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The Social Intelligence Hypothesis



The social intelligence hypothesis is a scientific hypothesis proposing that social complexity was the main selective force shaping the evolution of sophisticated intelligence and large brains in extant animals.
The Social Intelligence Hypothesis
Lily Johnson-Ulrich
Michigan State University, East Lansing, MI,
Machiavellian intelligence hypothesis;Social
brain hypothesis;Social complexity hypothesis
The social intelligence hypothesis is a scientic
hypothesis proposing that social complexity was
the main selective force shaping the evolution of
sophisticated intelligence and large brains in
extant animals.
The social intelligence hypothesis (SIH) is a pop-
ular hypothesis that purports to explain the evolu-
tion of large brains and sophisticated cognitive
abilities. The SIH proposes that social complexity
is cognitively demanding and is thus the key
selective pressure affecting brain size and, by
extension, intelligence (Dunbar 1998; Humphrey
1976; Jolly 1966). The SIH was originally devel-
oped to explain the large brains and intelligent
behavior of primates compared to other animals
(Dunbar 1998). It has also found support across
many mammal and bird species to explain varia-
tion in both brain size and cognitive abilities
(Dunbar and Shultz 2007; Shultz and Dunbar
2010). Though often pitted against ecological
hypotheses, which emphasize the role of diet and
environmental challenges in brain evolution, pro-
ponents of the SIH often claim that the two are not
mutually exclusive. Instead, they propose that
ecological problems are solved socially, not indi-
vidually, and that ecological selection thus acts
indirectly on brain size through selection for
social intelligence (Dunbar and Shultz 2007).
More conservative forms of the SIH simply posit
that more complex social groups favor specialized
social cognition. But ultimately, the SIH suggests
that the primary function of intelligence is in the
social domain.
Origins of the SIH
The SIH was originally formulated based on the
observation that primates in general, and great
apes in particular, have unusually large brains
and uniquely complex social systems. The origins
of the social intelligence hypothesis are usually
credited to Humphrey (1976). Though Chance
and Mead (1953) and Jolly (1966) had previously
developed similar ideas, they were not as widely
read or detailed as Humphreys(1976) work.
Chance and Mead (1953) suggested that male-
male competition for access to mates in primates
may have been a strong driving force in the
#Springer International Publishing AG 2017
T.K. Shackelford, V.A. Weekes-Shackelford (eds.), Encyclopedia of Evolutionary Psychological Science,
evolution of the human cortex. Years later, after
observing that lemurs have quite complex socie-
ties, but do not show the intelligence displayed by
simiiforme primates (monkeys and great apes)
when dealing with the physical world, Jolly
(1966) suggested that social complexity preceded
and dened the nature of general intelligence.
Independently, Humphrey (1976) suggested that
the social realm offers far more opportunity for
cognitive challenges than the physical world. He
observed that, although primates did not need to
be particularly strong innovators, their survival
required a high level of practical knowledge
about their environment and that this knowledge
was acquired socially. This type of society, with
mixed age and sex members, creates a degree of
complexity where social intelligence can have
large payoffs, ultimately leading to the develop-
ment of culture and human intelligence.
Eventually, with advent of empirical data relat-
ing social complexity, social intelligence, and
brain size, the SIH became the most popular
hypothesis for the evolution of intelligence. Over-
all, the SIH makes four key predictions: (1) social
complexity is the main selective force behind
enlarged brains and general intelligence, (2) com-
plex social groups select for greater social intelli-
gence than less complex groups, (3) social
intelligence may be transferred for use in the
physical domain, and (4) large brains and intelli-
gence are primarily used for solving social
Social Intelligence in Primates
Primates possess many sophisticated socio-
cognitive skills (Barrett et al. 2003; de Waal
1982; Seyfarth and Cheney 2012). For example,
in complex primate societies, keeping track of
relationships among other individuals is critical
for access to mates and food resources. Two social
cognitive skills of particular interest are recogni-
tion of third-party relationships and theory of
mind. Not only do primates recognize other indi-
viduals in their group and understand their own
relationships to those individuals, but they also
recognize the relationships between group mem-
bers to whom they themselves are unrelated; this
entails recognizing third-party relationships. This
skill is particularly interesting because, although
remembering as many as 100 other individuals in
a primate group may be difcult, the number of
pair-wise relationships that are possible, even in
small groups, is combinatorially massive and thus
intellectually challenging (Seyfarth and Cheney
2015). Theory of mind, which is the ability to
recognize mental states in other individuals, is an
advanced cognitive skill that helps predict the
actions of others. Theory of mind likely came
about as a result of social pressures in humans,
but the rudiments of this ability appear to exist in
the great apes (Call and Tomasello 2008). For a
more complete summary of primate social intelli-
gence, see Barrett et al. (2003), Cheney and
Seyfarth (1985), and Seyfarth and Cheney
(2012). Today, a vast number of social cognitive
skills have been observed in primates such as
reconciliation, reciprocity cooperation, and com-
munication to name a few. In general, the great
apes appear to outperform monkeys, which corre-
lates with the greater brain size observed in great
apes. The presence of sophisticated social cogni-
tion suggests a strong degree of selective pressure
for such skills, and these skills are related to
tness in primates (Seyfarth and Cheney 2015).
