The following article is a preçis of my PhD: Curry, O. (2005). Morality as Natural History: An adaptationist account of ethics. PhD, London School of Economics, London.
What is morality, and where does it come from? In 1739, the philosopher David Hume argued that people are naturally disposed, by passions such as sympathy and courage, to care about the welfare of others and to promote the common good (Hume, 1739/1985). These 'moral' passions, argued Hume, supply the motivation for moral behaviour, provide the criteria by which we judge others' actions, and guide our choices from among various social and political arrangements. By locating the basis of morality in human nature, Hume demystified ethics -- reclaiming it from the theologians, the supernaturalists and the transcendentalists -- and pointed towards a future in which morality would be studied like any other branch of psychology.
It has taken a while for science to catch up with Hume’s bold vision for ethics; but recent developments in evolutionary theory, animal behaviour, and human psychology suggest that he was right. We now understand why and how natural selection could have endowed humans and other animals with ‘moral’ instincts. And these discoveries are helping to chart a new course for moral philosophy.
The evolution of cooperation
At first blush, Charles Darwin seems an unlikely ally for Hume. After all, natural selection is often portrayed as a brutal struggle for survival that can produce only selfish individuals. However, since the 1960s it has been clear that natural selection consists of competition not between individuals but between genes. Genes can be thought of as instructions for building organisms; different genes build slightly different organisms; and, as a result, some genes succeed in getting more copies of themselves into the next generation than do other genes. As such evolutionary theory expects genes to be 'selfish' -- in the sense that they promote their own replication -- but it does not expect that individuals will necessarily be so. On the contrary, thanks to the theories of kin altruism, mutualism, reciprocity, and conflict resolution, evolutionary theorists have identified a number of ways in which 'selfish genes' can give rise to social, cooperative and even altruistic individuals -- individuals capable of love, sympathy, trust and respect. As Richard Dawkins has put it: "The position I have always adopted is that much of animal nature is indeed altruistic, cooperative, and even attended by benevolent subjective emotions, but that this follows from, rather than contradicts, selfishness at the genetic level. Animals are sometimes nice and sometimes nasty, since either can suit the self-interest of genes at different times. That is precisely the reason for speaking of 'the selfish gene' rather than, say, 'the selfish chimpanzee'." (Dawkins, 1998, p212).
Think of families. A gene in one individual can sometimes promote its replication by helping copies of itself that reside in other individuals (Hamilton, 1964). So, biologists expect natural selection to have designed organisms to provide benefits for their close relatives. Sometimes this involves the ultimate sacrifice. When a strain of the Escherichia coli bacterium runs out of food, it muscles in on other bacteria elsewhere. Some of the E. coli migrate ahead of the pack, into the ranks of the rival strain, and explode with a toxin that kills themselves and nearby rivals. The remaining E. coli then move in and finish off the rest. In this way, ‘suicide bomber’ bacteria give up their lives in order to help their extended family (Crespi, 2001; Lenski & Velicer, 2000). Less dramatic examples of 'kin altruism' include the parental care that is common among birds and mammals, and the intense division of labour practised by highly-related social insects such as bees, ants and wasps.
Genes can also benefit from building organisms that are good team players – participating in group hunts or herds (Boinski & Garber, 2000; Hamilton, 1964). Successful teamwork requires that individuals coordinate their behaviour with others. Sometimes this involves copying what others do (as in the case of herding), or doing what you did last time (as in the case of returning to 'traditional’ mating or migrating sites). At other times animals signal to one another. For example, North American prairie dogs adopt a variety of defensive formations in response to different types of predator. In order to coordinate their behaviour, prairie dogs make elaborate calls that tell others in their colony not only the identity of an approaching predator (coyote, human, dog or hawk) but also its colour, size, shape, speed, and direction of movement -- what one researcher has called "nounlike, adjectivelike and verblike elements" (Slobodchikoff, 2002, p258). Teamwork also fosters concern for the welfare of others – something akin to sympathy. As the primatologist Frans de Waal puts it: "We are not surprised to find that dolphins, elephants, canids, and most primates respond to each other's pain and distress, because the members of these species survive through cooperation in hunting and defense against enemies and predators." (de Waal, 1996, p80).
