Inequality is Biological and Adaptive Response to Group Competition, of Course…

Take Away –

“…the alpha males and females are ‘bad guys’ taking various resources from their group-mates.  However, in between-group conflicts they become ‘good guys’ and their presence and effort benefit everybody else…”

“Our ability to effectively collaborate with others is largely responsible for what our species came to be. The big question is how this ability first evolved when there are large metabolic and physiological costs related to human brain size and when collaboration can be easily undermined by free riders. The model offers an answer which emphasizes the role of between-group conflicts in shaping unique human features,”  Read more at:

In a series of mathematical models, researchers from the National Institute for Mathematical and Biological Synthesis and the University of Oxford uncovered a mechanism for explaining how between-group conflict influences within-group cooperation and how genes for this behavior might be maintained in the population by natural selection.

Humans are unique in their innate ability and willingness to cooperate within groups ranging in size from small-scale forager bands to nations of millions of individuals. Yet, cooperation has its downsides as it can lead to what scientists call “the collective action problem,” which says that if individual effort is costly and a group member can benefit from the action of group-mates, then there is an incentive to “free-ride,” whereby effort is reduced or withdrawn completely. If a number of group-mates follow this logic, the public good is not produced and all group members suffer. The collective action problem also occurs in conflicts between groups: everyone benefits from the group’s success, but achieving success requires costly contributions by individual members of the group.

The study, issued today as open access in the journal Nature Communications, shows that the collective action problem can be overcome in groups that have a hierarchical structure and high inequality. When within-group hierarchy and inequality are well established, high-rank individuals effectively spend their effort on competition with their peers in other groups. This competition then results in a seemingly altruistic behavior of the high-rank individuals as they make stronger effort, pay higher costs, and get smaller net benefit than their low-rank group mates who free-ride contributing nothing. The study also found that the total group effort that a group directs toward between-group conflict typically increases with the degree of hierarchy and inequality within the group.

The results are consistent with observations in nature across a range of species. The study cites chimpanzees, for example, whose high-rank males travel further into the periphery of the group during border patrols, and ring-tail lemurs and blue monkeys whose high-rank females participate more in the defense of communal feeding territories.

“As far as within-group interactions are concerned, the alpha males and females are ‘bad guys’ taking various resources from their group-mates. However, in between-group conflicts they become ‘good guys’ and their presence and effort benefit everybody else,” said Sergey Gavrilets, NIMBioS’ associate director for scientific activities and the study’s lead author.

While the study focuses on social instincts, those genetically-based biases affecting individual behavior in social interactions…The study suggests that humans may have an innate preference for an egalitarian social structure when there is relatively little between-group conflict and, conversely, an innate preference for a hierarchical social structure when levels of between-group conflict are high. The study also predicts that humans who find themselves in a leadership position may exhibit seemingly altruistic behavior.

Read more at:

The original paper digested:

“…collaborative ability is more likely to evolve first by between-group conflicts and then later be utilized and improved in games against nature. If collaborative abilities remain low, the species is predicted to become genetically dimorphic with a small proportion of individuals contributing to public goods and the rest free-riding. Evolution of collaborative ability creates conditions for the subsequent evolution of collaborative communication and cultural learning.”
1. Introduction

Our species is unique in a great variety of different ways but the most crucial of them are related to the size and complexity of our brain. Brain size in the genus Homo tripled in the past 2.5 Myr as a result of several punctuated changes supplemented by gradual within-lineage changes in Homo erectus and Homo sapiens. In modern humans, the brain is very expensive metabolically: it represents about 2% of the body’s weight but utilizes approximately 20% of the energy consumed. Other costs include a need for extended parental care owing to a longer growth period, difficulties at giving birth to larger-headed babies and some mental illnesses that come with brain complexity. A burning question is what factors were responsible for the evolution of human brain size and intelligence despite all these costs.

Two sets of explanations have been debated. Ecological explanations include climate variability and harshness, parasites’ and predators’ pressure, as well as changes in diet, habitat use and food extraction techniques. However, the empirical support for the role of ecology in human brain evolution is relatively weak. Neocortex size does not seem to correlate with several indices related to diet and habitat. There is a statistically significant association of cranial capacity with climate variability and harshness, and parasite pressure, but these factors are much less important than the population density.

An alternative set of explanations coming under the rubric of the social brain hypothesis focuses on selective forces resulting from interactions with conspecifics [1,13]. Several types of scenarios have been discussed.

