We and other closely-related primates live in family groups, but how did we come to live like this? Source: BS Thurner Hof
New Insight into Social Evolution
of Primates
Sarah Loftus, 20th November 2011
Research from the University of
Oxford has demonstrated that primates underwent a step-wise pattern of social
evolution, progressing from solitary foraging directly to living in large
groups, a transition that coincides with a move from nocturnal (night time) to diurnal (daytime)
living.
The research, carried out at the University’s Institute of Cognitive and Evolutionary Anthropology and published last week in the journal Nature, suggests that the transition from solitary living to large multi-male/multi-female groups happened approximately 52 million years ago and that pair living or single-male harem systems derived from this later (about 16 million years ago). Little research had been done previously on patterns social evolution since we cannot derive such information from fossils (which are used in the study of many other aspects of primate evolution). The team, led by Dr Susanne Shultz, used statistics to compare the probabilities of various social evolutionary models occurring. These models include a gradual increase in complexity (solitary living followed by pairwise living, living in small groups, then living in large groups), reversible movement between social states and a stepwise transition directly from solitary living to large groups. The study suggested the latter as the most likely representation of how primates evolved to live in groups. The study was possible because primate social behaviour is influenced by ancestors (a phenomenon celled phylogenetic inertia) and social traits cluster according to taxonomic grouping. Therefore statistical comparisons may be made to deduce changes in social behaviour with time.
Changes in the social structure of a species often coincide with changes in another aspect of their behaviour, for example the development of sex-biased dispersal in which one sex (typically males) migrates away from the family group leaving the other to form a co-operative group. This gives rise to kin selection in which members help each other’s survival (for example a bird raising an alarm call to warn others of predators) so that individuals ensure selective advantage, and therefore the propagation, of “family genes” rather than simply ensuring their own genes are passed on (as in the school textbook example of the rabbit with the fastest legs having the selective advantage). Sex-biased dispersal was previously considered to be the mammalian default, but the Shultz group were able to show that in primates, the transition from solitary to group living instead coincided with a change from nocturnal to diurnal living and that sex-biased dispersal occurred later, after the development of social grouping.
The prevalence of stable groups and bonded relationships between individuals differentiates higher primates from other social vertebrates. It is thought that living in a group has anti-predator benefits and so this may have counteracted the increased risk of predation resulting from a diurnal lifestyle. The shift to diurnal social living in primates would also have increased the possibility for further species adaptation. The Shultz group raise the possibility that the transition may even have played a role in the evolution of other traits characteristic of higher primates, such as coalition formation, cooperative resource defence and large brains.
Copyright Sarah Loftus, licensed under the Creative Commons Attribution-Share Alike 3.0 Unported
The research, carried out at the University’s Institute of Cognitive and Evolutionary Anthropology and published last week in the journal Nature, suggests that the transition from solitary living to large multi-male/multi-female groups happened approximately 52 million years ago and that pair living or single-male harem systems derived from this later (about 16 million years ago). Little research had been done previously on patterns social evolution since we cannot derive such information from fossils (which are used in the study of many other aspects of primate evolution). The team, led by Dr Susanne Shultz, used statistics to compare the probabilities of various social evolutionary models occurring. These models include a gradual increase in complexity (solitary living followed by pairwise living, living in small groups, then living in large groups), reversible movement between social states and a stepwise transition directly from solitary living to large groups. The study suggested the latter as the most likely representation of how primates evolved to live in groups. The study was possible because primate social behaviour is influenced by ancestors (a phenomenon celled phylogenetic inertia) and social traits cluster according to taxonomic grouping. Therefore statistical comparisons may be made to deduce changes in social behaviour with time.
Changes in the social structure of a species often coincide with changes in another aspect of their behaviour, for example the development of sex-biased dispersal in which one sex (typically males) migrates away from the family group leaving the other to form a co-operative group. This gives rise to kin selection in which members help each other’s survival (for example a bird raising an alarm call to warn others of predators) so that individuals ensure selective advantage, and therefore the propagation, of “family genes” rather than simply ensuring their own genes are passed on (as in the school textbook example of the rabbit with the fastest legs having the selective advantage). Sex-biased dispersal was previously considered to be the mammalian default, but the Shultz group were able to show that in primates, the transition from solitary to group living instead coincided with a change from nocturnal to diurnal living and that sex-biased dispersal occurred later, after the development of social grouping.
The prevalence of stable groups and bonded relationships between individuals differentiates higher primates from other social vertebrates. It is thought that living in a group has anti-predator benefits and so this may have counteracted the increased risk of predation resulting from a diurnal lifestyle. The shift to diurnal social living in primates would also have increased the possibility for further species adaptation. The Shultz group raise the possibility that the transition may even have played a role in the evolution of other traits characteristic of higher primates, such as coalition formation, cooperative resource defence and large brains.
Copyright Sarah Loftus, licensed under the Creative Commons Attribution-Share Alike 3.0 Unported
