Levels of sociality in animal communities

The highest level of sociality in animals is eusociality. The word “eusocial” is derived from the Greek “eu” meaning " good". Eusociality defined by Wilson (1971, 1975) as the state where “…individuals of the same species cooperate in caring for the young; there is reproductive division of labour, with more or less sterile individuals working on behalf of fecund individuals; and there is an overlap of at least two generations in life stage capable of contributing of colony labour, so that offspring assist parents during some period of their life”. Three important characteristics are essential for a species to be called eusocial. There are: (1) cooperative brood care, (2) overlap between generations, and (3) reproductive cast differentiation. Reproductive cast differentiation means division of labour into reproductive- and non-reproductive casts.

The last of the eusocial traits, the existence of a subordinate, or even completely sterile worker caste, is the rarest of the three. It is also by far the most significant with reference to the further evolutionary potential of social life, for when individuals can be turned into specialised working machines, an intricate division of labour can be achieved and a complicated social organisation becomes attainable even with a relatively simple repertoire of individual behaviour. Colonies of social insects strike by their strength and organization. For example, the gigantic colonies of African driver ants, with more than 20 million workers, that live in large excavated soil cavities and hunt in armies for a wide range of arthropod and small vertebrate prey (Hö lldobler and Wilson, 1990).

Eusociality had been earlier considered a unique insects’ social structure. Michener and Lin (Michener, 1969; Lin and Michener, 1972) provided a classification of various levels of sociality in insects that had been later adopted by Wilson (1975). Indeed, all levels of sociality have analogues in social systems of other animals. Semisocial and eusocial systems that were earlier considered specific for social insects have been recently discovered in other, although few, species. Here is a classification of social systems extended to Arthropods (see: Gadakar, 1987, 1992).

1. Solitary: this term characterises the absence of any extend of sociality so that members of a species may not interact with each other at all except during courtship and mating.

2. Subsociality: the adults care for their own young for some period of time. Subsociality is widely spread. Examples may be found among crustaceans, spiders, mites, scorpions, millipedes, centipedes, cockroaches, crickets, bugs, and beetles.

3. Communal: members of the same generation use the same composite nest without cooperation in brood care. Many spiders and digger wasps can serve as examples of such social system.

4. Quasi-social is one step higher that communal because it involves cooperative brood care. Several species of spiders and Euglossine bees are good examples of this. Thus, quasi-social includes one of the three features of eusociality, namely, cooperative brood care.

5. Semi-social refers to a situation which incorporates two features of eusociality, namely, cooperative brood care, as well as reproductive cast differentiation (workers and queens) but lacks overlappimg of generations. Many wasps and bees are semisocial. For instance, most Polistine wasp colonies are merely semi-social at the beginning of the colony cycle. Only after the first daughter emerges and begins to work for the colony, is there overlapping of generations to qualify for the title eusocial.

6. Parasociality is a relatively new term which includes communality, quasi-sociality and semisociality but excludes the subsociality. This term is useful because there appear to have been two routes in the evolution of eusociality, namely, the Subsocial route and the Parasocial route.

6. Eusociality: it is a common practice to distinguish two levels:

“Primitively eusocial” refers to the cases such as many wasps and bees where there is little or no morphological caste differentiation, and as a consequence, there is often considerable flexibility in social roles that a given animal may adopt. Reversal of roles from queen to worker and vice-versa is also sometimes seen.

“Highly eusocial” refers to the most advanced societies where there is clear cut morphological caste differentiation and little, if any, flexibility in the social roles that adult animals may adopt. Caste determination involves rather complicated nutritional and hormonal mechanisms. All termites, most ants and many bees and wasps such as the honey bees and the vespine wasps, are highly eusocial.

It has become clear in the last decades that complex social systems are more widespread in the Animal Kingdom than researchers had expected. Sociality has been discovered in such unexpected creatures as lizards and spiders. Lizards possess variety and sophistication in social organization. Territorial males beat up intruders and have harems of females in the defended area (see Lizard Social Behaviour, Fox et al. (eds.), 2003). Some spider species live in colonies from a few to several hundred individuals and cooperate in web building, prey capture and nest maintenance in contrast to solitary species that are often aggressive and cannibalistic towards other spiders. Social spiders have evolved independently in Africa, the Middle East, the Americas, and Australia (Avilé s and Tufico, 1998; Evans, 1999; Jones and Parker, 2000).

