The evolution of human cooperation

Jun 17 JDN 2458287

If alien lifeforms were observing humans (assuming they didn’t turn out the same way—which they actually might, for reasons I’ll get to shortly), the thing that would probably baffle them the most about us is how we organize ourselves into groups. Each individual may be part of several groups at once, and some groups are closer-knit than others; but the most tightly-knit groups exhibit extremely high levels of cooperation, coordination, and self-sacrifice.

They might think at first that we are eusocial, like ants or bees; but upon closer study they would see that our groups are not very strongly correlated with genetic relatedness. We are somewhat more closely related to those in our groups than to those outsides, usually; but it’s a remarkably weak effect, especially compared to the extremely high relatedness of worker bees in a hive. No, to a first approximation, these groups are of unrelated humans; yet their level of cooperation is equal to if not greater than that exhibited by the worker bees.

However, the alien anthropologists would find that it is not that humans are simply predisposed toward extremely high altruism and cooperation in general; when two humans groups come into conflict, they are capable of the most extreme forms of violence imaginable. Human history is full of atrocities that combine the indifferent brutality of nature red in tooth and claw with the boundless ingenuity of a technologically advanced species. Yet except for a small proportion perpetrated by individual humans with some sort of mental pathology, these atrocities are invariably committed by one unified group against another. Even in genocide there is cooperation.

Humans are not entirely selfish. But nor are they paragons of universal altruism (though some of them aspire to be). Humans engage in a highly selective form of altruism—virtually boundless for the in-group, almost negligible for the out-group. Humans are tribal.

Being a human yourself, this probably doesn’t strike you as particularly strange. Indeed, I’ve mentioned it many times previously on this blog. But it is actually quite strange, from an evolutionary perspective; most organisms are not like this.

As I said earlier, there is actually reason to think that our alien anthropologist would come from a species with similar traits, simply because such cooperation may be necessary to achieve a full-scale technological civilization, let alone the capacity for interstellar travel. But there might be other possibilities; perhaps they come from a eusocial species, and their large-scale cooperation is within an extremely large hive.

It’s true that most organisms are not entirely selfish. There are various forms of cooperation within and even across species. But these usually involve only close kin, and otherwise involve highly stable arrangements of mutual benefit. There is nothing like the large-scale cooperation between anonymous unrelated individuals that is exhibited by all human societies.

How would such an unusual trait evolve? It must require a very particular set of circumstances, since it only seems to have evolved in a single species (or at most a handful of species, since other primates and cetaceans display some of the same characteristics).

Once evolved, this trait is clearly advantageous; indeed it turned a local apex predator into a species so successful that it can actually intentionally control the evolution of other species. Humans have become a hegemon over the entire global ecology, for better or for worse. Cooperation gave us a level of efficiency in producing the necessities of survival so great that at this point most of us spend our time working on completely different tasks. If you are not a farmer or a hunter or a carpenter (and frankly, even if you are a farmer with a tractor, a hunter with a rifle, or a carpenter with a table saw), you are doing work that would simply not have been possible without very large-scale human cooperation.

This extremely high fitness benefit only makes the matter more puzzling, however: If the benefits are so great, why don’t more species do this? There must be some other requirements that other species were unable to meet.

One clear requirement is high intelligence. As frustrating as it may be to be a human and watch other humans kill each other over foolish grievances, this is actually evidence of how smart humans are, biologically speaking. We might wish we were even smarter still—but most species don’t have the intelligence to make it even as far as we have.

But high intelligence is likely not sufficient. We can’t be sure of that, since we haven’t encountered any other species with equal intelligence; but what we do know is that even Homo sapiens didn’t coordinate on anything like our current scale for tens of thousands of years. We may have had tribal instincts, but if so they were largely confined to a very small scale. Something happened, about 50,000 years ago or so—not very long ago in evolutionary time—that allowed us to increase that scale dramatically.

Was this a genetic change? It’s difficult to say. There could have been some subtle genetic mutation, something that wouldn’t show up in the fossil record. But more recent expansions in human cooperation to the level of the nation-state and beyond clearly can’t be genetic; they were much too fast for that. They must be a form of cultural evolution: The replicators being spread are ideas and norms—memes—rather than genes.

So perhaps the very early shift toward tribal cooperation was also a cultural one. Perhaps it began not as a genetic mutation but as an idea—perhaps a metaphor of “universal brotherhood” as we often still hear today. The tribes that believed this ideas prospered; the tribes that didn’t were outcompeted or even directly destroyed.

