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Dunbar's number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships—relationships in which an individual knows who each person is and how each person relates to every other person. This number was first proposed in the 1990s by British anthropologist Robin Dunbar, who found a correlation between primate brain size and average social group size. （加了一句话By using the average human brain size and extrapolating from the results of primates, he proposed that humans can comfortably maintain 150 stable relationships.[4]。）Dunbar explained it informally as "the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar".

Dunbar's number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships—relationships in which an individual knows who each person is and how each person relates to every other person. This number was first proposed in the 1990s by British anthropologist Robin Dunbar, who found a correlation between primate brain size and average social group size. （加了一句话By using the average human brain size and extrapolating from the results of primates, he proposed that humans can comfortably maintain 150 stable relationships.[4]。）Dunbar explained it informally as "the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar".

邓巴数是一个建议的认知极限，用来限制与之保持稳定社会关系的人数，即一个人知道每个人是谁，以及每个人与其他每个人之间的关系。这个数字最早是在20世纪90年代由英国人类学家 Robin Dunbar 提出的，他发现了灵长类动物大脑尺寸和平均社会群体大小之间存在相关性。通过人类大脑的平均大小并从灵长类动物的结果推断，他提出人类可以舒适地保持150种稳定的关系。邓巴通俗地解释它为“如果您碰巧来到一个酒吧，里面的人数刚好不会让你为不请自来地喝酒而感到尴尬。”

邓巴数是一个建议的认知极限，用来限制与之保持稳定社会关系的人数，即一个人知道每个人是谁，以及每个人与其他每个人之间的关系。这个数字最早是在20世纪90年代由英国人类学家罗宾·邓巴 Robin Dunbar 提出的，他发现了灵长类动物大脑尺寸和平均社会群体大小之间存在相关性。通过人类大脑的平均大小并从灵长类动物的研究结果推断，他提出人类可以舒适地保持150种稳定的关系。邓巴通俗地解释它为“如果您碰巧来到一个酒吧，里面的人数刚刚好不会让你为不请自来地喝酒而感到尴尬。”

Proponents assert that numbers larger than this generally require more restrictive rules, laws, and enforced norms to maintain a stable, cohesive group.  It has been proposed to lie between 100 and 250, with a commonly used value of 150. Dunbar's number states the number of people one knows and keeps social contact with, and it does not include the number of people known personally with a ceased social relationship, nor people just generally known with a lack of persistent social relationship, a number which might be much higher and likely depends on long-term memory size.

Proponents assert that numbers larger than this generally require more restrictive rules, laws, and enforced norms to maintain a stable, cohesive group.  It has been proposed to lie between 100 and 250, with a commonly used value of 150. Dunbar's number states the number of people one knows and keeps social contact with, and it does not include the number of people known personally with a ceased social relationship, nor people just generally known with a lack of persistent social relationship, a number which might be much higher and likely depends on long-term memory size.

Dunbar theorised that "this limit is a direct function of relative neocortex size, and that this in turn limits group size [...] the limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable inter-personal relationship can be maintained". On the periphery, the number also includes past colleagues, such as high school friends, with whom a person would want to reacquaint himself or herself if they met again.

Dunbar theorised that "this limit is a direct function of relative neocortex size, and that this in turn limits group size [...] the limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable inter-personal relationship can be maintained". On the periphery, the number also includes past colleagues, such as high school friends, with whom a person would want to reacquaint himself or herself if they met again.

邓巴推论说: “这个极限是相对新大脑皮层大小的直接函数，反过来它又限制了群体的大小。新大脑皮层处理能力的极限仅仅是与之保持稳定人际关系的个体的数量。“从定义的边缘看，这个数字还包括过去的同事，比如高中时期的朋友，如果他们再次见面，他们会想要重新认识自己。

邓巴推论说: “这个极限是受到相对新大脑皮层大小影响的一个直接函数，反过来它又限制了群体的大小。新大脑皮层处理能力的极限仅仅是与之保持稳定人际关系的个体的数量。“从定义的边缘看，这个数字还包括过去的同事，比如高中时期的朋友，如果他们再次见面，他们会想要重新认识自己。

Primatologists have noted that, due to their highly social nature, primates must maintain personal contact with the other members of their social group, usually through social grooming. Such social groups function as protective cliques within the physical groups in which the primates live. The number of social group members a primate can track appears to be limited by the volume of the neocortex.  This suggests that there is a species-specific index of the social group size, computable from the species' mean neocortical volume.

Primatologists have noted that, due to their highly social nature, primates must maintain personal contact with the other members of their social group, usually through social grooming. Such social groups function as protective cliques within the physical groups in which the primates live. The number of social group members a primate can track appears to be limited by the volume of the neocortex.  This suggests that there is a species-specific index of the social group size, computable from the species' mean neocortical volume.

