Jerome Kagan - Specialized Research AI at MIT

Jerome Kagan

The uniquely human in human nature

We can describe an object by listing its

features, as manufacturers do when they
provide a description of the parts of an
assembly-required crib; or by compar-
ing the object with one from a related
category, as parents do when they tell
their child that a zebra has stripes but
a horse does not. Most answers to the
question What is human nature? adopt
this second strategy when they nominate
the features that are either uniquely hu-
man or that are quantitative enhance-
ments on the properties of apes. I adopt

Jerome Kagan, a Fellow of the American Acade-
my since 1968 and chair of the Academy’s Com-
mittee on Publications and Public Relations, is
Daniel and Amy Starch Research Professor of
Psychology and former codirector of the Mind-
Brain-Behavior Initiative at Harvard University.
His research has addressed cognitive and emotion-
al development in children, with a special concern
for the role of the temperament in personality and
in understanding of the moral emotions. His most
recent book is “The Long Shadow of Tempera-
ment” (2004, written with Nancy Snidman).
Some ideas in this essay were drawn from a
forthcoming book, “A Young Mind in a Grow-
ing Brain” (written with Norbert Herschkowitz),
to be published next year.

such a comparative posture here and
describe seven psychological features
that are either restricted to or enhanced
in humans compared with our closest
relatives, the chimpanzees. Four are of
the ½rst category; the other three are
quantitative enhancements on chim-
panzee talents.

The distinct psychological qualities
of Homo sapiens are traceable to genetic
changes that permitted the founder cells
that become mature neurons to continue
to divide for an extra seventy-two hours.
Those additional cell divisions signi½-
cantly expanded the size of the human
cortex and contributed to the novel cog-
nitive, emotional, and motor skills that
emerge in humans over the course of
development.

However, some scientists remain inex-
plicably resistant to acknowledging that
any human quality is unique. When a
linguist claims that only humans have a
language with a grammar, a scientist will
reply that chimpanzees can be taught to
communicate with pieces of plastic. Jane
Goodall’s discovery that chimpanzees
use tools is celebrated because of its im-
plication that my use of a hammer to
hang my granddaughter’s recent artwork
on the wall is not fundamentally differ-
ent from a chimpanzee’s use of a twig to
ferret out termites. But the modern syn-

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Jerome
Kagan
on
human
nature

thesis in evolutionary biology does not
demand that every feature that belongs
to a particular family, genus, or species
has a homologous structure or function
in a related taxon.

Human and chimpanzee infants are

very similar to each other at the end of
the ½rst year. Both species locomote,
attend to unexpected or unfamiliar
events, and remember where an attrac-
tive object disappeared ten seconds ear-
lier. However, only twenty-four months
later, children have diverged permanent-
ly from their primate relatives because
maturational changes in the brain, in-
formed by experience, have permitted
the development of four uniquely hu-
man qualities. Children now infer varied
thoughts and feelings in others; use a
symbolic language with a grammar and
semantic categories for events that share
no physical features (for example: milk,
mother, and pink rabbits); understand
the concepts of good, bad, right, and
wrong, as well as experience a distinct
feeling when they contemplate or vio-
late an acquired prohibition; and be-
come consciously aware of some of
their intentions and feelings.1 I now
consider these four functions in more
detail.
1
The ability to infer the intentions, evalu-
ations, and feelings of others is evident
in an experiment where an adult hides
a toy under one of three covers behind
a barrier so that the child cannot see
where the toy is hidden. If, after remov-
ing the barrier, the adult directs her gaze
toward the toy’s location, two-year-olds,
but not one-year-olds, reach in the direc-

1 Jerome Kagan, The Second Year: The Emergence
of Self-Awareness (Cambridge, Mass.: Harvard
University Press, 1981).

tion of the adult’s gaze, indicating that
they assume the adult is looking at the
place where the toy rests. Such an in-
ferential ability is necessary for feeling
empathy with another. The two-year-old
who hears her mother scream in pain as
she catches her hand in a closing door
associates the scream with her memory
of past painful experiences, relates the
latter to the perception of distress in
the parent, and then announces with
her face and posture an empathic con-
cern for the victim. The child may even
run to her mother to offer a reassuring
embrace.

