Biol Philos (2012) 27:125–135 DOI 10.1007/s10539-011-9266-2 BOOK REVIEW
Evolution and the loss of hierarchies: Dubreuil’s ‘‘Human evolution and the origin of hierarchies: the state of nature’’ Catherine Driscoll
Received: 31 March 2011 / Accepted: 5 April 2011 / Published online: 5 May 2011 Ó Springer Science+Business Media B.V. 2011
Benoit Dubreuil’s Human Evolution and the Origins of Hierarchies, according to the jacket cover, is intended to provide ‘‘a natural history of [human social] hierarchies’’, and in particular to explain two transitions in the history of those hierarchies. The first transition is one that moved humans from social groups characterized by dominance hierarchies (such as those presumably had by our common ancestor with chimpanzees) to social groups characterized by egalitarian social relations (such as those in which all humans lived at one time and which still characterize modern foraging societies). The second transition is from such egalitarian foraging societies to modern state societies with their hierarchies of wealth and power. This second transition is particularly puzzling—why, given Homo sapiens evolved to live in egalitarian societies and apparently prefer egalitarian social relations, did we end up with social hierarchies again? Dubreuil’s purpose in his book is to describe the sequence of events involved in the evolution of cognitive capacities that permitted these two transitions to occur. This is a very ambitious project; to make his argument, Dubreuil appeals to work in evolutionary, physical and cultural anthropology, archeology, primatology, economics, cognitive science, political science and political philosophy. In this review I am going to address in most detail Dubreuil’s discussion of the anthropological and fossil evidence for his view (which occurs primarily in Chapters 2 and 3 of the book). While Dubreuil has provided an impressive and interesting discussion, I do have some worries about his account of the evolutionary history of hierarchies.
C. Driscoll (&) North Carolina State University, Raleigh, NC, USA e-mail:
[email protected]
123
126
C. Driscoll
Hierarchies lost The first part of Dubreuil’s book tries to explain how humans lost their dominance hierarchies and ended up living in largely egalitarian societies. In Chapter 2, Dubreuil discusses why (in the evolutionary functional sense) it is that true dominance hierarchies were lost in the human lineage (p. 67). Dominance hierarchies arise because individuals have an interest in obtaining as much food or as much access to mates as they can, this can mean intimidating and bullying other members of the group. However, this position of dominance can only be achieved by one individual at a time; few individuals stay at the top of the hierarchy for very long, and being subordinate in a group where individuals are trying to be dominant means being harassed and having reduced access to food and mates. Dubreuil argues that this means having an egalitarian social structure would actually be the optimal arrangement for most individuals. However, having such an arrangement requires that the dominance behavior of others in the group be suppressed or prevented—it involves costly sanctioning of dominant individuals for the benefit of everyone. Dubreuil claims that this makes solving the dominance hierarchy problem a public goods problem. So how might humans have managed to solve this problem? In Chapter 1, Dubreuil spends some time examining the human psychology involved in maintaining egalitarian social arrangements. Dubreuil argues that the ‘‘egalitarian ethos’’ in human societies is due partly to the fact that humans have ‘‘inequality aversion’’. However, inequality aversion is not solely responsible: humans might be better said to have norms of fairness rather than equality as such, and whether or not inequalities of wealth or power are perceived as fair depends greatly on how the context is framed; even perceived unfairness may provoke no sanction so long as it is expected (p. 28–32). What is responsible for current human egalitarian social arrangements is both a desire for equality and a more general capacity to follow norms and sanction norm violators (p. 20, 50). Dubreuil argues that egalitarian social arrangements also require certain sorts of social emotions that motivate responses to sufficiently extreme norm violations (p. 24–28) and which motivate us to follow norms ourselves (p. 32). They also require the capacity for joint attention, to draw attention to actions and label them as permitted, required or forbidden (p. 32–33 and p. 63–67). Dubreuil argues that that there is some evidence that primates (and thus presumably our common ancestor with chimpanzees) have a limited sort of inequality aversion (p. 60–61); the other capacities appear to be unique to the human lineage (p. 55–56). Dubreuil suggests that the time at which human dominance hierarchies were lost might be established by looking for instances in the fossil record where humans have solved other kinds of collective action problems, since solving these might have required similar sorts of cognitive capacities. Dubreuil then goes on to identify a number of such action problems faced by hominids, including acquiring sufficient ecological flexibility, managing a dietary shift, managing an increase in parental investment, managing the consequences of early parturition and secondary altriciality, accepting increased restrictions on sexual access to group members and providing support for incapacitated individuals
