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The evolution of unusually large brains in some groups of animals, notably primates, has long been a puzzle. Although early explanations tended to emphasize the brain's role in sensory or technical competence (foraging skills, innovations, and way-finding), the balance of evidence now clearly favors the suggestion that it was the computational demands of living in large, complex societies that selected for large brains. However, recent analyses suggest that it may have been the particular demands of the more intense forms of pairbonding that was the critical factor that triggered this evolutionary development. This may explain why primate sociality seems to be so different from that found in most other birds and mammals: Primate sociality is based on bonded relationships of a kind that are found only in pairbonds in other taxa.
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DOI: 10.1126/science.1145463
, 1344 (2007); 317Science
et al.R. I. M. Dunbar,
Evolution in the Social Brain
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Evolution in the Social Brain
R. I. M. Dunbar* and Susanne Shultz
The evolution of unusually large brains in some groups of animals, notably primates, has long been
a puzzle. Although early explanations tended to emphasize the brains role in sensory or technical
competence (foraging skills, innovations, and way-finding), the balance of evidence now clearly
favors the suggestion that it was the computational demands of living in large, complex societies
that selected for large brains. However, recent analyses suggest that it may have been the
particular demands of the more intense forms of pairbonding that was the critical factor that
triggered this evolutionary development. This may explain why primate sociality seems to be so
different from that found in most other birds and mammals: Primate sociality is based on bonded
relationships of a kind that are found only in pairbonds in other taxa.
he brain is one of the most expensive
organs in the body , second only to the
heart: The brains running costs are about
8 to 10 times as high, per unit mass, as those of
skeletal muscle (1, 2). Although the brains
ability to control t he bodys functions is obvi-
ously us eful, it entails something of an evolu-
tionary puzzle. The neurobiologist Harry Jerison
first pointed this out during the 1970s (3), when
he drew a distinction between the component of
the brain required to meet the bodys physical
needs and the component that was left over,
which could attend to tasks of a more cogni-
tively complex nature. This second component
of the brain has been increasing over evolution-
ary time across the birds and mammals, but fish
and reptiles continue to thrive with brains of
very modest size. Although it is easy to un-
derstand why brains in general have evolved, it
is not so obvious why the brains of birds and
mammals have grown substantially larger than
the minimum size required to stay alive.
T raditional explanations for the evolution of
large brains in primates focused either on eco-
logical problem solving or on developmental con-
straints. Early studies identified physiological
and life-history traitsincluding large body size,
metabolic rates, and prolonged development
that were associated with large brains (4, 5).
Some argued that this correlation was due to
the more efficient metabolism of larger-bodied
animals, which allowed more energy to be de-
voted to fetal brain growth and thereby made
the evolution of larger brains possible (6, 7). All
else being equal, big brains are a useful if un-
intended by-product of efficient energy use. In
addition to this theory, some evidence supported
ecological problem-solving as a possible ex-
planation: Among primates, for example, large-
brained species have larger home ranges (per-
haps requiring more sophisticated mental maps),
and frugivores have larger brains than folivores
(fruits are much less predictable in their location
and availability than leaves) (8).
On closer examination, most of the energetic
explanations that have been offered identify
constraints on brain evolution rather than selec-
tion pressures. In biology, constraints are inevi-
table, and crucial for understanding evolutionary
trajectories, but they do not constitute functional
explanationsthat is, just because a species can
afford to evolve a larger brain does not mean
that it must do so. Proponents of developmen-
tal explanations seem to have forgotten that
evolutionary processes involve costs as well as
benefits. Because evolution is an economical
process and does not often produce needless
organs or capacities, especially if they are ex-
pensive to maintain, it follows that some propor-
tionately beneficial advantage must have driven
brain evolution against the steep selection gra-
dient created by the high costs of brain tissue. In
this respect, most of the ecological hypotheses
proposed to date also fail. None can explain
why primates (which have especially large brains
for body mass, even by mammal standards) need
brains that are so much larger than, say, squir-
rels, to cope with what are essentially the same
foraging decisions.
As an alternative, Byrne and Whiten pro-
posed the Machiavellian Intelligence hypothesis
(9) in the late 1980s: They argued that what dif-
ferentiates primates from all other species (and,
hence, what might account for their especially
large brains) was the complexity of their social
lives. Unfortunately, the term Machiavellian
was widely interpreted as implying deceit, ma-
nipulation, and connivancetraits that most
people were reluctant to attribute to any species
other than humans. In fact, although these are
potential aspects of social complexity, they
did not lie at the heart of Byrne and Whitens
proposal. Instead, the proposal emphasized the
complex social environments in which pri-
mates lived. The less contentious label social
brain hypothesis (SBH) (10, 11) has thus been
Although initially criticized for being con-
ceptually vague, the SBH eventually began to
receive increasing quantitative
support. A series of studies dem-
onstrated that, among primates
at least, relative brain size [usu-
ally indexed as relative size of
the neocortex, the area that has
disproportionately expanded in
primates (12)] correlates with
many indices of social complex-
ity, including social group size
(Fig. 1) (13), number of females
in the group (14), grooming
clique size (15), the frequency
of coalitions (16), male mating
strategies (17), the prevalence
of social play (18), the frequen-
cy of tactical deception (19),
and the frequency of social learn-
ing (20).
