- Dec. 19, 2011
Social behavior among primates — including humans — has a substantial genetic basis, a team of scientists has concluded from a new survey of social structure across the primate family tree.
The scientists, at the University of Oxford in England, looked at the evolutionary family tree of 217 primate species whose social organization is known. Their findings, published in the journal Nature, challenge some of the leading theories of social behavior, including:
¶ That social structure is shaped by environment — for instance, a species whose food is widely dispersed may need to live in large groups.
¶ That complex societies evolve step by step from simple ones.
¶ And the so-called social brain hypothesis: that intelligence and brain volume increase with group size because individuals must manage more social relationships.
By contrast, the new survey emphasizes the major role of genetics in shaping sociality. Being rooted in genetics, social structure is hard to change, and a species has to operate with whatever social structure it inherits.
If social behavior were mostly shaped by ecology, then related species living in different environments should display a variety of social structures. But the Oxford biologists — Susanne Shultz, Christopher Opie and Quentin Atkinson — found the opposite was true: Primate species tended to have the same social structure as their close relatives, regardless of how and where they live.
The Old World monkeys, for example, a group that includes baboons and macaques, live in many habitats, from savanna to rain forest to alpine regions, and may feed on fruit or leaves or grass. Yet all have very similar social systems, suggesting that their common ancestry — and the inherited genes that shape behavior — are a stronger influence than ecology on their social structure.
“We were trying to test accepted models of social evolution and have shown that in primates it happens via a different pathway than we always assumed,” Dr. Shultz said.
The researchers suggest that sociality emerged about 52 million years ago. The earliest primates sought safety by being solitary and inconspicuous, moving only at night. It seems that when they shifted to daytime activity, they sought safety in numbers.
It was from these loose, unstructured groups that more specific forms of primate social behavior began to evolve, some 16 million years ago. These included pair bonding, an arrangement adopted by gorillas and humans, and the multi-male, multi-female groups typical of baboons and chimpanzees.
The fact that related species have similar social structures, presumably because the genes for social behavior are inherited from a common ancestor, “spells trouble” for ecological explanations, Joan B. Silk, a primate expert at the University of California, Los Angeles, wrote in a commentary in Nature. Also, the finding that there has not been a steady progression from small groups to large ones challenges the social brain hypothesis, Dr. Silk said.
The Oxford survey confirms that the structure of human society, too, is likely to have a genetic basis, since humans are in the primate family, said Bernard Chapais, an expert on human social evolution at the University of Montreal.
“Evolutionary change in any particular lineage is highly constrained by the lineage’s phylogenetic history,” Dr. Chapais said, referring to the evolutionary family tree. “This reasoning applies to all species, including ours. But in humans, cultural variation hides both the social unity of humankind and its biological foundation.”
Human multifamily groups may have arisen from the gorilla-type harem structure, with many harems merging together, or from stable breeding bonds replacing sexual promiscuity in a chimpanzee-type society, Dr. Chapais said.
In his book “Primeval Kinship” (Harvard, 2008), he describes a further stage in human social evolution that occurred when individual bands allied with those with whom they exchanged daughters. The bands in such a marital exchange system formed a tribe, taking human society to a level of organization beyond that of chimpanzee society.
With chimps, territorially based bands also exchange daughters to avoid incest but continue to fight with one another to the death because the males cannot recognize their kinship with relatives in neighboring bands.