123
Evolution and the loss of hierarchies
127
(p. 67). He identifies two distinct stages in the evolution of human cooperative capacities: first, a shift in ecology and diet, probably driven by mechanisms for joint attention, and second, a shift to cooperative breeding driven by enhanced cognitive control and the consequent ability for individuals to adhere to cooperative norms. Dubreuil claims the first of these two (‘‘cooperative feeding’’) occurred by the time of Homo erectus; the second (‘‘cooperative breeding’’) by the time of Homo heidelbergensis (p. 84–90). The two shifts in cognition that accompanied these social and ecological changes intensified resistance to dominant individuals; joint attention permitted cooperative resistance to dominant individuals and the evolution of norm following allowed dominance hierarchies to be eliminated altogether (p. 90). The most natural way to interpret Dubreuil’s approach here is as looking for evidence of cooperative capacities necessary and jointly sufficient for the loss of dominance hierarchies: if he can establish when these capacities were all in place, he has an earliest time for when hierarchies might have been lost. One problem, however, is that Dubreuil is never really clear about what these capacities are. He certainly spends a long time discussing which current human capacities permit us to maintain an egalitarian ethos in foraging societies, but spends very little time on which of these capacities (if any) would need to be in place in order to permit the loss of dominance hierarchies. Without this discussion, Dubreuil’s careful analysis of the evolution of solutions to other human collective action problems will not tell him when hierarchies were lost. One possibility is that Dubreuil thinks the full complement of skills used for maintaining modern egalitarian social relations (joint attention, punitive emotions, inequality aversion, norm following) are necessary to the loss of hierarchies. However, there are two problems with this interpretation. First, Dubreuil never discusses the origins of some of the capacities that maintain modern human egalitarian social relations. For example, while Dubreuil gives an account of the evolution of norm following generally, he does not elaborate on the evolution of norms of fairness, which are the most relevant subset of norms for his account, and the ones necessary, if any are, to the loss of hierarchies. Similarly, there is no account of the evolution of inequality aversion. Dubreuil at one point (p. 61) refers to studies on capuchin monkeys and chimpanzees which show these animals are in some circumstance willing to reject a reward if they see another individual getting a better reward for the same task (Brosnan and de Waal 2003; Brosnan et al. 2005). Dubreuil only cautiously follows Brosnan and de Waal in interpreting this as evidence of inequality aversion; and indeed, the apparent anger could be due to simple violated expectations. Furthermore, (as Dubreuil fully recognizes (p. 61)) even if we do accept that this is a form of inequality aversion, it is not the same as inequality aversion in humans, which includes the willingness to engage in third party punishment in order to reduce inequality. The second reason to think Dubreuil does not think all of the capacities maintaining modern human egalitarian social relations are necessary to the loss of hierarchies is his claim that hierarchies could have begun to be lost around the time of Homo erectus and the initial acquisition of only capacities for joint attention. Similarly, he claims that Homo heidelbergensis had lost dominance hierarchies with
123
128
C. Driscoll
norm following alone (he doesn’t address whether it had norms of fairness or inequality aversion of the modern human sort). I am sympathetic to the view that not all human capacities underlying egalitarian social relations would have been needed to suppress dominance hierarchies: indeed, I think the necessary abilities might be even simpler than Dubreuil is suggesting. Chimpanzees solve part of Dubreuil’s collective action problem on a relatively regular basis; small groups of males form alliances that overthrow the current dominant male—they reduce the costs of ‘‘sanction’’ by collectively ‘‘sanctioning’’. This seems to be achieved without the capacity for joint attention or norm following. The problem with chimpanzee alliances is not that they can’t ‘‘punish’’ dominants but that they replace the old dominants with new dominants (de Waal 1984; Nishida 1983). If our common ancestor with