This research supports the idea that selection has
favored the evolution of social intelligence.
Social Correlates with Brain Size in Primates
Interest in the SIH grew with the advent of
research that correlated specic measures of
social complexity with measurements of brain
size in primates. Group size was the rst quanti-
tative measure of social complexity, and it was
correlated with a quantitative measure of brain
size (Dunbar 1998). Group size was chosen as
the key measure of social complexity because
primates interact individually, in potentially
tness-affecting ways, with every member of
their groups, and because it is an easy number to
obtain for most species. The ratio of the neocortex
to the rest of the brain was preferred in much of the
research on the SIH because body size is a much
more evolutionary labile trait than brain size.
Other measures that were also related to neocortex
ratio include tactical deception, grooming clique
size, rates of social play, type of mating system,
2 The Social Intelligence Hypothesis
and the presence of long-term stable social bonds
(Dunbar 1998; Dunbar and Shultz 2007). Rates of
social learning have also been associated with
multiple measures of brain size (Reader and
Laland 2002).
Defining Social Complexity
Most of the aforementioned studies relating brain
size to some aspect of primate sociality also pur-
ported to identify the factor that makes primate
groups socially complex. Group size remains the
most popular measure of social complexity across
all species despite its shortcomings, and no other
measure has quite been able to replace it, despite
varied proposals regarding what makes an animal
society complex. Other measures of social com-
plexity that have been studied are ssion-fusion
dynamics, complex alliances, presence of a linear
dominance hierarchy, transactional interactions,
or even crèches (for a review and critique, see
Bergman and Beehner 2015). de Waal and Tyack
(2009, p. 1) suggest that a commonality underly-
ing various research on social complexity is the
idea that individual animals must keep track of
interactions with other individuals with whom
they must compete and cooperate.Complex
groups are those in which there are many such
individuals; simple groups are those in which
individual members are largely anonymous.
Primates certainly appear to possess sophisti-
cated social intelligence, but social intelligence
itself might be the cause of social complexity,
which creates a level of circularity (Gigerenzer
1997). However, others argue that one must
include social intelligence in the denition of
social complexity, because social complexity is
hypothesized to be cognitively demanding
(Bergman and Beehner 2015). Thus, when
researchers attempt to dene social complexity,
they should attempt to identify the cognitively
demanding features of a social group. Using this
logic, Bergman and Beehner (2015, p. 204)
suggested that social complexity should be
dened as the number of differentiated relation-
ships that members of a species have with con-
specics.This denition provides an objective
and easy to quantify metric where cognition is
clearly required to differentiate group members.
Unfortunately, no denition of social complexity
has been agreed upon to date; this is a major
shortcoming of the SIH because social complexity
is the key independent variable of the SIH.
Summary: Primates Are Specialized for Social
Overall there is good evidence supporting the SIH
in primates. Primates possess sophisticated social
intelligence, many measures of social complexity
correlate with brain size, and primate intelligence
appears to be highly social in nature. Specic
neurons and multiple brain regions have been
found in primates that are specialized to respond
to social features of the environment; this supports
the idea that social complexity among primates
favored social brains(Brothers 1990; Frith
2007). In addition to possessing sophisticated
social intelligence and complex societies, pri-
mates excel at technical skills which require gen-
eral intelligence (Byrne 1995; Reader et al. 2011).