A weakness of most analyses,
however , is that they invariably
test a single hypothesis without
ensuring that the same predic-
tions could not also arise from
other equally plausible explanations. Although
some attempts have been made to discri mi-
nate between ecological and social theories
(13, 21), and these have largely suppo rted the
social hypothesis, there has been little effort to
develop an explanatory framework that inte-
grates the many social, ecological, and life-
history correlates of brain size that have been
identified. As a result, constraint-type expla-
nations (e.g., correlations with life history)
Social Cognition
British Academy Centenary Research Project, School of
Biological Sciences, University of Liverpool, Liverpool L69
7ZB, UK.
*To whom correspondence should be addressed. E-mail:
Fig. 1. In anthropoid primates, mean social group size increases
with relative neocortex volume (indexed as the ratio of neocortex
volume to the volume of the rest of the brain). Solid circles,
monkeys; open circles, apes. Regression lines are reduced major
axis fits. [Redrawn from (47)]
on September 1, 2010 www.sciencemag.orgDownloaded from
have continued to be emphasized as though
they were alternative explanations for evolu-
tionary function.
Social Brain, Social Complexity
The broad interpretation of the social brain
hypothesis is that individuals living in stable
social groups face cognitive demands that in-
dividuals living alone (or in unstable aggre-
gations) do not. To maintain group cohesion,
individuals must be able to meet their own re-
quirements, as well as coordinate their behavior
with other individuals in the group. They must
also be able to defuse the direct and indirect
conflicts that are generated by foraging in the
same space.
Appreciating that the problem to be solved
lies at the level of the group (i.e., the need to
maintain group coherence through time) and not
just at the level of individual foraging strategies
might allow us to reconcile the apparent conflict
between the ecological and social hypotheses.
One example of this apparent conflict is the
suggestion that flexibility of foraging skills might
be more important than social skills. The evidence
that brain size correlates with technical innova-
tion and the acquisition of new food sources
through social learning (or cultural transmission)
in both birds (22) and primates (20) supports
this claim. However , in the final analysis, all of
these hypotheses (social and ecological alike)
are at root ecological: They allow animals to sur-
vive and reproduce more effectively . The SBH
proposes that ecological problems are solved
socially and that the need for mechanisms that
enhance social cohesion drives brain size evolu-
tion. In contrast, the more conventional ecolog-
ical hypotheses assume that animals solve these
same ecological problems individually by trial
and error learning and do not rely on any form of
social advantage.
For primates at least, sociality is specifically
driven by the need to minimize predation risk
(2325). However, we have shown that two dif-
ferent kinds of predators (chimpanzees and
felids) from five different ecological commu-
nities on two continents differentially select small-
brained prey species (relative to their availability
in the population) when we control for other
traits (including group size) (26). Predation thus
acts directly and indirectly (by means of group
size) on brain evolution. Nonetheless, whatever
its advantages, group living incurs substantial
costs, both in terms of ecological competition
and, for females, reproductive suppression
(23, 24). Hence, behavioral flexibility within a
social situation may be essential for individuals
to make the most of sociality. For anthropoid
primates, this behavioral flexibility is in part
reflected in the use of intense social bonds (often,
but not always, serviced by social grooming) to
prevent groups from disintegrating under these
pressures (15).
The net consequence of these kinds of pres-
sures is that species that evolve larger brains
ultimately have higher fitness. Jerison (3)him-
self pointed out that, in the Paleolithic record,
increases in brain size among carnivores and
their prey species (mainly ungulates) seem to
track each other closely over time, with un-
gulate brain size leading. These findings are
interesting in themselves and also mesh well
with findings that brain size can be associated
with other types of ecological flexibilityfor
example, that brain size is a predictor of both
extinction risk and invasion success in birds
(27, 28).
To tease out the relationship between the
nexus of factors that correlate with brain size,
we have recently undertaken path analyses of
primate and bird data to identify causes, con-
sequences, and constraints in brain evolution
(16). These analys es demonstrate not only
that energetics (i.e., ecology) and life history
impose constraints on brain size (such that
these constraints require solutions if a species
is to evolve a substantially larger brain) but
also that the key selection pressure promoting
the evolution of large brains is explicitly social
(Fig. 2).