chimps was the same in this regard, then the earliest hominids already had the capacity for cooperation necessary for the loss of dominance hierarchies. Final loss of dominance hierarchies could have occurred once there was also the willingness to engage in third party ‘‘punishing’’ of dominants (i.e. by those who would not also become dominants themselves). Another problem with Dubreuil’s discussion is that it is not obvious that he has correctly determined the nature and timing of the solutions to his ‘‘other collective action problems’’ from the evidence in the fossil record. I want to draw attention to Dubreuil’s discussion of the solutions to the two most important of these problems—‘‘cooperative feeding’’ and ‘‘cooperative breeding’’. The first occurred with the shift in the diet of hominids about the time of Homo habilis/erectus (most likely the latter). The diet of chimpanzees is composed largely of fruit, but by this time there is good reason to think that hominids’ diet now included at least some large game. Dubreuil’s suggestion is that this change in diet represented a change to what he calls ‘‘a cooperative feeding strategy’’ (p. 84). This is proposed to have led to the evolution of abilities for joint attention, in particular, for feeling pleasure in sharing attention with others. I found this discussion a bit confusing, because Dubreuil is less than clear at times exactly what he thinks are the collective action problems involved in cooperative feeding, and why they led to the evolution of capacities for joint attention in particular. In his discussion of the change in diet on p. 74–76, Dubreuil first asserts that Homo erectus was almost certainly an active scavenger, and then asserts that the nature of the public goods problem for Homo erectus is to be understood in terms of the large game hunting and food sharing problem faced by modern foragers. Large game hunting offers good average returns to the hunter, but high variability in returns: because large game are hard to catch most hunting days even good hunters return empty handed. Furthermore, a large animal is usually too much for a single family to consume before the meat goes off (Hawkes 1993). One possible way to smooth the erratic returns of hunting is by meat sharing, which is common amongst modern human foraging societies (Gurven 2004). Dubreuil suggests that this is the problem that Homo erectus solved. There are three problems with this. First, active scavenging is different from large game hunting in important regards. Food sharing is a necessary solution to foraging for a food source which is (1) a significant and regular part of the diet of a group (so individuals rely on it as a source of food), (2) where individuals engage in
123
Evolution and the loss of hierarchies
129
this foraging activity alone or in small subgroups, and (3) where sharing the returns helps smooth the erratic returns of these subgroups. Large game hunting in modern foraging societies has these features, but active scavenging for Homo erectus probably did not. Homo erectus was almost certainly a scavenger and not a large game hunter because it had none of the technologies that make hunting large, angry herbivores easier and safer (such as bows or spears) and a stereotyped tool industry that suggests it could not have socially learnt the hunting strategies which modern human foragers take as much as 30 years to learn and perfect (Kaplan et al. 2000; Klein 2000; O’Connell et al. 1988). Instead, Homo erectus probably had access to large game by chasing away other large predators (mostly large Pleistocene felids) from their kills. The problem is that carcasses suitable for scavenging become available only rarely even for modern hunter gatherers with projectile weapons; this suggests that actively scavenged meat was not a regular part of Homo erectus’ diet (as in 1) above) (O’Connell et al. 2002). If Homo erectus was not relying on scavenging, smoothing returns would not have been unnecessary. What’s more, separating very big Pleistocene cats from their kills with no projectile technology is extremely dangerous (Dominguez-Rodrigo 2002; O’Connell et al. 2002), and would probably require the efforts of large groups of individuals. But if large groups of individuals are involved, then food sharing is unnecessary because everyone involved is present to eat the carcass when it is retrieved and because there would be little or no excess food to share. Furthermore, if the groups of individuals are large, then there are probably few independently foraging sub-groups between which to smooth returns (as in 2 and 3). Now, while this would mean that active scavenging does not require a solution to a public goods problem of sharing, it might require a solution to a public goods problem of coordination of collective action. Dubreuil never really mentions the action coordination problem except once, on p. 86, where he suggests that ‘‘collective scavenging’’ might have been a part of the cooperative feeding strategy. The second problem with Dubreuil’s account