Primate Sociality In Evolutionary Theory
The Role of Primate Sociality in Evolutionary Theory
Introduction
Some animals, and more specifically primates, have been noted for having brains of an uncommonly large size. One explanation for this phenomenon is the ‘social brain’ or ‘social intelligence’ hypothesis, which states that brain sizes have increased in order to handle the demands of sociality (Lindenfors 2005; Pérez-Barbería et al. 2007). The increase in brain size can be attributed to the computational power needed to track others in the group and ensure individual and species survival (Müller & Soligo 2005; Pérez-Barbería et al. 2007). Sociality in primates – and thus also in humans – has then some evolutionary basis. This bibliography, and my final literature review, …show more content…
will discuss the possible reasons for the evolution of sociality in primates as a close approximation to humans. In particular, it will address whether sociality in primates evolved as a means of survival.
The annotation at the end of each article summary will describe the relevance and usefulness of the research to my specific question and indicate if I think I will be able to use it in m y final literature review.
Keywords: brains, survival, social evolution, eusociality, mammals, baboons.
1.
Social bonds of female baboons enhance infant survival
This article aimed to produce evidence to support the theory that social bonds have a unique positive influence on primate adaptability, regardless of other factors. The evidence was collected from a 16 year study of the Kenyan wild baboon population Papio cynocephalus. Social contact was defined by three estimates: the amount of time a baboon would be within five metres of another baboon, the amount of time a baboon would be grooming others and the amount of time it would be groomed by others. These factors encompass the social activities of the baboon population and are considered to be an accurate measure of primate sociality. The three estimates were then combined to form a combined sociality index score.
Female baboons engaging more frequently with other adult baboons, as well as those occupying definite social positions in the group hierarchy, were found to be most likely to succeed in raising their young. Females with higher index scores also produced children with marginally higher survival rates than those females with lower scores.
Furthermore these observations were found to be independent of other factors (e.g. female dominance) implying that primate sociality plays an important evolutionary role.
This article is central to my topic, and I can cite many concepts and results from it throughout my review.
Silk, JB, Alberts, SC, Altmann, J 2003. Social bonds of female baboons enhance infant survival. Science 302: 1231-1234.
2.
Primate Sociality in Evolutionary Context
The aim of this article was to examine sociality from an evolutionary perspective and see whether it affected certain factors that influence sociality. These factors were an individual’s weight, eating habits, movement patterns and use of environment. Rodents were used to create a model that could later be extrapolated to investigate primates, where a rodent genus was considered social if male and female social interactions occurred outside mating times and formed some kind of network with at least one adult animal. Rodents were considered a suitable group for examination as they are the largest group of mammals and display a wide range of characteristics over the given factors.
Data was collected from all rodent genera for which sociality could be measured using these four factors. The study concluded that these four factors, all impacting on animal sociality, were highly influenced by the evolution of the rodent. Large animals, those living in trees, and animals feeding on fruits, vegetables or animal matter were found to display the highest degree of sociality. This is believed to have evolved as a means for all animals to obtain food and hence be able to survive. This research implies that animals that mostly or exclusively consume fruit are instrumental in the development of social networks.
Because this article was based on a rodent model, it is still relevant, but I will probably try not to extrapolate too much to make generalisations about primates, specifically humans.
Müller, AE & Soligo, C 2005. Primate sociality in evolutionary context. American Journal of Physical Anthropology 128: 399-419.
3.
Neocortex evolution in primates: the ‘social brain’ is for females
This study used the size of the neocortex, the component handling complex mental processes in animal brains, to explore how these processes evolved. The research aimed to show that the social intelligence is only applicable to females. This was because females were known to cluster together as a result of environmental conditions, while for males the only important factor was the position of the females.
As neocortex size and brain size were correlated, and the individual’s weight and the group’s size were also factors affecting sociality, data was collected for all four variables.
The research concluded that those species containing large groups of social females showed larger neocortex sizes. Relatively large measurements of neocortex size for males was thought to show that it might be important for both sexes to know about female-female bonds.The research also concluded that brain development occurs alongside the social development of females. It also implies that in the more sociable groups, female neocortex sizes were larger than the male equivalents.
Good for demonstrating the nature of female sociality and its relationship to the size of parts of their brains. Linking sociality to more hard neuroscience like this is preferred for this review.
