-
ence to stretches of dna that code for a
21 marco, The Birth of the Mind; Ridley, Naturaleza
Via Nurture.
22 Ridley, Nature Via Nurture; Richard Dawk-
ins, The Extended Phenotype: The Gene as the Unit
of Selection (San Francisco: W.. h. Hombre libre &
Compañía, 1982); Seymour Benzer, “The Ele-
mentary Units of Heredity,” in A Symposium on
the Chemical Basis of Heredity, ed. William D.
McElroy and Bentley Glass (baltimore: Johns
Hopkins Press, 1957).
12
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protein. Some aspects of human nature
may be speci½ed in information carriers
other than protein templates, incluido
the cytoplasm, noncoding regions of the
genome that affect gene expression,
properties of genes other than their se-
quence (such as how they are imprint-
ed), and cross-generationally consistent
aspects of the maternal environment
that the genome has been shaped by
natural selection to expect. En cambio,
many genes direct the synthesis of pro-
teins necessary for everyday metabolic
función (such as wound repair, diges-
ción, and memory formation) sin
embodying the traditional notion of
human nature.
The various concepts of ‘environ-
mento,’ too, have to be re½ned. In most
nature-nurture debates, ‘environment’
refers in practice to aspects of the world
that make up the perceptual input to the
person and over which other humans
have some control. This encompasses,
Por ejemplo, parental rewards and pun-
ishments, early enrichment, role mod-
los, education, laws, peer influence, cul-
tura, and social attitudes. It is misleading
to blur ‘environment’ in the sense of the
psychologically salient environment of
the person with ‘environment’ in the
sense of the chemical milieu of a chro-
mosome or cell, especially when that
milieu itself consists of the products of
other genes and thus corresponds more
closely to the traditional notion of he-
redity. There are still other senses of
‘environment,’ such as nutrition and
environmental toxins; the point is not
that one sense is primary, but that one
should seek to distinguish each sense
and characterize its effects precisely.
A ½nal reason that the environment
dependence of the genes does not vitiate
the concept of human nature is that an
environment can affect the organism in
very different ways. Some aspects of the
perceptual environment are instructive
in the sense that their effects are pre-
dictable by the information contained in
the input. Given a child who is equipped
to learn words in the ½rst place, the con-
tent of her vocabulary is predictable
from the words spoken to her. Given an
adult equipped to understand contin-
gencies, the spot where he will park his
car will depend on where the No Parking
signs are posted. But other aspects of the
ambiente, a saber, those that affect
the genes directly rather than affecting
the brain through the senses, trigger ge-
netically speci½ed if-then contingencies
that do not preserve information in the
trigger itself. Such contingencies are per-
vasive in biological development, dónde
many genes produce transcription fac-
tors and other molecules that set off cas-
cades of expression of other genes. A
good example is the Pax6 gene, cual
produces a protein that triggers the ex-
pression of twenty-½ve hundred other
genes, resulting in the formation of the
ojo. Highly speci½c genetic responses
can also occur when the organism inter-
acts with its social environment, como
when a change of social status in a male
cichlid ½sh triggers the expression of
more than ½fty genes, which in turn al-
ter its size, aggressiveness, and stress
response.23 These are reminders both
that innate organization cannot be
equated with a lack of sensitivity to the
ambiente, and that responses to the
environment are often not speci½ed by
the stimulus but by the nature of the
organism.
“
Framing problems in terms of nature
and nurture prevents us from under-
standing human development and mak-
23 Russell Fernald, “How Does Behavior
Change the Brain? Multiple Methods to An-
swer Old Questions,” Integrative Comparative
Biología 43 (2003): 771–779.
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La caída de Dédalo 2004
13
Steven
Pinker
en
humano
naturaleza
ing new discoveries.” On the contrary,
some of the most provocative discover-
ies in twentieth-century psychology
would have been impossible if there
had not been a concerted effort to dis-
tinguish nature and nurture in human
desarrollo.
For many decades psychologists have
looked for the causes of individual dif-
ferences in cognitive ability (as mea-
sured by iq tests, school and job per-
rendimiento, and indices of brain activity)
and in personality (as measured by ques-
tionnaires, ratings, psychiatric evalua-
ciones, and tallies of behavior such as di-
vorce and crime). The conventional
wisdom has been that such traits are
strongly influenced by parenting prac-
tices and role models. But recall that this
belief is based on flawed correlational
studies that compare parents and chil-
dren but forget to control for genetic
relatedness.
