The Evolution of Cooperation

First of all, a personal triumph: I've had my first academic paper accepted! "A New Phylogenetic Diversity Measure Generalizing the Shannon Index with Application to Phyllostomid Bats" is tentatively accepted for publication at the American Naturalist, a venerable biology journal. Whooo!

But on to our main topic: It's one of evolution's oldest riddles. If evolution is a brutal battle for survival, in which only the fittest survive, why do we see so much cooperation in nature? Why, in extreme cases, do some animals sacrifice themselves to help others of their species? In the competition between individuals, genes, and species, what kind of advantage does this altruistic behavior confer?

This question is quite deep and has generated an array of possible answers, whose implications go beyond evolutionary biology. I'll outline the history of how this question has been explored, and offer something of a synthesis to conclude.

• Reciprocation-It pays to help someone else if that person will help you in return. This fact is incontrovertible, and helps explain many of the interactions we see in nature, like monkeys grooming each other. However, reciprocation does not explain the acts of extreme altruism sometimes seen in nature, such as cellular slime moulds that sacrifice themselves to help others find food. So it can’t be the whole story—some actions really are selfless.



• Group selection-This is the idea that Darwinian evolution acts on groups of organisms as well as on individuals. If the members of a group cooperate well together, then the group as a whole may survive, while other less cooperative groups die off. This idea fell out of favor in the 60's as mathematical analysis showed group selection is generally a much weaker evolutionary force than individual selection. New models, however, show that group selection can be important in some circumstances.



• Kin discrimination-This view holds that the real unit of Darwinian selection is not organisms or groups but genes. Since genes are the material that is passed on through generations, the genes that help themselves out will survive the best. So if your gene “sees” that another individual has the same gene, your gene will “want” to help that person out in order to further its own interests. Of course, genes can’t really see each other. But your genes can tell you to help out your relatives, who are likely to have the same genes as you. This is the kin discrimination theory: our genes tell us to help our immediate family members, and thereby further their own gene-centric interests. Preferential behavior toward relatives is commonly observed in animals, and one study even found closely-related plants helping each other out.



• Repeated interactions-Axelrod’s tournaments of Prisoner’s Dilemma games show that, while it may be beneficial to act selfishly in the short run, more cooperative strategies are better if you know you’ll be interacting with someone repeatedly. The best strategies for repeated interactions are those which reward others who cooperate with you and punish those who don’t.



• Spatial structure-Cooperators do best if they’re surrounded by other cooperators. One way this can happen is in ecosystems where offspring are born close to their parents and don’t move much. In this case, the children of cooperators stay and cooperate with their relatives, while the children of selfish bastards hang out with their selfish bastard relatives and be miserable. Thus, systems with a strong spatial structure and little movement tend to favor cooperators. The system breaks down if the selfish bastards can move fast enough to find the cooperators and exploit them. Robert Austin found that spatial separation could help "altruistic" bacteria survive coexist with their "selfish" bretheren.



• Punishment-Evolutionary biologists have also explored the idea that punishment can help enforce cooperative behavior. Punishment can be “vigilante-style”, where any individual who sees someone else acting unethically can hurt them, or there can be some kind of agreed-upon authority whose job it is to punish misbehavers. The question of if and how punishment works in nature seems still up for debate.

Bottom line is, it doesn’t pay to be a nice guy in a world of assholes. But if you can find other nice people to interact with, and some mechanism for keeping the assholes out of your little nice-people club, then you’re on to something.

Each of the proposed mechanisms for cooperation has interesting implications for human society. I’ll highlight just one of them for now: spatial structure. When humans first evolved, long-distance travel was difficult, and so different societies could develop independently with their own norms of cooperation or selfishness. But now we can travel across the world in a day, so the spatial separation is gone. Any thoughts on the implications of this change for the stability of human cooperation?

Further reading

HIV evolves inside the body

This post is also taken from the excellent Evolutionary Dynamics course taught by Martin Nowak at Harvard.

The progression of HIV in the human body was a mystery for a long time. It sits in your body for years, not doing much, then suddenly it takes over your immune system and BAM!---you have AIDS. (The actual sound it makes when it reaches this point is unclear.) Pictorially, the process looks like this:



The red line represents the amount of disease in your body. When HIV is first contracted, the amount of virus shoots up dramatically, but then decreases sharply as the immune system responds. The virus load then stays at a small level, increasing only gradually, until the mysterious trigger happens and it shoots up again, this time impervious to immune responses. The upper blue line represents the amount of CD4 cells in your body, which are the immune cells that HIV attacks. (The slide is stolen from Martin's lecture.)