There are many particular classifications of social systems created for different taxonomical groups of species. For example, all birds exhibit social behaviour, from pairing territoriality to common breeding. Brown (1978) suggested a general classification of avian communal systems. Detailed classification of communal breeding systems in birds is considered in the book edited by Koenig and Dickinson (2004). For ungulates Baskin (1976) suggested the following classification of social systems: companies based on personal acquaintance grouping around a dominating individual (typical for argali), parcels that syndicate several companies (typical for bison), harems, in which animals defend boundaries of communal territories (saiga, horses), and troops, in which males possessing local harems are tied by relations of dominance (some species of antelopes).

Eusociality recently has been expanded to a few more groups of organisms. In insects there are eusocial gall aphids (Aoki, 1977, 2003; Foster, 1990; Benton and Foster 1992; Abbot et al., 2001; Strassmann and Queller, 2001), gall-forming thrips (Thysanoptera), and a social weevil Austroplatypus incompertus (Kent and Simpson, 1992; for reviews see: Gadakar, 1993; Choe and Crespi, eds. 1997). In non-insects, eusociality has been described only for very specific rodents and shrimps. Naked mole rats live in complex underground tunnel systems in Africa and animals in the same nest are closely related, while only one female (the queen) reproduces, although workers, normally sterile, can ovulate when removed from the nest, presumably due to a lack of inhibition from the queen (see: Sherman, Jarvis and Alexander, eds. 1991). Snapping shrimp (Synalpheus regalis) lives inside sponges and each “colony” has 200-300 individuals, but only one queen reproduces, again the caster is probably not fixed- the workers remain totipotent and can potentially become queens when the queen shrimp is removed (Adler, 1996; Duffy, 1996). From the anthropomorphic point, it seems that “ eu ” does not sound good for sterile workers which are “enslaved” by members of reproductive castes. This is, however, a question of special discussion among students of eusocial organisms, who enslave whom. We will analyse some details of social structures of eusocial species further in this Part.

Besides truly eusocial species, many species of mammals and birds called cooperative breeders share the first and third characteristics of eusociality and partly the second in a sense that some members of a society serve as “ helpers ” in raising offspring and may not breed at all during their life. Nevertheless, vertebrate cooperative breeders are not eusocial because none but the naked mole rat has evolved a true sterile cast that works for the more fertile members of the community.

Further we will consider in details behavioural aspects of division of labour into reproductive and non-reproductive groups within communities.

34. EVOLUTIONARY AND BEHAVIOURAL ASPECTS OF ALTRUISM IN ANIMALS

The aim of this chapter is to analyse, although very briefly, roots of altruistic behaviour in animals in order to imagine the reasons for social and cognitive specialisation in animal communities.

An individual animal can play different roles in communities in dependence of its sex, age, relatedness, rank, and last but not least, intelligence. Individual’s path to the top of a hierarchically organised community may be paved by highly developed individual cognitive skills. A classical example came from Goodall’s (1971) book “In the shadow of man”: Mike, the young chimpanzee, gained top rank at once by making a terrible noise with empty metal jerricans stolen from researchers’ camp.

At the same time, the upper limit of the individual’s self-expression may be specified by the specific structure of communities. There are several variants of division of social roles, from division of labour in kin groups to thin balance between altruism and “parasitism” within groups of genetically unrelated individuals. Task allocation in animal communities can impose restrictions on display of members’ intelligence. For instance, rodents, termites and ants condemned to digging or baby-sitting or suicide defending can not forage, scout, or transfer pieces of information even if they are intelligent enough to do this. Furthermore, subordinate members of cooperatively breeding societies sacrifice their energy to dominating individuals serving as helpers or even as sterile workers.

If one should be sacrificed, why me? A problem of wild altruism. A famous Russian writer Lev Tolstoy in his novel “Anna Karenina” focused attention on several dramatic dilemmas in women’s life and among them on the dilemma: to give birth to children or to stay in a family as a perpetual helper. In many novels of the 19-th century lives of members of a facultative “sterile cast”, governess, were described: intelligent but poor members of the society often devoted their whole lives to caring for offspring of rich ones (recall, for example, Jane Eyre of Sharlotte Bronte). As we will see later in this Chapter, baby-sitting is one of the most costly and essential tasks in animal communities including humans. Some members of communities serve as helpers that are physically able to breed, but most never will.