Lindenfors, P 2005. Neocortex evolution in primates: the ‘social brain’ is for females. Biology Letters 1: 407-410.
4.
Evidence for Coevolution of Sociality and relative brain size in three orders of mammals
The aim of this study was to investigate the pairing between sociality and brain size over time. Though there is a correlation between these two variables, the literature does not indicate how the two became linked over time. Current developments in statistical analysis have now made it possible for this relationship to be understood.
Data was collected on the brain size and individual weight for 206 species comprising four different mammalian orders, of which 42 were primates. Sociality was able to be measured from all of these species, on the basis that a social group comprised at the least two adult animals who regularly communicated with each other. As primates are primarily social animals, the definition of sociality was further narrowed in their case – a social group was observed if the geometric mean of the group size was larger than that for the entire group.
While it seemed apparent that sociality and brain size evolved alongside each other in all orders, the study concluded that the way in which this occurred varied for each order. The increase in brain size could be attributed to the increase in mental processes needed to track other group members for various reasons important for survival – e.g. to avoid separation, or to generate ideas as to how to avoid competition, persecution etc. It is implied that the evolution of sociality, and its close linkage with brain size, has definitely lead to an increase in the chance of survival of a species.
This is a great article because it compares brain sizes across 3 orders, so I can get a feel for how humans might compare too. It also allowed me to define sociality a bit more specifically for primates, and think about my own definition of sociality.
Pérez-Barbería, FJ, Shultz, S, Dunbar, RIM 2007. Evidence for coevolution of sociality and relative brain size in three orders of mammals. Evolution 61: 2811-2821.
5.
Sociality in Callithrix penicillata: II Individual strategies during intergroup encounters
This article investigated interactions between groups of the same animals to determine their impact on various factors, e.g. territorial boundaries and access to various items. The interactions of a group of Brazilian black tufted-ear marmosets with each other were observed as part of the study. Both antagonistic and friendly behaviors were monitored, with the latter being much more predominant. However, antagonistic behavior can be important when it comes to defense of territory, which is closely related to reproductive success and hence survival. Data was collected based on observations of the marmosets during morning and afternoon periods. An intergroup meeting was recorded to have occurred if more than one marmoset of another group came into contact with the test group. The study concluded that most meetings between marmoset groups were harmonious, and in many exchanges the marmosets did not seem to respond to the presence of the other animal, instead feeding or resting as normal. Antagonistic behaviour without physical violence was mostly displayed by males to males and when present in females, was either directed towards males or against strange females. In the former, this was judged to occur as a result of an unsuccessful copulatory attempt, but in the latter no clear reason was evident. Where there was insufficient food available or intruders were present, particularly sexually aggressive ones, antagonistic behavior was more prevalent. The study implied that social interactions are used to protect and ensure the future survival of the species.
Not much hard science in this one, but still useful for the concepts I am discussing in my review. I’ll use it for comparisons between species.
Decanini, DP, Macedo, RM 2008. Sociality in Callithrix penicillata: II individual strategies during intergroup encounters. International Journal of Primatology 29: 627-639.
References
Decanini, DP, Macedo, RM 2008. Sociality in Callithrix penicillata: II individual strategies during intergroup encounters. International Journal of Primatology 29: 627-639.
Lindenfors, P 2005. Neocortex evolution in primates: the ‘social brain’ is for females. Biology Letters 1: 407-410.
Müller, AE & Soligo, C 2005. Primate sociality in evolutionary context. American Journal of Physical Anthropology 128: 399-419.
Pérez-Barbería, FJ, Shultz, S, Dunbar, RIM 2007. Evidence for coevolution of sociality and relative brain size in three orders of mammals. Evolution 61: 2811-2821.
Silk, JB, Alberts, SC, Altmann, J 2003. Social bonds of female baboons enhance infant survival. Science 302: 1231-1234.
Original abstracts
Primate Sociality in Evolutionary Context
Alexandra E. Müller1* and Christophe Soligo2
1Anthropological Institute and Museum, University of Zu¨ rich, 8057 Zu¨ rich, Switzerland
2Human Origins Group, Department of Palaeontology, Natural History Museum, London SW7 5BD, UK
KEY WORDS primate origins; rodents; social organization; social networks; frugivory
ABSTRACT Much work has been done to further our understanding of the mechanisms that underlie the diversity of primate social organizations, but none has addressed the limits to that diversity or the question of what causes species to either form or not form social networks.
