We often follow what are considered basic moral rules: don’t steal, don’t lie, help others when we can.
But why do we follow these rules, or any rules understood as “moral rules”? Does evolution explain why? If so, does evolution have implications for which rules we should follow, and whether we genuinely know this?
This essay explores the relations between evolution and morality, including evolution’s potential implications for whether morality or ethics exists at all.
1. Why Do We Have Moral Beliefs?
Evolution by natural selection occurs when genetic mutations spread in a population. This happens when individual organisms with a mutation outcompete those without it. For a mutation to spread, it must be working in the individual’s self-interest, e.g., by allowing the individual to run faster than his or her competitors.
Actions that are often considered morally good, however, can require sacrificing one’s self-interest. This is partly why “doing the right thing” can be difficult: returning a lost wallet of cash might not benefit us, but it’s the right thing to do. If morality ever requires actions that are not for our own benefit, how could it have evolved?
Genes for ethical, other-regarding, behavior can spread when individuals behave morally and thereby benefit their relatives, with whom they share genes, or reciprocators, who will return the favor. Genes for moral behavior can spread through the individual’s offspring, who share that individual’s genes, or by benefiting the individual him or herself in the long run.
It is still disputed, however, why moral behavior extends beyond a close circle of kin and reciprocal relationships: e.g., most people think stealing from anyone is wrong, not just stealing from family and friends. For moral behavior to evolve as we understand it today, there likely had to be selective pressures that pushed people to disregard their own interests in favor of their group’s interest. Exactly how morality extended beyond this close circle is debated, with many theories under consideration.
2. What Should We Do?
Suppose our ability to understand and apply moral rules, as typically understood, can be explained by natural selection. Does evolution explain which rules we should follow?
Gekko’s claims about what is good and right and what we ought to be comes from what he thinks we naturally are: we are greedy, so we ought to be greedy. But this reasoning is fallacious: an ought does not follow from what naturally is. It is a psychological fact that people tend to prefer their own groups over others, but this does not tell us that we ought to favor our own group: e.g., racists prioritize their own racial group, but they shouldn’t.
If we think we ought to do what’s “natural,” there is a further problem in that identifying what’s “natural” is often difficult. Do contraceptives prevent the ‘natural’ outcome of intercourse? Animals, like bonobos, have sex for fun: is that a, or the, ‘natural’ purpose of sex? It’s often unclear what the “natural” purpose of anything is, given the many possibilities. It’s clear, however, that doing what’s “unnatural” is often not wrong: e.g., computers aren’t “natural,” but using them isn’t wrong.
Understanding evolution’s impact on us, however, may help us make better moral decisions. Evolution explains in-group favoritism: our ancestors depended on their in-group for survival. The view that we must help people close to us, physically or emotionally, but need not help strangers, especially in faraway countries may reflect this past. But this view appears unjustified, if we consider the arguments for and against it. Recognizing evolutionary influences as the cause of some moral errors may help us achieve more justified moral beliefs.
3. Is there Moral Knowledge? Are there Moral Truths or Facts?
We have seen that there are evolutionary explanations for why it would, e.g., seem to us that stealing is usually wrong. But it’s possible that we could think that stealing is wrong, even if it is not, i.e., even if that belief is not made true by a moral fact. Evolution could cause us to hold useful beliefs that are not true.
This observation may lead us in two directions.
First, perhaps we should be less confident in our moral beliefs since we might hold them because they are beneficial, not because they are true. Recognizing this might lead to doubts that would prevent justified moral beliefs or knowledge: if we think that we might believe something only because it’s useful, that might prevent holding that belief with good reasons and so prevent moral knowledge.
Second, some might argue that, since we have moral beliefs, there must be moral facts that make those beliefs true. But evolutionary explanations for the causes of our moral beliefs make that argument doubtful: we have moral beliefs, but perhaps there are no moral facts or truths. So, genuine morality may not even exist in the light of evolution.
Both arguments can be challenged, however. Evolution does not show that our moral beliefs are false, only that they might be. Also, evolution may undercut one reason to believe in the existence of moral facts, but there are other reasons to believe in their existence that evolution doesn’t threaten: for one, it seems like society has seen moral improvement over the last few hundred years (ending slavery, allowing women to vote, etc.), and that might be difficult to explain without believing there are objective moral facts.
Our understanding of morality benefits from understanding its evolutionary origin. Many questions remain, however: e.g., what were the exact mechanisms by which any morality evolved? If evolution threatens moral beliefs’ truth or justifiability, might other influences, e.g., culture, have similar effects? Might understanding our evolutionary origins positively contribute to our moral thinking, e.g., by influencing our views about non-human animals?