Although chimpanzees occasionally
track the gaze of another animal and ap-
pear to be able to infer that another can-
not see a piece of food hidden behind a
barrier, they do not understand that an-
other animal intends to share informa-
tion with them. Chimpanzees watching
a human adult perform simple actions
with a tool and objects focus their at-
tention on the objects rather than the
adult’s movements, because they fail to
infer that the person’s manipulations are
guided by an intention and a plan. No
pair of juvenile or adult chimps would
throw a small ball back and forth be-
tween them, because they are incapable
of appreciating that a partner intends to
engage in a reciprocally cooperative act
that has no implication for the gaining
of food or protection. Every two-year-
old child makes this simple assumption
automatically.

Humans feel uncertain when they in-

fer that another person might harbor
undesirable thoughts about them; chim-
panzees feel uncertain when they antici-
pate actions another animal might direct
at them. Doubt over whether another
will regard one as dumb, disloyal, or
deviant is qualitatively different from
doubt over whether another animal is
about to attack, dominate, or seize a

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The
uniquely
human in
human
nature

piece of fruit. A major event in human
evolution was the replacement of a vig-
ilant posture toward the potentially
threatening actions of another with
worry over the possible opinions of
another.
2
Although apes can be taught, with con-
siderable training, to treat pieces of plas-
tic as symbolic of objects, no chimpan-
zee comes close to the linguistic ability
of the average four-year-old who uses
language to represent abstract ideas.
One four-year-old, on noting that her
dresses were closely packed in her closet,
said to her mother, “My dresses are
friends.” The capacity to infer another’s
intention is exploited in the acquisition
of language, for when a parent speaks to
the child, the latter assumes the former
intends to communicate information
about the world. The acquisition of
semantic networks permits the inven-
tion of symbolic similarities among very
different physical events. Chimpanzees
and children can detect a crescent shape
shared by a slice of lemon and a new
moon, but only the latter detect the sym-
bolic features shared by a cookie, a smil-
ing face, a pink sunset, and a curved geo-
metric ½gure because of words that link
these events in a semantic network for
the concept ‘pleasing.’

The psychologist Ellen Markman has
suggested that children begin the learn-
ing of language with the advantage of
three biologically based biases.2 The ½rst
is the assumption that when an adult
speaks a word in the presence of an ob-
ject, the word probably applies to the
whole object. Two-year-olds hearing

2 Ellen Markman, “Constraints on Word
Learning,” in Megan R. Gunnar and Michael
P. Maratsos, eds., Modularity and Constraints in
Language and Cognition (Hillsdale, N.J.: L. Erl-
baum Associates, 1992), 59–102.

their parent say “spider” as the latter
points to an unfamiliar dark object on
top of a sandpile assume that the word
refers to the entire insect and not to its
location, odd-looking appendages, or the
sandpile. (The philosopher Willard van
Orman Quine, who failed to acknowl-
edge this bias, wondered what a visitor
to a foreign land would conclude about
the meaning of an unfamiliar word
when he heard a native say “Gavagai”
as a rabbit sprinted across the grass.)

A second bias is the assumption that
a word probably refers to a category of
similar objects, rather than to the specif-
ic entity that is perceived. A child who
hears the parent say “Look at the squir-
rel” assumes that all objects with similar
features have the same name. The third
bias tempts young children to assume
initially that each object has only one
name. If three-year-olds hear an unfa-
miliar word (for example, ‘goox’) in the
presence of both a cup and an unfamiliar
object, they assume that the word must
apply to the latter object. A student
baby-sitter reported that our three-year-
old daughter was puzzled when the stu-
dent announced that she was planning
to be a mother and a doctor. Fortunately,
this third bias is tamed before children
enter school.

The universal emergence of language
in children with a healthy central nerv-
ous system exploits cognitive talents
that serve other purposes. These talents
include selective attention to adults,
detection of low-level correlations be-
tween events, sensitivity to physically
distinct sounds (for example, the sound
‘s’ at the end of a word to represent the
English plural), the assumption that
adults speaking to them are trying to
communicate information, and, ½nally,
the ability to detect and invent similari-
ties between the concepts that name
events as different as a fly and a tree.