here is that is that it really isn’t obvious why hunting and sharing requires capacities for joint attention and not norm following (that Dubreuil argues comes later with ‘‘cooperative breeding’’ but not ‘‘cooperative feeding’’). Dubreuil recognizes that food sharing requires the capacity for punishment; he suggests that Homo erectus had the capacity to punish those who didn’t share (p. 86–87)). I’m guessing that Dubreuil’s proposal is that the capacity to punish evolved before the capacity to follow norms. The trouble is, while the capacity to follow norms could have come later as a way of avoiding the costs of sanction it seems puzzling why it would have delayed until the time of Homo heidelbergensis when it would have been useful much earlier. Dubreuil’s claim is that cooperative breeding was a bigger problem requiring stronger adherence to norms than cooperative feeding. But this in itself is not reason why norm following would not be selected for to assist cooperative feeding, merely a reason to expect stronger selection pressure to help with cooperative breeding. Conversely, the third problem with Dubreuil’s account is that food sharing doesn’t seem to particularly require joint attention. As Dubreuil notes, chimpanzees can share food, and do under certain circumstances (even if they aren’t fond of it)
123
130
C. Driscoll
(Stanford 1996). However, if Dubreuil is right, they lack the capacity for joint attention. What Dubreuil suggests at one point (p. 87) is that joint attention motivates food sharing because joint attention is enjoyable for humans, and so it might have evolved because it promoted sharing. But this suggests joint attention has two components, the capacity itself and the pleasure that results from it: why joint attention and pleasure when any pleasure mechanism associated with sharing could serve the same purpose? What seems an obvious and much more plausible line for Dubreuil to take is that the evolution of joint attention was not driven by food sharing as such but instead by the collective scavenging described above— joint attention was necessary to the coordination of such collective action. Dubreuil has more trouble making his case, I think, when he addresses the collective action problem inherent in ‘‘cooperative breeding’’, especially his idea that monogamy and controlled access to females was part of the cross generational transfer solution. Most of the anthropologists who discuss the human life history problem accept that human investment in food acquisition involves significant transfers of food across generations from either (or both) males and females (Hawkes 2003; Kaplan 1994; Kaplan et al. 2007). Human infants are born very small compared to their mother’s size: the reason seems to be that this allows more infants to be packed into the human reproductive span. This requires women, however, to have some means of providing for extra and weaned children who cannot provide for themselves: this food comes from other people. Dubreuil argues that the main source of this food for a woman is her children’s father, who provides this food from the surpluses generated by his own large game hunting. The idea is that this investment on the part of the males raises the problem of paternity—men do not want to invest in children that are not their own. So there is selection pressure for group norms about who one may have sex with (especially for women) to get men to accept living in multi-male groups and to invest in their offspring. There would also have been some group interest in making sure that children were provided for properly, since the children of the group are each others’ future cooperators. I find this explanation confusing for several reasons; not least that it really isn’t clear what evolutionary processes Dubreuil thinks are driving the evolution of group norms in this case.1 Presumably, this would have to be some form of group selection. The problem is that paternity uncertainty is an individual level fitness problem for men. Perhaps Dubreuil thinks that these group norms evolved by group selection because only groups which had such norms were able to form at all— males would otherwise not agree to live in groups (p. 81). However, for humans, living in multi male groups is the primitive trait; the question is why men who were 1
This is a case of Dubreuil’s puzzling insistence that he is not going to discuss the selection processes involved in human evolution, merely what changes occurred (p. 5)–he does seem to have some unusual ideas about how and whether natural selection explanations can be arrived at for behavioral and morphological traits (p. 93–96). Unfortunately, (a) selection processes are part of natural history, and (b) what changes occurred in natural history are often obscure. To determine what did happen, Dubreuil repeatedly makes functional claims about what would have worked for humans and what would not. These are implicitly claims about the action of one of more selection processes and the selection pressures that made them possible.
