Updated on 2022/05/26

写真a

 
NAKAHASHI, Wataru
 
Affiliation
Faculty of Social Sciences, School of Social Sciences
Job title
Associate Professor

Education

  • 2004.04
    -
    2007.05

    東京大学大学院   理学系研究科   生物科学専攻博士課程  

  • 2002.04
    -
    2004.03

    東京大学大学院   理学系研究科   生物科学専攻修士課程  

  • 1998.04
    -
    2002.03

    The University of Tokyo   Faculty of Science   Department of Biological Sciences  

  • 1996.04
    -
    1998.03

    The University of Tokyo   College of Arts and Sciences   Natural Science II  

Research Experience

  • 2020.04
    -
    Now

    Waseda University   Faculty of Social Sciences   Associate Professor

  • 2018.04
    -
    2020.03

    Waseda University   Faculty of Social Sciences   Assistant Professor

  • 2013.10
    -
    2018.03

    The Graduate University for Advanced Studies   School of Advanced Sciences

  • 2013.04
    -
    2013.10

    University of the Ryukyus

  • 2009.01
    -
    2013.03

    Meiji University   Organization for the Strategic Coordination of Research and Intellectual Properties

  • 2007.10
    -
    2008.12

    東京大学大学院   理学系研究科生物科学専攻   大学院研究生

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Professional Memberships

  •  
     
     

    SOCIETY OF EVOLUTIONARY STUDIES, JAPAN

  •  
     
     

    HBES-J

  •  
     
     

    THE JAPANESE SOCIETY FOR MATHEMATICAL BIOLOGY

  •  
     
     

    THE ANTHROPOLOGICAL SOCIETY OF NIPPON

 

Research Areas

  • Physical anthropology

  • Ecology and environment

Research Interests

  • Mathematical model

  • Human Evolution

  • Theoretical Anthropology

  • Physical Anthropology

  • Gene-culture Coevolution

Papers

  • Cultural skill and language: How structuration affects cultural evolution

    Wataru Nakahashi

    Journal of Theoretical Biology   471   13 - 21  2019.03  [Refereed]

    DOI

  • Estimating hominid life history: the critical interbirth interval

    Wataru Nakahashi, Shiro Horiuchi, Yasuo Ihara

    Population Ecology   60 ( 1-2 ) 127 - 142  2018.04  [Refereed]

     View Summary

    Unlike any great apes, humans have expanded into a wide variety of habitats during the course of evolution, beginning with the transition by australopithecines from forest to savanna habitation. Novel environments are likely to have imposed hominids a demographic challenge due to such factors as higher predation risk and scarcer food resources. In fact, recent studies have found a paucity of older relative to younger adults in hominid fossil remains, indicating considerably high adult mortality in australopithecines, early Homo, and Neanderthals. It is not clear to date why only human ancestors among all hominoid species could survive in these harsh environments. In this paper, we explore the possibility that hominids had shorter interbirth intervals to enhance fertility than the extant apes. To infer interbirth intervals in fossil hominids, we introduce the notion of the critical interbirth interval, or the threshold length of birth spacing above which a population is expected to go to extinction. We develop a new method to obtain the critical interbirth intervals of hominids based on the observed ratios of older adults to all adults in fossil samples. Our analysis suggests that the critical interbirth intervals of australopithecines, early Homo, and Neanderthals are significantly shorter than the observed interbirth intervals of extant great apes. We also discuss possible factors that may have caused the evolutionary divergence of hominid life history traits from those of great apes.