This would explain why it had to be an intelligent species. We needed brains big enough to comprehend metaphors and generalize concepts. We needed enough social cognition to keep track of who was in the in-group and who was in the out-group.

If it was indeed a cultural shift, this should encourage us. (And since the most recent changes definitely were cultural, that is already quite encouraging.) We are not limited by our DNA to only care about a small group of close kin; we are capable of expanding our scale of unity and cooperation far beyond.
The real question is whether we can expand it to everyone. Unfortunately, there is some reason to think that this may not be possible. If our concept of tribal identity inherently requires both an in-group and an out-group, then we may never be able to include everyone. If we are only unified against an enemy, never simply for our own prosperity, world peace may forever remain a dream.

But I do have a work-around that I think is worth considering. Can we expand our concept of the out-group to include abstract concepts? With phrases like “The War on Poverty” and “The War on Terror”, it would seem in fact that we can. It feels awkward; it is somewhat imprecise—but then, so was the original metaphor of “universal brotherhood”. Our brains are flexible enough that they don’t actually seem to need the enemy to be a person; it can also be an idea. If this is right, then we can actually include everyone in our in-group, as long as we define the right abstract out-group. We can choose enemies like poverty, violence, cruelty, and despair instead of other nations or ethnic groups. If we must continue to fight a battle, let it be a battle against the pitiless indifference of the universe, rather than our fellow human beings.

Of course, the real challenge will be getting people to change their existing tribal identities. In the moment, these identities seem fundamentally intractable. But that can’t really be the case—for these identities have changed over historical time. Once-important categories have disappeared; new ones have arisen in their place. Someone in 4th century Constantinople would find the conflict between Democrats and Republicans as baffling as we would find the conflict between Trinitarians and Arians. The ongoing oppression of Native American people by White people would be unfathomable to someone of the 11th century Onondaga, who could scarcely imagine an enemy more different than the Seneca west of them. Even the conflict between Russia and NATO would probably seem strange to someone living in France in 1943, for whom Germany was the enemy and Russia was at least the enemy of the enemy—and many of those people are still alive.

I don’t know exactly how these tribal identities change (I’m working on it). It clearly isn’t as simple as convincing people with rational arguments. In fact, part of how it seems to work is that someone will shift their identity slowly enough that they can’t perceive the shift themselves. People rarely seem to appreciate, much less admit, how much their own minds have changed over time. So don’t ever expect to change someone’s identity in one sitting. Don’t even expect to do it in one year. But never forget that identities do change, even within an individual’s lifetime.

The vector geometry of value change

Post 239: May 20 JDN 2458259

This post is one of those where I’m trying to sort out my own thoughts on an ongoing research project, so it’s going to be a bit more theoretical than most, but I’ll try to spare you the mathematical details.

People often change their minds about things; that should be obvious enough. (Maybe it’s not as obvious as it might be, as the brain tends to erase its prior beliefs as wastes of data storage space.)

Most of the ways we change our minds are fairly minor: We get corrected about Napoleon’s birthdate, or learn that George Washington never actually chopped down any cherry trees, or look up the actual weight of an average African elephant and are surprised.

Sometimes we change our minds in larger ways: We realize that global poverty and violence are actually declining, when we thought they were getting worse; or we learn that climate change is actually even more dangerous than we thought.

But occasionally, we change our minds in an even more fundamental way: We actually change what we care about. We convert to a new religion, or change political parties, or go to college, or just read some very compelling philosophy books, and come out of it with a whole new value system.

Often we don’t anticipate that our values are going to change. That is important and interesting in its own right, but I’m going to set it aside for now, and look at a different question: What about the cases where we know our values are going to change?
Can it ever be rational for someone to choose to adopt a new value system?

Yes, it can—and I can put quite tight constraints on precisely when.

Here’s the part where I hand-wave the math, but imagine for a moment there are only two goods in the world that anyone would care about. (This is obviously vastly oversimplified, but it’s easier to think in two dimensions to make the argument, and it generalizes to n dimensions easily from there.) Maybe you choose a job caring only about money and integrity, or design policy caring only about security and prosperity, or choose your diet caring only about health and deliciousness.