Genes can also benefit by building organisms that do each other favours – ‘I’ll scratch your back if you scratch mine’ (Axelrod, 1984; Trivers, 1971). Cooperation of this kind requires that animals know whom they can trust to return the favour, are alert to cheating, and are able to deter cheats (by punishing them, or by refusing to help them next time). For example, some species of fish allow small 'cleaner fish' to remove dead cells, parasites and other debris from their mouth and gills. Both parties benefit: the large fish are groomed and the cleaners get an easy meal. However, the large fish run the risk that the cleaner will 'cheat' by taking a bite of healthy (and more nutritious) flesh. If this happens, and the large fish notices, it will respond by breaking off from the interaction, chasing the cleaner around for a while, and taking his business elsewhere in future. For their part, if the bite is accidental, cleaners reassure clients by massaging their bellies with their fins (Bshary, 2001).
Finally, genes can benefit from building animals that resolve disputes peacefully (Maynard Smith & Price, 1973). One way to do this is to stage ‘ritual contests’. Stag red deer compete for harems. But instead of fighting they settle the matter with a 'roaring match’ -- the one with the louder roar wins. A loud deep roar is a reliable indicator of size and strength; so the contest ensures that the stronger stag wins, and weaker defers to him, without either suffering the costs of combat (Clutton-Brock & Albon, 1979). In other species, displays of age, size, weight, strength, skill, experience, or number of allies carry the day (Riechert, 1998). Some displays even provide benefits for their audience. Ravens feed on carcasses, and male ravens compete to perform the risky task of checking whether an animal is in fact dead, and not asleep or injured. As de Waal observes: "the occasional boldness of corvids serves to enhance status and impress potential mates by demonstrating that they have the courage, experience, and quickness of reaction to deal with life's dangers" (de Waal, 1996, p134). And in some species, the results of these contests lead to the formation of 'dominance hierarchies' in which everyone knows their place, and the need for contests is reduced (Preuschoft & van Schaik, 2000). Some primates combine these features. Chimpanzees, for example, compete for dominance by performing acts of 'public service' -- leading hunts, distributing kills, and intervening to end violent fights (de Waal, 1989, 1996).
Another way to resolve disputes is to respect others’ property. For example, male speckled wood butterflies take possession of small patches of sunlight on the forest floor. Should another butterfly arrive at the same patch there is a brief tussle, but the interloper defers to the previous owner. By temporarily removing the butterflies, experimenters can fool both into thinking that they 'own' the patch. Now, deprived of their conventional means of settling disputes, the butterflies fight for up to 40 seconds (Cronin, 1992, pp315-6).
So, far from being a 'war of all against all', animals cooperate with one another in a variety of ways; they care for their families, work in teams, communicate, trade favours, punish cheats, and settle disputes peacefully by means of contests, dominance hierarchies, and the recognition of property.
Human moral sentiments
Equipped with a theory of what to look for, researchers in a variety of disciplines are now beginning to find equivalent cooperative dispositions in humans.
First, with regard to families, psychologists have discovered: that children treat other children brought up in the same home as siblings; that they avoid incestuous relations with these siblings later in life; and that children raised with opposite-sex siblings develop a more disapproving moral attitude to incest. This indicates that moral sentiments regarding incest are simply the product of biological and psychological mechanisms designed to avoid the deleterious consequences of inbreeding (Lieberman, Tooby, & Cosmides, 2003). Other studies have shown that men have special neural circuitry for assessing whether children resemble -- and hence are genetically related to – them, and that assessments of resemblance influence the degree to which men, but not women, are prepared to invest resources in a child (Platek, Burch, Panyavin, Wasserman, & Gallup Jr, 2002).
Second, when it comes to team-work, psychologists have discovered that humans are equipped with sophisticated software (called ‘theory of mind’) that enables them to interpret and predict the behaviour of others, and also to understand their vocal signals (called ‘language’) (Baron-Cohen, 1995; Pinker, 1994). Meanwhile, neurologists are homing in on the location of the brain’s 'sympathy circuits' (Decety & Chaminade, 2002).
Third, when it comes to reciprocal trade, experimental economists have found that people are consistently nicer, fairer, more trusting than their self-interested models of human nature predict (Ostrom, 1990). Psychologists have identified the hormonal basis of trust (Kosfeld, Heinrichs, Zak, Fischbacher, & Fehr, 2005); and they have discovered that people have special circuits for spotting cheats (L Cosmides & Tooby, 2005). And neurologists have found that people derive pleasure from successful cooperation (over and above its material rewards) (Rilling et al., 2002), and from punishing cheats (de Quervain et al., 2004; Price, Cosmides, & Tooby, 2002).