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Jerome
Kagan
on
human
nature

Detection of consistency, as well as
inconsistency, in the semantic networks
that comprise a belief system is a salient
human quality. It is not obvious why de-
tection of inconsistency among one’s
semantic networks evokes a subtle but
nonetheless uncomfortable feeling.
Members of each language community
have learned the transitional probabili-
ties between words in narratives, as well
as the differential strengths of associa-
tions between and among words. Most
Americans expect the word ‘ago’ to fol-
low ‘years,’ and respond with ‘moon’
when asked to report the ½rst word they
think of when they hear the word ‘sun.’
A violation of either probability elicits a
distinct brain response and a feeling that
psychologists call cognitive dissonance.
This may be one reason why magicians
in ancient Greece used unfamiliar com-
binations of words in their incantations.
Use of the counterfactual in sentences
(“If the sun were to die tomorrow . . . ”)
mutes the dissonance and allows the
person to consider the possible conse-
quences of a low-probability event. It is
unlikely that chimpanzees imagine im-
probable events, although this claim re-
quires more proof.

Some might argue that the uncertainty
created by cognitive dissonance is an in-
herent property of the brain, analogous
to the fact that dissonant musical chords
produce an evoked potential in the
cochlear nucleus that is distinctly differ-
ent from that produced by consonant
chords. The dissonant melodies provoke
four-month-old infants to turn away,
often with a facial expression of disgust.
A second view is that the uncertainty is
built on early experiences of seeing that
an object cannot be simultaneously big
and small, up and down, light and dark,
or inside and outside a container. How-
ever, this account does not explain why
statements that do not contain anto-

nyms also create dissonance (for exam-
ple, “dogs are vegetables”). No current
explanation of this phenomenon is satis-
fying.

Nonetheless, poets take advantage
of this property of mind, for they often
use semantic inconsistency to surprise
readers in order to achieve an aesthetic
effect. Consider, for instance, the follow-
ing word pairs from the ½rst ½ve lines
of T. S. Eliot’s poem “The Waste Land”:
April-cruellest; Lilacs-dead; Memory-
desire; Dull-spring; Winter-warm. The
½nal verse of Dylan Thomas’s poem “If
I Were Tickled by the Rub of Love” con-
tains three perfect examples: Fear-apple;
Bad-Spring; Thistle-kiss.
3
Although Enlightenment commentators
nominated language as the feature that
best separated humans from animals,
the ancients thought that morality en-
joyed that function. The author(s) of
the tree of knowledge allegory in Gene-
sis understood, long before Plato and
Hume, that humans are distinguished by
an obsessive concern with good and bad
events and spend most of each day try-
ing to gather evidence that af½rms their
membership in the former category.
Every human society has semantic
concepts for the ideas of good, bad,
right, and wrong, and most humans ex-
perience a changed feeling when they
contemplate, or commit, a behavior that
violates a standard they regard as proper.
The anthropologist George Murdock
once composed a list of sixty-seven fea-
tures present in all cultures. Almost half
of the features are ethical rules describ-
ing activities that ought or ought not
to be displayed. “Know thyself” and
“Nothing in excess,” statements in-
scribed at the oracle in Delphi, are ex-
amples of two of the moral imperatives
included in that list.

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The
uniquely
human in
human
nature

The argument that moral standards
derive from sensory pleasure and the re-
duction of pain cannot explain why peo-
ple become angry when they see strang-
ers violate standards they believe are
morally proper. Such acts provoke ob-
servers to question the correctness of
their moral commitments. Because these
beliefs are central to each day’s deci-
sions, their violation, even by a stranger,
threatens the rational foundation of
each observer’s conduct. No ape would
show signs of anger upon seeing an un-
familiar animal take food from another,
as long as the victim was not a genetic
relative.

The primatologist Frans de Waal tries

to persuade readers with anecdotes of
chimpanzee behavior that these animals
possess rules and punish those who
break them.3 De Waal concedes, howev-
er, that he has never seen a guilty chim-
panzee. It is unlikely he will ever see one,
because guilt requires an agent to know
that a voluntary act that could have been
suppressed has hurt another. Guilt re-
quires the ability to reflect on a past ac-
tion that injured another in some way, to
realize that the behavior could have been
inhibited, and to appreciate that the self
was the cause of the ethical violation.
Guilt is not a possible state for chim-
panzees.