Dunbar has argued that 150 would be the mean group size only for communities with a very high incentive to remain together. For a group of this size to remain cohesive, Dunbar speculated that as much as 42% of the group's time would have to be devoted to social grooming. Correspondingly, only groups under intense survival pressure, such as subsistence villages, nomadic tribes, and historical military groupings, have, on average, achieved the 150-member mark. Moreover, Dunbar noted that such groups are almost always physically close: "[...] we might expect the upper limit on group size to depend on the degree of social dispersal. In dispersed societies, individuals will meet less often and will thus be less familiar with each other, so group sizes should be smaller in consequence." Thus, the 150-member group would occur only because of absolute necessity—due to intense environmental and economic pressures.

Dunbar has argued that 150 would be the mean group size only for communities with a very high incentive to remain together. For a group of this size to remain cohesive, Dunbar speculated that as much as 42% of the group's time would have to be devoted to social grooming. Correspondingly, only groups under intense survival pressure, such as subsistence villages, nomadic tribes, and historical military groupings, have, on average, achieved the 150-member mark. Moreover, Dunbar noted that such groups are almost always physically close: "[...] we might expect the upper limit on group size to depend on the degree of social dispersal. In dispersed societies, individuals will meet less often and will thus be less familiar with each other, so group sizes should be smaller in consequence." Thus, the 150-member group would occur only because of absolute necessity—due to intense environmental and economic pressures.

邓巴认为，只有在机动性特别高以维持团结的社区中，平均群体规模为150人。为了使如此规模的团队保持凝聚力，邓巴推测，该团队多达42％的时间必须用于社交整饰。相应地，只有生存压力很大的团体，例如自给自足的村庄，游牧部落和历史军事团体，平均才能达到150人的标准。此外，邓巴指出，这样的群体几乎总是物理上接近：“我们可能期望群体规模的上限取决于社会分散程度。在分散的社会中，个人见面的频率会降低，因此彼此之间的熟悉程度也会降低，因此群体规模也应该缩小。”因此，由150名成员组成的团体之所以会出现，是因为绝对的必要性-由于强烈的环境和经济压力。

邓巴认为，只有在机动性特别高以维持团结的社区中，平均群体规模为150人。为了使如此规模的团队保持凝聚力，邓巴推测，该团队多达42％的时间必须用于社交梳理。相应地，只有生存压力很大的团体，例如自给自足的村庄，游牧部落和历史军事团体，平均才能达到150人的标准。此外，邓巴指出，这样的群体几乎总是物理上接近：“我们可能期望群体规模的上限取决于社会分散程度。在分散的社会中，个人见面的频率会降低，因此彼此之间的熟悉程度也会降低，因此群体规模也应该缩小。”因此，由150名成员组成的团体之所以会出现，是因为绝对的必要性-由于强烈的环境和经济压力。

Dunbar, in Grooming, Gossip, and the Evolution of Language, proposes furthermore that language may have arisen as a "cheap" means of social grooming, allowing early humans to maintain social cohesion efficiently. Without language, Dunbar speculates, humans would have to expend nearly half their time on social grooming, which would have made productive, cooperative effort nearly impossible. Language may have allowed societies to remain cohesive, while reducing the need for physical and social intimacy. This result is confirmed by the mathematical formulation of the social brain hypothesis, that showed that it is unlikely that increased brain size would have led to large groups without the kind of complex communication that only language allows.

Dunbar, in Grooming, Gossip, and the Evolution of Language, proposes furthermore that language may have arisen as a "cheap" means of social grooming, allowing early humans to maintain social cohesion efficiently. Without language, Dunbar speculates, humans would have to expend nearly half their time on social grooming, which would have made productive, cooperative effort nearly impossible. Language may have allowed societies to remain cohesive, while reducing the need for physical and social intimacy. This result is confirmed by the mathematical formulation of the social brain hypothesis, that showed that it is unlikely that increased brain size would have led to large groups without the kind of complex communication that only language allows.

== Applications 应用 ==

== Applications 应用 ==

Anthropologist H. Russell Bernard, Peter Killworth and associates have done a variety of field studies in the United States that came up with an estimated mean number of ties, 290, which is roughly double Dunbar's estimate. The Bernard–Killworth median of 231 is lower, due to an upward skew in the distribution, but still appreciably larger than Dunbar's estimate. The Bernard–Killworth estimate of the maximum likelihood of the size of a person's social network is based on a number of field studies using different methods in various populations. It is not an average of study averages but a repeated finding. Nevertheless, the Bernard–Killworth number has not been popularized as widely as Dunbar's.

Anthropologist H. Russell Bernard, Peter Killworth and associates have done a variety of field studies in the United States that came up with an estimated mean number of ties, 290, which is roughly double Dunbar's estimate. The Bernard–Killworth median of 231 is lower, due to an upward skew in the distribution, but still appreciably larger than Dunbar's estimate. The Bernard–Killworth estimate of the maximum likelihood of the size of a person's social network is based on a number of field studies using different methods in various populations. It is not an average of study averages but a repeated finding. Nevertheless, the Bernard–Killworth number has not been popularized as widely as Dunbar's.