The fact that all living primates typically live in social networks makes it highly likely that the last common ancestor of living primates already lived in social networks, and that sociality formed an integral part of the adaptive nature of primate origins. A characterization of primate sociality within the wider mammalian context is therefore essential to further our understanding of the adaptive nature of primate origins.
Here we determine correlates of sociality and nonsociality in rodents as a model to infer causes of sociality in primates. We found sociality to be most strongly associated with large-bodied arboreal species that include a significant portion of fruit in their diet. Fruits and other plant products, such as flowers, seeds, and young leaves, are patchily distributed in time and space and are therefore difficult to find. These food resources are, however, predictable and dependable when their location is known. Hence, membership in a social unit can maximize food exploitation if information on feeding sites is shared. Whether sociality evolved in the primate stem lineage or whether it was already present earlier in the evolution of Euarchontoglires remains uncertain, although tentative evidence points to the former scenario. In either case, frugivory is likely to have played an important role in maintaining the presence of a social lifestyle throughout primate evolution. Am J Phys Anthropol
128:399–414, 2005. © 2005 Wiley-Liss, Inc.
Neocortex evolution in primates: the ‘social brain’ is for females
Patrik Lindenfors*,†
Department of Biology, University of Virginia, Gilmer …show more content…
Hall,
Charlottesville, VA 22904-4328, USA
*( patrik.lindenfors@virginia.edu)
†Temporary address: P.O. Box 19423, 202 KNH-Nairobi, Kenya.
According to the social intelligence hypothesis, relative neocortex size should be directly related to the degree of social complexity. This hypothesis has found support in a number of comparative studies of group size. The relationship between neocortex and sociality is thought to exist either because relative neocortex size limits group size or because a larger group size selects for a larger neocortex. However, research on primate social evolution has indicated that male and female group sizes evolve in relation to different demands. While females mostly group according to conditions set by the environment, males instead simply go where the females are. Thus, any hypothesis relating to primate social evolution has to analyse its relationship with male and female group sizes separately. Since sex-specific neocortex sizes in primates are unavailable in sufficient quantity,
I here instead present results from phylogenetic comparative analyses of unsexed relative neocortex sizes and female and male group sizes.
These analyses show that while relative neocortex size is positively correlated with female group size, it is negatively, or not at all correlated with male group size. This indicates that the social intelligence hypothesis only applies to female sociality.
Sociality in Callithrix penicillata: II. Individual
Strategies During Intergroup Encounters
Daniel P. Decanini & Regina H. Macedo
Received: 28 May 2007 / Accepted: 9 October 2007 /
Published online: 5 June 2008
# Springer Science + Business Media, LLC 2008
Abstract In social animals, intergroup interactions, whether through agonistic and competitive behaviors or affiliative ones, can influence important parameters such as home range, territory sizes, and access to resources, which may directly affect both female and male fitness. We studied the intergroup interaction patterns of a wild group of black-tufted-ear marmosets (Callithrix penicillata) in central Brazil.
Agonistic interactions occurred at low frequencies during intergroup encounters.
The marmosets directed agonistic interactions without physical aggression primarily against same-sex individuals, suggesting that male and female aggression patterns are shaped by their sexual interests. However, females of the focal group also directed agonistic behavior toward extragroup males that attempted copulation. The marmosets appeared to use intergroup encounters to gather information about possible partners and extragroup reproductive opportunities. Intergroup sexual interactions occurred mainly in the form of copulations or attempted copulations by all adults, with the exception of the dominant female. Our results suggest that a possible reproductive strategy used by males is to attempt fertilization of extragroup females. Adult males copulated with the same extragroup female during several opportunities, which suggests sperm competition or the establishment of social bonds with neighboring females.