The extensive semantic networks for
the concepts of ethical propriety and im-
propriety have three branches. One re-
fers to the actions that violate communi-
ty standards for appropriate behaviors
that presumably apply to everyone. A
second entails the ethical obligations
linked to the particular social categories
to which one’s self belongs (for example,
most grandmothers believe they should
be affectionate with their grandchil-
dren). The third branch, which emerges

3 Frans de Waal, Good Natured (Cambridge,
Mass.: Harvard University Press, 1996).

by the seventh or eighth year, motivates
humans to attain ideal forms. The ability
to imagine the perfect parent, scientist,
or friend requires a brain/mind that can
generate cognitive representations of
what might be possible. Apes and hu-
mans create representations of experi-
ences that are psychological averages
of actual encounters. But only humans
possess conceptions of the most perfect
form for a particular class of experi-
ences.

Although an understanding of right
and wrong and a feeling of uncertainty
over violating moral standards are pres-
ent by the third year, humans require
an additional ten to twelve years before
they will feel morally obligated to hold a
consistent set of ethical beliefs. Adoles-
cents, but not ½ve-year-olds, wonder
about their place in society, make plans
for the future, and integrate memories of
childhood with their current experience
in order to understand their life circum-
stances.
4
An acute consciousness of one’s feelings,
intentions, and properties is a fourth
unique quality of Homo sapiens. The
term ‘consciousness’ probably does not
name a unitary phenomenon, because
the speci½c quality of consciousness,
and its biological foundations, varies
with the nature of the mental activity.
Moment-to-moment changes in sensa-
tion that originate, for example, in the
taste of chocolate or the smell of per-
fume, and which need not involve lan-
guage, comprise one category. A special
area of prefrontal cortex that receives
sensory information represents one of
the material bases for this form of con-
sciousness, which we might call sensory
awareness.

A second form, awareness of proper-
ties, is a consciousness of one’s physical

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Jerome
Kagan
on
human
nature

features, beliefs, talents, personality
traits, moods, and social categories. The
awareness of being politically conserva-
tive, Methodist, and shy, for example,
requires activation of a part of the cor-
tex different from the circuits activated
by the awareness of a toothache. The
awareness that one is about to imple-
ment or suppress an action, which re-
quires still another brain circuit, is a
third form of consciousness. The neuro-
scientist Michael Gazzaniga believes
that a fourth form is the interpretation
of one’s feelings, perceptions, and ac-
tions through the construction of a co-
herent explanation of the state of con-
sciousness at the moment.

Some might argue that even though
these phenomena recruit different brain
circuits, they share a common feature
and therefore constitute a single pro-
cess. For example, a common set of hand
muscles is used to pick up a cup, brush
one’s teeth, or sign a check. Those who
believe in multiple forms of conscious-
ness would claim that because the pro½le
of brain activity and the subjective state
are distinct for each form, it is reason-
able to reject the assertion of a single
state of awareness. A consciousness of
the smell of smoke from a bedroom, of
a well-constructed argument, and of
the ½nger movements while playing the
piano are easily differentiated, both psy-
chologically and neurobiologically.

Further, the four forms of conscious-
ness may not have evolved at the same
time, for they do not emerge simultane-
ously in the individual. The earliest signs
of awareness of sensory events appear in
the ½rst year, before children are aware
of their symbolic features. It is not until
the second birthday that children smile
following completion of a dif½cult task
because they are aware of having at-
tained a goal, or lower their head in em-
barrassment when they cannot repro-

duce an adult action because they are
aware of having violated an adult expec-
tation. By the third birthday, children
describe what they are doing as they are
doing it because they are aware of their
intentions. And by the fourth birthday,
children regularly integrate the present
moment with their recollections of the
past and begin to impose the interpreta-
tions that Gazzaniga regards as an essen-
tial function of consciousness. Chim-
panzees might be aware of the taste of
particular fruits, and of the patterns of
light and shadow on the forest floor,
but it is unlikely they possess forms of
consciousness beyond the sensory. No
primatologist claims that apes reflect on
their age or wonder whether they will be
able to control the number of offspring
they will bring into the world.