    DOI

  • Evolution of emotional contagion in group-living animals

    Wataru Nakahashi, Hisashi Ohtsuki

    Journal of Theoretical Biology   440   12 - 20  2018.03  [Refereed]

     View Summary

    Emotional contagion refers to an instantaneous matching of an emotional state between a subject and an object. It is believed to form one of the bases of empathy and it causes consistent group behavior in many animals. However, how this emotional process relates to group size remains unclear. Individuals with the ability of emotional contagion can instantaneously copy the emotion of another group member and can take relevant behavior driven by this emotion, but this would entail both cost and benefit to them because the behavior can be either appropriate or inappropriate depending on the situation. For example, emotional contagion may help them escape from a predator but sometimes induce mass panic. We theoretically study how these two aspects of emotional contagion affect its evolution in group-living animals. We consider a situation where an environmental cue sometimes indicates a serious event and individuals have to make a decision whether to react to them. We show that, as the group size increases, individuals with the ability of emotional contagion would evolutionarily weaken their sensitivity to environmental cues. We also show that a larger group yields a larger benefit to them through such evolutionary change. However, larger group size prevents the invasion of mutants with the ability of emotional contagion into the population of residents who react to environmental cues independently of other group members. These results provide important suggestions on the evolutionary relationship between emotional contagion and group living.

    DOI

  • Cultural sexual selection in monogamous human populations

    Wataru Nakahashi

    ROYAL SOCIETY OPEN SCIENCE   4 ( 6 ) 160946  2017.06  [Refereed]

     View Summary

    In humans, both sexes sometimes show peculiar mating preferences that do not appear to increase their fitness either directly or indirectly. As humans may transmit their preferences and target culturally, and these may be artificially modifiable, I develop theoretical models where a preference and/or a trait are culturally transmitted with a restriction of the trait modification. I assume a monogamous population where some individuals fail to find a mate, and this affects the preference and the trait in the next time step. I show that a strong aversion to, or high tolerance of, failed individuals are necessary for the evolution of irrational preferences that neither seek good genes nor any direct benefit. This evolution is more likely to occur when the preference and/or the trait are cultural rather than genetic. These results may partly explain why humans sometimes show mating preferences for exaggerated physical and cultural traits.

    DOI

  • The effect of trauma on Neanderthal culture: A mathematical analysis

    W. Nakahashi

    HOMO-JOURNAL OF COMPARATIVE HUMAN BIOLOGY   68 ( 2 ) 83 - 100  2017  [Refereed]

     View Summary

    Traumatic lesions are often observed in ancient skeletal remains. Since ancient medical technology was immature, severely traumatized individuals may have frequently lost the physical ability for cultural skills that demand complex body movements. I develop a mathematical model to analyze the effect of trauma on cultural transmission and apply it to Neanderthal culture using Neanderthal fossil data. I estimate from the data that the proportion of adult individuals who suffered traumatic injuries before death was approximately 0.79-0.94, in which 0.37-0.52 were injured severely and 0.13-0.19 were injured before adulthood. Assuming that every severely traumatized individual and a quarter to a half of the other traumatized individuals lost the capacity for a cultural skill that demands complex control of the traumatized body part, I estimate that if an upper limb is associated with a cultural skill, each individual had to communicate closely with at least 1.5-2.6 individuals during adulthood to maintain the skill in Neanderthal society, and if a whole body is associated, at least 3.1-11.5 individuals were necessary. If cultural transmissions between experts and novices were inaccurate, or if low frequency skills easily disappeared from the population due to random drift, more communicable individuals were necessary. Since the community size of Neanderthals was very small, their high risk of injury may have inhibited the spread of technically difficult cultural skills in their society. It may be important to take this inhibition into consideration when we study Neanderthal culture and the replacement of Neanderthals by modern humans. (C) 2017 Elsevier GmbH. All rights reserved.

    DOI

  • Coevolution of female ovulatory signals and male-male competition in primates

    Wataru Nakahashi

    JOURNAL OF THEORETICAL BIOLOGY   392   12 - 22  2016.03  [Refereed]