EVIDENCE FOR COEVOLUTION OF SOCIALITY
AND RELATIVE BRAIN SIZE IN THREE ORDERS
OF MAMMALS
F. Javier Pe´ rez-Barber´ıa,1,2 Susanne Shultz,3,4 and Robin I. M. Dunbar3,5
1The Macaulay Institute, Craigiebuckler, Aberdeen, AB15 8QH, Scotland, United Kingdom
2E-mail: j.pe´ rez-barberı´a@macaulay.ac.uk
3British Academy Centenary Research Project, School of Biological Sciences, University of Liverpool, Crown St. Liverpool
L69 7ZB, United Kingdom
4E-mail: susanne.shultz@liv.ac.uk
5E-mail: rimd@liv.ac.uk
Received September 8, 2006
Accepted July 17, 2007
As the brain is responsible for managing an individual’s behavioral response to its environment, we should expect that large relative brain size is an evolutionary response to cognitively challenging behaviors.
The “social brain hypothesis” argues that maintaining group cohesion is cognitively demanding as individuals living in groups need to be able to resolve conflicts that impact on their ability to meet resource requirements. If sociality does impose cognitive demands, we expect changes in relative brain size and sociality to be coupled over evolutionary time. In this study, we analyze data on sociality and relative brain size for 206 species of ungulates, carnivores, and primates and provide, for the first time, evidence that changes in sociality and relative brain size are closely correlated over evolutionary time for all three mammalian orders. This suggests a process of coevolution and provides support for the social brain theory. However, differences between taxonomic orders in the stability of the transition between small-brained/nonsocial and large-brained/social imply that, although sociality is cognitively demanding, sociality and relative brain size can become decoupled in some cases. Carnivores seem to have been especially prone to this.
Social Bonds of Female
Baboons
Enhance Infant Survival
Joan B. Silk,1* Susan C. Alberts,2,4 Jeanne Altmann3,4,5
Among nonhuman primates, females often form strong bonds with kin and other group members. These relationships are thought to have adaptive value for females, but direct effects of sociality on fitness have never been demonstrated.
We present 16 years of behavioral data from a well-studied population of wild baboons, which demonstrate that sociality of adult females is positively associated with infant survival, an important component of variation in female lifetime fitness. The effects of sociality on infant survival are independent of the effects of dominance rank, group membership, and environmental conditions.
Our results are consistent with the evidence that social support has beneficial effects on human health and well-being across the life span. For humans and other primates, sociality has adaptive value.
NOTE – This example does not include a turnitin report.
Introduction
Some animals, and more specifically primates, have been noted for having brains of an uncommonly large size. One explanation for this phenomenon is the ‘social brain’ or ‘social intelligence’ hypothesis, which states that brain sizes have increased in order to handle the demands of sociality (Lindenfors 2005; Pérez-Barbería et al. 2007). The increase in brain size can be attributed to the computational power needed to track others in the group and ensure individual and species survival (Müller & Soligo 2005; Pérez-Barbería et al. 2007). Sociality in primates – and thus also in humans – has then some evolutionary basis. This bibliography, and my final literature review, …show more content…
will discuss the possible reasons for the evolution of sociality in primates as a close approximation to humans. In particular, it will address whether sociality in primates evolved as a means of survival.
The annotation at the end of each article summary will describe the relevance and usefulness of the research to my specific question and indicate if I think I will be able to use it in m y final literature review.
Keywords: brains, survival, social evolution, eusociality, mammals, baboons.
1.
Social bonds of female baboons enhance infant survival
This article aimed to produce evidence to support the theory that social bonds have a unique positive influence on primate adaptability, regardless of other factors. The evidence was collected from a 16 year study of the Kenyan wild baboon population Papio cynocephalus. Social contact was defined by three estimates: the amount of time a baboon would be within five metres of another baboon, the amount of time a baboon would be grooming others and the amount of time it would be groomed by others. These factors encompass the social activities of the baboon population and are considered to be an accurate measure of primate sociality. The three estimates were then combined to form a combined sociality index score.
Female baboons engaging more frequently with other adult baboons, as well as those occupying definite social positions in the group hierarchy, were found to be most likely to succeed in raising their young. Females with higher index scores also produced children with marginally higher survival rates than those females with lower scores.
Furthermore these observations were found to be independent of other factors (e.g. female dominance) implying that primate sociality plays an important evolutionary role.
This article is central to my topic, and I can cite many concepts and results from it throughout my review.
Silk, JB, Alberts, SC, Altmann, J 2003. Social bonds of female baboons enhance infant survival. Science 302: 1231-1234.