Brain Evolution in Birds and Mammals
Although the SBH was originally conceived
for primates, the same principle could apply
more widely, and several attempts have been
made to extend the hypothesis to nonprimate
taxa, including ungulates (29, 30), carnivores
(31), bats (32),andevenbirds(33), albeit with
somewhat mixed results. Indeed, several studies
have argued that sexual selection rather than
sociality might be a more important factor
driving brain evolution (32, 34). Yet evidence
shows that the correlation is the reverse of
what one might expect (polygamous species
actually have the smallest brains), making
sexual selection an unlikely suggestion, al-
though it may influence some components of
the brain [such as the limbic system in male
primates (35, 36)].
Although it is possible that the SBH applies
exclusively to primates, biologists are usually
reluctant to argue for special cases. Fortunately,
the recent availability of more powerful statisti-
cal tools has allowed us to resolve this enigma.
First, we have shown that there is a strong co-
evolutionary relationship between relative brain
size and the evolution of sociality from an
asocial (or less social) state in primates, un-
gulates, and carnivores (31). Second, for four
orders of mammals (primates, bats, artiodactyl
ungulates, and carnivores) and 135 species of
birds representing a wide cross-section of avian
orders, we have shown that, in all taxa except
anthropoid primates, the relationship between
brain size and sociality is qualitative and not
Fig. 2. Path analysis of correlates of brain size in primates. The best model for group size included
just three variables (neocortex size, activity, and range size). Factors that are more remote in the
path diagram provide a significantly poorer fit, suggesting that they act as constraints rather than
driving variables. BMR, basal metabolic rate. [Reproduced with permission from (16)] SCIENCE VOL 317 7 SEPTEMBER 2007
on September 1, 2010 www.sciencemag.orgDownloaded from
quantitative: In each case, large relative brain
size is associated explicitly with pairbonded
(i.e., social) monogamy (Fig. 3).
These findings suggest that it may have
been the cognitive demands of pairbonding
that triggered the initial evolution of large brains
across the vertebrates. More important, pair-
bonding is the issue, not biparental care. This is
obvious in the case of ungulates: Biparental care
does not occur at all in this taxon, yet ungulates
that mate monogamously have substantially
larger brains than those that mate polygamously
(Fig. 3).
How Complex Can Pairbonds Be?
The important issue in the present context is the
marked contrast between anthropoid primates
and all other mammalian and avian taxa (in-
cluding, incidentally, prosimian primates): Only
anthropoid primates exhibit a correlation be-
tween social group size and relative brain (or
neocortex) size. This quantitative relationship
is extremely robust; no matter how we analyze
the data (with or without phylogenetic cor-
rection, using raw volumes, or residuals or
ratios against any number of alternative body
or brain baselines) or which brain data set we
use (histological or magnetic resonance imag-
ing derived, for whole brain, neocortex, or just
the frontal lobes), the same quantitative rela-
tionship always emerges. This suggests that, at
some early point in their evolutionary history ,
anthropoid primates used the kinds of cogni-
tive skills used for pairbonded relationships
by vertebrates to create relationships between
individuals who are not reproductive partners.
In other words, in primates, individuals of the
same sex as well as members of the opposite
sex could form just as intense and focused a
relationship as do reproductive mates in non-
primates. Given that the number of possible
relationships is limited only by the number of
animals in the group, primates naturally ex-
hibit a positive correlation between group size
and brain size. This would explain why, as
primatologists have argued for decades, the
nature of primate sociality seems to be qual-
itatively different from that found in most other
mammals and birds. The reason is that the
everyday relationships of anthropoid primates
involve a form of bo ndedness that is only found
elsewhere in reproductive pairbonds.
This suggestion merely adds to the puzzle
of social bonding. What is it about social
bonds that is cognitively so demanding? There
seem to be two obvious possibilities in the case
of reproductive pairbonds. One is that lifelong
monogamy is a risky commitment; to avoid
the risk of bearing a disproportionate share of
the costs of reproduction, individuals must be
especially careful in choosing good-quality
(i.e., fertile) mates who will be reproductively
loyal and play their full role in the processes
of rearing. The other possibility is that a work-
ing reproductive relationship that involves sub-
stantial postnatal parental investment requires
very close coordination and behavioral syn-
chrony; if successful rearing requires both
partners to invest time and energy in the rear-
ing process, then the pair needs to regulate its
activities so that each has enough time for
feeding and rest. That will usually necessitate
some degree of activity synchronizationin
some cases, to ensure the pair do not drift
apart as a result of different activity schedules,
and in other cases, to ensure that rearing or
vigilance duties are time-shared appropriately
(37). Which of these two has been the key
driver for brain evolution, or whether both
have been equally important, remains to be
It has become apparent that we lack ade-
quate language with which to describe rela-
tionships, yet bondedness is precisely what
primate sociality is all about. Intuitively, we
know what we mean by bondedness because
we experience it ourselves, and we recognize
it when it happens. The problem, perhaps, is
that bondedness is an explicitly emotional ex-
perience and language is a notoriously poor
medium for describing our inner, emotional
experiences. Because relationships do not
have a natural objective cognitive dimension
that we can easily express in language, com-
paring the bondedness of different species is
difficult (this may also explain why ethologists
have invariably ducked the problem completely,
preferring observable descriptions of behavior
to grappling with what is going on inside the
Part of the problem here is that social rela-
tionships have been seen as mere epiphenomena
spawned by the issues of real biological interest,
namely mate choice and parental investment.
