Genes and environment are the raw material out of which we construct ourselves
The first half of the 20th century belonged to the physicists, whose apotheosis came in Hir-oshima and Nagasaki. But in recent decades we have seen the rise of the biologists, with their strident claims to have uncovered the molecular, genetic and evolutionary roots of almost every aspect of the human condition. Our millennial prophets are eager to tell us that our fate lies in our genes, albeit transmitted via the "mental modules" that Darwinian evolution has bestowed upon us. Biology is destiny. Yet in parallel, a new breed of biotech entrepreneurs offer the Promethean prospect of conquering destiny through genetic manipulation, making us smarter, more beautiful and eternally young.
Both faces of this biology are grounded in a profound reductionism: the claim that the multidimensional complexity of living processes can be read off from the one-dimensional "book of life," the "code of codes," inscribed within our DNA. Irrespective of the ethical, social and legal consequences of such a philosophy, I believe this is based in a deep misunderstanding of living processes. The misunderstanding derives in part from the philosophical and ideological framework within which modern science-biology included-has developed since its birth in the 17th century.
We must begin, however, with the question of how our knowledge itself is shaped. Natural science claims that its methods of hypothesis, observation and experiment permit something like a true representation of reality. But for 30 years philosophers, historians and sociologists of science have rightly pointed to the ways in which our scientific knowledge is culturally constructed-offering at best a constrained interpretation of the world. One such constraint is provided by the nature of our brains and the biology of perception. How we perceive the world is affected by our hormonal, immunological and physiological state. We perceive the world as we do because our visual system is capable of sensing only a limited range of wavelengths; our mass and volume give us a particular relationship to gravity not shared, for example, by bacteria or beetles, or by whales or elephants. Our sense of the temporality of events is shaped by the fact that we live for anything up to a century. Bacteria divide every 20 minutes or so, mayflies live for a day, redwood trees for thousands of years. Technologies enable us to escape these limitations, to observe in the ultraviolet, weigh atoms and measure time in anything from nanoseconds to light-years. Yet even when considering the inconceivably small or distant, we do so by scales which relate to our human condition: the measure of man is man.
A second constraint is defined by the limits of our technology. Until the means of circumnavigating the earth were available it was legitimate to maintain that the earth was flat. Until Lavoisier weighed the products of combustion, phlogiston theory was as good as oxygen theory. A third constraint comes from the social and historical nature of science itself. The ways in which we view the world, the types of experiments we conceive and evidence we accept, the theories we construct, are not culturally free. This means that we cannot understand today's biology-and its reductionist bias-without reference to the history of the discipline.
throughout its post-Cartesian and Newtonian history, western science has seen physics as its explanatory model. The pre-scientific world gave way to one in which all our day-to-day experiential richness of colour and sound, of love and anger, came to be seen as secondary qualities, underlying which were the changeless particles, waves and forces of the physicists' world. The task of other sciences-chemistry, biology and, later, psychology, sociology and economics-was to make themselves as like physics as possible. A further problem for biology is that there is a tendency to understand living processes via metaphors drawn from the most advanced forms of current human artefact. Many origin myths, including the Judaeo-Christian one, refer to humankind created from the dust of the earth, as if by a potter's wheel. Hydraulic images persisted through the Renaissance, giving way to electrical ones in the 18th and 19th centuries. Brains became telegraph systems, then telephones and now computers. But brains are not computers, and genes are not selfish.
Let me offer a fable to demonstrate the limits of reductionism in biology. Five biologists, on a picnic, see a frog jump into a pond. They fall to discussing why the frog has jumped. The first, a physiologist, describes the frog's leg muscles and nervous system. The frog jumps because impulses have travelled from the frog's retina to its brain and thence down motor nerves to the muscle. The second, a biochemist, points out that the muscles are composed of actin and myosin proteins. The frog jumps because the properties of these fibrous proteins enable them to slide past one another. The third, a developmental biologist, describes the processes whereby the fertilised ovum divides, in due course forming the nervous system and musculature. The fourth, a student of animal behaviour, points to a snake in a tree above where the frog was sitting. The frog jumps to escape the snake. The fifth, an evolutionist, explains the processes of natural selection which ensured that only those frog ancestors able both to detect snakes and jump fast enough to escape them had a chance to survive and breed.