To be serious, analysing the problem of division of roles in animal societies, we face the paradox of “ altruism ” - that is, when some individuals subordinate their own interests and those of their immediate offspring in order to serve the interests of a larger group beyond offspring. In evolutionary biology, an organism is said to behave altruistically when its behaviour benefits other organisms, at a cost to itself. The costs and benefits are measured in terms of reproductive fitness, or expected number of offspring. So by behaving altruistically, an organism reduces the number of offspring it is likely to produce itself, but increases the number that other organisms are likely to produce.

Eusociality can be considered an extreme of altruism in animal communities because sterile members of a group sacrifice the opportunity to produce their own offspring in order to help the alpha individuals to raise their young. How might such behaviour evolve if the genes promoting it are at such a disadvantage in competition with genes that oppose it? Evolution favours individuals whose inherited predisposition enabled them to behave in ways that maximise their reproductive success. What induces individuals to be engaged in behaviour that decreases their individual fitness?

Here is one of many interesting examples of biological altruism. The trade-off between individual sacrifice and colony welfare in social insects can be easily estimated in the cases of colony defence. Thus, in the green tree ant of Australia (Oecophylla smaragdina) ageing workers emigrate to special " barrack nests" located at the territorial boundary of the colony. When workers from neighbouring nests or other invaders cross the line, guards are the first to attack and to be attacked. Hö lldobler and Wilson (1990) joke that a principal difference between human beings and ants is that whereas we send our young men to war, they send their old ladies.

Charles Darwin saw that the paradox of altruistic behaviour of animals, in particular, social insects, was dangerous to his theory of evolution by natural selection. In his " Origin of Species" (1859) Darwin thought that sterile workers in a bee colony, being unable to transmit their genes, represent a special challenge to his theory of natural selection. This is because natural selection depends on the transmission of traits that convey selective advantages to the individuals, and these traits have to be determined genetically (so they are heritable). If workers are sterile, how can they transmit the " helping traits" to the next generation? Even more simple cases of cooperation in animal communities which are not based on differentiation between sterile and fertile castes can be difficult for evolutionary explanation in terms of individual fitness.

Darwin’s followers, and among them Thomas Henry Huxley (1888), the most enthusiastic popularizer of natural selection as a factor of evolution, concentrated mainly on inter- and intra-species competition arguing that “the animal world is on about the same level as the gladiator’s show” and thus nature is an arena for pitiless struggle between self interested creatures. This concerns also human beings, although Darwin himself discussed the idea of how altruism can evolve in human societies in “ The Descent of Man” (1871). Kropotkin (1902) was one of the first thinkers who countered these arguments and considered mutual aid as a factor of evolution in particular of human evolution in his famous book “Mutual Aid: A Factor in Evolution”. He viewed cooperation as an ancient animal and human legacy.

A thin balance between conflicts and cooperation in animal societies met genetic explanation when the theory of heredity had been developed. The question was raised whether altruistic behaviour may be advantageous for genes in populations.

To see the problem, let us consider an example from social life of group-living animals. In settlements of wild rabbits one can observe that some rabbits drum by hind legs when they see a predator instead of flying immediately to the nearest hole. Being informed by this alarm signal, other rabbits have time to fly. Some members of a group of rabbits give alarm drums when they see predators, but others do not. By selfishly refusing to give an alarm signal, a rabbit can reduce the chance that it will itself be attacked, while at the same time benefiting from the alarm signals of others. So we should expect natural selection to favour those rabbits that do not give alarm signals over those that do. If we consider a set of genes within a community, then the number of relatives of an “altruistic” individual should be taken into account. If there are no relatives of the drumming rabbit within the group, then genes which determine the drumming behaviour will die with this hero in jaws of a predator. But if the number of relatives which share genes with the drummer untimely deceased is enough to increase inclusive fitness of the group, then natural selection will favour “drumming” genes to be transmitted to next generations.

Of course, this does not mean that the drumming rabbit makes a decision to sacrifice its own life to the rest of community (Fig. X-4). It simply acts with accordance with its inherited behavioural program. Drumming movements by hind legs as a signal of vigilance are characteristic for many species and display early in the ontogenesis. Just put a baby porcupine with non-solidified needles on your palm and feel how it is clattering by its hind legs.