The combination of semantic net-
works, an appreciation of right and
wrong, and conscious awareness of
properties of self leads inevitably to
categorizations of self that have strong
evaluative connotations. All adolescents
have learned semantic categories for
their gender, family name, and develop-
mental stage. Some add categories for
their clan, caste, religion, or region of
residence. More important, all are aware
of the behaviors appropriate for each of
these categories, and feel obligated to
maintain semantic consistency between
the features that de½ne the category, on
the one hand, and their thoughts and
behaviors, on the other. Adolescent
boys assume they should not wear girls’
clothes even if they have never done so,
have never been punished for such ac-
tions, nor have seen others criticized for
this behavior.

The assignment of self to class, ethnic,

national, and religious semantic cate-
gories has a profound influence on hu-
man emotions and behaviors. The writer
Michael MacDonald, born to a very poor

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The
uniquely
human in
human
nature

Boston family, remembers in a memoir
feeling proud of his Irish heritage when
his neighborhood resisted the judicial
decision to bus school children from
South Boston in the service of racial
integration. Humans can feel shame,
anxiety, or guilt if they think the com-
munity regards their family or any one
of their social categories as possessing
undesirable qualities. Many adults born
to Holocaust victims after 1945 carry a
burden of guilt or shame because of the
horrible atrocities experienced by their
parents. Many Americans felt a vicarious
shame for their national category when
they learned that American soldiers
were destroying the homes of innocent
Vietnamese.

The moral power of the self’s social
categories derives from the fact that the
child’s initial words are for observable
objects and events that have stable, es-
sential features. All objects called dogs
should bark and have fur; if they do not,
they are less than ideal dogs. Thus, when
children learn the terms for social cate-
gories like ‘girl,’ ‘boy,’ ‘Palestinian,’ or
‘Hispanic,’ they are prepared to believe
that these words, too, name a set of in-
herent psychological characteristics be-
longing to those in the category. Chil-
dren feel obligated to be loyal to the fea-
tures that de½ne the categories to which
they belong, and experience as much
cognitive dissonance if they stray from
those obligations as they would if they
saw an animal without fur that never
barked that was called a dog.

There are two types of social cate-
gories. Nominal categories, like gender
and stage of development, have relative-
ly ½xed features and appear early in de-
velopment. The ethical obligations at-
tached to these categories are not linked
to a speci½c other person and apply
across a broad array of contexts. The
second class of categories, acquired lat-

er, is de½ned by a particular social rela-
tionship between the self and another,
and includes the categories ‘friend,’
‘son,’ ‘daughter,’ ‘parent,’ ‘brother,’ and
‘sister.’ The ethical obligations linked to
these categories (usually loyalty, affec-
tion, honesty, and nurture) are attached
to speci½c others. The social category
‘friend,’ for example, applies to a speci½c
peer; hence, the obligations appropriate
for one friend might differ from those
appropriate for a different playmate. If a
friend happens to be cautious much of
the time, a child will feel obligated to
dominate the dyad; but the same child
may feel obliged to display deference to a
different friend who likes to be dominat-
ing.

Egalitarian societies try to award

greater signi½cance to the ethical direc-
tives tied to relational categories because
nominal ones imply differential status
and privilege. In order to derive pride
from a relational category, the individual
must implement the obligatory actions.
Egalitarian societies want their members
to feel virtuous because of their achieve-
ments or benevolent behaviors toward
others, not because they are members
of a particular group.

Americans complain about the obvi-
ous increase in materialism in our socie-
ty over the last half century. I suspect
that one important reason for the obses-
sion with accumulating clothes, cars,
homes, and winter cruises is that the hu-
man moral sense requires knowing that
some actions, and the symbolic prizes
they may lead to, imply that one is more
virtuous than another. Meanwhile, our
society’s desire to honor an egalitarian
ethos requires a denial of special privi-
lege to some categories that, in earlier
centuries, were more automatic sources
of virtue. Nineteenth-century white
Christian males whose fathers and
grandfathers attended college could

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Jerome
Kagan
on
human
nature

reassure themselves of their virtue by
simply reminding themselves of their
membership in this quartet of cate-
gories. The ethic of egalitarianism, on
the other hand, denies the prize of self-
satisfaction to any nominal category.
Every American must attain his or her
daily supply of virtue through personal
accomplishments, through perfecting a
talent, establishing a relationship, or
acquiring status or wealth. Because gain-
ing wealth, which most believe requires
effort and talent, seems to be a possibili-
ty for most citizens, it has become a pri-
mary symbol of virtue in contemporary
America. If a person cannot use gender,
skin color, ethnicity, family pedigree, or
occupation as a sign of worth, one of the
few remaining symbols is the accumula-
tion of property. No goal as glittering as
equality of dignity can be had without a
price.

