The myth of human nature

Appeals to human nature won’t help us make complex ethical decisions about new technologies like genome editing

Tim Lewens 

Source -

Nature cover cutout copy"What,” asked the distinguished evolutionist Michael Ghiselin in 1997, “does evolution teach us about human nature?” The answer he gave will surprise those who suppose that the evolutionary sciences describe the deepest and most ubiquitous aspects of our psychological makeup. Ghiselin informed his readers that evolution “teaches us that human nature is a superstition.” Why would anyone say such a thing? Doesn’t talk about human nature amount to talk about the ways we are all the same? What could be objectionable about that? We can begin to understand the problems if we look back 180 years.

On 2 October 1836, HMS Beagle landed at Falmouth. She had finally returned to England, after a five-year circumnavigation of the globe. One of the Beagle’s passengers was a 27-year-old Charles Darwin. After disembarking he first went to stay at his father’s house in Shrewsbury, but by March of 1837 he had moved to London. It was here that Darwin began to speculate in a series of notebooks on a wide range of topics in natural history and beyond. He formulated his “transmutationist” view of how species had come into existence, he pointed to intense struggle as the primary agent of change in the natural world, and he reflected openly on the impact this image of life’s history might have for human psychology, morality and aesthetic sensibilities. Many of these notebook jottings were transformed, in 1842, into a short “sketch” of Darwin’s theory. By 1844 that short sketch had expanded into a 230-page statement of the evolutionary view. But it was not until 1859 – 15 years later – that the Origin of Species was published. What had Darwin been doing in the meantime?

The answer is that he spent the eight years between 1846 and 1854 working on a gigantic study of barnacles. This period – sometimes referred to as a “delay”, as though Darwin was ready to publish the Origin in the mid-1840s, but somehow lost his nerve – was a puzzle to historians for some time. But it now seems clear how Darwin used his barnacle work as a detailed empirical testing ground for many of his earlier theoretical speculations. One of the most important lessons Darwin took from his meticulous study of barnacle anatomy concerned the ubiquity of variation: “Not only does every external character vary greatly in most of the species,” he wrote, “but the internal parts very often vary to a surprising degree.” He went so far as to assert that it is “hopeless” to find any part or organ “absolutely invariable in form or structure”.

Variability in all parts of all species is a primary fact of nature, says Darwin, and this ubiquitous variation is the fuel that powers natural selection. It is the conviction, inherited from Darwin, that species vary in all respects at any moment in time, and that natural selection causes those species to change in profound ways over time, that has made the likes of Ghiselin so sceptical of the thought that species have “natures”.

Evolutionists are not, however, united in their rejection of “human nature”. The eminent evolutionary psychologists Leda Cosmides and John Tooby announced back in 1990 their intention to defend “the concept of a universal human nature”, and Stephen Pinker’s 2002 book The Blank Slate: The Modern Denial of Human Nature implies through its title that the deniers of human nature are misguided. But even more recent work – especially an important and widely discussed article by the evolutionary anthropologist Joseph Henrich and his colleagues, from 2010 – demonstrates that evolutionary thinkers are increasingly placing stress on how cultural differences drive human psychological variability, often in the most surprising quarters.

* * *

Henrich et al point out that the vast bulk of psychological research is done in universities in places like North America, Australia and Western Europe. That means that when researchers are looking for experimental subjects, they typically rely on students from those universities. The result is that we know a lot about the psychology of people in what Henrich and co call “WEIRD” societies: those that are Western, Educated, Industrial, Rich and Democratic. But they move on to argue that just because WEIRD subjects’ minds work in a certain way, it by no means follows that all – or even most – human minds work like that.

Henrich et al illustrate their case with multiple examples. One of them concerns human responses to what psychologists call the Müller-Lyer illusion. Look at these two lines:

Mueller lyer

Most readers of this essay are likely to see the top line as longer than the bottom one, even though in fact their lengths are identical. But travel the world, and you will find that not all people are as susceptible to the illusion as this magazine’s WEIRD readers. As long ago as 1901, the Cambridge physiologist and anthropologist W.H.R. Rivers found that the students he tested in Cambridge seemed far more vulnerable to the illusion than the Murray Islanders whom he tested during his expedition to the Torres Straits. Henrich et al report a rather more recent study from the 1960s by Marshall Segall and others, who found that San foragers of the Kalahari desert in southern Africa did not see the two lines as having different lengths at all. It is still not clear why people vary in their response to the Müller-Lyer illusion. Segall and colleagues suggested susceptibility was due to being brought up in environments full of clean edges and straight lines. But the fact of variation is well established.

