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Contributions of family social structure to the development of ultrasociality in humans
Published online by Cambridge University Press: 30 June 2016
Abstract
The evolution of ultrasociality in humans may have involved the evolutionarily significant mechanisms that govern family social structure in many animal species. Adverse effects of ultrasociality in humans may be mediated by maladaptive effects of modern civilization on family groups, as many of the effects on both families and societies are especially severe in dense populations made possible by agriculture.
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An additional topic that is relevant to this discussion of the evolution of ultrasociality in insects and humans is human family groups and the evolutionarily significant mechanisms that mediate family social structure in many animal species, especially mammals. There is clearly a robust genetic component to ultrasociality in insects that is more similar to family groups in humans than entire civilizations, but it is likely that the mechanisms that mediate family social behavior also mediate ultrasociality at the civilization level. Human culture (mediated by conserved affiliation–based social mechanisms) is a strength that has maintained the important independence between genes and phenotypes. This independence allows for flexibility in life trajectories and the appearance of individuals with no roles in the production, defense, or stock of agricultural products.
Gowdy & Krall (G&K) compare insect colonies with human societies, but many characteristics of insect colonies could be compared with vertebrate family groups: related individuals (Nehring et al. Reference Nehring, Evison, Santorelli, d'Ettore and Hughes2011), alloparental care (Lopes et al. Reference Lopes, Hughes, Camargo and Forti2005), or adoptions (Fouks et al. Reference Fouks, d'Ettorre and Nehring2011). Interestingly, the social behavior of ultrasocial insects is almost entirely driven by chemical communication, which is also involved in kin recognition in vertebrates, including humans (Schaal & Porter Reference Schaal, Porter and Doty2003). The adverse effects of ultrasociality in humans may be mediated by maladaptive effects of modern agricultural civilization on family groups, as many of the effects on both families and society are especially severe in regions with high population densities made possible by modern agriculture.
Family based drivers of ultrasociality
Compared with other ultrasocial species, humans present a unique case of extensive cooperation with unrelated individuals (Bowles & Gintis Reference Bowles and Gintis2004; Rand & Nowak Reference Rand and Nowak2013), and it is suggested that agriculture and extensive food provisioning played a role in the evolution of this unique social complexity. While initially considered to be composed of close kin, highly cooperative hunter-gatherer bands exhibit low relatedness (data obtained from present-day foraging societies), suggesting that this cooperation with non-related individuals could be older than the development of agriculture (Hill et al. Reference Hill, Walker, Božičević, Eder, Headland, Hewlett, Hurtado, Marlowe, Wiessner and Wood2011). Complex social interactions between humans depend not only on kinship and multilevel and spatial selection, but also on social experience, including direct and indirect reciprocity (Rand & Nowak Reference Rand and Nowak2013). The social behavior of humans at the societal level is mediated by the same neurochemical mechanisms as affiliative family interactions, often involving the neuropeptides oxytocin and arginine vasopressin (De Dreu et al. Reference De Dreu, Greer, Handgraf, Shalvi, Van Kleer, Baas, Ten Velden, Van Dijk and Feith2010), which have been implicated in the evolution of social behavior (Insel & Young Reference Insel and Young2000). These genetic and experiential mechanisms give much more phenotypic flexibility than the rapid and almost absolute responses of ultrasocial insects towards unrelated individuals (i.e., individuals that do not wear the chemical signature of the colony).
The unit determining the social group of ultrasocial insects is clearly delineated as the colony, but humans belong to several clustered social groups including family and society. Agriculture gave greater significance to both family and society and to their mutual influence on phenotypic development. In terms of the transition from hunter-gatherers to agriculture and the role of the family, the hunter-gatherer lifestyle involves greater challenges to survival and reproduction compared to a more stable agricultural existence. There are risks to survival involved with hunting and a nomadic lifestyle, as well as exposure to related stresses that decrease reproductive success (e.g., unpredictable food supply, decreased social support for offspring care) and pose challenges to maternal care. Agriculture fosters the development of larger families with more extensive maternal care. Improved survival of individuals with longer periods of maternal care may have facilitated the growth of agricultural communities through larger families. Agriculture also affected social group sizes, which, given the extensive ability of human for innovation and social learning, accelerated the development of global culture.
This effect of maternal care on the development of ultrasociality in humans involves both increased offspring survival as well as the enhanced development of social behavior during the extended nurturing. Early life care in altricial species is selected for not only through increases in survival, but also through the development of improved environment-specific physiological responses to stressors and improved reproductive success of offspring. Social behaviors, including same sex affiliation, reproductive affiliation, parental care, and alloparental care involve transgenerational mechanisms that could lead to the establishment and growth of societies over time (Champagne Reference Champagne2008).
Adverse consequences of ultrasociality in humans
The adverse effects of ultrasociality in humans can be most easily seen in large urban areas where there are high crime and disease rates as well as excessive pollution (Phillips Reference Phillips1993). Just as family structure mediates the development of large interdependent communities, the adverse effects of ultrasociality on humans may be mediated through transgenerational maladaptive changes in family dynamics. Intense competition for space and resources results in exposure to elevated levels of social stress, associated neural changes (Lederbogen et al. Reference Lederbogen, Kirsch, Haddad, Streit, Tost, Schuch, Wust, Pruessner, Rietschel, Deuschle and Meyer-Lindenberg2011), and increases in mood and anxiety disorders (Peen et al. Reference Peen, Schoevers, Schoevers, Beekman and Dekker2010), which can lead to the fracturing of families. These developments decrease social support for mothers, increase rates of maternal depression and anxiety (Robertson et al. Reference Robertson, Grace, Wallington and Stewart2004), and impair the social development of offspring and future generations through impaired parental care (Goodman et al. Reference Goodman, Rouse, Connell, Broth, Hall and Heywood2011). As explained by E. O. Wilson and mentioned in the G&K article, humans do not benefit from imitating ants, yet what is often found in cities is a perceived and/or real lack of flexibility in life trajectories that is similar to that observed in ant societies. It is suggested that the key to healthy social development at any level is the preservation of a strong family structure, the foundation of a sustainable society.