The social learning version of SBH (20, 22)in-
herits a sense of that assessment: Sociality is of
interest only in so far as it provides a context
in which animals can acquire foraging informa-
tion that has immediate benefits for them in
terms of individual fitness. However, this misses
the point of primate socialityindeed, the nature
of sociality , and especially pairbondingin all
higher vertebrates. In these intensely social spe-
cies, social relationships are not so much an
emergent property of mating and parenting strat-
egies as the means to achieving those strategies.
A group of this kind is an implicit social con-
tract: To form a group that provides a benefit
of cooperation (for example, reducing preda-
tion risk), members are necessarily obliged
to trade off short-term losses in immediate
benefits in the expectation of greater gains in
the long term through cooperation. Fitness
payoffs are determined not by an individuals
immediate here-and-now personal fitness,
but by the extent to which the group can gen-
erate longer-term payoffs for the individual. In
effect, we are dealing explicitly with multi-
level selection and the long-overlooked topic
of niche construction (38). Once we understand
this, the reasons why animals should invest in
relationships become clear. Relationships pro-
vide the key to fitness benefits at the group
level, and the trickle-down benefits are reaped
by the individual (39). An individual will be
prepared to invest in social strategies that create
groups if, by doing so, it gains higher net
Fig. 3. Mean (±SE) of residual brain volume (controlling for body size and phylogeny) in species
with pairbonded (purple bars) versus all other mating systems (gray bars) in birds and four orders
of mammals. The differences are significant in all cases except primates.
Social Cognition
on September 1, 2010 www.sciencemag.orgDownloaded from
fitness (i.e., at the end of its lifetime) than
pursuing more individualistic strategies.
What Microneurobiology Has to Tell Us
There has, of course, been growing interest in
recent years in some of the neurobiological
correlates of social bonding. Particular interest
has focused the role of oxytocin (and its male
equivalent, vasopressin) in pairbonded species
(40), but other neuropeptides have also been
identified as playing an important role in so-
cial bonding [e.g., endorphins (41)]. In addition,
a parallel interest has been developing in the role
of several specific neuronal assemblages, includ-
ing mirror neurons (42) and so-called spindle
cells in the anterior cingulate cortex (43), as well
as in specific genes such as GLUD2 [a retro-
gene, derived from glutamate dehydrogenase,
which is responsible for clearing the by-products
of neuron activity (44)] and the abnormal spindle-
like microcephaly-associated (ASPM) gene and
microcephalin, which are implicated in brain
growth (45).
Each of these has been seen by their respective
protagonists as the holy grail for understanding
both social cognition generally, and, in particular,
for explaining the differences between humans,
apes, and monkeys (43, 46). There is no question
that these are individually important and novel
discoveries, and they undoubtedly all play a
role in the nature of sociality. However , there is
a great deal more to how and why humans are
different from other apes, or why apes are dif-
ferent from monkeys. We will need better studies
of cognition and behavior to answer these ques-
tions. More important, perhaps, is one key point:
Species differences in a handful of very small
neuronal components do not explain the apparent
need for massive species differences in total brain
size. Most of these studies fall into the same
trap as the developmental explanations for brain
size did in the 1980s: They mistake mechanistic
constraints for evolutionary function. It is un-
clear why this point continues to be ignored, but
we will still have a lot of explaining to do about
volumetric differences in brains.
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Social Components of Fitness in
Primate Groups
Joan B. Silk
There is much interest in the evolutionary forces that favored the evolution of large brains in the
primate order. The social brain hypothesis posits that selection has favored larger brains and more
complex cognitive capacities as a means to cope with the challenges of social life. The hypothesis is
supported by evidence that shows that group size is linked to various measures of brain size. But it
has not been clear how cognitive complexity confers fitness advantages on individuals. Research in
the field and laboratory shows that sophisticated social cognition underlies social behavior in
primate groups. Moreover, a growing body of evidence suggests that the quality of social
relationships has measurable fitness consequences for individuals.
ife in primate groups rivals the best tele-
vision soap operathe weak are often
exploited by the powerful; strong alli-
ances and lasting bonds are formed; dynasties
are established, but are occasionally toppled;
and not all of your favorite characters survive
the season. Ecological constraints generate the
dramatic tension, and natural selection crafts the
plot. The complicated storylines reflect the fact
that primates have evolved large brains, sophis-
ticated social cognition, and complex social
relationships (Fig. 1). There has been consider -
able discussion of the selective pressures that
favor the evolution of large brains in social
species (14), but it has has not been clear how
large brains, social cognition, and social rela-
tionships are translated into fitness advantages
for individuals. New evidence indicates that the
competitive success and reproductive perform-
ance of individuals in primate groups is affected
by the nature and quality of the relationships
that they form. These data enable us to tie to-
gether what we have learned from comparative
analyses of brain morphology, experimental
studies of social cognition, and naturalistic
observations of the structure of social relation-
ships in primate groups.
