How the invention of weapons could have led to the evolution of human cooperation

What is it about?

The development of weapons in human evolution would have helped our ancestors enjoy a more protein-rich diet. However, some have suggested that weapons would also have had a major impact on relationships between early humans as they would have made it far easier to kill or be killed in disputes. Weapons would have equalized power within human groups in that greater size, strength, intimidation and fighting ability would have counted for less compared with the use of weapons i.e. spears and darts, bows and arrows. We take this idea further by suggesting that, in an environment where it would have been relatively easy to kill or be killed, cooperative individuals could have gained considerable advantages. This is because cooperators, more inclined to help others within their group, might have been less likely to have become involved in such lethal disputes due to more favourable treatment of others towards them. In contrast, non-cooperators might well have experienced greater involvement in such lethal disputes and thus faced a greater risk of injury or death. We used computer simulation to test this hypothesis. We took a version of the Prisoner’s Dilemma (PD) model, which is used widely to simulate the effects of decisions on individuals deciding on whether or not to cooperate. We also designed a version of the PD model in which weapons use was simulated. We then compared the effects of a ‘with weapons’ and ‘without weapons’ environment on 25 PD strategies, some cooperative and some non-cooperative, to test what would have happened.

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Why is it important?

This is important because evolutionary theory predicts rigorous competition between individuals to survive and transfer their genes into future generations. Examples where individuals reduce their ability to compete through selfless or altruistic behaviour therefore appear to contradict evolutionary theory. Evolutionary theory also predicts that individuals in a group will behave selfishly and try to contribute less than others while gaining the advantages of others’ efforts. Good cooperators therefore pose a similar problem. Furthermore, humans seem to display more altruistic and cooperative behaviour towards non-relatives than other species. Any new explanation as to why and how human altruistic and cooperative behaviour evolved is therefore of considerable importance. In our simulation we found that individuals who pursued cooperative strategies were significantly better able to survive and transfer their genes into future generations in a ‘with weapons’ environment compared with a ‘without weapons’ environment. Our hypothesis was therefore supported. We also examined the performance of each of the 14 cooperative strategies in a ‘with weapons’ environment and were surprised to discover that the most generously cooperative strategy of all (‘Always Cooperate’) performed significantly better than the average of all other cooperative strategies.

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