2.
Primate Sociality in Evolutionary Context
The aim of this article was to examine sociality from an evolutionary perspective and see whether it affected certain factors that influence sociality. These factors were an individual’s weight, eating habits, movement patterns and use of environment. Rodents were used to create a model that could later be extrapolated to investigate primates, where a rodent genus was considered social if male and female social interactions occurred outside mating times and formed some kind of network with at least one adult animal. Rodents were considered a suitable group for examination as they are the largest group of mammals and display a wide range of characteristics over the given factors.
Data was collected from all rodent genera for which sociality could be measured using these four factors. The study concluded that these four factors, all impacting on animal sociality, were highly influenced by the evolution of the rodent. Large animals, those living in trees, and animals feeding on fruits, vegetables or animal matter were found to display the highest degree of sociality. This is believed to have evolved as a means for all animals to obtain food and hence be able to survive. This research implies that animals that mostly or exclusively consume fruit are instrumental in the development of social networks.
Because this article was based on a rodent model, it is still relevant, but I will probably try not to extrapolate too much to make generalisations about primates, specifically humans.
Müller, AE & Soligo, C 2005. Primate sociality in evolutionary context. American Journal of Physical Anthropology 128: 399-419.
3.
Neocortex evolution in primates: the ‘social brain’ is for females
This study used the size of the neocortex, the component handling complex mental processes in animal brains, to explore how these processes evolved. The research aimed to show that the social intelligence is only applicable to females. This was because females were known to cluster together as a result of environmental conditions, while for males the only important factor was the position of the females.
As neocortex size and brain size were correlated, and the individual’s weight and the group’s size were also factors affecting sociality, data was collected for all four variables.
The research concluded that those species containing large groups of social females showed larger neocortex sizes. Relatively large measurements of neocortex size for males was thought to show that it might be important for both sexes to know about female-female bonds.The research also concluded that brain development occurs alongside the social development of females. It also implies that in the more sociable groups, female neocortex sizes were larger than the male equivalents.
Good for demonstrating the nature of female sociality and its relationship to the size of parts of their brains. Linking sociality to more hard neuroscience like this is preferred for this review.
Lindenfors, P 2005. Neocortex evolution in primates: the ‘social brain’ is for females. Biology Letters 1: 407-410.
4.
Evidence for Coevolution of Sociality and relative brain size in three orders of mammals
The aim of this study was to investigate the pairing between sociality and brain size over time. Though there is a correlation between these two variables, the literature does not indicate how the two became linked over time. Current developments in statistical analysis have now made it possible for this relationship to be understood.
Data was collected on the brain size and individual weight for 206 species comprising four different mammalian orders, of which 42 were primates. Sociality was able to be measured from all of these species, on the basis that a social group comprised at the least two adult animals who regularly communicated with each other. As primates are primarily social animals, the definition of sociality was further narrowed in their case – a social group was observed if the geometric mean of the group size was larger than that for the entire group.
While it seemed apparent that sociality and brain size evolved alongside each other in all orders, the study concluded that the way in which this occurred varied for each order. The increase in brain size could be attributed to the increase in mental processes needed to track other group members for various reasons important for survival – e.g. to avoid separation, or to generate ideas as to how to avoid competition, persecution etc. It is implied that the evolution of sociality, and its close linkage with brain size, has definitely lead to an increase in the chance of survival of a species.
This is a great article because it compares brain sizes across 3 orders, so I can get a feel for how humans might compare too. It also allowed me to define sociality a bit more specifically for primates, and think about my own definition of sociality.
Pérez-Barbería, FJ, Shultz, S, Dunbar, RIM 2007. Evidence for coevolution of sociality and relative brain size in three orders of mammals. Evolution 61: 2811-2821.
5.