     View Summary

    Visual signals of ovulation vary among primate species. Although slight ovulatory signals are considered primate ancestral traits of which some species still exhibit, some show prominent swelling of their perineal skin (exaggerated sexual swellings) and others do not exhibit any signals of ovulation (concealed ovulation). These signals strongly affect male mating behaviors. I develop an evolutionary model of female ovulatory signals and male-male competition. I assume that each male allocates his effort between attraction of females and male-male competition for dominance. Each female gains a benefit if she is fertile and free from the alpha male who always guards one of the, most fertile females in the group, but suffers a cost if she expresses a different ovulatory signal from an ancestral trait. I show that various types of ovulatory signals may evolve and can be multistable. Male-male competition becomes intense when the signal honestly indicates ovulation. Ovulatory signals may evolve to be less exaggerated in unimale groups than in multimale groups and monogamy is more likely to evolve when ovulation is concealed. These results may partly explain why various types of primate ovulatory signals evolved and how they have affected primate societies. (C) 2015 Elsevier Ltd. All rights reserved.

    DOI

  • When is emotional contagion adaptive?

    Wataru Nakahashi, Hisashi Ohtsuki

    JOURNAL OF THEORETICAL BIOLOGY   380   480 - 488  2015.09  [Refereed]

     View Summary

    Empathy plays an important role in animal social behavior. Since emotional contagion forms one of the bases of empathy, here we study conditions for emotional contagion to be adaptive, compared with other behavioral rules such as behavioral mimicry. We consider the situation where the focal individual (=observer) reacts to a behavior of another individual (=demonstrator). By emotional contagion one spontaneously copies the emotional state of the demonstrator and takes a behavior driven by that emotion. By behavioral mimicry, in contrast, one copies the behavior of the demonstrator itself. Through mathematical models we show that emotional contagion is adaptive when the environmental similarity between the demonstrator and the observer is intermediate. The advantage of adopting emotional contagion over behavioral mimicry increases when observing others' behavior is difficult or cognitively demanding. We show that emotional contagion is often a more flexible strategy than behavioral mimicry in order to cope with the living environment. In other words, emotional contagion often works as a better social learning strategy. These results suggest some ecological conditions that would favor the evolution of emotional contagion, and give a part of the explanations of why emotional contagion is frequently observed in group-living animals. (C) 2015 Elsevier Ltd. All rights reserved.

    DOI

  • The evolution of culturally transmitted teaching behavior

    Wataru Nakahashi

    Learning Strategies and Cultural Evolution During the Palaeolithic     23 - 33  2015.01  [Refereed]

     View Summary

    The replacement of Neanderthals by modern humans may possibly have been influenced by the different cultural transmission mechanisms of the two hominins. Since teaching is widespread in modern human societies, but extremely rare in animals, it may have played an important role in human cultural evolution. In modern humans, how and whom to teach may, in part, be transmitted culturally. Therefore, in this paper, I develop a cultural transmission model of teaching. I show that even when costly, teaching can evolve provided that teachers transmit their cultural traits more actively than non-teachers. Teaching is more likely to evolve when the cost of social learning is low relative to individual learning, social learning is accurate, the environment is stable, and the effect of teaching is extensive. Under certain conditions, two states, existence and non-existence of teaching in the population, are evolutionarily stable (bistable).When this happens, social learning is sometimesmaintained by teaching under unstable environments where social learning cannot exist without teaching. Differences in subsistence strategy and group structure between Neanderthals and modern humans may have affected the evolution of the teaching behaviors of the two hominins.

    DOI

  • The effect of cultural interaction on cumulative cultural evolution

    Wataru Nakahashi

    JOURNAL OF THEORETICAL BIOLOGY   352   6 - 15  2014.07  [Refereed]

     View Summary

    Cultural transmission and cultural evolution are important for animals, especially for humans. I developed a new analytical model of cultural evolution, in which each newborn learns cultural traits from multiple individuals (exemplars) in parental generation, individually explores around learned cultural traits, judges the utility of known cultural traits, and adopts a mature cultural trait. Cultural evolutionary speed increases when individuals explore a wider range of cultural traits, accurately judge the skill level of cultural traits (strong direct bias), do not strongly conform to the population mean, increase the exploration range according to the variety of socially learned cultural traits (condition dependent exploration), and make smaller errors in social learning. Number of exemplars, population size, similarity of cultural traits between exemplars, and one-to-many transmission have little effect on cultural evolutionary speed. I also investigated how cultural interaction between two populations with different mean skill levels affects their cultural evolution. A population sometimes increases in skill level more if it encounters a less skilled population than if it does not encounter anyone. A less skilled population sometimes exceeds a more skilled population in skill level by cultural interaction between both populations. The appropriateness of this analytical method is confirmed by individual-based simulations. (C) 2014 Elsevier Ltd. All rights reserved.

