One of the main criticisms of group level natural selection has been that we know relatively few examples in which group behaviour has led to biological evolution. However, among them is one now regarded as being a rare and significant evolutionary transition: the evolution of the human brain. Another objection has been that groups reproduce and die off at a far slower rate than individuals and, thus, biological evolution driven by group behaviour will take place at a similarly slow rate. However, this is contradicted by the relatively rapid evolution of our brain.
The human brain differs from that of our ancestors not only in size but also in attitudes and skills. Examples of the latter include our relative Finally, Wilson, Timmel and Miller, in their study of cognitive co-operation found that groups perform better at problem solving tasks than individuals, and that the gap increases with the difficulty of the task. In other words, groups perform better than individuals when solving complex problems.
Large brains consume a great deal of energy, approximately 20% in humans. Their growth probably began approximately 2.6 million years ago, when our previously vegetarian ancestors shifted to a higher reliance on meat. At the same time, it became more efficient to occupy a campsite and send out hunters than for the entire tribe to hunt. In return, the hunters benefitted from the protection of the campsite in which their young were raised. Family based social groups did exist prior to the shift to meat eating but the changes brought about by meat consumption began a process of increasing co-operation between families, initiating a shift to less kin-reliant groups.
An important factor in whether a group forms is its ability to benefit its members. Unlike kin selection, each member requires reassurance that the others have a similar outlook and takes their reciprocal support as evidence. Co-operation requires the individual to have an understanding of other group members and their motives together with considerable negotiating skills. It also requires an ability to recognise exploitation of the group by individual members; this necessitates moral systems, and processes for dealing with intransigence. It is important to mention that competition between individual group members and families is not extinguished but merely suppressed.
Within groups a culture develops comprising several memes, i.e., agreed values, norms, beliefs, and symbols. Values are those things that we hold “good”, norms are forms of behaviour expected from group members, beliefs those things that we hold true, and symbols are ceremonies, ornamentation, etc., which identify us as being members of the group. Memes are subject to a process like that of gene selection. They will survive and propagate if they are fit for their environment or fall into disuse if they are not. It is not necessary, however, for a group to become extinct for a culture to expire. Nor is a culture necessarily linked to an ethnic group as multi-ethnic cultures are also possible.
Culture propagates from generation to generation but, unlike biological inheritance, it can also propagate from group to group through social learning. If a culture is successful, it can be transferred by imitataion or by coercion. Thus, cultural evolution takes place through the exchange of ideas and practices, with the most successful cultures surviving and propagating whilst the less successful ones expire. This process is far more rapid and adaptive to changing circumstances than biological evolution. Significant changes can occur within a few generations or less. This has, for example, allowed us to populate different environmental niches, from the arctic to the desert.
The evolution of our large brains has been very rapid and is thought to have been brought about by a process of positive feedback between cultural evolution and biological evolution with the former taking the lead. As groups became more complex and effective, they needed the greater skills and pro-social tendencies provided by larger brains. These, in turn, enabled groups to become yet more complex and effective. Because groups that co-operated well were more successful than those that did not, the individuals with the brains, skills, and attitudes needed to facilitate this were subject to natural selection and, thus, came to predominate. Although this process is speculative, mathematical modelling by Luke Rendell et al., of the University of St. Andrews, has shown it to be capable of producing strong selection pressures and the rapid evolution of biological traits.
Successful group co-operation relies on individuals knowing one another and limits on an organism’s ability to do so mean that there is a maximum group size which varies from species to species. In the 1990s, the anthropologist and evolutionary psychologist, Robin Dunbar, found a correlation, in primates, between brain size and social group size. From this he proposed a maximum social group size for humans of about 150.
In the last 5000 years, human society has become more complex. It now comprises numerous inter-dependent groups, each with its own specific purpose. They are not necessarily kin groups and are often based entirely on mutual co-operation. Some even prohibit nepotism. Most of us now occupy cities whose populations can be in the tens of millions. Cities are co-operative groups on a very large scale. We even describe them as organisms, using phrases such as “the beating heart” or “the veins and arteries”. There is no doubt that urbanisation, and the greater specialisation and co-operation that it brings, have resulted in an explosion in our population. Although this is probably a result of cultural evolution, in time, biological adaptations may follow.
Most of the changes arising from group behaviour that we can observe This raises many questions about our future, of course, such as “Is the process accelerating?” and “Where will it ultimately lead?”.
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