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==Research background==

== Research background 研究背景 ==

[[Primatologist]]s have noted that, due to their highly social nature, [[primate]]s must maintain personal contact with the other members of their social group, usually through [[social grooming]]. Such social groups function as protective [[clique]]s 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.{{citation needed|date=May 2018}}

[[Primatologist]]s have noted that, due to their highly social nature, [[primate]]s must maintain personal contact with the other members of their social group, usually through [[social grooming]]. Such social groups function as protective [[clique]]s 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.{{citation needed|date=May 2018}}

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.

 

In 1992, Dunbar used the correlation observed for non-human primates to predict a social group size for humans.  Using a regression equation on data for 38 primate genera, Dunbar predicted a human "mean group size" of 148 (casually rounded to 150), a result he considered exploratory due to the large error measure (a 95% confidence interval of 100 to 230).

In 1992, Dunbar used the correlation observed for non-human primates to predict a social group size for humans.  Using a regression equation on data for 38 primate genera, Dunbar predicted a human "mean group size" of 148 (casually rounded to 150), a result he considered exploratory due to the large error measure (a 95% confidence interval of 100 to 230).

1992年，邓巴利用观察到的非人灵长类动物的相关性来预测人类的社会群体大小。利用38个灵长类动物属的数据回归方程，邓巴预测人类的“平均群体大小”为148(随意舍入到150) ，由于误差很大(95% 的置信区间为100到230) ，他认为这个结果是可探索的。

1992年，邓巴利用观察到的非人灵长类动物的相关数据来预测人类的社会群体大小。利用38个灵长类属的数据回归方程，邓巴预测人类的“平均群体大小”为148(通常四舍五入到150) ，由于误差很大(95% 的置信区间为100到230)，他认为这个结果是可探索的。

 

Dunbar then compared this prediction with observable group sizes for humans.  Beginning with the assumption that the current mean size of the human neocortex had developed about 250,000 years ago, during the Pleistocene, Dunbar searched the anthropological and ethnographical literature for census-like group size information for various hunter–gatherer societies, the closest existing approximations to how anthropology reconstructs the Pleistocene societies. Dunbar noted that the groups fell into three categories—small, medium and large, equivalent to bands, cultural lineage groups and tribes—with respective size ranges of 30–50, 100–200 and 500–2500 members each.

Dunbar then compared this prediction with observable group sizes for humans.  Beginning with the assumption that the current mean size of the human neocortex had developed about 250,000 years ago, during the Pleistocene, Dunbar searched the anthropological and ethnographical literature for census-like group size information for various hunter–gatherer societies, the closest existing approximations to how anthropology reconstructs the Pleistocene societies. Dunbar noted that the groups fell into three categories—small, medium and large, equivalent to bands, cultural lineage groups and tribes—with respective size ranges of 30–50, 100–200 and 500–2500 members each.

邓巴随后将这一预测与可观察到的人类群体大小进行了比较。从假设人类新大脑皮层目前的平均大小大约在25万年前更新世时期发展起来开始，邓巴在人类学和民族志文献中搜索各种狩猎采集社会的类似人口普查的群体大小信息，这是现存最接近人类学如何重建更新世社会的方式。邓巴指出，这些族群分为三类，即小型、中型和大型，相当于族群、文化宗族和部落，各自的人数范围分别为30-50人、100-200人和500-2500人。

邓巴随后将这一预测与可观察到的人类群体大小进行了比较。首先假设人类新大脑皮层的平均大小是在大约25万年前的更新世时期形成的，邓巴在人类学和人种学文献中搜索了各种与狩猎采集社会类似的人口普查的群体规模信息，这是现存最接近人类学如何重建更新世社会的方式。邓巴指出，这些族群分为三类，即小型、中型和大型，相当于族群、文化宗族和部落，各自的人数范围分别为30-50人、100-200人和500-2500人。

 

Dunbar's surveys of village and tribe sizes also appeared to approximate this predicted value, including 150 as the estimated size of a Neolithic farming village; 150 as the splitting point of Hutterite settlements; 200 as the upper bound on the number of academics in a discipline's sub-specialisation; 150 as the basic unit size of professional armies in Roman antiquity and in modern times since the 16th century; and notions of appropriate company size.

Dunbar's surveys of village and tribe sizes also appeared to approximate this predicted value, including 150 as the estimated size of a Neolithic farming village; 150 as the splitting point of Hutterite settlements; 200 as the upper bound on the number of academics in a discipline's sub-specialisation; 150 as the basic unit size of professional armies in Roman antiquity and in modern times since the 16th century; and notions of appropriate company size.

邓巴对村庄和部落规模的调查似乎也接近这一预测值，包括150作为一个新石器时代农村的估计规模; 150作为哈特人定居点的分裂点; 200作为一个学科的亚专业化学者人数的上限; 150作为罗马古代和16世纪以来现代职业军队的基本单位规模; 以及适当的连队规模的概念。

邓巴对村庄和部落规模的调查似乎也接近于这个预测值，其中包括新石器时代农庄的估计规模150人；哈特人定居点的分裂点150人;作为一个学科的亚专业学者人数的上限200人;自16世纪以来，在罗马古代和现代，专业部队的基本部队人数也均为150；同时这个数字差不多也是一个得体公司的规模。

 

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.

 

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==

==Applications==