However, the causal relationship between these
variables is unclear, and there is a dearth of evi-
dence suggesting that social complexity leads to
general intelligence in addition to social intelli-
gence. In sum, primates appear to have social
brains, and it also appears that their social com-
plexity does relate to social intelligence, but this
social intelligence may be more modularized than
the SIH predicts. Research on the SIH is limited
outside of primates, and support is much more
mixed in non-primate taxa.
Testing the SIH in Non-primates
Group size does not explain variation in brain size
in carnivores (Finarelli and Flynn 2009), instead
the hunting of large vertebrate prey best explains
brain size (Swanson et al. 2012), nor does physi-
cal problem-solving skill relate to sociality in
carnivores (Benson-Amram et al. 2016). Exten-
sive research on spotted hyenas, which have soci-
eties that exhibit convergent evolution with those
of cercopithecine primates, provide an interesting
case study into the evolution of social intelligence
(Holekamp et al. 2007). They exhibit comparable
social cognitive skills on every measure tested,
The Social Intelligence Hypothesis 3
including the recognition of third-party relation-
ships, and compared to other hyenids, they have
larger brains, are more social, and are better at
tasks of physical problem-solving (Holekamp
et al. 2015). Taken together, the data from
Hyaenidae strongly support the SIH. However,
compared to cercopithecine primates, spotted
hyenas are small brained and poor physical prob-
lem solvers which contradicts many predictions of
the SIH when considering their convergent soci-
ality. In bats, living in stable social groups and
smaller teste size were associated with an increase
in brain size (Barton and Dunbar 1997; Pitnick
et al. 2006). Within gregarious ungulates, those
that live in stable year-round groups of at least six
individuals had the largest brains (Pérez-Barbería
and Gordon 2005). Another study found that
monogamous ungulates that lived in mixed habi-
tats had the largest relative brain sizes. Elephants
are some of the largest brained and longest lived
mammals; they are extremely social, forming dif-
ferentiated relationships with many individuals.
Like primates, elephants use tools and may have
the rudiments of theory of mind (Hart et al. 2008).
In cetaceans, pod size and relative brain size are
associated (Marino 2002). Cetaceans also exhibit
remarkable convergence with primates of cogni-
tive abilities in both social and physical domains
(Marino 2002; Marino et al. 2007). As cetaceans
are among the largest brained mammals, this con-
vergence strongly supports the SIH. A large study
that included data from both the mammalian fossil
record and extant species showed that increases in
brain size in mammalian taxa across evolutionary
time were associated with greater proportions of
species, but not all species, within those taxa
living in stable bonded groups (Shultz and Dunbar
2010). This provides some support for the SIH but
does not explain the fact that many extant mam-
malian species with large brains are not social
(Holekamp and Benson-Amram 2017). In sum,
varied measures of social complexity sometimes
correlate with brain size in mammals, but this
relationship is not consistent, and there are notable
exceptions to this relationship (e.g., bears).
Birds are capable of many of same feats of social
cognition and tool use as primates (Emery and
Clayton 2004; Marler 1996). Beauchamp and
Fernández-Juricic (2004) found no relationship
between either mean or maximum ock size in
birds and forebrain size, possibly because ock
size is not a stable trait in most bird species.
However, Burish et al. (2004) found that telence-
phalic volume fraction, a measure similar to neo-
cortex ratios in primates, was related to a
categorical measure of social complexity.
Corvids, in particular among birds, appear to
show convergent evolution with apes when it
comes to brains and intelligence. Though corvids
have smaller overall brain sizes, their relative
brain to body size ratio is almost the same as that
in chimpanzees (Emery and Clayton 2004).
In a large study that included several mamma-
lian and bird taxa pair-bonding was found to be
the strongest predictor of brain size. One explana-
tion for why pair-bonding, as opposed to group
size, is related to brain size outside of primates is
because any groupings larger than a pair-bond in
non-primates could be temporary aggregations or
involve undifferentiated relationships (Dunbar
and Shultz 2007). That is, primate relationships
might be uniquely bonded such that group size
approximates the number of bonded relationships
only in primates. However, we now know that
many species outside of primates do form stable
bonds outside of pair-bonds (e.g., spotted hyenas
or elephants). In addition, recent research that
specically examined bird species that do live in
long-term stable groups found that stable group-
ings larger than the pair-bond were associated
with smaller brains (Fedorova et al. 2017)
contradicting the idea that long-term stable
bonds might be the main cause of social complex-
ity and larger brains.