Sociality in Callithrix penicillata: II Individual strategies during intergroup encounters
This article investigated interactions between groups of the same animals to determine their impact on various factors, e.g. territorial boundaries and access to various items. The interactions of a group of Brazilian black tufted-ear marmosets with each other were observed as part of the study. Both antagonistic and friendly behaviors were monitored, with the latter being much more predominant. However, antagonistic behavior can be important when it comes to defense of territory, which is closely related to reproductive success and hence survival. Data was collected based on observations of the marmosets during morning and afternoon periods. An intergroup meeting was recorded to have occurred if more than one marmoset of another group came into contact with the test group. The study concluded that most meetings between marmoset groups were harmonious, and in many exchanges the marmosets did not seem to respond to the presence of the other animal, instead feeding or resting as normal. Antagonistic behaviour without physical violence was mostly displayed by males to males and when present in females, was either directed towards males or against strange females. In the former, this was judged to occur as a result of an unsuccessful copulatory attempt, but in the latter no clear reason was evident. Where there was insufficient food available or intruders were present, particularly sexually aggressive ones, antagonistic behavior was more prevalent. The study implied that social interactions are used to protect and ensure the future survival of the species.
Not much hard science in this one, but still useful for the concepts I am discussing in my review. I’ll use it for comparisons between species.
Decanini, DP, Macedo, RM 2008. Sociality in Callithrix penicillata: II individual strategies during intergroup encounters. International Journal of Primatology 29: 627-639.
References
Decanini, DP, Macedo, RM 2008. Sociality in Callithrix penicillata: II individual strategies during intergroup encounters. International Journal of Primatology 29: 627-639.
Lindenfors, P 2005. Neocortex evolution in primates: the ‘social brain’ is for females. Biology Letters 1: 407-410.
Müller, AE & Soligo, C 2005. Primate sociality in evolutionary context. American Journal of Physical Anthropology 128: 399-419.
Pérez-Barbería, FJ, Shultz, S, Dunbar, RIM 2007. Evidence for coevolution of sociality and relative brain size in three orders of mammals. Evolution 61: 2811-2821.
Silk, JB, Alberts, SC, Altmann, J 2003. Social bonds of female baboons enhance infant survival. Science 302: 1231-1234.
Original abstracts
Primate Sociality in Evolutionary Context
Alexandra E. Müller1* and Christophe Soligo2
1Anthropological Institute and Museum, University of Zu¨ rich, 8057 Zu¨ rich, Switzerland
2Human Origins Group, Department of Palaeontology, Natural History Museum, London SW7 5BD, UK
KEY WORDS primate origins; rodents; social organization; social networks; frugivory
ABSTRACT Much work has been done to further our understanding of the mechanisms that underlie the diversity of primate social organizations, but none has addressed the limits to that diversity or the question of what causes species to either form or not form social networks.
The fact that all living primates typically live in social networks makes it highly likely that the last common ancestor of living primates already lived in social networks, and that sociality formed an integral part of the adaptive nature of primate origins. A characterization of primate sociality within the wider mammalian context is therefore essential to further our understanding of the adaptive nature of primate origins.
Here we determine correlates of sociality and nonsociality in rodents as a model to infer causes of sociality in primates. We found sociality to be most strongly associated with large-bodied arboreal species that include a significant portion of fruit in their diet. Fruits and other plant products, such as flowers, seeds, and young leaves, are patchily distributed in time and space and are therefore difficult to find. These food resources are, however, predictable and dependable when their location is known. Hence, membership in a social unit can maximize food exploitation if information on feeding sites is shared. Whether sociality evolved in the primate stem lineage or whether it was already present earlier in the evolution of Euarchontoglires remains uncertain, although tentative evidence points to the former scenario. In either case, frugivory is likely to have played an important role in maintaining the presence of a social lifestyle throughout primate evolution. Am J Phys Anthropol
128:399–414, 2005. © 2005 Wiley-Liss, Inc.
Neocortex evolution in primates: the ‘social brain’ is for females
Patrik Lindenfors*,†
Department of Biology, University of Virginia, Gilmer …show more content…
Hall,
Charlottesville, VA 22904-4328, USA
*( patrik.lindenfors@virginia.edu)
†Temporary address: P.O. Box 19423, 202 KNH-Nairobi, Kenya.
According to the social intelligence hypothesis, relative neocortex size should be directly related to the degree of social complexity. This hypothesis has found support in a number of comparative studies of group size. The relationship between neocortex and sociality is thought to exist either because relative neocortex size limits group size or because a larger group size selects for a larger neocortex. However, research on primate social evolution has indicated that male and female group sizes evolve in relation to different demands. While females mostly group according to conditions set by the environment, males instead simply go where the females are. Thus, any hypothesis relating to primate social evolution has to analyse its relationship with male and female group sizes separately. Since sex-specific neocortex sizes in primates are unavailable in sufficient quantity,
I here instead present results from phylogenetic comparative analyses of unsexed relative neocortex sizes and female and male group sizes.