What the Social Brain Knows
The capacity to develop complex social relation-
ships may be an important benefit derived from
having a social brain. According to the social
Department of Anthropology, University of California, Los
Angeles, CA 90095, USA. E-mail: SCIENCE VOL 317 7 SEPTEMBER 2007 1347
on September 1, 2010 www.sciencemag.orgDownloaded from
... This attitude differs from praising it as a foundation of knowledge to rejecting it as logical nonsense [1,15]. With no pretensions to solve this millennial mystery, this study aimed to review some recent advances in theories of consciousness and the evolutionary history of humans [16][17][18][19]. The concept of entropy as a constant tendency to equalize the possibilities of future states is used to synthesize recent advances in anthropology, neuroscience, and other disciplines [20][21][22][23][24]. From the epistemological perspective, one can define entropy as a measure of the uncertainty in light of our ability to predict the future of the system, which provides a link to the "point of view" concept, comprehensively described in [25]. ...
... The higher the cognitive abilities of an individual organism, the more sophisticated the strategies for acquiring knowledge from the other. Notably, in many cases, bonds between individuals are more important than their kinship, with bonds between sexual partners being among the most stable and efficient [16]. ...
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Despite recent advances, the origin and utility of consciousness remains under debate. Using an evolutionary perspective on the origin of consciousness, this review elaborates on the promising theoretical background suggested in the temporospatial theory of consciousness, which outlines world-brain alignment as a critical predisposition for controlling behavior and adaptation. Such a system can be evolutionarily effective only if it can provide instant cohesion between the subsystems, which is possible only if it performs an intrinsic activity modified in light of the incoming stimulation. One can assume that the world-brain interaction results in a particular interference pattern predetermined by connectome complexity. This is what organisms experience as their exclusive subjective state, allowing the anticipation of regularities in the environment. Thus, an anticipative system can emerge only in a regular environment, which guides natural selection by reinforcing corresponding reactions and decreasing the system entropy. Subsequent evolution requires complicated, layered structures and can be traced from simple organisms to human consciousness and society. This allows us to consider the mode of entropy as a subject of natural evolution rather than an individual entity.
... Most aggregation sites have been suggested to provide important feeding grounds for white sharks [65], and aggregations have been shown to be driven by the seasonal availability and abundance of prey species [64,66,67]. At the same time, sharks have been observed to develop and maintain complex social behaviors such as dominance hierarchies [13,14] and stable social bonds [68], as well as to be able to learn social information [69,70]; these abilities are due to the fact that sharks are characterized by a high ratio between brain mass and body mass [71][72][73], comparable to that of mammals. ...
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Knowledge about the social behavior of sharks is a growing research field, but not many observations are available on the social interactions between pairs of sharks in the presence of passive surface bait and mainly related to aggregations. Between 2009 and 2018, in Gansbaai, South Africa, 415 white sharks were sighted, and 525 surface-generated social interactions were identified, exhibited by 169 different white sharks. The mean sighting rate was 0.91 (range 0.18-1.53) white sharks per hour. Eight patterns of social interaction were exhibited: swim by, parallel swim, follow/give way, follow, give way, stand back, splash fights, and piggyback. Non-random interactions occurred when pairs of specimens approached the passive surface bait, confirming that the white sharks made a real choice, showing a dominance hierarchy during the ten years of data collection. Evidence of non-random social interactions in the surface behavior of bait-attracted white sharks Carcharodon carcharias in Gansbaai's transient population was the goal of this research.
... We constantly and seemingly effortlessly infer the thoughts, feelings, and beliefs of other people, and much of our mental life is spent preparing to engage or engaging with the task of processing information about social agents [76]. A sociobiological picture that many researchers in the field have adopted is that the evolutionary advantages of living in relatively large social groups helped humans to evolve the capacities to interpret, explain, and predict each other's actions, and to use these capacities to share and accumulate experiences, to plan, collaborate, and attain joint goals that they would not have been able to achieve as individuals or as members of smaller groups [77][78][79]. There are excellent neuroscientific experimental studies providing ample evidence that mentalizing, as indicated by the activation (or inhibition) of the brain's mentalizing network (see "The neuroscience of mentalizing, attachment and resilience" below) is critical for assessing the morality of others, making judgements about how competitors might act and for learning from individuals with specialist information [80]. ...