Finally, when it comes to settling disputes, physiologists have found that, testosterone – the hormonal system that is responsible for prompting competitive displays, elating winners and deflating losers – operates in the same way in humans as in other mammals and birds (Mazur, 2005). Anthropologists have documented the variety of means by which human males compete for status through acts of altruism (Hawkes, F, & al, 2001). And psychologists have found that people routinely place a higher value on objects in their possession than on the same object when owned by someone else (Kahneman & Tversky, 1979).
And, as predicted, these dispositions seem to be universal features of human nature. Anthropologists have found that families, cooperative labour, empathy, promises, reciprocal exchanges, trade, punishment, leadership, generosity, and private property are present in every society in the world (Brown, 1991, pp137-140).
Hume and moral philosophy
Hume would have applauded the discovery of cooperative dispositions in human nature, not least because these are exactly the traits that he and others have argued are responsible for 'morality'.
First, within families, Hume recognised that "the relation of blood produces the strongest tie the mind is capable of"; this is manifest primarily "in the love of parents to their children”, but also to other members of the family to “a lesser degree . . . as the relation lessens" (Hume, 1739/1985, p401). Hume thought that this natural affection gave rise to a duty of care of parents to their children. And anthropologists have found that people everywhere agree that parents have a moral obligation to provide such care (Edel & Edel, 1959/1968, p34). Other moral philosophies -- such as Confucianism -- place the duties that one has to one's family above all others (Wong, 1991). And some feminists, appealing to the same intuition, have argued that the world would be a much better place if only we could treat everyone as if they were members of our family (Ruddick, 1980).
Second, Hume regarded ‘sympathy’ as central to human moral psychology. "[S]ympathy with public interest,” wrote Hume, “is the source of the moral approbation" (Hume, 1739/1985, p551). Others agree. Darwin argued that sympathy was the "foundation-stone" of a "moral sense or conscience" (Darwin, 1871, pp70-2). And Adam Smith's Theory of Moral Sentiments made sympathy paramount: "to feel much for others and little for ourselves, . . . to restrain our selfish, and to indulge our benevolent affections, constitutes the perfection of human nature." (Smith, 1759/1976). Hume also argued that, in a weaker form, sympathy gives rise to “a general sense of common interest” that induces “all the members of the society "to regulate their conduct by certain rules" called "conventions" (Hume, 1739/1985, p541). And of course, for countless philosophers, anthropologists, and sociologists, a large part of morality consists of adopting the norms, customs and conventions of one’s society.
Third, with regard to reciprocity, Hume noted that trade presents an opportunity to cheat; but he argued that people can be trusted to keep their side of the deal because they want to maintain a reputation for honesty. They "will return my service, in expectation of another of the same kind, and in order to maintain the same correspondence of good offices with me or with others" (Hume, 1739/1985, p573). Numerous other philosophers -- from Annette Baier and J S Mill, to Confucius and Bishop Butler -- have emphasised the importance of trust, patience, returning favours, punishment (as well as gratitude, guilt and forgiveness) to maintaining reciprocal cooperation. And "social contract" theorists -- from 'Glaucon' to Hobbes to Rawls -- have attempted to view all of morality through a reciprocal lens.
Finally, on the subject of resolving disputes, Hume anticipated many of the recent findings on animal contests. He argued that many animals take pride in their "beauty, strength, swiftness"; in addition, humans take pride in their "imagination, judgment, memory or disposition; wit, good-sense, learning, courage, justice, [and] integrity" (Hume, 1739/1985, pp376, 330-1, 648-9). And Hume noted that differences in ability give rise to hierarchies in which "certain deferences and mutual submissions” are required “of the different ranks of men towards each other" (Hume, 1739/1985, p650). High status then motivates altruistic acts by fostering the “heroic virtues”: "[c]ourage, intrepidity, ambition, love of glory, magnanimity, and all the other shining virtues" (Hume, 1739/1985, pp548-50). Aristotle, Machiavelli and Nietzsche have celebrated similar “virtues”, for similar reasons (Curry, forthcoming).