So, one of possible explanations of altruistic behaviour of those wild heroes that “cry wolf” at their own risk is that they support their own relatives. There are enough drummers in wild populations because each of them supports enough of its relatives sharing genes with it. A group containing a high proportion of drummers will have a survival advantage over a group containing a lower proportion of them. This concerns alarm-calling birds and monkeys, ungulates defending calves of herd members, beavers that spend their time to keep watch over “common” babies of the group and many others.

There are two main evolutionary ideas underlying explanations of altruistic behaviour: the idea of group selection and the idea of kin selection. The idea that group selection might explain the evolution of altruism was first broached by Darwin. In “ The Descent of Man” (1871), Darwin discussed the origin of altruistic and self-sacrificial behaviour among humans and suggested that the altruistic behaviour may have evolved by a process of between-group selection.

A fundamental work of Ronald Fisher “The Genetical Theory of Natural Selection” (1930) grounded neo-Darwinism on the base of ideas of gene dominance and fitness. Fisher was a mathematician and elaborated new theorems and methods in statistics. In particular his “Statistical Methods for Research Workers (1925) has served to generations of researchers. Design of experiments suggested by Fisher was based on his own breeding experiments with mice, snails and poultry. Fisher's fundamental theorem of natural selection was originally stated as: " The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time." On the base of Fisher’s concept the modern genetic theory of evolution started to develop, pointing out how selflessness could evolve even if individuals are not organized into societies.

Kin selection and reciprocal altruism. In 1932 and again in 1955 Haldane suggested that one’s genes can be multiplied in a population even if an individual never reproduces, providing its actions favour the differential survival and reproduction of collateral relatives, such as siblings, nieces, and cousins, to sufficient degree. This hypothesis later came to be known as kin selection, the phrase coined by Maynard Smith.

In the 1960s and 1970s two theories emerged which tried to explain evolution of altruistic behaviour: “kin selection” or “ inclusive fitness ” theory, due to Hamilton (1964), and the theory of reciprocal altruism, due primarily to Trivers (1971) and Maynard Smith (1974). In this section we will briefly consider the theory of inclusive fitness.

Hamilton introduced a concept of “inclusive fitness” reasoning that altruistic behaviour should evolve when the altruist obtains an evolutionary gain via the genes it shares with the recipient of its altruism. This concept can explain how a trait can be inherited without direct reproduction. Someone could still have a reproductive fitness, even if he/she has no direct offspring. So while the “traditional fitness” only counts how many children one has, inclusive fitness takes into account all others who share genes with the individual. Hamilton demonstrated rigorously that an altruistic gene will be favoured by natural selection when a certain condition, known as Hamilton's rule, is satisfied. In its simplest version, the rule states that

rb > c

where

r = the genetical relatedness of the recipient to the actor, usually defined as the probability that a gene picked randomly from each at the same locus is identical by descent.

b = the additional reproductive benefit gained by the recipient of the “altruistic” act,

c = the reproductive cost to the individual performing the act.

Technically, the correct definition for relatedness (r) in Hamilton's rule describes it as a regression measure. Regressions, unlike probabilities, can be negative, and so it is not implausible for there to be negative relatedness between two individuals. Negative relatedness simply means that two individuals are less genetically alike than average, and this can lead to the evolution of spiteful behaviours. The reader can find an analysis of limitations concerning Hamilton's rule in Rice (2004).

Kin selection theory explains cooperation in a wide variety of species although recent studies suggest alternative models of evolution of eusociality in social insects (for reviews see: Ratnieks, 1988; Page et al., 1989; Boomsma and Grafen, 1991; Heinze et al., 1994; Queller et al., 1997; Crozier and Pamilo, 1996; Kaib, 1999; Gadakar, 1994, 2001; Reznikova, 2003; Wilson and Hö lldobler, 2005).

Brown (1970) was one of the first field ethologists who incorporated Hamilton’s ideas on altruism and inclusive fitness applying them to his field studies on Mexican Jays and interpreted behaviour of nest helpers in terms of the theory of inclusive fitness. Since that, the 70-th saw the initiation of many long term studies of cooperative breeders. Not counting eusocial species, cooperative breeding has been described in several hundreds of bird species, in primates (marmosets), carnivorous (African wild dogs), and mongooses (such as dwarf mongooses and meerkats).