Five biologists, five different types of explanation. Which is the right one? All of them are right-just different. The biochemist's explanation is the reductionist one, but it does not eliminate the need for the others. The most we can ask for is that explanations in the different discourses do not contradict one another. Each explanation answers a different question about the world. As a materialist-as all biologists must be-I believe that the world is an ontological unity, and that therefore our explanations must reflect this coherence. But which type of explanation we prefer depends on the purposes for which it is required. If we are concerned with diagnosing and treating diseases like muscular dystrophy, genetic and biochemical approaches may point the way. But they are almost entirely useless if we want to understand why a person chooses to take a swim or a baby learns to walk. It might in principle be possible to "translate" the phrase "I am angry" into a statement about the firing patterns and past history of the neurons in my brain, my hormonal and immunological state. But it is doubtful that such a translation would represent an explanatory gain. And for most of our social lives we can't even go that far. As the philosopher Mary Midgley puts it, neither the value of money nor the rules of football are collapsible into biology or physics. As she says, in her plea for pluralism: we surely live in one world, but it is a big one.
Yet over the 140 years since Darwin's On the Origin of Species, biology's pluralism has been steadily eroded. Physiology has been folded into biochemistry and biochemistry into chemistry and physics. Skinner's behaviouristic attempt to reduce psychology to physics and skip the intervening biological level may have been rejected, but a new school of "neurophilosophers" typified by Patricia Churchland and Daniel Dennett seek to dismiss what they call "folk psychology" in favour of neurocomputation, in which brains are indeed computers. In the hands of Richard Dawkins and John Maynard Smith, evolutionary biology has replaced the study of the living world with mathematical calculations about changes in the population frequencies of individual selfish genes. Indeed, the living organism itself (what geneticists call the phenotype) has been emptied of any function other than that of being the "lumbering robot" (Dawkins) serving for the replication of its genes. Molecular geneticists offer to predict our entire lifeline from birth to death, from the diseases we will die of to the political parties we will vote for.
yet there are limits to reductionism's onward march. Try as we may to collapse our sciences into grand physical theories of everything, such attempts must fail. The dream of writing a single equation to embrace the world resembles the search for an alchemical philosopher's stone. The Vienna School's philosophical attempt in the 1930s to impose a unity on the sciences-built upon physics-was doomed to failure. In his latest book, Consilience, the sociobiologist EO Wilson has again invoked this dream, in which even ethics, religion and art must be brought to heel, subordinate to the grand strategy of the genes. I will draw on three areas of current biology-neuroscience, development/genetics and evolution, to demonstrate the limits to reductionism's dream.
Many philosophers and neuroscientists claim that even the most subjective aspects of what it is to be human are explicable in the language of the neurons. But to understand how the human brain functions, it is not sufficient simply to extrapolate from the firing properties of its hundred billion neurons. Nor is the brain to be understood as an information processing device, a claim made most recently by Steven Pinker in his book How the Mind Works. In Pinker's view, the brain/mind is not a general purpose computer; rather it is composed of a number of specific modules (a speech module, a number sense module, a face-recognition module, and so forth). It is argued that these modules have evolved quasi-independently during the evolution of early humanity, and have persisted unmodified, underlying the mechanisms which traditional psychology describes in terms of motivation, drive and so on. They do not emerge through development, by interaction with the physical, biological, social and cultural environment, but are innate-hard-wired into the brain as a result of prehistoric evolutionary imperatives. Whether such modules are more than theoretical entities is doubtful-at least to neuroscientists. Indeed, Pinker goes to some length to make it clear that the "mental modules" do not necessarily map on to specific brain structures.
Modules or no, brains/minds do not just deal with information. They are concerned with living meaning. What distinguishes brains from computers is their capacity to experience emotion. As Antonio Damasio argues in his book Descartes' Error, emotion is primary; affect as much as cognition is engaged in all brain and mind processes, creating meaning out of information. Our brains are affected by what is going on in the rest of our body-hormonal and immunological surges, for example. Neurons and their connections are bathed in a continually varying soup of tens of hundreds of different hormones, growth factors, modulators, all affecting the way we think and act-our states of consciousness. And beyond this our minds are constructed not merely out of our own intrinsic biology but through the interaction, during our development, with many other minds and bodies, and the social, technological and cultural environment within which we function. The emphasis must be on dynamism, development and openness.
One of the problems for 20th century biology has been that whereas at the beginning of the century developmental biology and genetics were seen as a single endeavour, by the 1930s they had become quite distinct. Development became the science of similarities, genetics the science of differences. Explaining how it is that almost all humans are between 1.5 and 2.5 metres high, are more or less bilaterally symmetrical and have pentadactyl limbs was a subject for developmental study. Why some of us have differently coloured eyes, hair or skin became part of genetics. Only now, at the beginning of the new century, does there seem to be a chance of bringing the two together again-but only by transcending the reductionism within which they have been embedded. To follow this requires a detour into the biochemistry of DNA and its relationship with the rest of the cell.