Hume also provided a uniquely prescient analysis of private property. He observed that "[m]en generally fix their affections more on what they are possessed of, than on what they never enjoyed” (Hume, 1739/1985, p534); he noted that property rights are acquired primarily though "first possession" or "occupation" (Hume, 1739/1985, p556); and he argued that property rights served to "to cut off all occasions of discord and contention" (Hume, 1739/1985, p553).
So it appears that, with a little help from Darwin, Hume was basically right. People are social animals, with social or ‘moral’ instincts that dispose them to care about the welfare of others, to cooperate, and therefore to promote the common good.
The future of ethics
Echoing Hume, the philosopher John Rawls has suggested that moral philosophy begins with “the attempt to describe our moral capacity” (Rawls, 1971, p46). If so, then moral philosophy is on the verge of a period of unprecedented growth.
With Hume and Darwin looking over their shoulders, geneticists will compile a true ‘genealogy of morals’. By looking for the 'genes for' morality in humans and other species they will be able to trace different aspects of moral psychology back to the species in which they first appeared, and reveal with which species alive today we share them.
Behavioural geneticists will be able to tell whether and to what extent differences in genes give rise to differences in moral attitudes. Current estimates suggest that around 50% of the difference between people in most behavioural and personality traits is due to differences in genes; we should expect a similar figure for moral sentiments (Pinker, 2002, p50).
Neuro-anatomists will establish Hume’s “correspondence of passions in men and animals” (Hume, 1739/1985, p376). They will study the locations of social instincts in the brains of other species in order to get a better idea of where to find the equivalent moral sentiments in human brains. And they will work with clinicians to identify which sentiments are absent or damaged in various types of psychopath (Mealey, 1997).
Psychologists will investigate whether -- as evolutionary theory predicts, and some feminist philosophers have urged -- men and women have different moral values. Perhaps kin altruism looms larger in women’s psychologies, and conflict resolution looms larger in men’s.
Developmental psychologists will investigate how moral attitudes change during an individual’s life. After all, infancy, childhood, adolescence, sexual maturity, parenting, and grandparenting present different problems, and we might expect distinct psychological mechanisms to have been designed to come on- and off-line at appropriate times to deal with them. For example, we might expect individuals to have different adaptations: for competing fairly with siblings for parental investment; for fine-tuning moral competences through play during childhood; for identifying with a particular peer group during adolescence; for competing for status through the display of ‘virtues’ during early adulthood; and for evaluating and amending local conventions as a mature adult.
Psychologists will also investigate how moral instincts develop differently in different environments. We know that aversion to incest is triggered by growing up with opposite-sex siblings -- perhaps China’s one-child policy will have produced a nation for whom the thought of sibling incest is not repugnant. Or, perhaps trustworthiness depends on one's assessment of the future -- those who expect to 'live fast and die young' don't need to worry about maintaining a good reputation. Or perhaps respect for authority depends on whether the contests used to establish hierarchies are fair and accurate assessments of ability.
Anthropologists and sociologists will use these theories to help explain cross-cultural differences in moral values. If men and women, old and young, have different moral values, then societies with different mixes of people will exhibit different moral attitudes; and attitudes will change in predictable ways over time as the population ages. Different ways of making a living may also evoke different aspects of moral psychology. Hunting puts a premium on teamwork, gathering does not; and it has been found that hunting societies and gathering societies have predictably different attitudes to sharing food (Leda Cosmides & Tooby, 1992). Perhaps the dispersal of families in the West, as compared to the East, explains the relative lack of family values. Or perhaps unequal societies put greater emphasis on cultivating the ‘virtues’.
In ways such as these, moral philosophers and experimental scientists will together arrive at a deeper understanding of how moral psychology works, and how it generates differing values in different people from different backgrounds.
David Hume’s ‘bold conjecture’ that morality is a part of the natural world, and can be studied using the tools of natural science, is transforming moral philosophy. A profusion of mysteries has been replaced by a series of tractable problems. Numerous disciplines are coming together to solve these problems, shedding new light on the mechanisms underlying human morality. And not a moment too soon -- for only once we have the full circuit-diagram of the moral sentiments can begin the difficult task of investigating whether intuitions designed for the Stone Age remain reliable guides for life in the Space Age.
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