123
Evolution and the loss of hierarchies
131
living in such groups would evolve to invest in children, not the other way around. So could investment in children by males evolve without those males having paternity certainty? Yes: as long as the individuals within the group that happens to invest in children out-reproduce those in other groups, investing in children could evolve by group selection. Suppose this investment takes the form of hunting and sharing food very liberally and large game hunters share out widely each of the kills they bring home—a realistic assumption, since in some well studied modern foraging groups, 80 per cent or more of the calories brought home by a large game hunter are eaten outside of his nuclear family (Hawkes 1991). Large game hunting and sharing permits humans to exploit a valuable resource they couldn’t otherwise exploit; third party punishment of the sort also seen in modern human foraging groups could also prevent males living in the group from defecting whilst living in it. Under these circumstances, hunting and sharing increases the amount of calories available to all of the women in the group and raises their fertility; the group grows as a consequence. Notice that, for these purposes it simply doesn’t matter who the fathers of the children are, not for group level selection purposes and not really for individual level selection purposes, either. Hunting and sharing with punishment protects the individual-level fitness interests of males, since their own children (whoever those turn out to be) are being fed by other men, just as they are feeding the children of others. A man in such a group doesn’t have to control whether other men have sex with the women whose children he is supporting, because he is, in effect, supporting all the women and all the children, as are all the other men.2 Finally, there is a problem with Dubreuil’s assertion that cooperative feeding and breeding evolved separately. The evidence Dubreuil presents for thinking this was a two part process is tenuous at best: the fossil evidence such as that from teeth (Dean 2007) suggests that the introduction of these two features of human social life was a gradual process, starting with Homo erectus. Large game hunting and sharing patterns were probably not present until at least the common ancestor of Neanderthals and modern humans, and fully modern life histories not present in any species except modern Homo sapiens (not even in Neanderthals) (Smith et al. 2010, 2007). Dubreuil, however, imposes a binary division on the evidence for each trait in a variety of hominid species (see the table, p. 85). Worse, there’s no model here for processes permitting the two strategies to evolve separately—what would cooperative breeding constitute if it didn’t constitute contributions of food? According to the two best regarded current hypotheses for the evolution of human life history, cooperative breeding involves the sharing of food which increases female fertility (Hawkes 2003; Kaplan et al. 2000). In my own work I argue that hunting and sharing is a cooperative enterprise that evolves by group selection because it raises the fertility of all the females in the group, allowing them to have more children with closer birth spacing and thus promotes changes in life history (Driscoll 2009). Of course, if the cooperative feeding hypothesis and cooperative 2
Another problem for Dubreuil is that the sexual norms of modern foraging groups vary in content and in the reasons given for them by the members of those groups. For example, conflict reduction seems to be the recognized reason for a form of marriage amongst the San foragers (Marshall 1976). Other groups, such as the Ache, because of their beliefs about how children develop in the womb, have greater sexual freedom and strong norms for a lack of jealousy amongst the men (Hill and Hurtado 1996).
123
132
C. Driscoll
breeding hypotheses involve different sorts of cooperative foraging problems (cooperative active scavenging as the ‘‘cooperative feeding’’ for Homo erectus followed by individual large game hunting and sharing raising female fertility as the ‘‘cooperative breeding’’ for later hominids) then Dubreuil might be able to avoid this problem.
Hierarchies regained So far, Dubreuil has argued that the loss of dominance hierarchies occurred gradually during the time of Homo erectus and Homo heidelbergensis, and on the grounds that these two species solved other public goods problems that involved the cognitive capacities necessary for removing hierarchies but missing in other primates. But only Homo sapiens had the capacities which led to new kinds of hierarchies arising. In Chapter 3, Dubreuil gives an extremely lengthy discussion of the human fossil record, in an attempt to figure out which changes in both brain and behavior (and therefore cognitive capacities) were unique to Homo sapiens. Dubreuil argues that the relevant capacity in Homo sapiens was the capacity for symbolic thinking, or, more generally, ‘‘perspective taking’’ (thinking of something as more than one thing, or thinking of how others see it). Significant changes in human artifacts that require the capacity for perspective taking occur only in the fossil record of Homo sapiens. What’s more, these occur together with evidence from skull fossils suggesting significant expansion in the temporal and parietal cortices, areas which Dubreuil believes are implicated in perspective taking. The capacity for perspective taking, Dubreuil