The main mechanism of kin-selection is nepotism, that is, preferential treatment for kin. Many social species including humans form nepotistic alliances to keep the flag of family interests flying. There is much evidence that animals behave nepotistically when facing vital problems in their life. For example, pig-tailed macaques, when helping group members who were attacked, do so most readily for close relatives, less readily for more distant relatives, and least readily for non-relatives (Massey, 1977). To do so, animals should recognise their relatives but there is no a strong correlation between nepotism and recognition ability. Mateo’s (2002, 2004) data on close species of ground squirrels support a hypothesis that kin favouritism and recognition capacities can evolve independently, depending on variation in the costs and benefits of nepotism for a given species. A highly nepotistic species, Spermophilus beldingi, produces odours from two different glands that correlate with relatedness (“kin labels”). Using these odours ground squirrels make accurate discriminations among never before encountered unfamiliar kin. A closely related species S. lateralis similarly produces kin labels and discriminates among kin, although it shows no evidence of nepotistic behaviour.

For kin-selection to occur it is not strongly necessary for individuals to recognise their kin. Returning to the example with rabbits that alarm its neighbours by drumming, it is not that these animals must have the ability to discriminate relatives from non-relatives, less still to calculate coefficients of relationship. Many animals can in fact recognize their kin, often by smell, but kin selection can operate in the absence of such ability. If an animal behaves altruistically towards those in its immediate vicinity, then the recipients of the altruism are likely to be relatives, given that relatives tend to live near each other.

The ability to discriminate between kin and non kin display in many species either due to the innate recognition of character traits associated with relatedness or due to the recognition of specific individuals with whom they have grown up (Wilson, 1987; Hepper, 1991; see also: “Kin recognition in animals”, ed. by Fletcher and Michener, 1987; “Kin recognition” ed. Hepper, 2005). Nepotism is not always clearly altruistic or even necessarily requiring genuine cognitive skills. For instance, most young plains spadefoot toads are detritivorous and congregate with kin. Some of tadpoles become carnivorous, and such individuals live more solitarily and at least when satiated prefer to eat non-kin than kin reducing the damage they might otherwise do to the survivorship of their relatives (Pfennig, 1992). Cannibalistic tiger salamander larvae, Ambystoma tigrinum, also discriminate kin and preferentially consume less related individuals (Pfenning et al., 1999). Genetic analyses of numerous fish species have shown that shoals formed by larvae often consist of closely related kin (Krause et al., 2000). Recent experiments have shown that juvenile zebrafish can recognise and prefer their siblings to unrelated conspecifics based on olfactory cues (Mann et al., 2003).

Chimpanzees possibly solve much more complex problem of kin recognition. Mechanisms underlying male cooperation in chimpanzee’s communities are still enigmatic (van Hooff and van Schaik, 1994). Chimpanzees live in unit-groups, whose members form temporary parties that vary in size and composition. Females usually leave their natal groups after reaching sexual maturity whereas males do not disperse (Goodall, 1971, 1986; Ghiglieri, 1984; Nishida, 1990). Male chimpanzees develop strong bonds with others in their communities being engaged in a variety of social behaviour. Field observations together with DNA analysis showed that such affiliations join together males of close rank and age rather than males belonging to the same matrilines (Mitani et al., 2000; Mitani and Watts, 2005; Lukas et al., 2005). It is worth to note that females give birth to a single offspring only once every 5-6 years, so brothers obviously should have essential disparity in years. Do chimpanzees bias their behaviour to non-kin? Although current evidence indicates that Old World monkeys are unable to discriminate paternal relatives (Frederikson and Suckett, 1984; Erhart et al., 1997), a recent study suggests that chimpanzees may be able to identify kin relationships between others on the basis of facial features alone overmatching humans in sorting photographs by features of family relatedness (Parr and deWaal, 1999). As Mitani et al. note (2002), this raises an intriguing possibility that male chimpanzees might be able to recognise their paternal relatives.

The importance of kinship for the evolution of altruism is widely accepted today, on both theoretical and empirical grounds. Kin selection provides a persuasive explanation of eusocial behaviour and communal breeding in many species. However, as it has been noted before, altruism is not always kin-directed, and there are many examples of animals behaving altruistically towards non-relatives.