Humans, in addition, display three

abilities that are quantitative enhance-
ments on chimpanzee talents, rather
than unique characteristics: humans
have a greater capacity to recall the past
and imagine the future, to seek novelty,
and to separate survival from inclusive
½tness.
5
Although apes can remember the past
and anticipate the future, humans ex-
pand both timelines to distant horizons.
Sixty-year-olds can recall their ½rst day
at school and can anticipate what might
occur two decades in the future when se-
nility is imminent. There is no evidence,
at least at present, that chimps sitting
quietly on the forest floor can anticipate
or recollect events several decades be-
fore or after the current moment.

Human adults who hear a seven digit
telephone number for the ½rst time can
hold it in awareness for as long as thirty

seconds in a process called working
memory. Chimps possess a working
memory, but its capacity is more limited.
The ability to manipulate several ideas
simultaneously on the stage of working
memory often leads to the detection of
novel relations among mental structures
or to an insight that reorganizes current
understanding. Semantic networks were
reshuffled when nineteenth-century
readers of Darwin’s Origin of Species be-
gan to entertain the notion that humans
probably evolved from a primate ances-
tor. The automatic reshuffling of old as-
sumptions permits one to avoid the un-
easiness that follows recognition of a
logical inconsistency in related beliefs.
6
The human attraction to new experi-
ences also expands a primate compe-
tence. Chimpanzees seek new fruits to
eat, new places to rest, and new mating
partners, but humans spend more time
than any other animal looking for unfa-
miliar events that can be comprehended
and new skills that can be mastered. No
other primate would risk survival, and a
curtailment of reproductive ½tness, by
climbing Mount Everest, parachuting
from a plane, or swimming across the
English Channel.

The desire for and the ability to adapt
to novel conditions is due, in part, to the
structure of the human brain. The amyg-
dala, a small, almond-shaped structure
with several neuronal clusters tucked in-
side the temporal lobe, is an important
site responsive to unexpected or unfa-
miliar events. When such experiences
occur, excited neurons in the central nu-
cleus of the amygdala send messages to
bodily targets that lead to changes in
heart rate and body posture. Over the
millions of years of evolution from
mouse to human, the central nucleus be-
came smaller. As a result, humans are

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The
uniquely
human in
human
nature

less likely than chimpanzees to become
immobile or to experience a racing heart
when they encounter an unfamiliar
member of their species. When a mam-
malian species is domesticated, not only
does the central nucleus become smaller,
but the snout (nose, mouth, and mandi-
ble) becomes flatter because of the ac-
tions of genes that control the migration
and ½nal functions of a small necklace of
cells, called the neural crest, that appears
during the ½rst six weeks following con-
ception. The human face is considerably
flatter than the face of a chimpanzee.
The suggestion that humans are do-
mesticated apes may strike some readers
as absurd, given the daily media an-
nouncements of murder, rape, and tor-
ture committed within our species. But
these cruelties, although horri½c, are
statistically infrequent anomalies. If
one could sit atop Mount Olympus and
count the number of acts of kindness,
nurture, honesty, cooperation, civility,
and affection, as well as the number of
hostile, rude, dishonest, aggressive, or
violent behaviors that occurred across
the world each day, the value of the for-
mer would always be larger than that
of the latter–a fact that is not true for
chimpanzees.

Still, the balance, even for human
beings, may be shifting–not because
our species is innately vicious, but rather
because of the assumption, greatly rein-
forced in modern societies after the sev-
enteenth century, that one should only
pursue individual rather than collective
goals.
7
This brings us to a ½nal quality, admit-
tedly more controversial, that distin-
guishes humans from apes. We are the
only species that, during some historical
eras, can dissociate survival to reproduc-
tive maturity from inclusive ½tness. The

biological concept of inclusive ½tness, a
relative property, is de½ned by the repro-
ductive success of each agent and all her
genetic relatives, compared with the suc-
cess of a related strain or species in the
same ecological setting.