Reductionism regards biological development as the reading out of genetically coded instructions present within the "master molecule," DNA. Hence the popular references to DNA as the blueprint of life. In the selfish gene view of the world, the organism is DNA's way of making more DNA, the vessel constructed by the DNA in order to ensure its safe replication. But DNA itself is an inert molecule (hence the possibility of recovering it intact from amber many tens of thousands of years old, as in Jurassic Park). What brings it to life is the cell in which it is embedded. DNA cannot make copies of itself unaided; it cannot therefore "replicate" in the sense that this term is usually understood. Replication requires an appropriately protected environment, the presence of a variety of complex molecular precursors, a set of protein enzymes, and a supply of chemical energy.
Within the cellular economy, DNA forms the "code" enabling proteins-the molecules which actually do the day-to-day work of the cell-to be synthesised. As Francis Crick said, the "central dogma" of molecular biology in its early days was the belief that there was a one-way flow of information from DNA to protein. In those days it was assumed that there was a one-for-one relationship between a strand of DNA-a gene-and the protein for which it coded. But this is not the case. The "read-out" into protein is subject to endless checks, controls and adjustments-by the proteins themselves. And individual coding sequences of DNA are distributed along chromosomes, punctuated by long sequences with no known coding function (in humans 98 per cent of the DNA in the genome comes into this non-coding category). There are no master molecules in cellular processes. Even the metaphor of the cellular orchestra is wrong, as orchestras require conductors. Better to see cells as complex versions of string quartets or jazz groups, whose harmonies arise in a self-organised way through mutual interactions.
Despite the near identity of our genes, no one would mistake a human for a chimpanzee-we even share some 35 per cent of our genes with daffodils. What distinguishes even closely related species are the developmental processes which build on the genes, the mechanisms which transform the single fused cell of a fertilised ovum into the thousand trillion cells of the human body, hierarchically and functionally organised into tissues and organs. Developmental processes have trajectories which constitute the individual lifeline of any organism. These are neither "instructed" by genes nor selected by the environment, but constructed by the organism out of the raw materials provided by both genes and environment.
All the molecules of an organism, and almost all its cells, are continuously being transformed in a cycle of life and death which goes on from the moment of conception until the end. This means that living systems are open; never in thermodynamic equilibrium but constantly choosing, absorbing and transforming their environment. They are in constant flux, always both being and becoming. To take an example from Pat Bateson (see his and Paul Martin's book Design for a Life), a newborn infant has a suckling reflex; within months the infant begins to chew food. Chewing is not simply a modified form of suckling; it involves different sets of muscles and physiological mechanisms. So a baby has to be at the same time a competent suckler and to transform himself into a competent chewer-to be and to become.
Being and becoming are not to be partitioned into the tired dichotomy of nature versus nurture. Rather, they are defined by a different dichotomy: specificity and plasticity. As an example, consider the relationship between eye and brain. The retina of the eye is connected, via a series of neural staging posts, to the visual cortex at the back of the brain. A baby is born with most of these connections in place, but during the first years of life, the eye and the brain both grow, at different rates. This means that the connections between eye and brain have continually to be broken and remade. If the developing child is to be able to retain a coherent visual perception of the world, this breaking and remaking must be orderly and relatively unmodifiable by experience. This is specificity. However, laboratory animal experiments and our own experience show both the fine details of the "wiring" of the visual cortex, and how and what we perceive of the world are directly and subtly shaped by early experience. This is plasticity. All living organisms, especially humans with our large brains, show both specificity and plasticity in development; both properties are enabled by our genes and shaped by our experience. Neither genes nor environment dictate development; they are the raw materials out of which we construct ourselves. A living organism is an active player in its own destiny, not a robot responding to genetic imperatives. This is why the genetic view of the "empty organism" must be replaced by a developmental perspective.
for the reductionists, the process of evolutionary change itself has become simplified. By contrast with Darwin's own view, an ultra-Darwinian orthodoxy has emerged, exemplified by Dawkins, Pinker and Dennett. Three main theses characterise this new fundamentalism. First, most of the features of any organism that we can observe (known as "characters") are adaptive; second, they are generated by natural selection; and third, natural selection acts solely or primarily at the level of individual genes.