These analyses show that while relative neocortex size is positively correlated with female group size, it is negatively, or not at all correlated with male group size. This indicates that the social intelligence hypothesis only applies to female sociality.
Sociality in Callithrix penicillata: II. Individual
Strategies During Intergroup Encounters
Daniel P. Decanini & Regina H. Macedo
Received: 28 May 2007 / Accepted: 9 October 2007 /
Published online: 5 June 2008
# Springer Science + Business Media, LLC 2008
Abstract In social animals, intergroup interactions, whether through agonistic and competitive behaviors or affiliative ones, can influence important parameters such as home range, territory sizes, and access to resources, which may directly affect both female and male fitness. We studied the intergroup interaction patterns of a wild group of black-tufted-ear marmosets (Callithrix penicillata) in central Brazil.
Agonistic interactions occurred at low frequencies during intergroup encounters.
The marmosets directed agonistic interactions without physical aggression primarily against same-sex individuals, suggesting that male and female aggression patterns are shaped by their sexual interests. However, females of the focal group also directed agonistic behavior toward extragroup males that attempted copulation. The marmosets appeared to use intergroup encounters to gather information about possible partners and extragroup reproductive opportunities. Intergroup sexual interactions occurred mainly in the form of copulations or attempted copulations by all adults, with the exception of the dominant female. Our results suggest that a possible reproductive strategy used by males is to attempt fertilization of extragroup females. Adult males copulated with the same extragroup female during several opportunities, which suggests sperm competition or the establishment of social bonds with neighboring females.
EVIDENCE FOR COEVOLUTION OF SOCIALITY
AND RELATIVE BRAIN SIZE IN THREE ORDERS
OF MAMMALS
F. Javier Pe´ rez-Barber´ıa,1,2 Susanne Shultz,3,4 and Robin I. M. Dunbar3,5
1The Macaulay Institute, Craigiebuckler, Aberdeen, AB15 8QH, Scotland, United Kingdom
2E-mail: j.pe´ rez-barberı´a@macaulay.ac.uk
3British Academy Centenary Research Project, School of Biological Sciences, University of Liverpool, Crown St. Liverpool
L69 7ZB, United Kingdom
4E-mail: susanne.shultz@liv.ac.uk
5E-mail: rimd@liv.ac.uk
Received September 8, 2006
Accepted July 17, 2007
As the brain is responsible for managing an individual’s behavioral response to its environment, we should expect that large relative brain size is an evolutionary response to cognitively challenging behaviors.
The “social brain hypothesis” argues that maintaining group cohesion is cognitively demanding as individuals living in groups need to be able to resolve conflicts that impact on their ability to meet resource requirements. If sociality does impose cognitive demands, we expect changes in relative brain size and sociality to be coupled over evolutionary time. In this study, we analyze data on sociality and relative brain size for 206 species of ungulates, carnivores, and primates and provide, for the first time, evidence that changes in sociality and relative brain size are closely correlated over evolutionary time for all three mammalian orders. This suggests a process of coevolution and provides support for the social brain theory. However, differences between taxonomic orders in the stability of the transition between small-brained/nonsocial and large-brained/social imply that, although sociality is cognitively demanding, sociality and relative brain size can become decoupled in some cases. Carnivores seem to have been especially prone to this.
Social Bonds of Female
Baboons
Enhance Infant Survival
Joan B. Silk,1* Susan C. Alberts,2,4 Jeanne Altmann3,4,5
Among nonhuman primates, females often form strong bonds with kin and other group members. These relationships are thought to have adaptive value for females, but direct effects of sociality on fitness have never been demonstrated.
We present 16 years of behavioral data from a well-studied population of wild baboons, which demonstrate that sociality of adult females is positively associated with infant survival, an important component of variation in female lifetime fitness. The effects of sociality on infant survival are independent of the effects of dominance rank, group membership, and environmental conditions.
Our results are consistent with the evidence that social support has beneficial effects on human health and well-being across the life span. For humans and other primates, sociality has adaptive value.
NOTE – This example does not include a turnitin report.