Survival to reproductive maturity is
usually positively correlated with inclu-
sive ½tness in every species. But the in-
vention of inexpensive, effective contra-
ceptives has allowed many human cou-
ples to limit the size of their family or, in
some cases, to have no children at all. In-
creasing numbers of European, North
American, and Japanese couples are re-
stricting the size of their families in or-
der to gain signs of virtue through per-
sonal accomplishment, education, en-
hanced social status, and new sensory
delights. This decision is inconsistent
with the biological demand to maxi-
mize inclusive ½tness. The historical
events of the past twenty thousand
years created social conditions in eco-
nomically developed societies that
placed the almost conscious desire to
regard oneself as virtuous in competi-
tion with the silent, unconscious bio-
logical urge for inclusive ½tness.

The genome of contemporary hu-
mans is essentially the same as that of
our founding ancestors. But the ½rst
modern humans, who appeared be-
tween one hundred and one hundred
½fty thousand years ago in a warm ecol-
ogy, and whose social organization con-
sisted of foraging bands of thirty to ½fty
individuals, many of whom were geneti-
cally related, were cooperative with and
loyal to their group.4 Successful adapta-
tion demanded the suppression of exces-
sive competition, sel½shness, and self-
aggrandizement.

Even though the ½rst humans were
perfectly capable of self-interest, un-

4 Peter Bogucki, The Origins of Human Society
(Walden, Mass.: Blackwell, 1999).

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Jerome
Kagan
on
human
nature

checked displays of this intention would
have provoked rejection, exile, or, in
some cases, murder. The gradual re-
placement of resource sharing and sup-
pression of an exuberant celebration of
the self with their opposites over the
past twenty thousand years required a
number of events, but, especially, the
receding of the glaciers, which enabled
the establishment of agriculture and the
growth of cities; and, more recently, dis-
tant communication through books, ra-
dio, television, and the Internet; inex-
pensive and ef½cient forms of transpor-
tation and contraception; and the belief,
partially a product of science, that an
ethic demanding kindness, honesty, and
loyalty to non-kin could not be defend-
ed, on biological grounds, as having an a
priori validity.

In many parts of the industrialized
world these events have created a social
ambience characterized by geographical
and psychological isolation from parents
and siblings; awareness of the economic
circumstances of millions of strangers in
distant places; a larger status differential
within and among populations and,
therefore, greater uncertainty over one’s
relative status; decreased likelihood of
punishment for disloyalty to one’s pri-
mary groups; control of fertility; and the
legal protection of infants, children, and
the elderly with serious physical impedi-
ments. These characteristics are incon-
sistent with the original human tenden-
cy to place the vitality and potency of the
group ahead of the psychological satis-
factions of the individual.

Celebrated novelists, poets, and play-
wrights are able to articulate the domi-
nant moods within their societies. Con-
temporary Western writers who enjoy
the respect of discerning readers regular-
ly depict loneliness, sadness, cynicism,
and lack of loyalty to lover, spouse, child,
employer, aging parent, or nation–com-

pare Brontë with Bellow or Beckett. A
short story in The New Yorker in 2003 de-
scribes a loving husband who, having
reluctantly agreed to his wife’s request
to perform euthanasia because of her
painful cancer, leaves her bedroom after
the act, goes downstairs, and has sex
with her best friend. The editors of the
magazine would not have published this
story if they thought their readers would
have found it offensive. I suspect that the
editors of a comparable publication in
Beijing or Cairo would not have accepted
this story.

Even though improved nutrition, pota-

ble water, ef½cient disposal of sewage,
and modern medicine have permitted a
longevity twice as long as the life span
enjoyed by the foragers, survival is only
one component of inclusive ½tness; the
number of healthy offspring is the more
important feature. History exploited the
competences of self-awareness and a
moral sense to allow some humans to
dissociate survival from inclusive ½tness.
Although Adam Smith believed that so-
ciety would prosper if each individual
pursued his own interests ½rst, he was
equally certain that each person’s natu-
ral concern for the opinions of others
would effectively restrain unbridled self-
interest. Smith could not have imagined,
two hundred years after he wrote The
Wealth of Nations, that large numbers of
humans would live in cities with mil-
lions of strangers to whom they were in-
different. Few chimpanzees could sur-
vive under such conditions.