Fish have both relatively and absolutely small
brains, but sh have been shown to exhibit social
intelligence with a diverse array of social cogni-
tive skills documented, including reciprocation,
transitive inference, coordination and coopera-
tion, and the ability to remember past interactions
4 The Social Intelligence Hypothesis
with other individuals (Bshary et al. 2014). This
research suggests that relatively simple brains can
accomplish many of the same feats seen as intel-
ligent in primates, which at the least suggests that
a closer look at the rules governing social behav-
ior may be required to measure social intelligence.
That is, not all complex social behavior may be
indicative of social intelligence. However, in one
clade of sh, increased telencephalic size was
related to monogamy (Pollen et al. 2007) which,
similar to ndings in birds, suggests pair-bonds
may be related to relative increases in brain size.
Insects possess remarkably miniaturized brains
but can also show highly sophisticated social
skills, among other cognitive abilities. This
research suggests that brain structure or function
may be more important to social intelligence than
brain size (Lihoreau et al. 2012). Octopuses also
provide an interesting case study. They are large
brained relative to other invertebrates and show
high general intelligence; they use tools, differen-
tiate individual humans, and show advanced per-
formance on a variety of cognitive tests
(Darmaillacq et al. 2014); however they are
strictly solitary. Overall, invertebrates possess a
rich repertoire of cognitive abilities, which chal-
lenges the assumption of the SIH that complex
cognition requires a large brain (for a full review
of invertebrate cognition, see Roth 2013).
Overall, the SIH explains substantial variation in
cognition and brain size within primates, particu-
larly between monkeys and apes. Primates,
including humans, do appear to have brains spe-
cialized for social cognition, and primate intelli-
gence may be primarily social. Outside of
primates, both support and opposition have been
found for the SIH; it is not yet clear what the major
selective force favoring large brains and intelli-
gence might be outside of primates, though soci-
ality may have played a role. Certainly, the SIH
has drawn attention to the fact that cognition in the
social realm is both varied and complex and has a
strong impact on tness and daily lives of animals
as well as highlighting the role sociality may have
had in human brain evolution. Humans, as well as
possessing high general intelligence, are largely
unique in the realm of social cognition with regard
to our language and culture.
However, the SIH still faces several serious
challenges in addition to the described challenges
dening social complexity. The SIH has yet to
adequately account for grade shifts between dif-
ferent taxa. When comparing brain size to body
size, or some other scaling variable, there are
marked differences in the y-intercepts or slopes
of the regression lines for different taxa. These
grade shifts can bias measures of relative brain
size and are often not taken into account when
comparing measures of brain size to measures of
social complexity. For example, orangutans are
relatively solitary compared to other apes, but
also large brained, in part because the great ape
lineage lays on a higher grade than other primates
(also see Finarelli and Flynn 2009). A recent
paper that reanalyzed the data from primates
using updated phylogenies and a larger number
of species found no relationship between several
measures of social complexity and brain size.
Instead, frugivory was the strongest predictor of
brain size (DeCasien et al. 2017). Frugivory may
require both technical skill through the extractive
foraging of fruits and seeds and increased spatial
cognitive abilities for remembering when and
where to nd ripe fruit; this would tend to support
ecological hypotheses for brain evolution rather
than the SIH (Parker 2015). This nding high-
lights the fact that the SIH cannot explain general
intelligence. Though the SIH hypothesizes that
social intelligence may be used to solve physical
problems, it seems that social intelligence instead
is quite specialized; there is little evidence for
transference between social and general intelli-
gence. Though specialized social skills are related
to size of certain brain areas, there is a lack of
research that directly relates social intelligence to
brain size.
Despite these problems, the SIH currently
remains one of the most popular hypotheses for
the evolution of intelligence. Overall, there is
ample evidence to support the claim that social
The Social Intelligence Hypothesis 5
complexity, large brains, and intelligence are
strongly associated in many taxa. Just why or
how they are related, and what selective pressures
are involved when they are not related, must still
be determined.