The question, then, is what is HIV doing in the long "asymptomatic" phase, and how does whatever it's doing enable it to suddenly explode after such a long time?

Nowak gave a surprising answer in a 1999 paper: it is evolving.

The idea is that when a person is first infected, they have only one strain of the disease in them (i.e. whatever strain they got from whoever transmitted it to them.) The immune system can handle this: it makes an antibody designed to attack that strain, at beats it back down to a miniscule level. It can't kill it completely though, because HIV can hide in healthy immune cells.

Now, while HIV is hiding in plain sight, it's also reproducing and mutating at a very high rate. Once it's mutated enough, the antibodies can't recognize it, so different antibodies must be produced to contain it. This processes continues and the disease becomes more and more diverse within you.

But there's a limit on the number of different campaigns your immune system can wage at once. Nowak found a mathematical diversity threshold--i.e. a critical number of strains of the virus, beyond which the immune system can't deal with all of them at once (though any one of them at a time would be fine.) And then, BAM!

I found this fascinating because, while we all know the power of evolution to produce remarkable organisms, we don't usually think of this process happening within our own bodies. Also, this hints at the difficulty of finding a cure for HIV, since it is specifically designed to mutate its way out of trouble.

Evolution of Irregular Verbs

I'm currently taking an amazing class offered by the Program for Evolutionary Dynamics (PED) at Harvard. The goal of the course (and the research program) is to study evolution---of animals, diseases, languages, and other entities---with full mathematical rigor. Today's class included a presentation by one of the PED researchers on the evolution of irregular verbs, based on an article that appeared in Nature in 2007.

Anyone who has ever studied a foreign language will remember with a sense of frustration that all the screwy irregular verbs were precisely the verbs like "to be" or "to go" that get used more often than any others. Obscure, rarely used verbs tend to conjugate in regular patterns.

These researchers found that early on in the English language, many verbs that are now regular, such as "help" or "walk", were once irregular ("I halp my friend study for his quiz yesterday.") As time went on, these verbs regularized (their conjugations evolved to the regular form) one by one, except for those very common verbs like "to be" and "to go" that remain highly irregular (how do you get "went" from "go"?)

Moreover, the speed at which these verbs regularized is directly related to the frequency of their usage. This relationship can be expressed in a remarkably simple mathematical law: the speed at which a verb regularizes is inversely proportional to the square root of its frequency. In other words, if verb A is used 100 times as much as verb B, verb B will regularize 10 times as fast.

The simplicity of this law suggests that there must be some kind of fundamental explanation---a simple model of language use that predicts this law mathematically. No such explanation has been found to date, but you can bet I'll be looking for one!

Evolution and Interdependence

So President Bush has finally taken a complex systems view of the economy:



Stupidity aside, he's entirely correct: our economy is highly interdependent. We discussed this situation last post, now I'd like to give some perspective on how interdependence comes to be.

Our economy, like life, is an evolutionary system, featuring competition, innovation, and adaptation to internal and external challeges. And I think some of the difficulty in understanding the current financial crisis comes from a misconception about evolution.

We usually think of (biological) evolution as a species-level process: each species makes its own incremental improvements in search of competetive advantage. But this is too simple a picture. Species do not evolve in isolation; they co-evolve in concert with all they interact with: plants, animals, microbes, and even minerals. In this co-evolutionary process, species develop relationships with each other; sometimes competitive, but often symbiotic or mutually beneficial in some way.

In the long run, co-evolution seems to produce increasing interdependence. Consider that all life started out as single-celled organisms, and that the co-evolution of these organisms led to multicellularity, which is a form of indterdependence so advanced that the component cells can no longer live on their own. On a larger scale, multicellular organisms co-evolved to form ecosystems. While not as interdependent as a multicellular organism, an ecosystem still has the property that if you remove enough vital components, the whole system fails.

An interesting thing happens now. As interdependence grows, so does the scale at which evolution occurs. Life started with cells competing against cells, grew into organsims competing with organisms, and now, in a sense, we also have ecosystems competing with ecosystems. The rainforest, for example, is competing with the desert in Africa. If the rainforest fails, so do all species that live there.

A similar process happens with economies. They begin with small, relatively self-suffient businesses. These businesses develop relationships with each other, co-evolve, and grow webs of interdependence. In the US, the webs have become so complex that an obscure industry known has mortgage-backed securities has sunk our entire economy.

