Why do so many animals choose to live in social groups?

By Jemima Frame

There are a huge number of animal species that choose to live in social groups, despite the negative consequences that this brings to the individuals, especially lower ranking ones. So why do so many animals choose to do this? While there are most definitely benefits that come with living in a group, these do not necessarily outweigh the cons, and so many animals have evolved to survive in this way. Could there be unknown benefits to this social dynamic, or do they, just like humans, live for more than just survival and enjoy others company?

It is important to note that living in a social group can bring many benefits to an animal. Arguably the most important benefit being a lowered risk of predation which is decreased in three ways; if there are more individuals on the lookout predators are more likely to be detected, a larger group leads to a lower risk of predation to each individual (an effect called ‘selfish herd theory’) and finally, a group of prey can successfully drive a predator away (Swedell, 2012). An increased group size can also mean that food is more easily detected due to more animals foraging for it, and in certain social groups, where mating occurs within the community, mates are readily available leading to higher reproductive success (Swedell, 2012). These benefits are certainly not small and lend significant advantages to animals living in social groups. Other advantages include infants having the ability to play with one another, and in doing so learning key motor skills such as fighting, as well as adult animals keeping each other clean through allogrooming. 

While there are many benefits to living in a social group there are also significant cons. While animals living in a group are more likely to be able to defend themselves against predators, they also bring more attention to themselves and are more likely to be spotted by a predator, putting their infants at risk. One animal by themself can easily be discreet and stay relatively hidden from predators, a group cannot hide, and they therefore have to rely on strength in numbers to defend themselves. The increased social contact that comes with living in a group also means an increased risk of disease. There is an increased transmission of pathogens throughout social communities, meaning that a single disease could wipe out a whole community at an exponential rate (Swedell, 2012). A solitary animal with a disease would be far less likely to pass on the pathogens to another individual, and the spread of the disease would occur at a much slower rate as a consequence. While these threats to animals living in a social group are important, the most important threat is within the group. Conflict will often arise between individuals of a group, whether it be over a mating partner, food or a higher ranking status, these fights can be deadly, occasionally resulting in serious injuries which renders the animal unable to protect itself against predators (McGlynn, 2010). These conflicts not only put the two individuals fighting at risk, it also increases the stress levels of others in the group and studies have shown that animals involved in a number of conflicts can develop chronic psychological stress, which is extremely bad for their health. 

Individuals in a social group will generally have a hierarchical society, with some animals ranking higher than others. These higher-ranking individuals will benefit much more from a social group than the lower ranking individuals who will reap very little of the benefits but all of the costs. For example, in meerkat mobs there is a dominant female and a dominant male, and between 2 to 50 subordinate individuals, who will protect and feed the dominant pairs offspring. These subordinate individuals will put the dominant female’s offspring ahead of furthering their own lineage and will put themselves at risk in order to protect the offspring, for no apparent benefit other than the protection of living in a group (Meerkat: A Dynasties Special, 2020). While protecting meerkat infants is beneficial for the species as a whole, it provides no benefit to an individual with no relation to the offspring, and yet these animals have evolved to live in a social group where this occurs. 

There is no evidence that living in a social group is better than solitary individuals, or vice versa, and different animals have evolved to live in both these ways with neither outcompeting the other in terms of survival rate. For example, mosquitoes are asocial creatures and are thriving with a population of trillions, whereas bees are very social creatures who also have a healthy population of trillions (McGlynn, 2010). Neither population dynamic seems to be better than the other, they have just evolved in different ways. Evolution occurs based on the benefit of an overall species, not an individual’s selfish benefit, which might explain why lower ranking individuals will continue to remain in social groups despite it not being in their best interests for survival and reproduction. From an overall perspective for the meerkat mob the subordinate individuals protecting the infants ensures that there is a new generation of meerkats after them, even if it costs a few of the individuals their lives, therefore the social group is beneficial overall and hence evolved that way. While animals living in a social group may be costly to some individual’s reproductive success and survival, the overall benefit outweighs the cost of these individuals, therefore a huge amount of (very different!) animals have evolved to have this social dynamic in their populations. 

References:

  • Swedell, L. (2012) Primate Sociality and Social Systems. Nature Education Knowledge 3(10):84
  • McGlynn, T. (2010) How Does Social Behavior Evolve? Nature Education Knowledge 3(10):69
  • Meerkat: A Dynasties Special. (2020) Dynasties. BBC One. Monday 28th December.

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