Bird Tool Use
Brain Size and Intelligence
Cephalod Tool Use
Cognitive Buffer Hypothesis, The
Communication and Social Cognition
Convergent Evolution of Hyena and Primate
Social Systems
Convergent Evolution of Intelligence
Convergent Evolution of Intelligence Between
Corvids and Primates
Cultural Intelligence Hypothesis, The
(Herrmann et al. 2007)
Encephalization Quotient
Evolution of Intelligence, The
Evolution of the Brain, The
Extractive Foraging Hypothesis, The (Parker
and Gibson 1997, 2015)
General Intelligence Factor G(Reader et al.
Nonhuman Intelligence
Primate Tool Use
Relative Brain Size
Social Learning and Social Cognition
Social Tool
Technical Intelligence Hypothesis, The
Theory of Mind and Nonhuman Intelligence
Vygotskian Intelligence Hypothesis, The (Moll
et al. 2007)
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The Social Intelligence Hypothesis 7
In diesem Kapitel nimmt die Ausgestaltung des Buchmottos langsam Fahrt auf: Vertrauen Sie Ihrer Intuition, nachdem Sie sich mit den Fakten vertraut gemacht haben. Es geht darum, dass bestimmte Verhaltensmuster als Relikte aus unserer prähistorischen Vergangenheit bis heute erhalten sind, die ursprünglich der Erhaltung der Art dienten und sehr sinnvoll waren – Heuristiken und intuitive Vorgehensweisen, die in der Gegenwart allerdings aus guten Gründen kritisch hinterfragt werden sollten. Das kann regelmäßig verhindern, dass der Mensch auf eine Vielzahl literaturbekannter kognitiver Irrtümer hereinfällt, wie sie hier erläutert werden. Die Bündelung erfolgt abweichend von der reinen Lehre der Verhaltensökonomik und mit einem Augenzwinkern nach phänomenologischen Themenfeldern. Los geht es mit der Tierwelt (z. B. Truthahnillusion, Vogel-Strauß- und Kobraeffekt, Ziegenproblem). Scheunentore werden geschlossen und Zielscheiben nachträglich aufgemalt. Und auch zahlreiche Wissenschaftler (Allais, Dunning, Fechner, Forer, Jevons, Kruger, Peltzman, Semmelweis, Weber und andere) und sonstige Berühmtheiten (wie Babe Ruth, Benjamin Franklin, Murphy und Rumpelstilzchen) stehen Pate für weitere Effekte.
The number, duration and depth of social relationships that individuals maintain impact social cognition, but the connection between sociality and other aspects of cognition has hardly been explored. To date, the link between social living and intelligence has been mainly supported by studies on primates, and far fewer tests connecting sociality to cognitive abilities have used other taxa. Here, we present the first comparative study in fishes that examines whether complex social living is associated with better performance on a cognitively demanding spatial task. Using three cooperative, group-living cichlid fish species and three of their non-cooperative, more solitary close relatives, we studied maze learning and employed a new statistical extension for the ‘lme4’ and ‘glmmTMB’ packages in R that allows phylogeny to be included as a random effect term. Across trials, the three cooperative and the three non-cooperative species completed the maze faster, made fewer mistakes, and improved their inhibitory control. Although fish improved their performance, we did not detect any differences in the extent of improvement between cooperative and non-cooperative species. Both the cooperative species and the non-cooperative species took similar amounts of time to complete the maze, had comparable numbers of mistakes, and exhibited similar inhibitory control while in the maze. Our results suggest that living and breeding in complex social groups does not necessarily imply enhancement of other forms of cognition nor, more specifically, an enhanced spatial learning capacity.