Another study from 2007 by Jonathan Winawer and co-workers indicates that human colour vision, or at least our ability to judge differences in colour between different surfaces, may be also affected by how we are raised. In English we have a general term for blue, and we distinguish between light and dark shades. Russian speakers instead have two entirely unrelated terms – goluboy for what we call “light blue”, and siniy for what we call “dark blue” – and no overarching term that corresponds to any more general category of “blue”. The availability of these sharply different colour terms allows Russian speakers to make discriminations more quickly than English speakers when presented with two patches of colour that lie across the goluboy/siniy (light blue/dark blue) boundary. All of these studies show that even our perceptual capacities are subject to the same variation that Darwin saw in his barnacles.

Modern biologists do not remotely agree on how to define what a species is. But they do agree that it is misleading to ask, “What sort of anatomical, physiological, mental or behavioural features must an organism have for it to be considered a member of Homo sapiens?” Darwin’s insistence on the ubiquity of variation within species has led most modern biologists to understand species not as groups of organisms with internal and external properties in common, but instead as twigs on the tree of life. Species are segments of the great genealogical nexus. What matters for species membership – that is, what it takes for an organism to be a member of a species such as Canis familiaris (the domestic dog), or Homo sapiens – is determined by genealogical relations. Just as membership of the Royal Family is decided by who one’s parents are, rather than by one’s internal or external bodily features, so membership of a larger genealogical unit like a biological species is also settled by appeal to ancestry. If “human nature” is supposed to pick out a set of traits that define what it is to be human, then human nature is a myth.

* * *

But does the presence of variation really show, as Ghiselin would have us believe, that human nature is a superstition? Or have we simply been too demanding in our conception of what human nature is supposed to be? It is hardly news that humans differ in terms of how they see colours. We have known about colour-blindness for centuries. Even so, the great majority of humans have three classes of cone cell in their retinas, and are free of colour-blindness because of this. What is more, there is a plausible evolutionary story to be told about why this “trichromatic” form of vision emerged: my Cambridge colleague John Mollon has argued that it was favoured by natural selection because it enabled our primate ancestors to detect ripe fruits against a dappled, leafy background. Biologists these days do not feel the need to find any catalogue of properties that are uniquely found in all and only humans. But this leaves alive the thought that some properties – psychological and physical – are present in almost all humans, and that evolutionary processes explain why those properties became and remain so prevalent in our species. Perhaps that is all we mean when we say that colour vision is a part of human nature, and, if that is all we mean, who could deny human nature’s reality?

One problem that arises from defining human nature as a set of features common in our species due to evolutionary processes is that it is scientifically arbitrary. Variability can sometimes be actively maintained by natural selection. The marine crustacean species Paracerceis sculpta gives us a nice example. The males of this species come in three quite different types, with different body shapes and different behaviours. The large male type guards “harems” of females within sponges. Another much smaller, faster male type darts into the sponges to grab mating opportunities when it can. And a third male type looks just like the females, and sneaks into the sponges to mate in disguise. No one form dominates over the others, and natural selection maintains all three. So while natural selection might sometimes make a single “design” more or less omnipresent in a species, this is only one potential result of evolutionary processes. Variability is another.

This brings us to a second problem with human nature. Recall that the subtitle Pinker chose for The Blank Slate was The Modern Denial of Human Nature. That suggests that we vindicate human nature to the extent that we are able to show that our minds are not blank slates at birth. In other words, human nature names those traits that are somehow “hardwired” into our psychological or behavioural repertoires. This might seem to be a stylistic variant of the idea that human nature names the traits that more or less all humans possess as part of their evolutionary heritage. After all, what difference is there between pointing to “hardwired” traits and “evolved” traits?

There is a big difference. Consider the capacity to imitate: to observe the actions of other humans, and copy those actions. Imitation is highly developed in humans. Very few other species have the capacity to imitate, and some evolutionists have suggested that our accentuated ability to imitate may help to explain why humans are so much better than other species at producing increasingly refined tools, traditions and bodies of knowhow. So the capacity to imitate is one that is present in an especially acute form in humans. It is found in all human societies, and it seems to have been of enormous importance in explaining our technological and behavioural development over thousands of years. For all those reasons it sounds like a good candidate for being part of human nature. But the psychologist Cecilia Heyes, while accepting much of this, has been arguing for some years that the capacity to imitate is something that human babies acquire by learning. If she is right, it is not “hardwired”.

There is a puzzle in explaining how the capacity to imitate is acquired. An imitator needs to observe an action in another person, and then produce a similar one. The problem is that how an action looks to an observer does not resemble how it feels for someone executing it. The puzzle is especially acute when one’s own bodily movements are hard to observe. If a baby sees me contorting my face in a certain way, how is she able to copy that action? She cannot look at her own face to check on how it is moving, and the feel of her own face moving does not resemble the look of my own face moving in the same way.

* * *  PART.2