Behavioral geneticists have remedied
those flaws with studies of twins and
adoptees, and have discovered that in
fact virtually all behavioral traits are
partly (though never completely) heri-
table.24 That is, some of the variation
among individual people within a cul-
ture must be attributed to differences in
their genes. The conclusion follows from
repeated discoveries that identical twins
reared apart (who share their genes but
not their family environment) are highly
similar; that ordinary identical twins
(who share their environment and all
their genes) are more similar than frater-
nal twins (who share their environment
24 Plomin, Owen, and McGuf½n, “The Genet-
ic Basis of Complex Human Behaviors”; eric
Turkheimer, “Three Laws of Behavior Genetics
and What They Mean,” Current Directions in
ciencia psicológica 9 (5) (2000): 160–164;
Tomas J.. Bouchard, Jr., “Genetic and Environ-
mental Influences on Intelligence and Special
Mental Abilities,” Human Biology 70 (1998):
257–259.
but only half their variable genes); y
that biological siblings (who share their
environment and half their variable
genes) are more similar than adoptive
siblings (who share their environment
but none of their variable genes). Estos
studies have been replicated in large
samples from several countries, and have
ruled out the most common alternative
explanations (such as selective place-
ment of identical twins in similar adop-
tive homes). Por supuesto, concrete behav-
ioral traits that patently depend on con-
tent provided by the home or culture–
which language one speaks, which reli-
gion one practices, which political party
one supports–are not heritable at all.
But traits that reflect the underlying tal-
ents and temperaments–how pro½cient
with language a person is, how religious,
how liberal or conservative–are partially
heritable. So genes play a role in making
people different from their neighbors,
and their environments play an equally
important role.
At this point it is tempting to con-
clude that people are shaped both by
genes and by family upbringing: cómo
their parents treated them and what
kind of home they grew up in. Pero el
conclusion is unwarranted. conductual
genetics allows one to distinguish two
very different ways in which people’s
environments might affect them. El
shared environment is what impinges
on a person and his or her siblings alike:
their parents, home life, and neighbor-
hood. The unique environment is every-
thing else: anything that happens to a
person that does not necessarily happen
to that person’s siblings.
Extraordinariamente, most studies of intelli-
gence, personality, and behavior turn up
few or no effects of the shared environ-
ment–often to the surprise of the re-
searchers themselves, who thought it
was obvious that nongenetic variation
14
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had to come from the family.25 First,
adult siblings are about equally correlat-
ed whether they grew up together or
apart. Segundo, adoptive siblings, cuando
tested as adults, are generally no more
similar than two people from the same
culture chosen at random. And third,
identical twins are no more similar than
one would expect from the effects of
their shared genes. Setting aside cases of
extreme neglect or abuse, whatever ex-
periences siblings share by growing up
in the same home in a given culture
make little or no difference to the kind
of people they turn into. Speci½c skills
like reading and playing a musical in-
strument, por supuesto, can be imparted by
padres, and parents obviously affect
their children’s happiness and the quali-
ty of family life. But they don’t seem to
determine their children’s intellects,
tastes, and personalities in the long run.
The discovery that the shared family
environment has little to no lasting ef-
fect on personality and intelligence
comes as a shock to the traditional wis-
dom that “as the twig is bent, so grows
the branch.” It casts doubt on forms of
psychotherapy that seek the roots of an
adult’s dysfunction in the family envi-
ambiente, on theories that attribute ado-
lescents’ alcoholism, smoking, and de-
linquency to how they were treated in
early childhood, and on the philosophy
of parenting experts that parental micro-
management is the key to a well-adjust-
ed child. The ½ndings are so counterin-
tuitive that one might doubt the behav-
ioral genetic research that led to them,
but they are corroborated by other
25 Rowe, The Limits of Family Influence;
harris, The Nurture Assumption; Turkheimer,
“Three Laws of Behavior Genetics”; Roberto
Plomin and Denise Daniels, “Why Are Children
in the Same Family So Different from One An-
otro?”Ciencias del comportamiento y del cerebro 10 (1987):
1–60.
data.26 Children of immigrants end up
with the language, acento, and mores of
their peers, not of their parents. Wide
variations in child-rearing practices–
day-care versus stay-at-home mothers,
single versus multiple caregivers, mismo-
sex versus different-sex parents–have
little lasting effect when other variables
are controlled. Birth order and only-
child status also have few effects on be-
havior outside the home.27 And an ex-
tensive study testing the possibility that
children might be shaped by unique as-
pects of how their parents treat them (como
opposed to ways in which parents treat
all their children alike) showed that dif-
ferences in parenting within a family are
efectos, not causes, of differences among
the children.28
The discovery of the limits of family
influence is not just a debunking exer-
cise, but opens up important new ques-
ciones. The ½nding that much of the vari-
ance in personality, intelligence, y se-
havior comes neither from the genes nor
from the family environment raises the
question of where it does come from.
Judith Rich Harris has argued that the
phenomena known as socialization
–acquiring the skills and values needed
to thrive in a given culture–take place
in the peer group rather than the family.
26 harris, The Nurture Assumption.
27 Ibídem.; Judith Rich Harris, “Context-Speci½c
Aprendiendo, Personality, and Birth Order,” Current
Directions in Psychological Science 9 (2000): 174–
177; Jeremy Freese, Brian Powell, and Lala Carr
Steelman, “Rebel Without a Cause or Effect:
Birth Order and Social Attitudes,” American
Sociological Review 64 (1999): 207–231.
