For centuries now, conservative thinkers have argued that significant social reform is impossible, because human nature is inherently limited. The argument goes something like this: sure, it would be great to change the world, but it will never work, because people are too flawed, lacking the ability to see beyond their own interests and those of the groups to which they belong. They have permanent cognitive, motivational and emotional deficits that make any deliberate, systematic attempt to improve human society futile at best. Efforts to bring about social or moral progress are naive about the natural limits of the human animal and tend to have unintended consequences. They are likely to make things worse rather than better.

It’s tempting to nod along at this, and think humans are irredeemable, or at best, permanently flawed. But it’s not clear that such a view stands up to empirical scrutiny. For the conservative argument to prevail, it is not enough that humans exhibit tendencies toward selfishness, group-mindedness, partiality toward kin and kith, apathy toward strangers, and the like. It must also be the case that these tendencies are unalterable, either due to the inherent constraints of human psychology or to our inability to figure out how to modify these constraints without causing greater harms. The trouble is, these assumptions about human nature are largely based on anecdote or selective and controversial readings of history. A more thorough look at the historical record suggests they are due for revision.

Some conservative thinkers have argued that evolutionary theory provides a scientific foundation for the idea that human nature is fixed in this way. Unlike religious conservatives who reject Darwinian theory and the broader naturalistic world-view of modern science, these ‘evo-conservatives’ embrace evolutionary explanations of morality, and use them to bolster their political philosophy. Appealing to contemporary evolutionary accounts of human nature and morality might seem like an improvement on the pre-Darwinian conception of human nature that has dominated conservative philosophies since Edmund Burke in the 18th century. But in the end, evo-conservatism fails for largely the same reasons that its predecessor failed: it overestimates the ‘natural’ (read: biological) constraints on human moral capacities. As a consequence, it underestimates the potential that we humans have for moral progress.

Many evolutionists believe we can explain morality by appealing to Darwinian mechanisms, in particular to natural selection. Just as physical traits affect an organism’s chances of surviving and reproducing, they argue, so too can behavioural adaptations. Many traits, such as eyes and hearts, have straightforward adaptive functions, whereas others are functionally opaque. Some traits seem paradoxical from a Darwinian perspective because they appear on the face of things to reduce rather than enhance biological fitness. These traits are paradoxical because evolutionary theory entails that, all else being equal, costly traits should not proliferate. One important class of these paradoxical traits involves an organism performing some costly behaviour that confers fitness benefits on another individual, without any obvious return to the helper or its close genetic relatives (note this kind of altruism is different from helping of kin which has a well-established evolutionary explanation as ‘inclusive fitness’).

Of course, altruistic behaviour of precisely this sort is pervasive in human societies, and morality appears to have played an important role in its history. Many evolutionary anthropologists, such as Chris Boehm and Robert Boyd, argue that morality helped to sustain high levels of co-operation in early hunter-gatherer groups. Morality did this, so the explanation goes, by managing free-riding and other patterns of selfish behaviour via threat of punishment, and through the internalisation of moral norms that enable individuals to resist temptations to act in selfish ways. Higher levels of co-operation were beneficial to individual members of the co-operating group, since they allowed for a greater evolutionary return than if individuals had acted alone or as part of a group that did not co-operate effectively. Hunting large dangerous game such as mammoths and buffalo with simple weapons is impossible or prohibitively risky for any single individual. But in a large coordinated assault the risks are far lower, and the rewards reaped by co-operation are substantial.

In larger non-kin groups, however, co-operation will be undermined if some individuals are permitted to free-ride on the efforts of others, or if the spoils are hogged by a single individual or small subset of individuals. Many different evolutionary models have been put forward to account for the evolution of co-operation in humans, including theories of reciprocal altruism, indirect reciprocity, and punishment-reinforced reciprocity. But all of them maintain that morality evolved to enhance co-operation within a group.

