Reason, per se, can inhibit no impulses; the only thing that can neutralize an impulse is an impulse the other way. Reason may, however, make an inference which will excite the imagination so as to set loose the impulse the other way; and thus, though the animal richest in reason might also be the animal richest in instinctive impulses, too, he would never seem the fatal automaton which a merely instinctive animal would be.4
This is an extraordinary passage, not least because its impact on early twenty-first-century thought can be said to be almost nil. Very few people, on the side of either nature or nurture, took up such an extreme nativist position in the century to come, and almost everybody assumed for the following hundred years that reason was indeed the opposite of instinct. Yet James was no fringe lunatic. His work has influenced generations of scholars on consciousness, sensation, space, time, memory, will, emotion, thought, knowledge, reality, self, morality and religion – to name just the chapter headings of a modern book about his work. So why does this same book of 628 pages not even have the words ‘instinct’, ‘impulse’ or ‘innate’ in its index?5 Why, for more than a century, has it been considered little short of indecent even to use the word ‘instinct’ in the context of human behaviour?
James’s ideas were indeed immensely influential at first. His follower, William McDougall, founded a whole school of instinctivists, who became adept at spotting new human instincts for every circumstance. Too adept: speculation outstripped experiment and before long a counter-reformation was inevitable. In the 1920s the very empiricist ideas attacked by James, embodied in the notion of the blank slate, swept back to power not just in psychology (with John B. Watson and B.F. Skinner), but in anthropology (Franz Boas), psychiatry (Freud) and sociology (Durkheim). Nativism was almost totally eclipsed until 1958, when Noam Chomsky once again pinned its charter to the door of science. In a famous review of a book on language by Skinner, Chomsky argued that it was impossible for a child to learn the rules of language from examples: the child must have innate rules to which the vocabulary of the language was fitted. Even then, the blank slate dominated human sciences for many years. It was not until a century after his book was published that William James’s idea of uniquely human instincts was at last taken seriously again in a new manifesto of nativism, written by John Tooby and Leda Cosmides (see chapter 9).
More of that later. First, a digression on teleology. It was Darwin’s genius to turn the old theological argument from design on its head. Until then, the obvious fact that parts of organisms appear to be engineered for a purpose – the heart for pumping, the stomach for digesting, the hand for grasping – seemed logically to imply a designer, just as a steam engine implied the existence of an engineer. Darwin saw how the entirely backward-looking process of natural selection could none the less produce purposeful design – what Richard Dawkins called the blind watchmaker.6 Though in theory it makes teleological nonsense to talk of a stomach having its own purpose, since the stomach has no mind, in practice it makes perfect sense so long as you engage the grammatical equivalent of four-wheel drive, the passive voice: stomachs have been selected to appear as if equipped with purposeful design. Since I have an aversion to the passive voice, I intend to avoid this problem throughout this book by pretending that there is indeed a teleological engineer thinking ahead and planning purposefully. The philosopher Daniel Dennett calls such an artefact a ‘skyhook’,7 since it is the rough equivalent of a civil engineer hanging his scaffolding from the sky, but for the sake of simplicity I shall call my skyhook the Genome Organising Device, or GOD for short. This may keep religious readers happy, and allows me to use the active voice. So the question is: how does the GOD build a brain that can express an instinct?
Back to William James. To support his assertion that human beings have more instincts than other animals, James systematically enumerated the human instincts. He began with the actions of babies: sucking, clasping, crying, sitting up, standing, walking and climbing were all, he suggested, expressions of impulse, not imitations or associations. So, as the child grew, were emulation, anger and sympathy. So was a fear of strangers, loud noises, heights, the dark, reptiles. (The ordinary cock-sure evolutionist ought to have no difficulty in explaining these terrors,’ wrote James, neatly anticipating the argument of what is now called evolutionary psychology, ‘as relapses into the consciousness of the cave-men, a consciousness usually overlaid in us by experiences of more recent date.’) He moved on to acquisitiveness, noting the tendency of boys to collect things. He noticed the very different play preferences of boys and girls. Parental love, he suggested, was at least initially stronger in women than in men. He tripped quickly through sociability, shyness, secretiveness, cleanliness, modesty and shame. ‘Jealousy is unquestionably instinctive,’ he remarked.
The strongest of the instincts, he believed, was love. ‘Of all propensities, the sexual impulses bear on their face the most obvious signs of being instinctive, in the sense of blind, automatic and untaught.’8 But, he insisted, just because sexual attraction was instinctive did not mean it was irresistible. Other instincts, like shyness, prevent us acting upon every sexual attraction.
So let me take James at his word, provisionally at least, and examine the idea of the love instinct in a little more depth. If he is right, there must be some heritable factor, which gives rise to a physical or chemical change in our brains when we fall in love, that change causing, rather than caused by, the emotion of falling in love. Such as this, from the scientist Tom Insel:
A working hypothesis is that oxytocin released during mating activates those limbic sites rich in oxytocin receptors to confer some lasting and selective reinforcement value on the mate.9
Or, to put it more poetically, you fall in love.
What is this oxytocin and why does Insel make such an extravagant claim for it? The story starts in an almost ridiculously unromantic process: urination. Some 400 million years ago, when the ancestors of our species first left the water, they were equipped with a tidy little hormone called vasotocin, a miniature protein made out of a chain of just nine amino acids formed into a ring. Its job was to regulate salt and water balance in the body, and it performed this job by rushing about switching on cells in the kidney or other organs. Fish still use two different versions of vasotocin for this purpose today, and so do frogs. In the descendants of reptiles – and that includes human beings – there are two slightly different copies of the relevant gene lying next to each other, facing different ways (in human beings on chromosome 20). The result today is that all mammals have two such hormones, called vasopressin and oxytocin, that differ at two of the links in the chain.
They still do their old job. Vasopressin tells the kidney to conserve water; oxytocin tells it to excrete salt. But, like vasotocin in modern fish, they also have a role in the regulation of reproductive physiology. Oxytocin stimulates the contraction of muscles in the womb during birth; it also causes milk to be expelled from the ducts in the breast. The GOD is an economiser: having invented a switch for one purpose, he readapts it for other purposes, by expressing the oxytocin receptor in a different organ. But a much greater surprise came in the early 1980s, when scientists suddenly realised that vasopressin and oxytocin had a job to do inside the brain as well as being secreted from the pituitary gland into the bloodstream.
So they tried injecting oxytocin and vasopressin into the brains of rats to see what effect they had. Bizarrely, a male rat injected with intracerebral oxytocin immediately begins yawning and simultaneously gets an erection.10 So long as the dose is low, the rat also becomes more highly sexed: it ejaculates sooner and more frequently. In female rats, intracerebral oxytocin induces