Proa valdearinnoensis is a relatively large‐headed and stocky iguanodontian dinosaur from the latest Early Cretaceous of Spain. Its braincase is known from three specimens. Similar to that of other dinosaurs, it shows a mosaic ossification pattern in which most of the bones seem to have fused together indistinguishably while a few (frontoparietal, basioccipital) might have remained loosely attached. The endocasts of the three specimens are described based on CT data and digital reconstructions. They show unmistakable morphological similarities with the endocast of closely related taxa, such as Sirindhorna khoratensis (which is close in age but from Thailand). This supports a high conservatism of the endocranial cavity. The issue of volumetric correspondence between endocranial cavity and brain in dinosaurs is analysed. Although a brain‐to‐endocranial cavity (BEC) index of 0.50 has been traditionally used, we employ instead 0.73. This is indeed the mid‐value between the situation in adults of Alligator mississippiensis and Gallus gallus, which are members of the extant bracketing taxa of dinosaurs (Crocodilia and Aves). We thence gauge the level of encephalisation of Proa valdearinnoensis through the calculation of the Encephalisation Quotient (EQ), which remains valuable as a metric for assessing the degree of cognitive function in extinct taxa, especially those with fully ossified braincases like dinosaurs and other archosaurs. The EQ obtained for Proa valdearinnoensis (3.611) suggests that this species was significantly more encephalised than most if not all extant non‐avian, non‐mammalian amniotes. Our work adds to the growing body of data concerning theoretical cognitive capabilities in dinosaurs and supports the idea that an increasing encephalisation was fostered not only once in theropods but also in parallel in the shorter‐lived lineage of ornithopods. Proa valdearinnoensis was ill‐equipped to respond to theropod dinosaurs and possibly lived in groups as a strategy to mitigate the risk of being predated upon. We hypothesize that group‐living and protracted caring of juveniles in this and possibly many other iguanodontian ornithopods favoured a degree of encephalisation that was outstanding by reptile standards. This article is protected by copyright. All rights reserved. Proa valdearinnoensis is a stocky iguanodontian dinosaur from the Early Cretaceous of Spain. The endocasts of the three braincases of Proa valdearinnoensis known to date are described based on CT data and digital reconstructions and the level of encephalisation of this species is gauged through the calculation of the Encephalisation Quotient (EQ). The EQ obtained (3.611) suggests that Proa valdearinnoensis was significantly more encephalised than most if not all extant non‐avian, non‐mammalian amniotes. This supports the idea that an increasing encephalisation was fostered not only once in theropods but also in parallel in the shorter‐lived lineage of ornithopods. It is hypothesised that group‐living and protracted caring of juveniles in Proa valdearinnoensis and possibly many other iguanodontian ornithopods favoured a degree of encephalisation that was outstanding by reptile standards.
In this chapter, I consider the decades of research carried out on Einstein’s brain and why they have proved to be, and indeed were destined to be, sterile. Intelligence, creativity, and genius are social phenomena. Einstein did stand alone and did not create ab novo. Genius is not as commonly supposed an individual attribute. It clusters, and genius clusters are associated with the rise and decline of civilizations and cultural areas. The myth of individualism supports the idea that Einstein made discoveries “merely by thinking” and that he embodied pure intellect.
This chapter introduces my perspective on and my model of the social brain. The development of the social brain paradigm reflects a general development from hierarchical to network thinking across the intellectual spectrum during the latter part of the twentieth century. I discuss the evolution of the social intelligence hypothesis into the social brain hypothesis, and the reigning myths about the brain that have obstructed social brain thinking. I review the key developments in the history of neuroscience at its nexus with the life- and social sciences and their connections to social brain research and theory. The chapter ends with a presentation of my model of the social brain as a networked information system situated in and coupled with a social ecology (Appendix 1). In Appendix 2, I review the concept of connectomics, and in Appendix 3, I list links to glossaries on brain terminology to aid readers in understanding the terms used in the text to describe the structure and function of the brain.
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Although intelligence should theoretically evolve to help animals solve specific types of problems posed by the environment, it is unclear which environmental challenges favour enhanced cognition, or how general intelligence evolves along with domain-specific cognitive abilities. The social intelligence hypothesis posits that big brains and great intelligence have evolved to cope with the labile behaviour of group mates. We have exploited the remarkable convergence in social complexity between cercopithecine primates and spotted hyaenas to test predictions of the social intelligence hypothesis in regard to both cognition and brain size. Behavioural data indicate that there has been considerable convergence between primates and hyaenas with respect to their social cognitive abilities. Moreover, compared with other hyaena species, spotted hyaenas have larger brains and expanded frontal cortex, as predicted by the social intelligence hypothesis. However, broader comparative study suggests that domain-general intelligence in carnivores probably did not evolve in response to selection pressures imposed specifically in the social domain. The cognitive buffer hypothesis, which suggests that general intelligence evolves to help animals cope with novel or changing environments, appears to offer a more robust explanation for general intelligence in carnivores than any hypothesis invoking selection pressures imposed strictly by sociality or foraging demands. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
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The social brain hypothesis posits that social complexity is the primary driver of primate cognitive complexity, and that social pressures ultimately led to the evolution of the large human brain. Although this idea has been supported by studies indicating positive relationships between relative brain and/or neocortex size and group size, reported effects of different social and mating systems are highly conflicting. Here, we use a much larger sample of primates, more recent phylogenies, and updated statistical techniques, to show that brain size is predicted by diet, rather than multiple measures of sociality, after controlling for body size and phylogeny. Specifically, frugivores exhibit larger brains than folivores. Our results call into question the current emphasis on social rather than ecological explanations for the evolution of large brains in primates and evoke a range of ecological and developmental hypotheses centred on frugivory, including spatial information storage, extractive foraging and overcoming metabolic constraints.