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This article reviews the current status of research on the relationship between attachment and trauma in developmental psychopathology. Beginning with a review of the major issues and the state-of-the-art in relation to current thinking in the field of attachment about the impact of trauma and the inter-generational transmission of trauma, the review then considers recent neurobiological work on mentalizing and trauma and suggests areas of new development and implications for clinical practice.
... Research on the evolution of intelligence, for example, has proposed that it was in large part the need to navigate social life that pressured for bigger brains and cognitive flexibility [77]. Unlike most other primates, humans also have the tendency to develop relationships beyond pair bonds and kin [78]. Recent research has also shown that being well connected leads to greater personal autonomy [79], increases in motivation [80], improvements in cognitive functioning [81], and better decision making [82]. ...
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Globalization, technological advances, economic and geopolitical shocks, pandemics, and any number of novel or unanticipated events have one thing in common: they represent change and require dynamic responses and adaptation from organizations, teams, and individuals. A critical resource for individuals to be adaptive are broad skills relevant to varied organizational conditions. These adaptive skills have been discussed in diverse venues but rarely in the organizational literature. Also, most, if not all, of extant conceptual frameworks related to adaptive skills remain unvalidated. The purpose of this research was to organize these skills, define and situate them in the relevant organizational and psychological literatures, and empirically test a proposed four-category framework. The experimental results supported the C+MAC framework, as skills were better categorized in terms of their theoretically related category. Additionally, the four-category framework proved a better fit to the skills compared to an influential, alternative model. The findings' implications are discussed, noting how an empirically validated framework can facilitate understanding of how individuals engage with organizational environments and organizations get their work done.
... The drivers of brain size in social vertebrates, which can lead to a positive relationship between brain size and cognitive performance (e.g. competition and mate selection), do not occur in social insect workers (Lindenfors 2005;Dunbar and Shultz 2007). Our results suggest that, despite size being the predominant polyethistic factor in B. terrestris-with larger workers being mostly foragers and smaller workers mostly feeding and incubating brood (Jandt and Dornhaus 2009;Holland et al. 2021)-their capacity for associative learning is not limited by size, and therefore role, within a colony. ...
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Eusocial insect colonies act as a superorganism, which can improve their ability to buffer the negative impact of some anthropogenic stressors. However, this buffering effect can be affected by anthropogenic factors that reduce their colony size. A reduction in colony size is known to negatively affect several parameters like brood maintenance or thermoregulation, but the effects on behaviour and cognition have been largely overlooked. It remains unclear how a sudden change in group size, such as that which might be caused by anthropogenic stressors, affects individual behaviour within a colony. In this study, the bumblebee Bombus terrestris was used to study the effect of social group size on behaviour by comparing the associative learning capabilities of individuals from colonies that were unmanipulated, reduced to a normal size (a colony of 100 workers) or reduced to a critically low but functional size (a colony of 20 workers). The results demonstrated that workers from the different treatments performed equally well in associative learning tasks, which also included no significant differences in the learning capacity of workers that had fully developed after the colony size manipulation. Furthermore, we found that the size of workers had no impact on associative learning ability. The learning abilities of bumblebee workers were thus resilient to the colony reduction they encountered. Our study is a first step towards understanding how eusocial insect cognition can be impacted by drastic reductions in colony size. Significance statement While anthropogenic stressors can reduce the colony size of eusocial insects, the impact of this reduction is poorly studied, particularly among bumblebees. We hypothesised that colony size reduction would affect the cognitive capacity of worker bumblebees as a result of fewer social interactions or potential undernourishment. Using differential conditioning, we showed that drastic reductions in colony size have no effect on the associative learning capabilities of the bumblebee Bombus terrestris and that this was the same for individuals that were tested just after the colony reduction and individuals that fully developed under the colony size reduction. We also showed that body size did not affect learning capabilities. This resilience could be an efficient buffer against the ongoing impacts of global change.
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Notre cerveau est plus que la somme de ses parties. Le quand, le où, et le comment des processus d'apprentissage et de mémoire impliquent encore de nombreuses hypothèses non-élucidées et donc qui doivent être investiguées. Comment le cerveau humain encode ses propres processus d'apprentissage et de mémoire et comment la topologie de son réseau social élargi présente des modèles neuronaux similaires aux modèles neuronaux de nos amis et de nos liens communautaires ?
Primates are among the most well‐known animals; however, compiling a list of their distinctive characters is challenging. Most mammal groups have acquired enough unique modifications to make distinguishing one group from another relatively straightforward. The stakes are significant because they bear directly on the priority given to features that bracket the Order as well as where we draw the primate–non‐primate boundary. Descriptions of primates often begin with statements similar to the following: primates are generalized mammals that have retained a primitive body plan with comparatively few modifications. Primates have evolved an array of locomotor adaptations that include quadrupedalism, forelimb suspension, knuckle‐walking, vertical clinging and leaping, and bipedality. Primate teeth are characterized by a combination of trends generally not found in other mammals. Strepsirrhines possess the primitive primate features such as a simple post‐orbital bar, two mobile bones in the forearm, and five digits.