A new biology must transcend each of these propositions. Present day understanding of how genes work, which I described in the previous section, makes untenable the view that individual genes are the only level of selection. To play their part in the creation of a functioning organism, many genes are involved-some 100,000 in humans. For the organism to survive and replicate, the genes are required to cooperate. Antelopes which can outrun lions are more likely to survive and breed than those which cannot. So a mutation in a gene which improves muscle efficacy might be regarded as fitter, and therefore likely to spread in the population. However, as enhanced muscle use requires other physiological adaptations-such as increased blood flow to the muscles-the individual mutation is unlikely to prove advantageous without changes to other genes.
Thus it is not only single genes which get selected, but also genomes. Selection operates at the level of gene, genome and organism, pace Dawkins. Nor does it stop there. Wynne-Edwards said 30 years ago that selection occurred at the level of the group as well as the individual. He based this claim on a study of grouse, arguing that they distributed themselves across a moor and regulated their breeding in a way which was optimum for the group rather than any individual member. Orthodox Darwinians treated this claim with derision.
Today, however, it is clear that the attack was misjudged. There are many organisms whose behaviours can most economically be described by group selectionist equations. Elliott Sober and David Sloan Wilson recently published a reassessment of group selectionist models showing mathematically how even such counter-intuitive (for ultra-Darwinians) phenomena as altruism can occur, in which an individual sacrifices its own fitness, not merely for the inclusive fitness of its kin but for the benefit of the group as a whole. Non-human examples of "altruism" include the alarm calls of birds within a flock when they observe a potential predator, thus drawing attention to themselves but at the same time alerting the rest of the flock and enabling them to take evasive action.
Nor is natural selection the only mode of evolutionary change. Sexual selection is one mechanism and there are others, too. Stephen Jay Gould argues that much evolutionary change is accidental and that, as he puts it, if we were to wind the tape of history backwards and replay it, it is highly unlikely that mammals, let alone humans, would evolve.
Finally, an assumption of ultra-Darwinism is that all observed "characters" must be adaptive. But what constitutes a character-and what constitutes an adaptation-is as much in the eye of the beholder as in the organism to which the character belongs. It was once suggested that the flamingo's pink coloration is an adaptation to make it less visible to predators against the pink evening sky. But the coloration is a consequence of the flamingo's shrimp diet, and fades if the diet changes. Thus, even if we were to assume that the coloration was indeed protective, it is an epiphenomenal consequence of a physiological-dietary-adaptation, rather than a selected property in its own right.
Natural selection's continual scrutiny does not give it the freedom to accept or reject any genotypic variation. Evolutionary mechanisms are not infinitely flexible but must work within the limits of what is physically or chemically possible.The limits to the possible lift of any conceivable wing structure make it impossible to engineer humans genetically to sprout wings and fly.
If we are to transcend reductionism and create an understanding of living processes more in accord with the real world than our present, one-eyed view, we need some principles with which to work. These principles will not reject the explanatory power of reductionism, but will recognise its limitations. The new science will rejoice in complexity, in dynamics, and in an emphasis as much on process as on objects. In my book, Lifelines, I enumerate a set of such principles; by chance there are ten. Here is my decalogue.
First, scientific knowledge is not absolute, but provisional, being culturally, technologically and historically constrained. Second, we live in a world that is ontologically unitary, but our knowledge of it is epistemologically diverse. There are multiple legitimate ways of describing and explaining any living process. Third, different sciences deal with different levels of organisation of matter of increasing complexity. Concepts applicable at one level are not necessarily applicable at others. Thus genes cannot be selfish; it is people, not neurons or brains, who think, remember and show emotion. Fourth, causes are multiple, and phenomena richly interconnected. Adequate explanation demands that we find the determining level. (One example: the high levels of murder in the US by comparison with Europe or Japan are best explained not by some special feature of the US genotype but by the high number of personal handguns in society, and a history of their use.) Fifth, living organisms exist in a developmental trajectory of both being and becoming. Sixth, organism and environment interpenetrate; environments select organisms (natural selection); but organisms choose and transform environments, they are active players in their own destiny. Seventh, living organisms are open systems far from thermodynamic equilibrium; continuity is maintained by a constant flow of energy and information. Eighth, evolutionary change occurs at the intersection of lifeline trajectories with changing environments. Ninth, organisms cannot predict patterns of change, and selection therefore always tracks environmental change. Thus, nothing in biology makes sense except in the context of history. And finally, because we exist at the interface of multiple determinisms, the future, for humans and other living organisms, is radically unpredictable. We make our own history, as someone once said, although in circumstances not of our own choosing.
