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How to Unify Knowledge
Keynote Address
EDWARD O. WILSON
Museum of Comparative Zoology, Harvard University, Cambridge,
Massachusetts 02138, USA
ABSTRACT: The central question of general scholarship is whether all of knowledge is intrinsically consilient, that is, whether it can be united by a continuous
skein of cause-and-effect explanation and across levels of increasingly complex
organization. The answer lies in the recognition that the traditional line separating the great branches of learning (natural sciences, social sciences, and humanities) is not a barrier or even a line, but rather a broad domain of poorly
explored material phenomena now being cooperatively entered from all sides.
The key to bridge-building is the discovery and analysis of human nature,
which consists of the epigenetic rules — the hereditary regularities in mental
development. Their study is now well under way, at the biological, social science, and humanities levels. Examples of epigenetic rules include the origin of
color vocabularies, incest avoidance, optimum arousal in artistic design, and
response to the natural environment. The convergence of the great branches of
learning is mostly an empirical process, light on formal logic and theory in its
initial stages. The value of the consilience program is that at long last we appear to have acquired the means either to establish the intrinsic truth of the
fundamental unity of knowledge, or to discard it. I will argue the likelihood of
its existence and early establishment.
KEYWORDS: Consilience; Human nature; Epigenetic rules; Cognitive neuroscience; Human genetics; Environmental biology; Human sociobiology
Since the decline of the Enlightenment in the 18th century, Western scholars have
steadfastly partitioned knowledge into three great branches: the natural sciences, the
social sciences, and the humanities. They have also assumed that the line between
the natural sciences on one side (“science”) and the humanities and more humanistic
social sciences on the other side is a permanent epistemological discontinuity. This
belief has promoted the fragmentation of learning and multiplication of disciplines,
each with its own principles, methods, and even criteria of validation.
Interdisciplinary studies have also mushroomed, receiving much attention and
praise. But the bridges they build have rarely been more than attempts to bring nomenclature into conformity. In particular the social sciences and humanities have
Address for correspondence: Edward O. Wilson, Harvard University, Museum of Comparative
Zoology, 26 Oxford Street, Cambridge, MA 02138-2902. Voice: 617-495-2315; fax: 617-4951224.
[email protected]
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WILSON: HOW TO UNIFY KNOWLEDGE
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rarely been subjected to a true layering of theory in the manner of the natural sciences. An important cause of this lapse has been the general avoidance of biology as a
possible foundational discipline. An important result has been the “Babelization” of
studies on the human species and the decline in the liberal arts.
Meanwhile, reversing the trend throughout the 20th century, the natural sciences
have evolved on their own toward internal unification. After sustained exponential
growth, doubling in content about every 15 years or so since the 17th century, they
are now almost fully consilient, interconnected across the disciplines by cause-andeffect explanation, in the course of which principles at each level of organization
(subatomic particles, atoms, molecules, cells, et seq.) are rendered coherent at adjacent levels above and below it. Thus for the most part, particle physics is now consilient with atomic chemistry, atomic chemistry with macromolecular physical
chemistry, macromolecular physical chemistry with genetics and cell biology, and
so on, in rising steps of complexity and particularity, to the highest levels of ecology
and cognitive neuroscience. The more that science has grown, the more coherent its
constituent disciplines have become in cause-and-effect explanation. Consilience, in
short, is the mother’s milk of the natural sciences.
IS ALL KNOWLEDGE CONSILIENT?
The central question of general scholarship now is whether all of knowledge is
intrinsically consilient. The trend toward the vertical binding of the natural sciences
would seem to point that way. After all, mind and culture, which are the subjects of
the social sciences and humanities, are material entities and processes. They do not
exist in an astral plane above the tangible world and are therefore intrinsically open
to analysis in the natural scientific mode. To say that mind and culture are too complex to submit to reductionistic analysis is to ignore the fact that scientists have broken down one complex biological system after another. And to assert, as many social
scientists and humanities scholars have, that mind and culture comprise emergent
properties independent of the levels of organization below them is not a denial of
universal consilience. It is simply the assertion of an alternative hypothesis. So let us
find out which of the two opposing hypotheses is true.
Does a fault line exist between the great branches of learning? Or, to put the issue
in a more memorable context, are the scientific and literary cultures, as defined by
C. P. Snow in his famous 1959 Rede Lecture, permanent? The solution to this problem, I believe, is the recognition that the divide is not a fault line, and in fact it is not
a line at all. It is instead a broad domain of poorly understood mental phenomena
awaiting cooperative exploration from both sides.
