Sociality
From the bustling colonies of ants to the complex social structures of primates, the animal kingdom is rich with examples of sociality—the tendency for individuals to live and cooperate in groups. This deep-seated drive shapes entire ecosystems and species' survival strategies, revealing fascinating insights into the evolutionary pressures that bind individuals together. Join us as we explore the diverse spectrum of social life, from simple parental care to the most intricate societies on Earth. Sociality is an evolutionary adaptation, driven by pressures like predation and the need for cooperative resource management. Animal sociality exists on a broad spectrum, ranging from basic parental care to highly complex societies with specialized roles. Eusociality, the most advanced form, involves overlapping generations, cooperative care, and a division of labor, often with specialized castes.
AI Summary
From the bustling colonies of ants to the complex social structures of primates, the animal kingdom is rich with examples of sociality—the tendency for individuals to live and cooperate in groups. This deep-seated drive shapes entire ecosystems and species' survival strategies, revealing fascinating insights into the evolutionary pressures that bind individuals together. Join us as we explore the diverse spectrum of social life, from simple parental care to the most intricate societies on Earth.
- Sociality is an evolutionary adaptation, driven by pressures like predation and the need for cooperative resource management.
- Animal sociality exists on a broad spectrum, ranging from basic parental care to highly complex societies with specialized roles.
- Eusociality, the most advanced form, involves overlapping generations, cooperative care, and a division of labor, often with specialized castes.
What is Sociality?
At its heart, sociality is about connection—the degree to which animals in a population choose to associate in groups and form cooperative societies. This inclination to gather is often called gregariousness, and it underpins many of the most fascinating behaviors we observe in the natural world.
Why would animals choose to live together? It's often a direct response to evolutionary pressures. Imagine a mother wasp staying diligently by her nest, protecting her larvae from hungry parasites. This simple act of parental care significantly boosts the survival chances of her young, showcasing how social behaviors can be selected through natural selection.
The Foundation: Parental Investment
This wasp's dedication introduces us to a fundamental concept: parental investment. It's any resource—be it time, energy, or even social standing—a parent expends to benefit their offspring. While crucial for survival, this investment also means fewer resources for future reproduction or aiding other relatives.
An animal that simply cares for its young without exhibiting other social traits is described as subsocial. But if an animal takes sociality to a higher level, consistently interacting and cooperating with others beyond just raising young, it earns the title of a 'social animal'.
The Pinnacle: Eusociality
The absolute peak of sociality, as recognized by scientists, is eusociality. Think of ant colonies or beehives. A eusocial species displays a remarkable set of characteristics: overlapping adult generations, cooperative care of young, and a clear division of labor in reproduction.
In its most refined form, eusociality even involves a biological caste system, where individuals are born into specific roles, like workers, soldiers, or queens. This level of specialization is incredibly efficient and allows eusocial species to dominate many ecosystems.
Beyond the structural advantages, social animals often exhibit higher cognitive abilities. Predators like spotted hyenas and lions, which hunt in groups, have been observed to be more innovative problem-solvers than their solitary counterparts, such as leopards and tigers. Teamwork, it seems, can make you smarter.
Presociality: The Middle Ground
While jaguars live solitary lives, only coming together for courtship and mating, many species show a degree of sociality that falls short of full eusociality. This intermediate category is known as presociality. Though presocial species are far more common, eusocial species often achieve disproportionately large populations due to their extreme cooperation.
The entomologist Charles D. Michener, building on Suzanne Batra's earlier work, developed a classification system for presociality in 1969. He introduced terms like subsocial, communal, and semisocial to categorize the varying degrees of social behavior observed, especially in insects like bees.
Subsociality: A Parent's Touch
Subsociality is a widespread phenomenon across the animal kingdom. It's defined by parents caring for their offspring for some duration. Even a short period of parental attention qualifies a species as subsocial. However, if adults also associate with other adults, they move into different social classifications.
This behavior has evolved independently many times, particularly among winged insects. It's a testament to the evolutionary benefit of protecting one's young directly, ensuring their survival beyond the vulnerable egg or larval stages.
Solitary but Social: The Best of Both Worlds?
Then there are the 'solitary but social' animals. These fascinating creatures forage alone, maintaining their individual space, but choose to share communal sleeping sites or nests. It's a balance between independence and the safety that comes from proximity.
Among primates, this is common in nocturnal species like mouse lemurs, lorises, and orangutans. Females often have overlapping home ranges, creating a loose social network, while males typically remain more isolated and are often evicted from the group upon reaching maturity.