– One is within-group competition which puts a premium on individuals being able to devise and use ‘Machiavellian’ strategies (including deception, manipulation, alliance formation, exploitation of the expertise of others, etc.) increasing social and reproductive success. Comparative studies suggest that species in which Machiavellian-like strategies have been documented have larger brain sizes than related species that do not commonly use these strategies. The plausibility of this scenario is also supported by mathematical modelling.
– Another scenario emphasizes selection for the ability to maintain social cohesion in large groups (which become increasingly unstable owing to increasing within-group conflicts). It is assumed that larger group sizes are more advantageous because of predatory pressure or in between-group competition. Data do show that brain size correlates with both the group size and the population density.
– The third scenario stresses the advantages of social learning over individual learning under conditions of an increasingly fluctuating environment which was characteristic of the Plio-Pleistocene. Copying the innovations of others through social learning can be advantageous in such environments especially if the population size is sufficiently high. As mentioned above, cranial capacity correlates weakly with environmental variation but strongly with population density. Mathematical models do show that the capacity for social learning can increase when an environment changes in spite of its costs.

Humans are also unique in their innate ability and willingness to cooperate at a variety of different scales…because of economies of scale, cooperation and collaboration between multiple social partners can result in significantly larger rewards than that in dyadic interactions, and thus could potentially be a very strong selective force for increased social-cognitive competencies.

There are two general types of collective actions in which our ancestors were almost certainly engaged. The first includes group activities such as defence from predators, some types of hunting or food collection, use of fire, etc. The success of a particular group in these activities largely does not depend on the actions of neighbouring groups. I will refer to such collective actions as ‘us versus nature’ games. The second, which I will refer to as ‘us versus them’ games, includes conflicts and/or competition with other groups over territory and other resources including mating. The success of a particular group in an ‘us versus them’ game definitely depends on the actions of other neighbouring groups. The outcomes of both types of games strongly affect individual reproduction as well as group survival.

Collective actions often lead to the collective action problem: if individual effort is costly and a group member can benefit from the action of group-mates, then there is an incentive to ‘free-ride’, i.e. reduce one’s effort or withdraw it completely. But if enough group-mates follow this logic, the public good is not produced and all group members suffer. Overcoming a collective action problem is a major challenge facing many animal and human groups. During the evolution of our species, however, this problem has apparently been solved as humans have strong innate preferences for cooperative and collaborative actions as demonstrated in experiments with small children. My goal here is to answer the following questions: Can the need for within-group cooperation and collaboration in collective actions select for increased cognitive abilities overcoming both the collective action problem and various costs of increased intelligence? If yes, which types of collective actions are most conducive in this regard?

A couple of additional clarifications are in order. First, the models to be considered below focus specifically on the evolution of collaborative ability rather than on the evolution of cognitive abilities in general. The former was preceded by a general increase in brain size throughout the Cenozoic in many mammalian lineages [37]. Greater brain size is expected to correlate with better cognitive abilities. Second, high cognition obviously has other benefits besides the ability to collaborate. These, however, are outside of the scope of this paper. Third, my models focus exclusively on social instincts (encoded in genes) and on deeper evolutionary roots of human social behaviour. As such, they intentionally neglect the effects of language, culture and social institutions which are crucial for human ability to cooperate in very large groups.

Overall, my results lead to the following scenario for the evolution of collaborative ability and collective action participation.
– First, individuals start contributing to collective actions involving direct competition with neighbouring groups of conspecifics (‘us versus them’ games). – Subsequently, they evolve improved ability to collaborate in these actions.
– Once this ability is established at some level, it becomes used in other collective actions.

Specifically, individuals start participating in ‘us versus nature’ collective games which then produces additional selection for further increases in collaborative ability and social intelligence. Evolution of collaborative ability creates conditions for the subsequent evolution of collaborative communication and cultural learning…

..Both types of models considered here include individual and group selection as well as public goods production. However in the ‘us versus nature’ games, the success of one group in a public goods production does not affect that of another group. By contrast, in ‘us versus them’ games one group’s success means another group’s failure. This difference results in stronger selection in the ‘us versus them’ models which in turn produces a larger evolutionary response both in individual contributions and collaborative ability.

The evolution of collaborative ability as studied here requires between-group competition. However, strong competition by itself is not enough. In terms of my models, the crucial factors are
(i) the level of baseline collaborative ability,
(ii) benefits and costs of collective actions,
(iii) costs of collaborative ability, and
(iv) presence of relevant genetic variation.

…it has been argued that between-group conflict was a driving force in the emergence of many human abilities, biases and preferences (such as cooperation, belligerence, leadership, altruism, parochialism and ethnocentrism) as well as human social norms and institutions….

…My results suggest that within-group coalitions were preceded and promoted by between-group conflicts…

…cooperation increases dramatically in the presence of direct between-group competition to a level that ‘cues of group competition have an automatic or unconscious effect on human behaviour that can induce increased within-group cooperation’. A variety of other facts and observations about human psychology (e.g. in-group/out-group biases, widespread obsession with team sports and sex differences in the motivation to form and skill at maintaining large competitive groups) strongly support the idea about the importance of between-group conflicts in shaping human social instincts.

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