Gowdy & Krall (G&K) propose treating social insect colonies and groups of humans as evolutionary individuals (i.e., units of selection) in virtue of their ultrasociality. They argue that economic factors connected to the development of agriculture explain ultrasociality's emergence. While it is indisputable that there is an important link between agriculture and the social organization of humans and some insects, we think viewing human societies as evolutionary individuals obscures more than it explains. In neither ants nor humans is the connection between agriculture and individuality as tight as G&K suggest, and individualist models are better suited than the second type of multilevel selection (MLS2) to shed light on the puzzles associated with the human transition from foraging to farming.
Ultrasociality among insects does not depend on agriculture. Many non-agricultural social insect species are ultrasocial, and colonies of these insects are also reasonably treated as evolutionary individuals because they exhibit reproductive specialization, a criterion biologists often use to identify units of selection (Maynard Smith & Szathmary Reference Maynard Smith and Szathmary1995). The division of labor may well reach its zenith in the agricultural ants, but G&K ignore the fact that agriculture followed, rather than led to, individuality. While agriculture in ants is about 50 million years old (Schultz & Brady Reference Schultz and Brady2008), reproductive division of labor probably originated in the mid-Cretaceous, over 100 million years ago (Grimaldi & Engel Reference Grimaldi and Engel2005). Thus, even if it were true that agriculture facilitated the emergence of individuality at the level of human societies, this would be a disanalogy rather than a similarity between the evolutionary histories of humans and social insects.
Human societies, however, cannot be treated as evolutionary individuals. Modern thinking about the evolution of individuality emphasizes the need for bottlenecks separating generations, reproductive specialization, and demarcation mechanisms (Clarke Reference Clarke2013; Godfrey-Smith Reference Godfrey-Smith2009). These features are absent or only weakly present in human groups and almost never obligate. For example, reproductive skew in human societies never rose to the levels seen in social insects (Summers Reference Summers2005), and in many agricultural societies it stayed very low through institutions of monogamous marriage. The rate of migration between human groups is high enough to prevent sharp genetic or cultural demarcation of one group from another, which reduces the potential for them to act as distinct evolutionary units.
In making their case for the insufficiency of multilevel selection 1 (MLS1), G&K conflate individual well-being and fitness. The MLS1 framework explains how apparently costly traits can evolve by providing an indirect fitness benefit to the individual possessing them. G&K argue that the human transition to agriculture does not provide such a benefit because the emergence of agriculture meant poorer nutrition, a shorter lifespan, and a loss of individual autonomy for the average person. But unless these decreases in quality of life led to a net loss of reproductive success, they did not constitute a loss of Darwinian fitness. On the contrary, as reviewed by Lambert (Reference Lambert2009), the transition to agriculture was associated with increased fertility. This finding is perfectly consistent with basic life-history theory, which shows that reduced longevity and body condition can be selected to increase or decrease, depending on their trade-offs with reproduction (Stearns Reference Stearns1992). In other words, a less healthy life is consistent with increased individual fitness if it leads to higher reproduction.
One model that successfully disentangles quality of life and fitness comes from the tradition of human behavioral ecology. Testart et al. (Reference Testart, Forbis, Hayden, Ingold, Perlman, Pokotylo, Rowley-Conwy and Stuart1982), Watkins (Reference Watkins and Scarre2005; Reference Watkins2010), and Sterelny (Reference Sterelny2015) respectively provide an incremental account of the transition from a hunter-gatherer lifestyle to an agricultural one, despite the physical and cultural costs this transition exacted. On their model, hunter-gatherers have incentive to develop agriculture under two conditions: (1) if their foraging activities lead to resource scarcity; and (2) if efficient harvesting and storage options allow them to take advantage of predictable seasonal variation in resource availability. When these conditions hold, it is individually rational to adopt storage-dependent foraging and establish permanent bases around which groups can conduct foraging trips. Permanent storage and a reliable resource flow leads, in turn, to a larger and more sedentary population. As the larger population places additional stress on the available supply of resources, it prompts people to experiment with organized planting and cultivation of the resources they had previously gathered but not actively managed.
After the establishment of permanent communities, subsequent generations face food shortages due to overuse of foraging and hunting grounds. The costs of migration are high, so people come to rely more heavily on cultivated crops, even if the yield is lower or less diverse than that produced by migrant hunting and gathering. Groups engineer more complex divisions of labor to better exploit their agricultural resources, and these, in conjunction with a less diverse diet, may lead to the decreases in quality of life that G&K allude to.
Even so, available evidence does not support the assertion that the “good of the group” took precedence over individual preferences in agricultural societies. G&K's scenario implicitly assumes agriculture is a collective activity that requires group-level coordination on tasks performed for the good of the group. Yet archeological evidence shows that early agriculture was done in small plots belonging to a household who stored their production (except meat) privately, even in very large settlements like Çatalhöyük (Bogaard et al. Reference Bogaard, Charles, Twiss, Fairbairn, Yalman, Filipović, Demirergi, Ertuğ, Russell and Henecke2009). Evolutionary models further suggest that agriculture coevolved with individual property rights that made it beneficial for individuals to invest in intense cultivation (Bowles & Choi Reference Bowles and Choi2013). We think that individual incentives responding to economic institutions, as Adam Smith observed, is a more plausible explanation for task specialization than the group subjugating individuals to act against their own will.
These examples demonstrate that individualist models already capture much of what G&K desire to explain: how rational choices on the part of individuals can accumulate over time to produce undesirable economic and social conditions. Individual fitness benefits are compatible with poor living conditions, and individualist models express this reality better than MLS2.