Remarkably, some individual cetaceans—dolphins and whales—also exhibit this behavior, choosing to live apart from their own kind but regularly interacting with humans. Famous examples include Pelorus Jack, Tião, and Fungie, who became beloved local figures in their respective coastal communities.
Parasociality: Shared Homes, Shared Lives
Sociobiologists group communal, quasisocial, and semisocial animals into a broader meta-category called parasociality. The defining traits here are parental investment and a shared, cooperative dwelling. These groups build upon subsociality by adding varying degrees of communal living.
Within parasociality, distinctions exist: communal groups share a nest but each adult cares for its own young. Quasisocial animals take it a step further, cohabiting and sharing the responsibilities of brood care. Semisocial populations have all these features, plus a nascent biological caste system where individuals might be reproductively specialized.
The crucial step from parasociality to full eusociality involves overlapping adult generations. This means not only do adults cooperate in raising young, but older generations continue to contribute to the care of the newest offspring, creating a continuous, multi-generational effort within the colony.
The Wonders of Eusociality
Eusocial societies are truly marvels of the natural world, characterized by overlapping adult generations, cooperative brood care, and a strict division of reproductive labor. When individuals are born with physical traits specific to their caste that never change, it represents the highest degree of this social organization.
Eusociality has evolved independently across several insect orders. The most famous examples are found among the Hymenoptera—ants, bees, and wasps—and the Blattodea, which include termites. Other insects like certain beetles, bugs, and thrips also exhibit this complex social structure. Species lacking morphological caste differentiation are considered primitively eusocial.
Beyond insects, some mammals present intriguing, albeit debated, cases of primitive eusociality. The naked mole-rat and Damaraland mole-rat, for instance, live in highly inbred colonies with a single reproductive queen. They cooperatively raise their siblings and relatives, especially in challenging environments where resources are scarce.
Even some crustaceans display eusociality. The snapping shrimp, Synalpheus regalis, forms colonies of closely related individuals within tropical reefs and sponges. Here, a single breeding female is protected by numerous male defenders with enlarged claws, creating a fortress defense strategy for their shared living space.
However, the definition of eusociality remains a lively topic of scientific debate. Some argue that a truly eusocial species must have an irreversibly sterile caste. If this strict criterion is applied, then the mole-rats and, indeed, humans, would not quite fit the bill for full eusociality.
Are Humans Eusocial?
In a controversial claim, renowned biologists E. O. Wilson and Bert Hölldobler suggested in 2005 that humans exhibit sufficient sociality to be considered a eusocial species. Their argument points to our complex division of labor, cooperative child-rearing, and multi-generational living arrangements. It's a thought-provoking idea that challenges our understanding of both human nature and the very definition of sociality.
Article
Sociality
Herd of American bison at Genesee Park
Sociality is the degree to which individuals in an animal population tend to associate in social groups (for which, the desire or inclination is known as gregariousness) and form cooperative societies.
Sociality is a survival response to evolutionary pressures. For example, when a mother wasp stays near her larvae in the nest, parasites are less likely to eat the larvae. Biologists suspect that pressures from parasites and other predators selected this behavior in wasps of the family Vespidae.
This wasp behaviour demonstrates the most fundamental characteristic of animal sociality: parental investment. Parental investment is any expenditure of resources (time, energy, social capital) to benefit one's offspring. Parental investment detracts from a parent's capacity to invest in future reproduction and aid to kin (including other offspring). An animal that cares for its young but shows no other sociality traits is said to be subsocial.
An animal that exhibits a high degree of sociality is called a social animal. The highest degree of sociality recognized by sociobiologists is eusociality. A eusocial taxon is one that exhibits overlapping adult generations, reproductive division of labor, cooperative care of young, and—in the most refined cases—a biological caste system.
One characteristic of social animals is the relatively high degree of cognitive ability. Social mammal predators such as spotted hyena and lion have been found to be better than non-social predators such as leopard and tiger at solving problems that require the use of innovation.
Presociality
Sociality
Solitary animals such as the jaguar do not associate except for courtship and mating. If an animal taxon shows a degree of sociality beyond courtship and mating, but lacks any of the characteristics of eusociality, it is said to be presocial. Although presocial species are much more common than eusocial species, eusocial species have disproportionately large populations.
The entomologist Charles D. Michener published a classification system for presociality in 1969, building on the earlier work of Suzanne Batra (who coined the words eusocial and quasisocial in 1966). Michener used these terms in his study of bees, but also saw a need for additional classifications: subsocial, communal, and semisocial. In his use of these words, he did not generalize beyond insects. E. O. Wilson later refined Batra's definition of quasisocial.