    DOI

  • Evolution of division of labor: Emergence of different activities among group members

    Wataru Nakahashi, Marcus W. Feldman

    JOURNAL OF THEORETICAL BIOLOGY   348   65 - 79  2014.05  [Refereed]

     View Summary

    The division of labor is an important component of the organization of human society. However, why this division evolved in hominids requires further investigation. Archeological evidence suggests that it appeared after the emergence of Homo sapiens and contributed to the great success of our species. We develop a mathematical model to investigate under what conditions division of labor should evolve. We assume two types of resources the acquisition of which demands different skills, and study the evolution of the strategy that an individual should use to divide its lifetime into learning and using each skill. We show that division of labor likely evolves when group size is large, skill learning is important for acquiring resources, and there is food sharing within a group. We also investigate division of labor by gender under the assumption that the genders have different efficiencies in acquiring each resource. We show that division of labor by gender likely evolves when skill learning is important and the difference in efficiencies between genders in acquiring resources is large. We discuss how the results of our analysis might apply to the evolution of division of labor in hominids. (C) 2014 Elsevier Ltd. All rights reserved.

    DOI

  • Evolution of improvement and cumulative culture

    Wataru Nakahashi

    THEORETICAL POPULATION BIOLOGY   83   30 - 38  2013.02  [Refereed]

     View Summary

    Humans have created highly developed cultures, brought about by iterative improvements in technology. Using a mathematical model, I investigated the conditions under which cultural traits tend to be improved for a higher level of culture to evolve. In the model, I consider three ways of learning: individual learning, simple social learning, and improvements of socially learned cultural traits (social improvement). I obtain the evolutionarily stable number of cultural traits acquired through each way of learning. I show that organisms improve many socially learned cultural traits under the following conditions: (1) environmental stability is intermediate; (2) the environment is severe; (3) the success rate of individual learning is high; (4) the utility of cultural traits acquired by individual learning is large; (5) the accuracy of social learning is high; and (6) the increase in the utility of beneficial cultural traits attained by social improvement is large. I also show that when organisms have greater ability for social improvement, the average utility of the beneficial cultural trait increases, the proportion of beneficial cultural traits among all cultural traits decreases, and the total number of cultural traits acquired by the three ways of learning is constant. These results shed light on the origins of human cumulative culture. (C) 2012 Elsevier Inc. All rights reserved.

    DOI

  • Cultural Evolution and Learning Strategies in Hominids

    Wataru Nakahashi

    Dynamics of Learning in Neanderthals and Modern Humans Volume 1     245 - 254  2013  [Refereed]

    DOI

  • A Mathematical Model of Cultural Interactions Between Modern and Archaic Humans

    Wataru Nakahashi

    Dynamics of Learning in Neanderthals and Modern Humans Volume 1     255 - 263  2013  [Refereed]

    DOI

  • Adaptive Social Learning Strategies in Temporally and Spatially Varying Environments How Temporal vs. Spatial Variation, Number of Cultural Traits, and Costs of Learning Influence the Evolution of Conformist-Biased Transmission, Payoff-Biased Transmission, and Individual Learning

    Wataru Nakahashi, Joe Yuichiro Wakano, Joseph Henrich

    HUMAN NATURE-AN INTERDISCIPLINARY BIOSOCIAL PERSPECTIVE   23 ( 4 ) 386 - 418  2012.12  [Refereed]