During the past two decades four borderlands originating from biology have begun to bridge the intermediate domain. They are, first, cognitive neuroscience, also
known as the brain sciences, now mapping brain activity with increasing resolution
in time and space while including ever more sophisticated and even subjective mental events. Second, human genetics: the base pair sequences are mostly completed as
I write (in early 2000), and maps of the more than 50,000 genes are in sight—many
of which effect the elements of social behavior. The third borderland discipline is human sociobiology, also known as evolutionary psychology, the study of the biologi-
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cal basis and evolutionary history of all forms of human social behavior. Finally,
there is environmental biology, providing an ever deeper understanding of the living
world in which the human species evolved and to which it is exquisitely adapted in
both body and mind. From the side of the social sciences the bridging disciplines include cognitive psychology and biological anthropology, which are consilient with
the biology-born disciplines. They have begun to anastamose with them through
common cause-and-effect explanations that connect biological phenomena to complex forms of human social behavior.
Both sides in the bridge-building agree in distinguishing two fundamental and
complementary modes of biological explanation. The first is the functional explanation, concerned with proximate causes, an account of the elements, and in this case
the elements and processes that compose human social behavior. The second mode
of biological explanation is the evolutionary, concerned with ultimate causes, which
are the forces that have shaped the evolution of brain and behavior.
In general, the overwhelmingly dominant, creative force for biological evolution
has so far proved to be natural selection, and there is no reason to doubt its great importance in the evolution of the foundations of human social behavior. Natural selection is not a dogma but rather a body of theory that creates hypotheses for testing.
The method has proved very successful in human sociobiology. The usefulness of
adaptive hypotheses based on natural selection has been proved repeatedly in evolutionary studies. In fact, it is the only effective way to demonstrate cases of nonadaptiveness that might in time reveal other causes of evolution. Most criticisms of
sociobiology have arisen from a misunderstanding of this relation of theory to hypothesis in evolutionary studies.
Why is the conjunction among the great branches of learning important? Because
it provides the characterization of human nature with greater objectivity and precision, an exactitude that is the key to human self-understanding. The intuitive grasp
of human nature has been the substance of the creative arts. Its scientific study is the
logical underpinning of the social sciences and the source of an ultimate fundamental theory of scholarship in the humanities. It is a beckoning mystery to the natural
sciences. To grasp human nature objectively, to explore its depths scientifically, and
thence to connect in a common skein of cause-and-effect explanation its seemingly
endless ramifications, would be to approach if not attain the holy grail of scholarship
and fulfill the dreams of the Enlightenment.
DEFINING HUMAN NATURE AS EPIGENETIC RULES
What, then, is human nature? Before I attempt a definition, let me say first what
it is not. Human nature is not the genes, which prescribe it. To provide a biological
explanation of human nature, it is necessary to define the role of genes but not to suggest that the final product of social behavior is determined, hence “hard-wired,” by
the genes. Human nature is moreover not encompassed by the well-known cultural
universals, such as incest taboos and rites of passage. They are the products of human nature. Rather, human nature is the epigenetic rules, the inherited regularities
of mental development. These rules are highly diverse. They stem from particular
processes scattered through the endocrine, sensory, and central nervous systems.
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They are the genetically determined biases in the way our senses perceive the world,
the symbolic coding by which we represent the world, the options we open to ourselves, and the responses we (more precisely, our working brains) find easiest and
most rewarding to make.
In ways that are beginning to come into focus at the physiological and even in a
few cases the genetic level, the epigenetic rules alter the ways we see and classify
color. They cause us to evaluate the aesthetics of artistic design, to acquire elementary fears and phobias concerning dangers in the environment (as from snakes and
heights), to communicate with certain facial expressions and forms of body language, to avoid incest, to bond with infants, to bond conjugally, and so on across a
wide range of categories in behavior and thought. Most, like incest avoidance, are
evidently very ancient, dating back millions of years in mammalian ancestry. Others,
like the biological stages of linguistic development, are uniquely human and probably at most hundreds of thousands of years old. Several examples of epigenetic rules
will serve to illustrate their diversity.
Color
The following set of rules affect classification and vocabulary, in this case of color. The coding of wavelength by the interneurons of the visual system is relatively
well understood, from the response of the color pigments in the color cones of the
retina to the coded neuronal response of the optical interneurons to the final integrating centers in the visual cortex. The primary colors are particular bands of wavelength within the visible spectrum that are sensed with relatively little change across
each band, with the brain perceiving rapid change between the bands. Little change
across a wavelength band means relatively low ambiguity in interpretation, while
rapid change means high ambiguity. As an apparent consequence, cultures around
the world have tended to locate their color terms well within the unambiguous bands
and to avoid the narrow, ambiguous intermediate zones. To this straightforward relation between biological and cultural evolution can be added another, unexpected
trend in the evolution of vocabulary. Humanity as a whole has a total of 11 elementary color terms that are semantically interchangeable. That is, any one of the terms
in one language can be matched to another term or set of terms in a second language,
whether one to one, one to many, or many to one. The number of such conformable
terms in a given language can vary from 2 to 11, and it is a reasonable assumption
that the number grows or recedes during cultural evolution. As a rule, when the number is two, the colors are (in English) black and white; when three, black, white, and
red; when four, these colors plus yellow or green; when five, these colors plus both
yellow and green; and so forth. The possible number of pathways from 2 to 11 is
2,036, but humanity evidently has followed only about 22. This curious restriction
in cultural evolution is likely to have a biological foundation, but its nature and functional significance (or lack thereof) remain to be demonstrated.