All social primate species should display social behaviours, including physical behaviours and vocal and visual displays relevant to the species. Normal behaviour is that expected of physically and psychologically healthy animals. Changes in behaviour and the presence/absence of particular behaviours can provide a valuable indication of the animal's welfare state. Keepers should be familiar
with the full normal behavioural repertoire of the species and individuals they keep, including facial expressions, vocalisations, postures and activities. Primate keepers should recognise signs of good and poor welfare, as abnormal behaviour can mean disease, injury or stress. They should know what steps to take if signs of poor welfare are observed. All gregariously social primate species should display social behaviours,
including physical behaviours and vocal and visual displays relevant to the species. These include, but are not limited to, social grooming, food sharing, communal resting, and interactive play that's applicable to the species. Primates should be housed in stable groups of suitable size and composition to allow the full expression of these behaviours. Social interaction with companions of the same species not only provides essential stimulation
and learning opportunities, but it also provides a source of comfort, reassurance and enjoyment. Removing a primate from its family or social group may have adverse psychological, emotional and physical welfare implications for the individual, and for the remaining primates. This is particularly so for an infant and its mother, and for species forming pair bonds. Social grooming is an extremely important behaviour, as it maintains and strengthens social bonds, provides a source of comfort
and reassurance, and helps maintain coat condition. However, over-grooming and hair plucking are associated with poor welfare states. Social interactive play is often used as one indicator of good welfare. But this behaviour may not be visible in older animals. Keepers need to regularly and attentively observe primates' overall behaviour. Primates should not display persistent signs of aggression, antisocial behaviour or long term conflict behaviour
towards other animals or people. Such behaviour includes physical aggression, physical or vocal threats, and aggression displays. Conflict is a natural part of the behaviour of many social animals. However, dominant (controlling) individuals should not dominate or bully other primates in the group. Individual animals may sometimes show aggression towards their keeper, but persistent undue aggression is a cause for concern. Sporadic, acute aggressive behaviour is fairly common in
some primate societies, but this is generally kept in check by learnt social skills. A thorough knowledge of species-typical behaviour is essential for interpretation of observed behaviour. Persistent aggression can develop when the size and structure of the environment does not allow animals to avoid and escape from one another. Individuals, deprived of the opportunity to learn the full range of social skills, may have problems with other animals
socially, leading to aggressive interactions. Animals experiencing pain, or frustration, as a result of an inadequate environment, may become very aggressive. Changes to group composition can lead to aggressive interactions, and so great care needs to be taken and advice sought to minimise these risks. Established compatible social groups should not generally be altered. Aggressive interactions can also arise in mixed species environments, either because of species characteristics or
individual behaviours. Problems with aggression should be tackled at the source, by correcting the causes. It is never acceptable to mitigate effects of aggression, for instance by removing canine teeth for the purposes of handling or husbandry, or extended separation/isolation from the group. The following key resources should be considered when keeping primates:Expectations of normal behaviour
Signs of good and poor welfare amongst primates
Social interaction and primates
Aggression and primates
Persistent aggression and primates
Resources for keeping primates
- group composition
- changes to group composition
- enclosure size
- visual barriers
- access to resources
- security
Primates should be able to express suitable defence and escape behaviours.
In their natural environment, primates that come into conflict can escape from one another to avoid physical and visual contact and disperse to other areas (for example, once sexual maturity is reached). They are also free to move away and escape from other stimuli or situations they find aversive.
The captive environment places certain restrictions on such strategies, which can lead to stress. It is important that adequate refuges and visual barriers are provided, including from people. Vertical space is particularly important, as escape responses tend to be upwards, and dominance relationships are often expressed, in part, by occupation of perches at different heights.
Self-grooming, feeding and drinking
Primates should display self-grooming, feeding and drinking behaviours relevant to the species concerned.
These maintenance behaviours are essential for primates’ physical well being and also provide stimulation.
Changes in maintenance behaviours can provide an early warning sign of a problem. For instance, reduced feeding or drinking can mean a problem before body weight or condition is affected. Over-drinking and over-eating can be indicative of a problem.
Self-grooming is a normal behaviour, but over-grooming (which has been linked to tension and anxiety) can result in hair loss and skin sores. Hair-plucking is a health concern, especially if the hair is swallowed and forms hair-balls in the digestive tract.
Primates should display physical activities relevant to the species concerned.
These include:
- walking
- running
- climbing
- turning
- reaching
- stretching
- bending
- pushing
- pulling
- swinging
- jumping
Tarsiers, some lemurs and bush-babies typically cling to and leap between perches, marmosets and tamarins cling to tree-trunks and gibbons swing from branch to branch. Performance of such natural activities is essential to both the physical and psychological health of primates, and it is important that they are provided with a wide variety of suitable facilities, that are the right size and spatial design to display these behaviours.
A change in activity levels, in both directions, can result in a welfare problem.