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Large brains provide adaptive cognitive benefits but require unusually high, near-constant energy inputs and become fully functional well after their growth is completed. Consequently, young of most larger-brained endotherms should not be able to independently support the growth and development of their own brains. This paradox is solved if the evolution of extended parental provisioning facilitated brain size evolution. Comparative studies indeed show that extended parental provisioning coevolved with brain size and that it may improve immature survival. The major role of extended parental provisioning supports the idea that the ability to sustain the costs of brains limited brain size evolution.
As a social species, ready exchange with peers is a pivotal asset - our "social capital". Yet, single-person households have come to pervade metropolitan cities worldwide, with unknown consequences in the long run. Here, we systematically explore the morphological manifestations associated with singular living in ∼40,000 UK Biobank participants. The uncovered population-level signature spotlights the highly associative default mode network, in addition to findings such as in the amygdala central, cortical and corticoamygdaloid nuclei groups, as well as the hippocampal fimbria and dentate gyrus. Both positive effects, equating to greater gray matter volume associated with living alone, and negative effects, which can be interpreted as greater grey matter associations with not living alone, were found across the cortex and subcortical structures Sex-stratified analyses revealed male-specific neural substrates, including somatomotor, saliency and visual systems, while female-specific neural substrates centred on the dorsomedial prefrontal cortex. In line with our demographic profiling results, the discovered neural pattern of living alone is potentially linked to alcohol and tobacco consumption, anxiety, sleep quality as well as daily TV watching. The persistent trend for solitary living will require new answers from public-health decision makers. SIGNIFICANCE STATEMENT: Living alone has profound consequences for mental and physical health. Despite this, there has been a rapid increase in single-person households worldwide, with the long-term consequences yet unknown. In the largest study of its kind, we investigate how the objective lack of everyday social interaction, through living alone, manifests in the brain. Our population neuroscience approach uncovered a gray matter signature that converged on the 'default network', alongside targeted subcortical, sex and demographic profiling analyses. The human urge for social relationships is highlighted by the evolving COVID-19 pandemic. Better understanding of how social isolation relates to the brain will influence health and social policy decision-making of pandemic planning, as well as social interventions in light of global shifts in houseful structures.
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We report the existence and distribution of an unusual type of projection neuron, a large, spindle-shaped cell, in layer Vb of the anterior cingulate cortex of pongids and hominids. These spindle cells were not observed in any other primate species or any other mammalian taxa, and their volume was correlated with brain volume residuals, a measure of encephalization in higher primates. These observations are of particular interest when considering primate neocortical evolution, as they reveal possible adaptive changes and functional modifications over the last 15–20 million years in the anterior cingulate cortex, a region that plays a major role in the regulation of many aspects of autonomic function and of certain cognitive processes. That in humans these unique neurons have been shown previously to be severely affected in the degenerative process of Alzheimer’s disease suggests that some of the differential neuronal susceptibility that occurs in the human brain in the course of age-related dementing illnesses may have appeared only recently during primate evolution.
Extensive variation in life-history patterns is documented across primate species. Variables included are gestation length, neonatal weight, litter size, age at weaning, age at sexual maturity, age at first breeding, longevity, and length of the estrous cycle. Species within genera and genera within subfamilies tend to be very similar on most measures, and about 85% of the variation remains when the subfamily is used as the level for statistical analysis. Variation in most life-history measures is highly correlated with variation in body size, and differences in body size are associated with differences in behavior and ecology. Allometric relationships between life-history variables and adult body weight are described; subfamily deviations from best-fit lines do not reveal strong correlations with behavior or ecology. However, for their body size, some subfamilies show consistently fast development across life-history stages while others are characteristically slow. One exception to the tendency for relative values to be positively correlated is brain growth: those primates with relatively large brains at birth have relatively less postnatal brain growth. Humans are a notable exception, with large brains at birth and high postnatal brain growth.
Conventional wisdom over the past 160 years in the cognitive and neurosciences has assumed that brains evolved to process factual information about the world. Most attention has therefore been focused on such features as pattern recognition, color vision, and speech perception. By extension, it was assumed that brains evolved to deal with essentially ecological problem-solving tasks. 1.
Like many small African antelopes, klipspringer (Oreotragus oreotragus) live in territorial pairs. The structure of the pairbond and the ways in which it is maintained through time are described quantitatively, using data on co-ordination of behaviour, activity budgets, progression orders and visual monitoring. Although both partners play an active role, the female's behaviour tends to be more concerned with efficient foraging, while the male's behaviour seems to emphasize those activities that allow him to maintain, contact with the female. Because the male needs to spend less time feeding than does the female, he detects predators more frequently, a behaviour that probably allows the female to feed more efficiently. Both sexes apparently defend the territory against intruders, although the functional significance of the territory remains unclear.