Subsociality
Subsociality is common in the animal kingdom. In subsocial taxa, parents care for their young for some length of time. Even if the period of care is very short, the animal is still described as subsocial. If adult animals associate with other adults, they are not called subsocial, but are ranked in some other classification according to their social behaviours. If occasionally associating or nesting with other adults is a taxon's most social behaviour, then members of those populations are said to be solitary but social. See Wilson (1971) for definitions and further sub-classes of varieties of subsociality. Choe & Crespi (1997) and Costa (2006) give readable overviews.
Subsociality is widely distributed among the winged insects, and has evolved independently many times. Insect groups that contain at least some subsocial species are shown in bold italics on a phylogenetic tree of the Neoptera (note that many non-subsocial groups are omitted):
Solitary but social
The mouse lemur is a nocturnal, solitary-but-social lemur native to Madagascar.
Solitary-but-social animals forage separately, but some individuals sleep in the same location or share nests. The home ranges of females usually overlap, whereas those of males do not. Males usually do not associate with other males, and male offspring are usually evicted upon maturity. However, this is opposite among cassowaries, for example. Among primates, this form of social organization is most common among the nocturnal strepsirrhine species and tarsiers. Solitary-but-social species include mouse lemurs, lorises, and orangutans.
Some individual cetaceans adopt a solitary but social behavior, that is, they live apart from their own species but interact with humans. This behavior has been observed in species including bottlenose dolphin, common dolphin, striped dolphin, beluga, Risso's dolphin, and orca. Notable individuals include Pelorus Jack (1888–1912), Tião (1994–1995), and Fungie (1983–2020). At least 32 solitary-sociable dolphins were recorded between 2008 and 2019.
Parasociality
Sociobiologists place communal, quasisocial, and semisocial animals into a meta-class: the parasocial. The two commonalities of parasocial taxa are the exhibition of parental investment, and socialization in a single, cooperative dwelling.
Communal, quasisocial, and semisocial groups differ in a few ways. In a communal group, adults cohabit in a single nest site, but they each care for their own young. Quasisocial animals cohabit, but they also share the responsibilities of brood care. (This has been observed in some Hymenoptera and spider taxa, as well as in some other invertebrates.) A semisocial population has the features of communal and quasisocial populations, but they also have a biological caste system that delegates labor according to whether or not an individual is able to reproduce.
Beyond parasociality is eusociality. Eusocial insect societies have all the characteristics of a semisocial one, except overlapping generations of adults cohabit and share in the care of young. This means that more than one adult generation is alive at the same time, and that the older generations also care for the newest offspring.
Eusociality
Sociality
Giant honey bees cover the honeycomb of their nest.
Eusocial societies have overlapping adult generations, cooperative care of young, and division of reproductive labor. When organisms in a species are born with physical characteristics specific to a caste which never changes throughout their lives, this exemplifies the highest acknowledged degree of sociality. Eusociality has evolved in several orders of insects. Common examples of eusociality are from Hymenoptera (ants, bees, sawflies, and wasps) and Blattodea (infraorder Isoptera, termites), but some Coleoptera (such as the beetle Austroplatypus incompertus), Hemiptera (bugs such as Pemphigus spyrothecae), and Thysanoptera (thrips) are described as eusocial. Eusocial species that lack this criterion of morphological caste differentiation are said to be primitively eusocial.
Two potential examples of primitively eusocial mammals are the naked mole-rat and the Damaraland mole-rat (Heterocephalus glaber and Fukomys damarensis, respectively). Both species are diploid and highly inbred, and they aid in raising their siblings and relatives, all of whom are born from a single reproductive queen; they usually live in harsh or limiting environments. A study conducted by O'Riain and Faulkes in 2008 suggests that, due to regular inbreeding avoidance, mole rats sometimes outbreed and establish new colonies when resources are sufficient.
Eusociality has arisen among some crustaceans that live in groups in a restricted area. Synalpheus regalis are snapping shrimp that rely on fortress defense. They live in groups of closely related individuals, amidst tropical reefs and sponges. Each group has one breeding female; she is protected by a large number of male defenders who are armed with enlarged snapping claws. As with other eusocial societies, there is a single shared living space for the colony members, and the non-breeding members act to defend it.
It remains debated whether a species needs to have an irreversibly sterile caste to be considered "eusocial". In such a narrowed definiton, the two mammals mentioned above as well as humans cannot be considered eusocial.
Human eusociality
E. O. Wilson and Bert Hölldobler controversially claimed in 2005 that humans exhibit sufficient sociality to be counted as a eusocial species.