Sleeping and resting patterns and primates
Primates should display sleeping and resting patterns relevant to the species and individual concerned.
Primate species are generally nocturnal or diurnal. However, some species may be active at times by day and night, or most active at dawn and dusk. The environment and its management should take account of individual needs.
The way in which primates sleep and rest differs between species. For instance, some sleep together in groups in tree cavities, others may build nests. Furnishings and substrates to allow sleeping and resting behaviours should therefore be provided, relevant to the species.
An increase or decrease in the frequency of sleeping and resting behaviours show that there's a welfare problem.
Foraging and primates
Primates should display a wide range of foraging behaviours, relevant to the species. This encompasses exploration, search, capture, restraint (of prey items), manipulation, processing and consumption.
Primates spend a large part of their day foraging for food that may be widely dispersed or patchily distributed. In foraging, they use well-developed memory skills and the ability to solve complex problems, together with an advanced ability to use tools for acquiring food, for instance to extract kernels from hard nuts.
Foraging behaviours vary widely between species, and one species may employ a wide range of strategies. For instance, marmosets typically gouge holes in trees and eat the gum, but also forage for invertebrates among leaves. Keepers should make sure ample opportunities for their primates to do all such behaviours, in order to provide both mental and physical stimulation.
Access to food for primates
Primates should not show anxiety over access to food.
Care should be taken to prevent any individual animal becoming unduly dominant. All animals must have access to all components of the diet, and food should be dispersed sufficiently widely to make sure that normal social hierarchies do not result in anxiety in subordinate animals and prevent them from having access to food.
Parenting behaviours and primates
If allowed to breed, primates should express normal parenting behaviours for a suitable period of time that's relevant to the species concerned.
Primates have an extended period of maternal dependency, lasting well beyond nutritional dependency. Infants removed from their mother and natal group early, and as a result deprived of the opportunity to learn vital survival and social skills, are likely to develop behavioural and hormonal abnormalities, fail to integrate well with individuals of the same species, and are often unable to raise their own young successfully.
A poorly-designed and managed environment for breeding animals can cause stress, impair fertility, inhibit mating behaviour, and adversely affect care of the young, leading to infanticide, abandonment or stealing of young animals.
Activity and primates
Primates of all species display a wide repertoire of activities and behaviours. You should know the normal behaviour in captivity of the species you keep.
A restricted or restriction of the range of behaviours displayed can show that the environment is unsuitable for the animal’s needs, or that the animal is unwell. A general lack of or limited focus of, activity should be taken as a warning sign.
Scent-marking and primates
Scent-marking is a normal behaviour for many species. It plays a role in the development of social structures, social interaction, reproductive health, and in breeding behaviour. Cleaning regimes should be developed that do not adversely inhibit scent communication.
Too much repetition of normal behaviour should also be taken as a warning sign.
Effect of poor welfare
The common adverse welfare consequences of poor management include discomfort, boredom, fear, pain and stress, which, if unchecked, may lead to self-harm, and other abnormal behaviours, such as overt and persistent displays of submission, aggression or anxiety, be they physical or vocal. However, suitable enrichment can help reduce these behaviours.
A stimulating environment for primates
Primate groups need a relevant environment that is stimulating and gives individuals a sense of control and choice.
An inadequate environment may be associated with primates displaying abnormal behaviour. Pay attention to any changes in primates' behaviour including:
- abnormal repetitive behaviour (for example, pacing, rocking, self-clasping)
- self-harm (for example. self-biting)
- apathetic/depressed behaviour
- abnormal behaviour (for example, over-grooming, drinking urine and eating faeces)
Once primates develop abnormal behaviours as a result of poor welfare, these may persist throughout their lives. Everything possible should be done to prevent such behaviours developing, by providing a rich physical and social environment, and by being aware of, and looking for, early indications that the environment is not providing for the animals’ needs.
Signs of fear in primates
Signs of fear differ between species and include withdrawal, grimace, too much lip smacking, aggression and specific vocalisations.
Some primates may show instinctive fear of other species (for example, dogs, cats or snakes), and should be protected from the distress of being housed close to these creatures. The herding or predatory behaviour of a dog can easily cause distress to a caged primate.
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