     View Summary

    Long before the origins of agriculture human ancestors had expanded across the globe into an immense variety of environments, from Australian deserts to Siberian tundra. Survival in these environments did not principally depend on genetic adaptations, but instead on evolved learning strategies that permitted the assembly of locally adaptive behavioral repertoires. To develop hypotheses about these learning strategies, we have modeled the evolution of learning strategies to assess what conditions and constraints favor which kinds of strategies. To build on prior work, we focus on clarifying how spatial variability, temporal variability, and the number of cultural traits influence the evolution of four types of strategies: (1) individual learning, (2) unbiased social learning, (3) payoff-biased social learning, and (4) conformist transmission. Using a combination of analytic and simulation methods, we show that spatial-but not temporal-variation strongly favors the emergence of conformist transmission. This effect intensifies when migration rates are relatively high and individual learning is costly. We also show that increasing the number of cultural traits above two favors the evolution of conformist transmission, which suggests that the assumption of only two traits in many models has been conservative. We close by discussing how (1) spatial variability represents only one way of introducing the low-level, nonadaptive phenotypic trait variation that so favors conformist transmission, the other obvious way being learning errors, and (2) our findings apply to the evolution of conformist transmission in social interactions. Throughout we emphasize how our models generate empirical predictions suitable for laboratory testing.

    DOI

  • Evolution of ape and human mating systems

    Wataru Nakahashi, Shiro Horiuchi

    JOURNAL OF THEORETICAL BIOLOGY   296   56 - 64  2012.03  [Refereed]

     View Summary

    Humans (Homo sapiens) generally form multiple-male-multiple-female groups that include multiple family units. This social structure is maintained because dominant males do not monopolize females and, thus, allow subordinate males to mate, and human females are not generally promiscuous. Although apes show great variation in mating systems, the human-type mating system is unique among primates. The mating systems of apes and humans have evolved in response to their adaptation to different ecological conditions. We created and analyzed a mathematical model to investigate the conditions for each type of mating system to evolve. We focused on the mating strategy of alpha males and the mating and grouping strategies of females. We defined the human-type mating system as one with multiple-male-multiple-female groups in which alpha males do not monopolize females and females are not promiscuous. We demonstrated that the human-type mating system could evolve when a large group is advantageous and the cost of female promiscuity is great. Moreover, the human- and Pan-type mating systems can be bistable. Our results shed light on the origin of the human family. (C) 2011 Elsevier Ltd. All rights reserved.

    DOI

  • Evolution of learning capacities and learning levels

    Wataru Nakahashi

    THEORETICAL POPULATION BIOLOGY   78 ( 3 ) 211 - 224  2010.11  [Refereed]

     View Summary

    Humans strongly depend on individual and social learning, both of which are highly effective and accurate. I study the effects of environmental change on the evolution of the effectiveness and accuracy of individual and social learning (individual and social learning levels) and the number of pieces of information learned individually and socially (individual and social learning capacities) by analyzing a mathematical model. I show that individual learning capacity decreases and social learning capacity increases when the environment becomes more stable; both decrease when the environment becomes milder. I also show that individual learning capacity increases when individual learning level increases or social learning level decreases, while social learning capacity increases when individual or social learning level increases. The evolution of high learning levels can be triggered when the environment becomes severe, but a high social learning level can evolve only when a high individual learning level can simultaneously evolve with it. (C) 2010 Elsevier Inc. All rights reserved.

    DOI

  • Evolution of learning in subdivided populations that occupy environmentally heterogeneous sites

    Kenichi Aoki, Wataru Nakahashi

    THEORETICAL POPULATION BIOLOGY   74 ( 4 ) 356 - 368  2008.12  [Refereed]

     View Summary

    We study the effects of natural selection and migration on the numbers of individual learners and social learners in subdivided populations that occupy environmentally heterogeneous sites. The island model and the circular stepping model each have four classes of globally stable equilibria (fixation of individual learners, polymorphism of individual and social learners, fixation of social learners, and extinction). The linear stepping stone model has an additional class of equilibria, which are characterized by the complete absence of phenotypes adapted to the interior sites. Low and high rates of migration favor social and individual learners, respectively, in all three models. In addition, we use the stepping stone models to study the range expansion of a species, initially confined to one environmentally homogeneous site, into the spatially heterogeneous world. The successive peaks of the transient spatial distributions of the number of individual learners occur at initially empty sites. (c) 2008 Elsevier Inc. All rights reserved.