In everyday life we tend to think of morality as warm and fuzzy, as ‘being good’: it might include virtues such as compassion, empathy, charity, and self-sacrifice. We often contrast our moral tendencies with our more aggressive or deceptive impulses. But once we realise that morality is, from a functional standpoint, an inherently group-based affair, we can see that it has a much darker side. Indeed, human societies typically enforce moral rules through institutionalised punishment in which many individuals within a given group must participate. Morality involves judgment, shame and exclusion as much as kindness. What is more, modelling work by the anthropologist Robert Boyd, the biologist Peter Richerson, the economist Samuel Bowles and their collaborators has shown that moralising punishment is likely to evolve only in the context of selection between groups. Which means that morality most likely evolved in an arena of intergroup conflict, in which violence and vigorous economic competition between groups was commonplace. This conclusion is consistent with archaeological, ethnographic and ethological data, too. As the archeologist Lawrence Keeley, the psychologist Steven Pinker, the anthropologist Chris Boehm, the primatologist Richard Wrangham and others have observed, intergroup conflict is common in extant and prehistoric hunter-gatherer bands, and is well established in chimpanzees.

Given this picture, we should expect human beings to extend moral consideration to members of their own group, while at the same time ruthlessly exploiting people from other groups. In short, we should expect evolution to have produced a human moral psychology that is group-ish and strategic in nature — one that takes other individuals to be part of the moral community if they are part of one’s co-operative group, or otherwise capable of contributing to or disrupting co-operative goods. Extending moral consideration to outsiders — especially those who are not in a position to reciprocate or who could be exploited without fear of reprisal — is maladaptive in a moral system that arose from competition between groups. In other words, a conventional evolutionary view is that morality involved as a way of bolstering in-groups and excluding others – that we are ‘hard-wired’ for tribal loyalties and conflicts.

This explanation has been used by some conservative thinkers to underpin a political belief – that human psychological limitations have placed significant constraints on the shape of plausible moral and political institutions. More inclusive moralities, they argue, premised on the equal moral worth of all human beings, or on the moral status of non-human animals, are not realistic for evolved beings such as us. The political philosopher Stephen Asma, the jurist Richard Posner, the international legal theorists Jack Goldsmith and Eric Posner, the political scientist Larry Arnhart and others argue that these evolved constraints on altruism undercut, or militate strongly against, the plausibility of a cosmopolitan political order.

But, this evo-conservative argument has more far-reaching implications than its proponents might realise. If our cultural evolution heavily constrains human morality, then we should not only find it unlikely that people will assign equal moral worth to all human beings and act accordingly, we should expect that human beings will refuse to recognise outsiders as having any moral standing at all. Furthermore, if the human capacity for altruism, solidarity, and mutual identification beyond an immediate group were as limited as evo-conservatives say, the very existence of the modern state would be inexplicable.

Nevertheless, the evo-conservative argument has some attractions. Human altruism does tend to be parochial, and people do often act as if they ascribe significantly greater moral worth to kin, kith and countryman. The trouble with this understanding of morality is that it cannot be the whole picture, or even most of it. After all, these evolutionary accounts are incapable of explaining a large swath of contemporary moral behaviour that we call the ‘inclusivist anomaly’. These are features of human morality that are strikingly more inclusive than evolutionary theory would lead us to expect, suggesting that human moral nature is far more flexible than evo-conservatives have acknowledged. This flexibility in turn offers ample room for the development of still more inclusive moralities that, on the evo-conservative view, evolution is purported to have ruled out.

The philosopher Peter Singer has argued that the moral community — the set of beings whose interests we give intrinsic moral consideration — has been expanding ever since the Enlightenment. This increasing inclusivity is due in part to a reconceptualisation of moral status. There have been, no doubt, very substantial setbacks — slavery, colonialism, and genocide are salient examples — but to paraphrase Martin Luther King Jr, the arc of the moral universe is long, and it bends toward increasing inclusiveness.

Gone are the days when watching cats burned alive was a common recreational pastime

One recent example of this increasing inclusiveness has to do with animal welfare, which increasing numbers of people have come to care about. Many now believe that non-human animals have interests that are valuable in and of themselves, whether or not humans happen to value them. This belief is reflected in a number of laws that are aimed at preventing the gratuitous suffering of animals. These include animal cruelty laws, the regulation of animal experimentation, and rules governing the treatment of animals raised for human consumption: these views and practices may not yet be dominant, but the populations of developed nations, at least, increasingly favour them. Gone are the days when watching cats burned alive was a common recreational pastime, as it was in France before the 19th century.

Another example of increasing moral inclusivity is the culture of human rights. The human rights movement is founded on the principle that all human persons are of equal basic moral worth, a value that is not dependent on strategic capacities, group membership, ethnicity, gender, sexual orientation, or any other contingencies of birth that we deem morally arbitrary. Such ‘cosmopolitan moral principles’ are enshrined in the major international human rights instruments, which have been formally incorporated into the domestic law of more than 200 nations. In some cases, a country’s ratification of a human rights treaty is more show than substance. But in others, cosmopolitan principles have transformed law and social policy.

