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Evolution of collective behaviour

This lecture introduces the concept of collective decision making in large groups.
In a previous lecture, we have looked at the evolution of decision making in social context, but mostly in cases where only a few individuals take part in each interaction. Now in this final lecture, we will look at the collective decision making in large groups. As discussed earlier in the course, a large number of interacting agents can give rise to emergent properties at the higher level without the need for any central coordination. One of the most striking examples of this in the animal kingdom is the great structures that are built by ants and termites. Termite mounds are amazing structures. They can be up to three metres high, and often have very distinct forms.
They have air channels and cavities that ensure that the temperature inside the mound hardly fluctuates, often only within one degree centigrade over an entire day. There’s no central organisation in a termite mound. There’s no architect termite that has a blueprint of what it will look like. A termite mound and all its properties, including thermal regulation, is an emergent property of the individual actions of single termites.
The decision rules of the individual termites in the colony are the result of evolution. So indirectly, the termite mound itself is also a product of evolution. If we look at human groups, we also see many kinds of emerging group properties that cannot simply be reduced to the sum of individual actions. They include cultural traditions and social institutions such as religions, markets, and judicial systems. Selection can act on individual characteristics, but also on the emergent properties of groups. If entire groups out compete other groups– for example, because one colony of termites has built a mound that is superior to another– selection can take place on the level of the group. This process is referred to as the Group Selection.
Interestingly, selection at the individual level and selection at the group level can pull genes in different directions. To see this, think about groups of humans. For hundreds of thousands of years until the invention of agriculture about 10,000 years ago, humans have lived in small groups that lived on hunting and gathering. These groups engaged in cooperative hunting. A number of group members would go out together and hunt large animals that a single individual would not be able to kill. The hunted animal would be brought back to the camp, and the meat would be shared among the group members. Now imagine that there is a cheater in the group.
This individual does not join the hunt and is therefore not exposed to the dangers of hunting. Also, he can spend his energy on other things– for example, gathering fruits for himself. But this individual still benefits from the hunting of the others. When the meat is shared in the camp, everybody gets a piece, including him. Now individual selection will favour this kind of behaviour. This individual gets all the benefits of hunting without paying the costs and will therefore be able to leave more offspring than the other group members. If his behaviour is heritable, in the next generation there will be even more social parasites that exploit the hunting efforts of others.
So over the course of evolution, we expect that individual selection will cause this cheating behaviour to become more and more common. But of course, this behaviour is not good for the group. If there are many cheaters in the group, cooperative hunting becomes less and less successful, and the group may risk going extinct because they don’t have enough food. Other groups that don’t have many cheaters are more effective at cooperative hunting and are much less likely to go extinct because of a food shortage. So you see that at the group level, selection acts against groups with many cheaters. This is an evolutionary conflict. Individual level selection favours cheating behaviour, but group level selection acts against it.
Let’s go back to emergent group properties. Consider yet another group of hunter gatherers in which a social institution has emerged. You can think of it as a very simple, non-centralized form of a legal system. It is basically a set of shared social norms that dictate the cheater should be punished. So in this group, a cheater will not be allowed to share in the food anymore, or he will even be expelled from the group. This social institution takes away the individual advantage of cheating. In other words, individual selection does not favour cheating anymore. Now both group selection and individual selection acts against cheating behaviour.
So you see that the group property– in this case, a system of norms– has resolved the conflict between selection at the individual level and selection at the group level. This evolved system of norms has aligned individual interest with group interests and has in fact led to an increased integration of individuals in the larger common structure.
In the history of evolution, some of the major innovative transitions in biological design have had to do with changing selection pressure on multiple levels, like in the example that we just saw. Think about multicellular organisms. In the beginning of life, they did not exist. For billions of years, there were only organisms such as bacteria that lived their lives as single cells. At some point during the evolution on our planet, some of these cells started cooperating, and some innovations– in many ways analogous to those social institutions that I just discussed– have helped align their evolutionary interests. Today, all the cells in your body cooperate for a single goal– your reproduction. Your cells are the individuals and you are the group.
You are a self-organized group of cells with many emergent properties such as an immune system and consciousness. But there is virtually no evolutionary conflict anymore between you and the individual cells that make up your body. In conclusion, group properties can emerge in groups of organisms. We have seen the termite mounds, the social institutions in humans. But you can also think about a school of fish that seems to move as a single unit or a group of chimpanzees in which social hierarchy has emerged. Natural selection can act on individuals within a group, but it can also select between multiple groups. In many cases, some degree of conflict will exist between these different levels of selection.
It depends on the details of the situation what the outcome of evolution will be in such cases. But a possibility is the emergence of group properties that alter the selection on the individual level, aligning the interests of individuals within the group, causing the groups the group to become further integrated until– like in the case of multicellular organisms– the group of individuals has again become an individual.
This lecture introduces the concept of collective decision making in large groups. What are the effects of evolution of group behaviour? There can be conflict between individual interests and group interests. How does this conflict resolve by evolution?
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