    DOI

  • Quantitative genetic models of sexual selection by male choice

    Wataru Nakahashi

    THEORETICAL POPULATION BIOLOGY   74 ( 2 ) 167 - 181  2008.09  [Refereed]

     View Summary

    There are many examples of male mate choice for female traits that tend to be associated with high fertility. I develop quantitative genetic models of a female trait and a male preference to show when such a male preference can evolve. I find that a disagreement between the fertility maximum and the viability maximum of the female trait is necessary for directional male preference (preference for extreme female trait values) to evolve. Moreover, when there is a shortage of available male partners or variance in male nongenetic quality, strong male preference can evolve. Furthermore, I also show that males evolve to exhibit a stronger preference for females that are more feminine (less resemblance to males) than the average female when there is a sexual dimorphism caused by fertility selection which acts only on females. (C) 2008 Elsevier Inc. All rights reserved.

    DOI

  • The evolution of conformist transmission in social learning when the environment changes periodically

    Wataru Nakahashi

    THEORETICAL POPULATION BIOLOGY   72 ( 1 ) 52 - 66  2007.08  [Refereed]

     View Summary

    Conformity is often observed in human social learning. Social learners preferentially imitate the majority or most common behavior in many situations, though the strength of conformity varies with the situation. Why has such a psychological tendency evolved? I investigate this problem by extending a standard model of social learning evolution with infinite environmental states (Feldman, M.W., Aoki, K., Kumm, J., 1996. Individual versus social learning: evolutionary analysis in a fluctuating environment. Anthropol. Sci. 104, 209-231) to include conformity bias. I mainly focus on the relationship between the strength of conformity bias that evolves and environmental stability, which is one of the most important factors in the evolution of social learning. Using the evolutionarily stable strategy (ESS) approach, I show that conformity always evolves when environmental stability and the cost of adopting a wrong behavior are small, though environmental stability and the cost of individual learning both negatively affect the strength of conformity. (c) 2007 Elsevier Inc. All rights reserved.

    DOI

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Research Projects

  • Couple or parent-child: which left Laetoli footprints?

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Project Year :

    2020.04
    -
    2023.03
     

  • Comparative biological analysis of human dispersal process

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

    Project Year :

    2020.04
    -
    2022.03
     

  • Investigating language evolution through structures of cultural skills

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

    Project Year :

    2018.04
    -
    2020.03
     

  • Hominid life history estimation by mathematical models

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)

    Project Year :

    2016.04
    -
    2019.03
     

    Nakahashi Wataru

     View Summary

    We estimated hominid life histories by using hominid fossil data and life-table data of apes and humans. We showed that the lifespans and interbirth intervals of australopithecines, early Homo, and Neanderthals were significantly shorter than those of extant great apes. Moreover, using a mathematical model and fossil data, we showed that Neanderthals frequently suffered severe traumatic injuries, which inhibited their cultural evolution. We also studied the effect of language ability on hominid culture. Furthermore, we investigated the evolution of hominid social structure, social interaction, and mating strategy by using mathematical models. We also studied why humans migrate and settle by analyzing modern Japanese data. From various studies above, we precisely discussed biological features of hominids.

  • 遺伝子文化共進化の数理的研究

    明治大学  現象数理若手プロジェクト

    Project Year :

    2012.04
    -
    2013.03
     

    中橋 渉

  • 家族制の進化の現象数理学

    明治大学  現象数理若手プロジェクト

    Project Year :

    2010.04
    -
    2011.03
     

    中橋 渉

  • 人間特有の現象に対する学習の影響―進化ゲーム理論による分析―

    明治大学  現象数理若手プロジェクト

    Project Year :

    2009.04
    -
    2010.03
     

    中橋 渉

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Syllabus

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