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Despite considerable interest in the forces shaping the relationship between brain size and cognitive abilities, it remains controversial whether larger-brained animals are, indeed, better problem-solvers. Recently, several comparative studies have revealed correlations between brain size and traits thought to require advanced cognitive abilities, such as innovation, behavioral flexibility, invasion success, and self-control. However, the general assumption that animals with larger brains have superior cognitive abilities has been heavily criticized, primarily because of the lack of experimental support for it. Here, we designed an experiment to inquire whether specific neuroanatomical or socioecological measures predict success at solving a novel technical problem among species in the mammalian order Carnivora. We presented puzzle boxes, baited with food and scaled to accommodate body size, to members of 39 carnivore species from nine families housed in multiple North American zoos. We found that species with larger brains relative to their body mass were more successful at opening the boxes. In a subset of species, we also used virtual brain endocasts to measure volumes of four gross brain regions and show that some of these regions improve model prediction of success at opening the boxes when included with total brain size and body mass. Socioecological variables, including measures of social complexity and manual dexterity, failed to predict success at opening the boxes. Our results, thus, fail to support the social brain hypothesis but provide important empirical support for the relationship between relative brain size and the ability to solve this novel technical problem.
Aside from those who have been inspired by Griffin’s writings on cognitive ethology (Griffin, 1984, 1992), most students of bird behavior are unaware that a major revolution has overtaken scientific thinking about the behavior of primates and other mammals. The cognitive revolution took psychology by storm some years ago and, for many primatologists and psychologists, supplemented, and even superseded, more traditional approaches to the study of behavior, especially behavior of a social nature. This revolution led students of primate social behavior to focus on new kinds of questions that rarely arise in more traditionally oriented studies of the social behavior of birds. Although research on avian cognition figured prominently in the activities of early ethologists (e.g. Koehler, 1943, 1956a, 1956b; Thorpe, 1963), it fell from fashion. Instead, in the hands of behavioral ecologists and students of social evolution, economically inspired cost–benefit studies and kin selection theorizing became the driving forces behind most investigations of the behavior of birds, both in the field and in the laboratory.
Group size predicts brain size in primates and some other mammal groups, but no such relationship has been found in birds. Instead, stable pair-bonding and bi-parental care have been identified as correlates of larger brains in birds. We investigated the relationship between brain size and social system within the family Picidae, using phylogenetically controlled regression analysis. We found no specific effect of duration or strength of pair-bonds, but brain sizes were systematically smaller in species living in long-lasting social groups of larger sizes. Group-living may only present a cognitive challenge in groups in which members have individually competitive relationships; we therefore propose that groups functioning for cooperative benefit may allow disinvestment in expensive brain tissue. © 2017 The Author(s) Published by the Royal Society. All rights reserved.
After having dealt with the nervous systems and brains of invertebrates, we will ask how intelligent these animals are. This is of particular interest, because even in the behavioral sciences many authors tend to attribute intelligence only to the “higher animals,” i.e., vertebrates or even only mammals or primates
Cephalopods are generally regarded as the most intelligent group among the invertebrates. Despite their popularity, relatively little is known about the range and function of their cognitive abilities. This book fills that gap, accentuating the varied and fascinating aspects of cognition across the group. Starting with the brain, learning and memory, Part I looks at early learning, memory acquisition and cognitive development in modern cephalopods. An analysis of the chambered nautilus, a living fossil, is included, providing insight into the evolution of behavioural complexity. Part II surveys environmental responses, especially within the active and learning-dependent coleoids. The ever-intriguing camouflage abilities of octopus and cuttlefish are highlighted, alongside bioluminescence, navigation and other aspects of visual and cognitive competence. Covering the range of cognitive function, this text underscores the importance of the cephalopods within the field of comparative cognition generally. It will be highly valuable for researchers, graduates and senior undergraduate students.