人类学家拉塞尔·伯纳德H. Russell Bernard，彼得·基尔沃思Peter Killworth及其同事在美国进行了各种田野研究，之后得出的社会平均关系数为290，约为邓巴估计的两倍。伯纳德-基尔沃思Bernard-Killworth的中位数为231，这是由于分布上的偏斜所致，但仍大大高于邓巴（Dunbar）的估计。伯纳德-基尔沃思对一个人的社交网络规模最大可能性的估计，是基于在不同人群中使用不同方法进行的大量实地研究。它不是研究平均值的平均值，而是反复去搜寻的结果。然而，伯纳德-基尔沃思数还没有像邓巴氏那样广泛普及。

人类学家拉塞尔·伯纳德H. Russell Bernard，彼得·基尔沃思Peter Killworth及其同事在美国进行了各种田野研究，之后得出的社会平均关系数为290，约为邓巴估计的两倍。伯纳德-基尔沃思Bernard-Killworth的中位数为231，这是由于分布上的偏斜所致，但仍大大高于邓巴的估计。伯纳德-基尔沃思对一个人的社交网络规模最大可能性的估计，是基于在不同人群中使用不同方法进行的大量实地研究。它不是研究平均值的平均值，而是反复去搜寻的结果。然而，伯纳德-基尔沃思数还没有像邓巴数那样广泛普及。

=== Criticism 评论 ===

=== Criticism 评论 ===

Philip Lieberman argues that since band societies of approximately 30–50 people are bounded by nutritional limitations to what group sizes can be fed without at least rudimentary agriculture, big human brains consuming more nutrients than ape brains, group sizes of approximately 150 cannot have been selected for in paleolithic humans.  Brains much smaller than human or even mammalian brains are also known to be able to support social relationships, including social insects with hierarchies where each individual "knows" its place (such as the paper wasp with its societies of approximately 80 individuals ) and computer-simulated virtual autonomous agents with simple reaction programming emulating what is referred to in primatology as "ape politics".

Philip Lieberman argues that since band societies of approximately 30–50 people are bounded by nutritional limitations to what group sizes can be fed without at least rudimentary agriculture, big human brains consuming more nutrients than ape brains, group sizes of approximately 150 cannot have been selected for in paleolithic humans.  Brains much smaller than human or even mammalian brains are also known to be able to support social relationships, including social insects with hierarchies where each individual "knows" its place (such as the paper wasp with its societies of approximately 80 individuals ) and computer-simulated virtual autonomous agents with simple reaction programming emulating what is referred to in primatology as "ape politics".

菲利普·利伯曼Philip Lieberman辩称，在没有最基本农业的情况下，社会群体会因为营养供给极限而导致规模上受到一定制约，大约在30至50人。人类的大脑相比较猿类会消耗更多的营养，因此，大约150人的群体规模在旧石器时代的人类范围内是不可能达到的。比人类甚至哺乳动物都要小得多的大脑也被认为能够支持社会关系，包括具有等级制度的社交昆虫，每个人都“知道”它的位置（例如大约由80只个体组成的黄蜂）以及计算机模拟的虚拟自治代理程序，它们具有简单的反应程序来仿效灵长类学中所称的“猿政治”。

菲利普·利伯曼Philip Lieberman辩称，在没有最基本农业发展的情况下，社会群体会因为营养供给极限而导致规模上受到一定制约，大约在30至50人。人类的大脑相比较猿类会消耗更多的营养，因此，大约150人的群体规模在旧石器时代的人类范围内是不可能达到的。比人类甚至哺乳动物都要小得多的大脑也被认为能够支持社会关系，包括具有等级制度的社交昆虫，每个人都“知道”它的位置（例如大约由80只个体组成的黄蜂集群）以及计算机模拟的虚拟自治代理程序，它们具有简单的反应程序来仿效灵长类学中所称的“猿政治”。

Comparisons of primate species show that what appears to be a link between group size and brain size, and also what species do not fit such a correlation, is explainable by diet. Many primates that eat specialized diets that rely on scarce food have evolved small brains to conserve nutrients and are limited to living in small groups or even alone, and they lower average brain size for solitary or small group primates. Small-brained species of primate that are living in large groups are successfully predicted by diet theory to be the species that eat food that is abundant but not very nutritious. Along with the existence of complex deception in small-brained primates in large groups with the opportunity (both abundant food eaters in their natural environments and originally solitary species that adopted social lifestyles under artificial food abundances), this is cited as evidence against the model of social groups selecting for large brains and/or intelligence.<ref>Alex R. DeCasien, Scott A. Williams & James P. Higham (2017). "Primate brain size is predicted by diet but not sociality"</ref>

Comparisons of primate species show that what appears to be a link between group size and brain size, and also what species do not fit such a correlation, is explainable by diet. Many primates that eat specialized diets that rely on scarce food have evolved small brains to conserve nutrients and are limited to living in small groups or even alone, and they lower average brain size for solitary or small group primates. Small-brained species of primate that are living in large groups are successfully predicted by diet theory to be the species that eat food that is abundant but not very nutritious. Along with the existence of complex deception in small-brained primates in large groups with the opportunity (both abundant food eaters in their natural environments and originally solitary species that adopted social lifestyles under artificial food abundances), this is cited as evidence against the model of social groups selecting for large brains and/or intelligence.<ref>Alex R. DeCasien, Scott A. Williams & James P. Higham (2017). "Primate brain size is predicted by diet but not sociality"</ref>