The theory of reciprocal altruism is an attempt to explain the evolution of altruism among non-kin. Reciprocity involves the non-simultaneous exchange of resources between unrelated individuals. The basic idea is straightforward: it may benefit an animal to behave altruistically towards another, if there is an expectation of the favour being returned in the future: “If you scratch my back, I'll scratch yours”. In his now classic paper “The evolution of reciprocal altruism”, Trivers (1971) argued that genes for cooperative and altruistic acts might be selected if individuals differentially distribute such behaviours to others that have already been cooperative and altruistic towards the donor. The cost to the animal of behaving altruistically is offset by the likelihood of this return benefit, permitting the behaviour to evolve by natural selection. This evolutionary mechanism is termed “reciprocal altruism”.

A study of blood-sharing among vampire bats cited before suggests that reciprocation does indeed play a role in the evolution of this behaviour in addition to kinship (Wilkinson, 1984, 1990). Vampire bats Desmodus rotundus typically live in groups composed largely of females, with a low coefficient of relatedness. It is quite common for a vampire bat to fail to feed on a given night. This is potentially fatal, for bats die if they stay without food for more than a couple of days. On any given night, bats donate blood (by regurgitation) to other members of their group who have failed to feed, thus saving them from starvation. Since vampire bats live in small groups and associate with each other over long periods of time, the preconditions for reciprocal altruism - multiple encounters and individual recognition - are likely to be met. Wilkinson's study showed that bats tend to share food with their close associates, and are more likely to share with those who had recently shared with them. These findings provide a confirmation of reciprocal altruism theory.

Maynard Smith (1974, 1989) suggested that cooperative behaviour can be an evolutionary stable strategy, that is, the strategy for which no mutant strategy has higher fitness (see details in Part VII). His concept is based on the game theory which, in turn, attempts to model how organisms make optimal decisions when these are contingent on what others do.

Cognitive aspects of reciprocal altruism are the source of a great deal of debates. Indeed, cooperation based on reciprocal altruism requires certain basic cognitive prerequisites, and among them repeated interactions, memory, and ability to recognize individuals. Experimental evidences that reciprocal altruism relies on cognitive abilities that make current behaviour contingent upon a history of interaction comes from primate studies. For example, deWaal and Berger (2000) made a pair of brown capuchins work for food by pulling bars to obtain trains with rewards. They have found that monkeys share rewards obtained by joint effort more readily than rewards obtained individually. DeWaal (1997, 2005) also demonstrates a strong tendency to “pay” for grooming by sharing food in captive chimpanzees who based their “service economy” on remembering reciprocal exchanges.

In many examples of cooperation among non related animals such as grooming and food sharing behaviour in primates, cooperative hunting in lions, wolves, hyenas and chimpanzees, it is still discussed whether they can be interpreted in terms of reciprocal altruism. Several alternative concepts exist which explain evolution of altruistic and cooperative behaviour (Dawkins, 1982; Clutton-Brock and Parker, 1995; Sober and Wilson, 1998). One can find detailed analysis of evolutionary aspects of cooperative behaviour in a chapter of “Behavioural Ecology” (1991) written by Emlen, as well as in “Cooperative breeding in mammals” edited by Solomon French (1997), and in Dugatkin (1997, 2005). In this book we will further consider several examples of social specialisation in animal communities in order to imagine how animal intelligence fall into patterns of social specificity.

35. INTELLIGENCE IN A CONTEXT OF THE FUNCTIONAL STRUCTURE OF ANIMALS’ COMMUNITIES

In recent experimental works devoted to animal cognition authors routinely indicate not only weight, age and sex of members of species investigated but also their rank in a local conspecific community or at least in a laboratory group. It is necessary because results obtained in experimental trials often depend on individual’s social role. Modern experimental cognitive ethology does not consider members of populations equal; instead, their membership in different functional structures is considered an important factor that impacts their intellectual potentials.

The main theme of this chapter is social specialisation in animal communities. In Part VII behavioural and cognitive specialisation of individuals within populations was described mainly from the viewpoint of individuals’ inherited predisposition for certain types of behaviour as well as certain forms of learning. Here we are interested in individual’s specialisation that can be based on its’ social role within local community. In some situations behavioural, social, and cognitive specialisation can be congruent. Perhaps in such situations individuals are lucky to be in harmony with their mentality and environment. May be this is the formula of happiness. It is an intriguing problem for cognitive ethologists: is there a room for intelligence within frames of social specialisation in animal communities?

There are many gradations of social specialization, from rigid caste division to constitutional and (or) behavioural bias towards certain roles in groups accomplishing certain tasks.