Most adults must bend their ethics a

little to permit the behaviors that the
shape of their social structure requires.
If they resist, they can become vulnera-
ble to corrosive tensions. A majority of
North Americans and Europeans, and
especially those who live and work in
metropolitan areas, deal with strangers
whom they suspect will lie, exploit them,

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The
uniquely
human in
human
nature

block access at crowded intersections,
and push ahead in long queues. Each in-
dividual must rationalize a ready access
to anger in order to resist exploitation
and to protect property and dignity.
Television plays dramatize how easily
rage can well up to force otherwise rea-
sonable people to behave in ways they
will regret, even though the characters
are usually forgiven if their intentions
were not irredeemably evil. In order to
rationalize the blizzard of cruelty, greed,
rudeness, and dishonesty, many have
come to believe that it is not always pos-
sible, and probably not adaptive, to exert
continuous control over anger, cupidity,
rivalry, and jealousy. Belief in this ra-
tionalization mutes guilt and dilutes a
sense of personal responsibility for
harshly competitive attitudes that might
hurt another. I suspect that the televi-
sion series The Sopranos owes its popular-
ity to the fact that most viewers will feel
morally arrogant because they are less
mean than the members of the Soprano
family.

The belief that anger, self-interest,
and competitiveness should not be sup-
pressed because they are natural emo-
tions has advantages in a society where a
large number of strangers must compete
for a small number of positions of digni-
ty, status, and economic security. Under
these conditions, it seems rational to be
self-interested, and irrational to be too
cooperative, too loyal, or too altruistic.

A rash of books published over the last

twenty years claims that unconflicted
sel½shness is to be expected given our
evolutionary history.5 After pointing to
examples of self-interest in many animal
species, these books imply that because
this motive is present throughout na-

5 David P. Barash, Whisperings Within (London:
Penguin, 1979).

ture, humans need not feel ashamed of
their narcissism. However, anyone with
a modest knowledge of animal behavior
and minimal inferential skill could ½nd
examples of animal behavior that sup-
port almost any ethical message. Those
who wish to sanctify marriage can point
to the pair-bonding of gibbons; those
who think in½delity is more natural can
nominate chimpanzees. If one believes
that people are naturally sociable, cite
baboons; if one thinks humans are soli-
tary, focus on orangutans. If one wants
mothers to care for their infants, rhesus
monkeys are the model; if one prefers
the father to be the primary caretaker,
point to titi monkeys. If one is certain
that men should dominate harems of
beautiful women, cite elephant seals; if
one believes women should be in posi-
tions of dominance, describe elephants.
Nature has enough diversity to ½t almost
any ethical taste.

Humans are sel½sh and generous,
aloof and empathic, hateful and loving,
dishonest and honest, disloyal and loyal,
cruel and kind, arrogant and humble;
but most feel a little guilt over an exces-
sive display of the ½rst member of each
of these seven pairs. This feeling is un-
comfortable, and we are eager to have it
ameliorated. Confession or psychothera-
py is effective for some, and it is likely
that many adults feel better when they
read that their less social urges are natu-
ral consequences of their phylogenetic
history. The currently high status of the
biological sciences has made it possible
for students of evolution to serve as
therapists to the community.

The psychological differences be-
tween the ½rst humans and contempo-
rary members of our species are suf½-
ciently dramatic to motivate a curiosity
over whether the current motive hierar-
chy of the latter group is a biologically
prepared propensity that has a natural

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Jerome
Kagan
on
human
nature

priority, or one demanded by the special
conditions history has created.

Most young monkeys in natural set-

tings play with other monkeys. But
rhesus monkey infants that have been
taken from their mother early in life
and placed with an inanimate wire ob-
ject will sit crouched in a corner of a cage
away from their peers.6 The capacity to
crouch alone in a corner is inherent in
the rhesus monkey genome, but actual-
ization of that pro½le requires very un-
usual and unnatural conditions. Thus, it
is relevant to wonder whether the cur-
rent prevalence of unconflicted self-
interest in many industrialized soci-
eties, like the rhesus monkey’s solitary
crouched posture, must overcome a bio-
logically stronger urge to be a loyal, co-
operative, and trusting member of a sta-
ble group that provides protection from
external threat.

Most species that violate their salient
natural propensities risk a loss in inclu-
sive ½tness. A warning may be hiding in
this biological fact.

6 Harry F. Harlow and Margaret K. Harlow,
“Social Deprivation in Monkeys,” Scienti½c
American 207 (1962): 136–146.

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