Primates including humans live in societies where individuals sustain relationships, whether emotional or utilitarian, in order to accomplish functions that would otherwise be impossible. Participation is such groups that can be very complex requires advanced learning methods in order to be able to perceive oneself and others in these relationships.
Some of the behaviours emerging from this learning are imitation and insight. Imitation involves observing the actions of another and mimicking them. Insight is an understanding of a cause and effect in a given situation. This gorilla is playing on a Nintendo DS.
Primates including humans form social groups based on a few distinguished models based on the size of the group and relationships between members: single female and her offspring, monogamous family group, polyandrous family group, one-male-several-female group, multimale-multifemale group and fission-fusion society.
The strongest group organisation in primates is the single female and her offspring which occurs commonly in orangutans. The monogamous family group is formed of both parents and their offspring and is represented by some New World monkeys, and is a prevalent group type in humans too, even in polygamous cultures.
Polyandrous family groups consist of multiple males mating and rearing offspring with a female, found in tamarins and some humans. One-male-several-female groups do what they say on the tin, and are exhibited by langurs, gorillas and some humans. In some species the females are the core part of the group and choose the male, while in others the male is dominant over the females.
Multimale-multifemale groups contain many individuals who mate freely within the group, but not outside the group. The group members do fit into dominance hierarchies, determined by the hierarchy of their mother before them. These groups are found in savanna baboons and macaques.
Fission-fusion societies involve the breaking away from the group and joining new groups by chimpanzees, mainly the females.
Complex primate social behaviour
The relatively long time spent by parents taking care of offspring means that they are able to learn more complex social behaviour. This includes strategies for reducing conflict such as ritualistic display and appeasement behaviour.
Ritualistic displays are typical of each species, and provide an outlet for conflict resolution and prevention that protects the population against harm and death. For example, gorillas have a characteristic chest-beating, staring display, while chimps open their mouth and hold their arms out. Male baboons test the strength of their bonds by varying degrees of closeness. Strong bonds are met with hugging rituals and showing their genitals.
Appeasement comes in response to the display, and represents conceding the hierarchical position that is being presented or challenged. Body language for appeasement includes submissive positions and gestures and grooming.
The specific behaviours and the complexity of the social structure differ between species, the state of their resource distribution, as well as their ecological niche. These are associated with different anatomical and physiological setups which enable certain behaviours, the stresses exerted by an abundance or lack of various resources needed for survival and reproduction, and how the environment promotes or prevents the association and migration of various numbers of individuals into groups.
Altruism and kin selection
Altruism consists of any behaviour that appears to be harmful to the donor but advantageous to the recipient. Altruism is common in groups and is correlated with kin selection where individuals engaging in altruistic behaviour are more related to each other.
The longer term rationale for this behaviour and kin selection is that the donor’s individual contribution, including genetic, to future generations can be accomplished indirectly via their relatives. The offspring of their relatives will carry on more of the donor’s contributions compared to a non-related individual, therefore being altruistic towards them has an overall advantage to themselves, too.
The prisoner’s dilemma is a model in game theory that shows how rational individuals may not cooperate. It presents a situation where two “prisoners” are isolated from each other and given the opportunity to betray their partner and get to walk away free.
The catch is that if their partner also betrays them, they go to prison. If they both say nothing, they still go to prison but for less time. The outcome in this situation is that both prisoners figure out that the best case scenario is to betray. Prosecutors benefit from both providing information on the other and prosecuting both.
In evolutionary biology, the prisoner’s dilemma can be played out multiple times, and therefore account is taken of each outcome to inform the next step. Vampire bats share their food between them, so that not all individuals have to succeed in obtaining food all the time.
There are four states that can come out of this situation. The reward of being fed when one doesn’t have one’s own food, with the expense of sharing one’s food when one does have it doesn’t seem too high a price to pay in exchange. Next, the temptation of having been fed on the bad hunting night by someone who succeeded, but then choosing not to share your food on a good night, after all.
Sucker’s Payoff follows next, when having fed a starving bat who might run into temptation, you then run the high risk of starving to death yourself. Finally, there is punishment when no sharing of food is initiated, at the expense of potentially starving oneself, having left the altruistic arrangement.
Benefits and costs
Living in social groups is beneficial to members in terms of defence from predators. The larger the group, the less likely it is that any given individual will be predated. As a group it is easier to face attacks and drive away danger.
Food and resources are more easily accessible as a group because there are more individuals searching for resources, and hence any good finds can be communicated quickly to others.
Mating is clearly beneficial within a group, as individuals do not have to find mates and rely on opportunistic encounters. Socialising can in itself be a benefit when facing challenges. Finally, socialising infants is an advantage in social groups because it enables teaching the young about life, their environment and their fellow people. It gives them experience of conflict, cooperation and how relationships with others work.
Costs inherent to being part of a social group include facing conflict and competition, as well as being at a higher risk of getting a contagious infectious disease due to the close proximity of individuals.
For example, the addition of a new male to a social group of females with young offspring creates stress. This happens in species where new males can become infanticidal (killing infants) with the offspring of a new group.
In human societies, breakouts of bird flu or Ebola can become pandemics because humans can be tightly connected via international and transcontinental flights, and settlement like metropolises have very high population densities.
Insect social structure
Some insects, notably ants and some bees, display the highest level of organisation in their social structure. This structure is called eusociality and it involves a population whose individuals are reproductive or non-reproductive, and undertake different roles based on a caste system.
There may be a queen and a king who are solely reproductive, such as in termites. The rest of the population are sterile workers whose job it is to provide food by foraging and other tasks, as well as individuals tasked with defence of the colony. The roles are so strongly established, that the huge jaws of the defensive termites prevent them from being able to feed themselves. Thankfully, and perhaps a testament to the rationale and success of eusociality, the worker termites can feed them.
Unlike communication between primates, insect communication within the social group is achieved by innate behaviours.
Other characteristics of this type of insect social structure include the presence of multiple generations of individuals overlapping in the colony, and workers looking after offspring that are not their own.
Since they are unlikely to even be able to reproduce themselves, this is not surprising. The division of labour in the colony means that while the queen is taking over the reproductive function on behalf of all members, all others carry out the non-reproductive duties.
The ecological importance is social insects is great, as they act as keystone species in their ecosystems. Keystone species are so-called because they are the critical element in the integrity and function of the entire ecosystem. In architecture, the keystone is the final stone in an arch that is placed in the middle (and at the top) of the arch. It holds everything else together and confers the structural strength of the arch.
Particularly in human economies, social insects provide large and invaluable services towards pollination and pest control. Pollination amplifies plant reproduction, including that of many crops, and the contribution of insect pollination to this process and the resulting plant products goes into the billions of dollars. Many people actively introduce pollinating species onto their land, or charge others for the pollinating services provided through the insects pollinating from their land to neighbouring fields.