Incest Avoidance
The second epigenetic rule I wish to cite is important in the evolution of morality.
It is the innate procedure by which people avoid incest, called the Westermarck effect after Edward Westermarck, the Finnish anthropologist who discovered it a cen-
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tury ago. When two people live in close domestic proximity during the first 30
months in the life of either one, both are desensitized to later close sexual attraction
and long-term bonding. The Westermarck effect is well documented in anthropological studies, although the genetic prescription and enabling neurobiological mechanisms remain to be studied. The human evidence is made the more convincing by the
fact that all of the nonhuman primates whose mating preference has been closely
studied also display the Westermarck effect. It therefore appears probable that the
trait prevailed in the human ancestral line millions of years before the origin of
Homo sapiens, the present-day human species.
Aesthetic Judgment
In another, wholly different realm, consider the origin of one aspect of aesthetic
judgment, through an epigenetic rule that affects the preferred complexity of design.
Neurobiological monitoring, in particular measurements of the damping of the alpha
wave, has revealed that the brain is most aroused by patterns in which there is approximately a 20% redundancy of elements — or put very roughly, the amount of
complexity found in a simple maze, two turns of a logarithmic spiral, or an asymmetric cross. It may be a coincidence, but about the same level of complexity is displayed by much of grillwork, friezes, colophons, logographs, and flag designs. It
appears in the glyphs of ancient Egypt and Mesoamerica, the pictographs of modern
Asian languages, “primitive” art, and much of abstract modern art.
Habitat Selection
In habitat selection, people across many countries choose, if given free choice,
home sites that combine several features understood intuitively by landscape architects and real estate entrepreneurs everywhere. People want to be on a height looking
down to and across open savanna-like terrain with scattered trees and copses and to
be close to a body of water such as a river or lake. They choose these elements if
possible, even if the appeal is purely aesthetic and not functional. In addition, they
want a retreat in which to live and a prospect of fruitful terrain through which to wander and forage, and in the prospect they like to see scattered large animals and trees
with low, horizontal branches. In short, people want to be in the environment in
which our species evolved over many years—camped in a copse or against a rock
wall, looking out over savanna and transitional woodland at acacias and similar dominant trees of the African environment. Is this so strange? All mobile animal species
have a powerful, often sophisticated inborn guide for habitat selection built into
much smaller brains. Why not such an instinct in human beings, or at least its residue
in the form of an epigenetic rule?
SUMMARY
Biologists, social scientists, and humanities scholars, by meeting within the borderland disciplines, have begun to discover increasing numbers of epigenetic rules
such as the ones just cited. Many more rules, I am confident, will come to light as
researchers shift their focus to search for the phenomenon explicitly.
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I grant that the conception of a biological foundation of complex social and cultural structures runs against the grain for many scholars. They object that too few
such inherited regularities have yet been found to make the argument solid, and in
any case higher mental processes and cultural evolution are too complex, shifting,
and subtle to be encompassed in this way. Reduction, they say, rips human thought
from its context, is vivisectional, and bleeds away the artist’s true meaning.
But much the same was said by the vitalists about the nature of life when the first
enzymes and other complex organic molecules were discovered. The same was declared about the physical basis of heredity even as early evidence pointed straight to
the relatively simple DNA molecule as the carrier of the genetic code. Only recently
have doubts about the accessibility of the physical basis of mind, and even the physical basis itself, faded before the advance of sophisticated imaging techniques. In the
history of the natural sciences, a common sequence has unfolded as follows. An entry point to a complex system is found by experimental probing. At first one and then
more such paradigmatic reductions are accomplished. Examples are multiplied as
the whole system opens up and the foundational architecture is laid bare. Finally,
when the mystery is at least partly solved, the cause-and-effect explanations seem in
retrospect to have been obvious, even inevitable.
The convergence of the great branches of learning is an empirical process, by
necessity light on theory in its initial stages. The value of the consilience program —
renewal of the Enlightenment if you prefer— is that at long last we appear to have
acquired the means either to establish the truth of the fundamental unity of knowledge, or to discard the idea. I believe we will establish it.
REFERENCES
The examples used in this essay come from many sources, which are cited in my syntheses
Sociobiology: The New Synthesis (Belknap Press of Harvard University Press, Cambridge,
MA, 1975 and 2000), On Human Nature (Harvard University Press, 1978), Biophilia (Harvard
University Press, 1984), and Consilience: The Unity of Knowledge (Knopf, New York, 1998),
as well as in two co-authored books, Charles J. Lumsden and E. O. Wilson, Genes, Mind, and
Culture (1981) and Promethean Fire (1983), both from Harvard University Press. Portions of
this article were previously published in my essay “On Science and the Humanities,” in Conversazione, Claudio Véliz, Ed. (Boston University, Boston, 2000).