Although human rights law is relatively recent, the cosmopolitan moral principles that ground it have roots in the Enlightenment and its philosophical wake. These principles underpin modern constitutional democracy and the rule of law, and they played an important role in the movements and discourse that ended institutionalised torture, slavery, and colonisation. Human rights are grounded in the ‘dignity’ of persons, which turns on the possession of certain ‘subject-centred’ properties, such as practical rationality. The animal ethics movement similarly depends on the widespread acceptance of a subject-centred morality, wherein the ability of non-rational animals to feel pleasure and pain places constraints on how humans may treat them.

According to this inclusivist moral outlook, moral standing depends on the cognitive capacities of the individual, not the ability of the individual to reciprocate or otherwise contribute to co-operative goods. Even if non-human animals, or young children, or persons with disabilities lack strategic capacities, this does not deprive them of moral status. Likewise, if a minority group or weaker nation can safely be exploited without risk of retaliation, we nonetheless deem such behaviour morally unacceptable. If the United States or any other great power intends to invade a foreign country, it must first offer moral justifications that go beyond pure self-interest or a desire to conquer, dominate, or exploit. This is not to say that such justifications do not often serve as pretexts for international aggression — the point is that it is now widely held that such justifications must be given, whereas this was not always so.

Evolutionary accounts of morality do a reasonably good job of explaining the morality of the Pleistocene’s small hunting bands, but they fare much worse in explaining this post-Enlightenment trend toward increasing inclusivity. Hunter-gatherers and Neolithic farmers who were overly concerned about cruelty to animals would have paid a high fitness price, for this would have placed significant limitations on their exploitation of both wild and domesticated creatures. The same is true of inclusive moral attitudes toward human beings who are outsiders: groups that extended moral community to individuals based on their humanity alone, rather than on the basis of their group membership or strategic capacities, would have foregone the fitness benefits that often flow from more aggressive behaviours, and would have constrained the tactics adopted in military conflicts.

Humans have had moral capacities for millennia, and yet inclusivist morality has emerged only in the most recent eye-blink of human history

Neither can we account for inclusivist morality as a simple evolutionary by-product of our evolved moral capacities. Humans have possessed moral capacities for many millennia, possibly even hundreds of thousands of years, and yet inclusivist morality has emerged only in the most recent eye-blink of human history. Of course, it’s possible that there could be delayed evolutionary by-products. Perhaps it is only recently that humans have possessed technologies — such as electronic images and writing — that allow for the extension of sympathy beyond one’s primary group. But even if inclusivist moral sentiments were just a technologically-enabled spillover of our biologically ‘hard-wired’ in-group psychology, they would still be inclusivist. In other words, the evolutionary leash would not be as short as evo-conservatives assert.

Evo-conservatives have tended to focus on aspects of human morality that evolutionary theory can plausibly explain, while glossing over progressive moral developments that it cannot shed much light on. This helps to explain why evo-conservatives have such a rigid view of human moral psychology. Evolutionary explanations of parochial, group-based, reciprocity-oriented altruism appear to vindicate the conservative conception of human nature, and so conservatives have seized upon this confirmatory evidence, while overlooking the inclusivist anomaly. The trend toward an increasing inclusivist morality among humans, which shows no sign of being a transient cultural artefact, demonstrates that both traditional conservatives and evo-conservatives underestimate our ability to extend our moral capacities well beyond the confines of our evolved moral psychology. This has been accomplished not just through technologies that extend the reach of our moral emotional responses, but also through reasoned debate, moral education, and the creation of domestic and international institutions tasked with making sure the expanding moral circle does not contract. We believe, and we hope, that this is the future of human morality.

Nothing we have said rules out the possibility that a more sophisticated evolutionary explanation can illuminate the recent development of inclusivist morality – indeed there are evolutionary thinkers, such as David Sloan Wilson, who argue for a progressive political philosophy of inclusion on the basis of their scientific research. It might turn out that the capacity for reflecting on and modifying prevalent moral norms can itself be given an evolutionary explanation, either as an object of natural selection or as a by-product of selection. But even so, no conservative implications will follow. What matters — from the standpoint of the possibility of moral progress — is not whether our capacity for inclusivist morality can be given an evolutionary explanation, but whether we have it. And we clearly do.