28 David Reiss, Jenae M. Neiderhiser, mi. Mavis
Hetherington, and Robert Plomin, The Relation-
ship Code: Deciphering Genetic and Social Influ-
ences on Adolescent Development (Cambridge,
Masa.: Prensa de la Universidad de Harvard, 2000).
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La caída de Dédalo 2004
15
Steven
Pinker
en
humano
naturaleza
Though children are not prewired with
cultural skills, they also are not indis-
criminately shaped by their environ-
mento. One aspect of human nature
directs children to ½gure out what is
valued in their peer group–the social
milieu in which they will eventually
compete for status and mates–rather
than to surrender to their parents’ at-
tempts to shape them.
Acknowledging this feature of human
nature in turn raises questions about
how the relevant environments, en esto
case peer cultures, arise and perpetuate
ellos mismos. Does a peer culture trickle
down from adult culture? Does it origi-
nate from high-status individuals or
groups and then proliferate along peer
redes? Does it emerge haphazardly
in different forms, some of which en-
trench themselves when they reach a
tipping point of popularity?
A revised understanding of how chil-
dren socialize themselves has practical
implications as well. Teen alcoholism
and smoking might be better addressed
by understanding how these activities
become status symbols in peer groups
than by urging parents to talk more to
their adolescents (as current advertise-
mentos, sponsored by beer and tobacco
companies, insist). A major determinant
of success in school might be whether
classes ½ssion into peer groups with
different status criteria, En particular
whether success in school is treated as
admirable or as a sign of selling out.29
The development of personality–a
person’s emotional and behavioral idio-
syncrasies–poses a set of puzzles dis-
tinct from those raised by the process of
socialization. Identical twins growing up
in the same home share their genes, su
padres, their siblings, their peer groups,
and their culture. Though they are high-
29 harris, The Nurture Assumption.
16
La caída de Dédalo 2004
ly similar, they are far from indistin-
guishable: by most measures, correla-
tions in their traits are in the neighbor-
hood of 0.5. Peer influence cannot
explain the differences, because identi-
cal twins largely share their peer groups.
En cambio, the unexplained variance in per-
sonality throws a spotlight on the role of
sheer chance in development: aleatorio
differences in prenatal blood supply
and exposure to toxins, pathogens, hor-
mones, and antibodies; random differ-
ences in the growth or adhesion of axons
in the developing brain; random events
in experience; random differences in
how a stochastically functioning brain
reacts to the same events in experience.
Both popular and scienti½c explanations
of behavior, accustomed to invoking
genes, padres, and society, seldom
acknowledge the enormous role that
unpredictable factors must play in the
development of an individual.
If chance in development is to explain
the less-than-perfect similarity of identi-
cal twins, it also highlights an interesting
property of development in general. Uno
can imagine a developmental process in
which millions of small chance events
cancel one another out, leaving no dif-
ference in the resulting organism. Uno
can imagine a different process in which
a chance event could disrupt develop-
ment entirely. Neither of these happens
to identical twins. Their differences are
detectable both in psychological testing
and in everyday life, yet both are (usual-
ly) healthy human beings. The develop-
ment of organisms must use complex
feedback loops rather than prespeci½ed
blueprints. Random events can divert
the trajectories of growth, but the trajec-
tories are con½ned within an envelope of
functioning designs for the species.
These profound questions are not
about nature versus nurture. Ellos son
about nurture versus nurture: acerca de
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qué, precisamente, are the nongenetic
causes of personality and intelligence.
But the puzzles would never have come
to light if researchers had not ½rst taken
measures to factor out the influence of
naturaleza, by showing that correlations be-
tween parents and children cannot glibly
be attributed to parenting but might be
attributable to shared genes. That was
the ½rst step that led them to measure
the possible effects of parenting empiri-
cally, rather than simply assuming that
parents had to be all-powerful. El
everything-affects-everything diagram
turns out to be not sophisticated but
dogmatic. The arrows emanating from
‘parents,’ ‘siblings,’ and ‘the home’ are
testable hypotheses, not obvious tru-
isms, and the tests might surprise us
both by the arrows that shouldn’t be
there and by the labels and arrows we
may have forgotten.
The human brain has been called the
most complex object in the known uni-
verso. No doubt hypotheses that pit na-
ture against nurture as a dichotomy or
that correlate genes or environment
with behavior without looking at the in-
tervening brain will turn out to be sim-
plistic or wrong. But that complexity
does not mean we should fuzz up the
issues by saying that it’s all just too com-
plicated to think about, or that some
hypotheses should be treated a priori as
obviously true, obviously false, or too
dangerous to mention. As with inflation,
cancer, and global warming, we have no
choice but to try to disentangle the mul-
tiple causes.30
30 The writing of this paper was supported by
nih Grant hd-18381. I thank Helena Cronin,
Jonathan Haidt, Judith Rich Harris, y mate
Ridley for comments on an earlier draft.
Why nature
& nurture
won’t go
away
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La caída de Dédalo 2004