You have
Access
Gowdy & Krall (G&K) propose treating social insect colonies and groups of humans as evolutionary individuals (i.e., units of selection) in virtue of their ultrasociality. They argue that economic factors connected to the development of agriculture explain ultrasociality's emergence. While it is indisputable that there is an important link between agriculture and the social organization of humans and some insects, we think viewing human societies as evolutionary individuals obscures more than it explains. In neither ants nor humans is the connection between agriculture and individuality as tight as G&K suggest, and individualist models are better suited than the second type of multilevel selection (MLS2) to shed light on the puzzles associated with the human transition from foraging to farming.
Ultrasociality among insects does not depend on agriculture. Many non-agricultural social insect species are ultrasocial, and colonies of these insects are also reasonably treated as evolutionary individuals because they exhibit reproductive specialization, a criterion biologists often use to identify units of selection (Maynard Smith & Szathmary Reference Maynard Smith and Szathmary1995). The division of labor may well reach its zenith in the agricultural ants, but G&K ignore the fact that agriculture followed, rather than led to, individuality. While agriculture in ants is about 50 million years old (Schultz & Brady Reference Schultz and Brady2008), reproductive division of labor probably originated in the mid-Cretaceous, over 100 million years ago (Grimaldi & Engel Reference Grimaldi and Engel2005). Thus, even if it were true that agriculture facilitated the emergence of individuality at the level of human societies, this would be a disanalogy rather than a similarity between the evolutionary histories of humans and social insects.
Human societies, however, cannot be treated as evolutionary individuals. Modern thinking about the evolution of individuality emphasizes the need for bottlenecks separating generations, reproductive specialization, and demarcation mechanisms (Clarke Reference Clarke2013; Godfrey-Smith Reference Godfrey-Smith2009). These features are absent or only weakly present in human groups and almost never obligate. For example, reproductive skew in human societies never rose to the levels seen in social insects (Summers Reference Summers2005), and in many agricultural societies it stayed very low through institutions of monogamous marriage. The rate of migration between human groups is high enough to prevent sharp genetic or cultural demarcation of one group from another, which reduces the potential for them to act as distinct evolutionary units.
In making their case for the insufficiency of multilevel selection 1 (MLS1), G&K conflate individual well-being and fitness. The MLS1 framework explains how apparently costly traits can evolve by providing an indirect fitness benefit to the individual possessing them. G&K argue that the human transition to agriculture does not provide such a benefit because the emergence of agriculture meant poorer nutrition, a shorter lifespan, and a loss of individual autonomy for the average person. But unless these decreases in quality of life led to a net loss of reproductive success, they did not constitute a loss of Darwinian fitness. On the contrary, as reviewed by Lambert (Reference Lambert2009), the transition to agriculture was associated with increased fertility. This finding is perfectly consistent with basic life-history theory, which shows that reduced longevity and body condition can be selected to increase or decrease, depending on their trade-offs with reproduction (Stearns Reference Stearns1992). In other words, a less healthy life is consistent with increased individual fitness if it leads to higher reproduction.
One model that successfully disentangles quality of life and fitness comes from the tradition of human behavioral ecology. Testart et al. (Reference Testart, Forbis, Hayden, Ingold, Perlman, Pokotylo, Rowley-Conwy and Stuart1982), Watkins (Reference Watkins and Scarre2005; Reference Watkins2010), and Sterelny (Reference Sterelny2015) respectively provide an incremental account of the transition from a hunter-gatherer lifestyle to an agricultural one, despite the physical and cultural costs this transition exacted. On their model, hunter-gatherers have incentive to develop agriculture under two conditions: (1) if their foraging activities lead to resource scarcity; and (2) if efficient harvesting and storage options allow them to take advantage of predictable seasonal variation in resource availability. When these conditions hold, it is individually rational to adopt storage-dependent foraging and establish permanent bases around which groups can conduct foraging trips. Permanent storage and a reliable resource flow leads, in turn, to a larger and more sedentary population. As the larger population places additional stress on the available supply of resources, it prompts people to experiment with organized planting and cultivation of the resources they had previously gathered but not actively managed.
After the establishment of permanent communities, subsequent generations face food shortages due to overuse of foraging and hunting grounds. The costs of migration are high, so people come to rely more heavily on cultivated crops, even if the yield is lower or less diverse than that produced by migrant hunting and gathering. Groups engineer more complex divisions of labor to better exploit their agricultural resources, and these, in conjunction with a less diverse diet, may lead to the decreases in quality of life that G&K allude to.
Even so, available evidence does not support the assertion that the “good of the group” took precedence over individual preferences in agricultural societies. G&K's scenario implicitly assumes agriculture is a collective activity that requires group-level coordination on tasks performed for the good of the group. Yet archeological evidence shows that early agriculture was done in small plots belonging to a household who stored their production (except meat) privately, even in very large settlements like Çatalhöyük (Bogaard et al. Reference Bogaard, Charles, Twiss, Fairbairn, Yalman, Filipović, Demirergi, Ertuğ, Russell and Henecke2009). Evolutionary models further suggest that agriculture coevolved with individual property rights that made it beneficial for individuals to invest in intense cultivation (Bowles & Choi Reference Bowles and Choi2013). We think that individual incentives responding to economic institutions, as Adam Smith observed, is a more plausible explanation for task specialization than the group subjugating individuals to act against their own will.
These examples demonstrate that individualist models already capture much of what G&K desire to explain: how rational choices on the part of individuals can accumulate over time to produce undesirable economic and social conditions. Individual fitness benefits are compatible with poor living conditions, and individualist models express this reality better than MLS2.