There are 2 main competing theories on the evolution of group living in diurnal non-human primates. 1) Predation avoidance favours group living; there are only disadvantages to feeding in a group and feeding competition increases with group size. 2) There is a feeding advantage to group living deriving from communal defence of high-quality food patches; predation is not important. A critical test is proposed: the theories differ in the predicted relationship between a female's birth rate and the size of the group in which she lives. An additional test is concerned with the predicted relationship between population density relative to food availability and average group size. Finally, a critical test is proposed of the hypothesis that increasing group size should lead to reduced predation risk by comparing demographic patterns between areas where predators are still present and where they have disappeared. In all 3 tests, results provide strong support for the predation-feeding competition theory and are clearly unfavourable for the theory postulating feeding advantages to group living. Such feeding advantages may, however, gain prominence under some conditions.-from Author
Extensive variation in life-history patterns is documented across primate species. Variables included are gestation length, neonatal weight, litter size, age at weaning, age at sexual maturity, age at first breeding, longevity, and length of the estrous cycle. Species within genera and genera within subfamilies tend to be very similar on most measures, and about 85% of the variation remains when the subfamily is used as the level for statistical analysis. Variation in most life-history measures is highly correlated with variation in body size, and differences in body size are associated with differences in behavior and ecology. Allometric relationships between life-history variables and adult body weight are described; subfamily deviations from best-fit lines do not reveal strong correlations with behavior or ecology. However, for their body size, some subfamilies show consistently fast development across life-history stages while others are characteristically slow. One exception to the tendency for relative values to be positively correlated is brain growth: those primates with relatively large brains at birth have relatively less postnatal brain growth. Humans are a notable exception, with large brains at birth and high postnatal brain growth.
Brain tissue is metabolically expensive, but there is no significant correlation between relative basal metabolic rate and relative brain size in humans and other encephalized mammals. The expensive-tissue suggests that the metabolic requirements of relatively large brains are offset by a corresponding reduction of the gut. The splanchnic organs (liver and gastro-intestinal tract) are as metabolically expensive organs in the human body that is markedly small in relation to body size. Gut size is highly correlated with diet, and relatively small guts are compatible only with high-quality, easy-to-digest food. The often -cited relationship between diet and relative brain size is more properly viewed as a relationship between relative brain size and relative gut size, the latter being determined by dietary quality. No matter what is selecting for relatively large brains in humans and other primates, they cannot be achieved without a shift to a high-quality diet unless there is a rise in the metabolic rate. Therefore the incorporation of increasingly greater amounts of animal products into the diet was essential in the evolution of the large human brain.
Primates use social grooming to service coalitions and it has been suggested that these directly affect the fitness of their members by allowing them to reduce the intrinsic costs associated with living in large groups. We tested two hypotheses about the size of grooming cliques that derive from this suggestion: (1) that grooming clique size should correlate with relative neocortex size and (2) that the size of grooming cliques should be proportional to the size of the groups they have to support. Both predictions were confirmed, although we show that, in respect of neocortex size, there are as many as four statistically distinct grades within the primates (including humans). Analysis of the patterns of grooming among males and females suggested that large primate social groups often consist of a set of smaller female subgroups (in some cases, matrilinearly based coalitions) that are linked by individual males. This may be because males insert themselves into the interstices between weakly bonded female subgroups rather than because they actually hold these subunits together.
The seemingly innocent observation that the activities of organisms bring about changes in environments is so obvious that it seems an unlikely focus for a new line of thinking about evolution. Yet niche construction--as this process of organism-driven environmental modification is known--has hidden complexities. By transforming biotic and abiotic sources of natural selection in external environments, niche construction generates feedback in evolution on a scale hitherto underestimated--and in a manner that transforms the evolutionary dynamic. It also plays a critical role in ecology, supporting ecosystem engineering and influencing the flow of energy and nutrients through ecosystems. Despite this, niche construction has been given short shrift in theoretical biology, in part because it cannot be fully understood within the framework of standard evolutionary theory. Wedding evolution and ecology, this book extends evolutionary theory by formally including niche construction and ecological inheritance as additional evolutionary processes. The authors support their historic move with empirical data, theoretical population genetics, and conceptual models. They also describe new research methods capable of testing the theory. They demonstrate how their theory can resolve long-standing problems in ecology, particularly by advancing the sorely needed synthesis of ecology and evolution, and how it offers an evolutionary basis for the human sciences. Already hailed as a pioneering work by some of the world's most influential biologists, this is a rare, potentially field-changing contribution to the biological sciences.