So here too, evolution has "scaled up." It's no longer just companies competing against companies, it's also our whole nation's economy competing against those of other nations, and indeed the whole world's economy competing against, well, itself.

I don't think interdependence can be avoided, but it certainly needs to be understood. When people speak of the "free hand of the market" correcting our economy's mistakes, they're thinking of individual companies competing idependently, and failing to grasp the reality that, to some extent, our economy lives or dies as a whole.

Too Important to Fail?

The federal government is set to take over mortgage companies Fannie Mae and Freddie Mac. Earlier this summer, the government rescued the investment bank Bear Stearns. In each case it was decided that, even though the companies were in trouble of their own making, the damage caused by their failure would be too great for the economy to bear.

Strictly speaking, this isn't how our economy is supposed to work. It's supposed to be survival of the fittest: the companies that make the best decisions survive, and others fail. In this way good practices are rewarded, better business models evolve, and society progresses.

The problem is that, as part of this evolutionary process, the US economy has become increasingly interdependent. Companies need each other to survive, so that if a big one goes down it could take others with it. In the cases of Fannie Mae, Freddie Mac, and Bear Stearns, it was deemed that the failure of these companies would take out entire sectors of the economy, and as a country we couldn't let that happen.

I won't argue the merits of these decisions, but I'm interested in what they say about our economy. We're accustomed to thinking of our economy in terms of a system of competing animals. If one dies, others arise to take its place. But it may turn out our economy is more like another system: the human body, wherein if one part fails, the system suffers as a whole.

If this is true, then the whole of economic theory is based on an incorrect assumption. We may have some fundamental rethinking to do about how our economy works and why.

The paradox of order and randomness

Consider the following two images:




First view each image as is, and then click on them to see larger versions. Ignore for a moment the different sizes, and the copyright notice in the second picture (hope I'm not breaking any laws!) What's going on in these pictures?

The first is a randomly generated image, in which a computer essentially flipped a coin to decide the color (black or white) of each pixel. The second is composed of alternating black and white pixels in a checkered pattern (click on the image to see this clearly.)

At this resolution, the first picture still has some texture to it. But zoom out a bit more and it would reduce to a uniform grey, just like the second.

This highlights something of a paradox in complex systems theory: complete randomness is actually pretty boring. Sure, it's unpredictable, but because it has no structure, there's not much else you can say about it. And if you squint at it, it all averages out to grey. Contrast this to the following fractal image:



Now this picture has a lot of interesting structure to describe, like most complex systems.

Why is this a paradox? Because according to the defintions of complexity we discussed some months ago, a completely random system is more complex than anything else! Any order or structure in a system makes it easier to describe, thereby reducing complexity according to conventional definitions. So the fractal is actually less complex than the random image.

Complex systems researchers have recognized this problem for a long time, but there's no consensus on how to resolve it. Some have suggested adopting a different definition of complexity that behaves something like this:



That is, complexity is greatest somewhere between total order and complete randomness. But this is unsatisfying; complexity is not a mere mixture between order and randomness, but a delicate balance combining features of the two.

Of course, I have my own opinion as to how this paradox should be resolved. But that's a tale for another time.

Free Will, Randomness, and Determinism

Astronomer, inventor, and old friend of the family/distant relative Bob Doyle has begun a project to address old philosophical problems using information theory.

One such problem, as he explained to me at my aunt's 75th birthday last weekend, is free will versus determinism. Philosophers have been arguing for eternity whether free will exists, and if it does, where it comes from. Disconcertingly, free will seems incompatible with the major theories of physics. In Newtonian physics, all future states of the universe are completely determined by its present state, so no choices can ever be made. In quantum physics, events happen randomly according to precise mathematical rules, so the only "choices" are simply rolls of God's dice. Neither one of these theories seem to allow for any human or animal agency in changing world events.

Bob's idea is that the combination of Newtonian determinism and quantum randomness can explain more than either theory separately. Randomness generates new information and ideas in our brains, giving us novel options to choose from. But our brain is deterministic enough to sort through these ideas and choose the ones that are consistent with our character and past experience. In other words, randomness provides the "free" aspect of free will, and determinism provides the "will."

I don't think this theory is complete, because there's no real explanation of what the choice-making process looks like. But it seems beyond dispute that both random and deterministic forces play a role in what we call "human creativity." Currently, Bob is scouring the history of philosophy for all that's been said on the free will question, and how information theory and physics could connect to this. The blog of his efforts is now a proud memeber of the plektix blogroll.