I can then represent your current state as a vector, a two dimensional object with a length and a direction. The length describes how happy you are with your current arrangement. The direction describes your values—the direction of the vector characterizes the trade-off in your mind of how much you care about each of the two goods. If your vector is pointed almost entirely parallel with health, you don’t much care about deliciousness. If it’s pointed mostly at integrity, money isn’t that important to you.

This diagram shows your current state as a green vector.


Now suppose you have the option of taking some action that will change your value system. If that’s all it would do and you know that, you wouldn’t accept it. You will be no better off, and your value system will be different, which is bad from your current perspective. So here, you would not choose to move to the red vector:


But suppose that the action would change your value system, and make you better off. Now the red vector is longer than the green vector. Should you choose the action?


It’s not obvious, right? From the perspective of your new self, you’ll definitely be better off, and that seems good. But your values will change, and maybe you’ll start caring about the wrong things.

I realized that the right question to ask is whether you’ll be better off from your current perspective. If you and your future self both agree that this is the best course of action, then you should take it.

The really cool part is that (hand-waving the math again) it’s possible to work this out as a projection of the new vector onto the old vector. A large change in values will be reflected as a large angle between the two vectors; to compensate for that you need a large change in length, reflecting a greater improvement in well-being.

If the projection of the new vector onto the old vector is longer than the old vector itself, you should accept the value change.

If the projection of the new vector onto the old vector is shorter than the old vector, you should not accept the value change.


This captures the trade-off between increased well-being and changing values in a single number. It fits the simple intuitions that being better off is good, and changing values more is bad—but more importantly, it gives us a way of directly comparing the two on the same scale.

This is a very simple model with some very profound implications. One is that certain value changes are impossible in a single step: If a value change would require you to take on values that are completely orthogonal or diametrically opposed to your own, no increase in well-being will be sufficient.

It doesn’t matter how long I make this red vector, the projection onto the green vector will always be zero. If all you care about is money, no amount of integrity will entice you to change.


But a value change that was impossible in a single step can be feasible, even easy, if conducted over a series of smaller steps. Here I’ve taken that same impossible transition, and broken it into five steps that now make it feasible. By offering a bit more money for more integrity, I’ve gradually weaned you into valuing integrity above all else:


This provides a formal justification for the intuitive sense many people have of a “moral slippery slope” (commonly regarded as a fallacy). If you make small concessions to an argument that end up changing your value system slightly, and continue to do so many times, you could end up with radically different beliefs at the end, even diametrically opposed to your original beliefs. Each step was rational at the time you took it, but because you changed yourself in the process, you ended up somewhere you would not have wanted to go.

This is not necessarily a bad thing, however. If the reason you made each of those changes was actually a good one—you were provided with compelling evidence and arguments to justify the new beliefs—then the whole transition does turn out to be a good thing, even though you wouldn’t have thought so at the time.

This also allows us to formalize the notion of “inferential distance”: the inferential distance is the number of steps of value change required to make someone understand your point of view. It’s a function of both the difference in values and the difference in well-being between their point of view and yours.

Another key insight is that if you want to persuade someone to change their mind, you need to do it slowly, with small changes repeated many times, and you need to benefit them at each step. You can only persuade someone to change their minds if they will end up better off than they were at each step.

Is this an endorsement of wishful thinking? Not if we define “well-being” in the proper way. It can make me better off in a deep sense to realize that my wishful thinking was incorrect, so that I realize what must be done to actually get the good things I thought I already had.  It’s not necessary to appeal to material benefits; it’s necessary to appeal to current values.

But it does support the notion that you can’t persuade someone by belittling them. You won’t convince people to join your side by telling them that they are defective and bad and should feel guilty for being who they are.

If that seems obvious, well, maybe you should talk to some of the people who are constantly pushing “White privilege”. If you focused on how reducing racism would make people—even White people—better off, you’d probably be more effective. In some cases there would be direct material benefits: Racism creates inefficiency in markets that reduces overall output. But in other cases, sure, maybe there’s no direct benefit for the person you’re talking to; but you can talk about other sorts of benefits, like what sort of world they want to live in, or how proud they would feel to be part of the fight for justice. You can say all you want that they shouldn’t need this kind of persuasion, they should already believe and do the right thing—and you might even be right about that, in some ultimate sense—but do you want to change their minds or not? If you actually want to change their minds, you need to meet them where they are, make small changes, and offer benefits at each step.

If you don’t, you’ll just keep on projecting a vector orthogonally, and you’ll keep ending up with zero.