 This essay focuses on moral beliefs, but feelings and attitudes can have ethical aspects, too, and similar questions arise about their origin.
 Kin selection is the process by which an individual’s actions favor the reproductive success of that individual’s relatives; it was briefly discussed already by Darwin and popularized by Hamilton (1963). Reciprocal altruism refers to the mechanism of how cooperation between non-relatives can evolve, provided that they are engaged in repeated interactions and able to keep track of the outcomes of their previous interactions: see Trivers (1971).
 Nobody denies that cultural, social, and personal factors play a role in individuals’ moral judgments: evolutionary processes do not explain everything. The relevant question, however, is whether the basic capacity to think and act morally is a product of natural selection. Our moral sense could be a by-product of another evolved trait that did not, by itself, help to spread the genes of individuals who had the trait in the next generation (biologists call traits that help organisms to spread their genes’ adaptations). Reasoning about what we morally ought to do might be an outgrowth of general reasoning abilities about, say, mathematics or causality, along with emotional responses such as empathy. Still, showing that morality is a by-product would count as providing an evolutionary explanation of morality and the same philosophical questions that are discussed in this essay would arise about the implications of it.
 See Henrich (2017) and Tomasello (2016) for accessible accounts of the evolution of morality that explain how morality could have evolved beyond a close circle of kin and reciprocal relationships. Herich emphasizes the role of cultural evolution (where selective processes operate on culturally transmitted traits), while Tomasello emphasizes the role of interdependence (where individuals quite literally depend on each other for survival).
 What are often called “normative” ethical theories, such as the theories of Kant, Mill and others, attempt to explain why actions are right or wrong and what rules we should follow: see, e.g., Introduction to Consequentialism by Shane Gronholz and Introduction to Deontology: Kantian Ethics by Andrew Chapman. But they have little to say about why we make moral judgments in the first place. Normative theories might correctly explain the proximate causes that lead us to make moral judgments now, but not address the ultimate cause for why we are following moral rules in the first place. This is where evolution comes in. Focusing on Kant’s view, e.g., we can as ask why we are creatures capable of the required degree of self-knowledge to properly grasp moral rules. Again, evolution seems to provide an important part of the answer.
 Gekko is cited in Morris (2015). Gekko’s sinister but merely fictional character must not obscure that the attempt to derive normative claims from evolutionary premises sometimes have had horrific real-world consequences. The murder of people regarded as ‘unfit for life’ in, e.g., the Third Reich, was often motivated by the thought that the strong or fit ought to dominate the weak. Farber (1994) provides a comprehensive introduction to this misuse of appeals to evolution in making ethical judgments or arguments.
 David Hume (1738 ) famously argued that arguments with premises without normative terms such as ‘should,’ ‘ought,’ ‘right,’ ‘wrong’, and so on cannot validly reach a conclusion with such terms: you can’t derive an ‘ought’ from an ‘is.’ Hume’s criticism of the is-ought fallacy is often mistakenly conflated with G. E. Moore’s (1903) criticism of the ‘naturalistic fallacy’. Moore in fact raised his criticism against early proponents of evolutionary ethics, but his criticism was based on the claim that ‘goodness’ cannot be further analyzed and thus not ‘naturalized’ (e.g., by equating goodness with happiness).
 See the vast literature on in-group preferences, beginning with Tajfel (1970).
 Moral decisions would be ‘better’ as understood by theories that attempt to explain the basic nature of wrong actions, such as consequentialism and deontology. See, e.g., Introduction to Consequentialism by Shane Gronholz and Introduction to Deontology: Kantian Ethics by Andrew Chapman.
 See Street (2006) and Joyce (2006) for arguments from the evolutionary causes of our moral beliefs and the claim that our moral beliefs are probably useful rather than true to the conclusion that we have reason to give up our moral beliefs.
 See Rachels (1990).
Download this essay in PDF.
Ethical Egoism by Nathan Nobis
Ethical Realism by Thomas Metcalf
Moral Error Theory by Ian Tully
Introduction to Consequentialism by Shane Gronholz
Introduction to Deontology: Kantian Ethics by Andrew Chapman.
I thank the editors for helpful comments on this essay.
About the Author
Michael Klenk is a lecturer in ethics and philosophy of technology at Delft University of Technology in the Netherlands. He received his PhD in philosophy from Utrecht University and published on epistemology, metaethics, and moral psychology in journals such as Synthese, Dialectica, Pacific Philosophical Quarterly, and Ethical Theory and Moral Practice. As a PhD candidate, he was a visiting fellow at Oxford University, Columbia University, and Harvard University. www.michael-klenk.com