argues, became vitally important in the emergence of new kinds of hierarchies later in human history (I’ll come to this part of the discussion shortly). There are, again, a number of problems in connecting the expansion of the temporal and parietal cortex with the origin of the capacity for perspective taking. Dubreuil’s argument to this effect is based on two pieces of evidence: first, that capacities for perspective taking are connected to areas of the temporal-parietal junction (TPJ), and second, that the capacity for perspective taking develops in human children at about the same time as their temporal and parietal cortex expands. I’m going to focus on the first of these two sets of evidence: I’ll just say that the expansion of the whole temporal parietal area in children is identified with the introduction of a lot of capacities, not just perspective taking. The question is whether Dubreuil is justified in arguing that the expansion of the whole temporal parietal area was due (even in part) to expansion in the relatively small TPJ, and whether the TPJ is really involved in perspective taking. Dubreuil identifies the primary function of the TPJ as ‘‘attentional flexibility’’. The studies he cites, however, take ‘‘attentional flexibility’’ to be something very different from perspective taking: simply, the process of interrupting and redirecting normal visual attention when a salient input comes in from an unexpected place in the visual field (e.g. when a visual target expected at one point is flashed somewhere else) (Astafiev et al. 2006; Decety and Lamm 2007; Mitchell 2008; Perner and Aichhorn 2008). It would also be very surprising if this capacity to shift attention were new to Homo
123
Evolution and the loss of hierarchies
133
sapiens. Fortunately for Dubreuil, there is evidence that the TPJ is also involved in perspective taking (Aichhorn et al. 2006), although these studies also implicate a few other areas of the brain. This puzzling role of the TPJ in both ‘‘theory of mind’’ (TOM) tasks like perspective taking and attentional flexibility has puzzled scientists; the resolution may be that there are separate regions of the TPJ involved in each (Scholz et al. 2009). If however, it is only the TOM areas of the TPJ that are involved in perspective taking, then the part of the temporal parietal area implicated in this task is very small. It seems unlikely the whole temporal parietal area would have needed to expand to support the evolution of just this part. It is possible, indeed, that the relevant sub-system of the TPJ was part of the smaller temporal parietal cortex present in earlier hominid species, and that the temporal parietal cortex expanded in human evolution to support other capacities (for various reasons, Dubreuil rejects the other possibility that expansion in the temporal lobe was mere allometry (p. 102–105). How then, does Dubreuil think the capacity for perspective taking might have permitted the reintroduction of hierarchies in modern humans? The central argument in Chapter 4 and 5 goes essentially like this: the main driver for the reoccurrence of hierarchies in human societies is increase in the size of those societies. Human cognitive capacities needed for managing modern groups included mechanisms to help them track those who violate norms. Once groups reach a certain size, doing this becomes impractical. There are then two solutions to this problem if those groups are to grow in size. One, the ‘‘corporate strategy’’ is to split groups into subgroups which have representatives; individuals only have to enforce norms in their own groups and track the behavior of the representatives who ‘‘stand for’’ other groups. This forces individuals to more strongly enforce norms in their own groups because the behavior of others affects their group’s reputation. This creates a kind of hierarchy of individuals within groups and group representatives, and a need not only to have norms of behavior, but also norms about who gets to enforce norms. Hierarchies of wealth and power derive from what Dubreuil calls ‘‘networking strategies’’. This is where powerful individuals (often the representatives from corporate strategies) are able to get other individuals to feel gratitude toward them, usually by indebting them in some way; this creates relationships of dependence. These individuals, if they are also able to get the power to enforce norms invested in them, then become politically powerful. These sets of dependence relations and norm enforcement rights can become nested, with dependent individuals having their own dependents. Eventually network strategy based groups can become genuinely state societies. According to Dubreuil, the formation of these societies is dependent on the presence of capacities for perspective taking that permit individuals to see groups as having their own attitudes, beliefs and characteristics, to see one individual ‘‘standing for’’ an entire group, and so on. Dubreuil’s biggest problem is to explain how the network strategy is compatible with the human desire for equality (or, at least, fairness). He claims that this is possible first, because people are only willing to enforce norms when violations of norms are also violations of expected degrees of unfairness, and second, because the relationships of gratitude individuals have to
123
134
C. Driscoll
those higher in the hierarchy make them willing to permit violations of norms of equality by those higher in the hierarchy. While Dubreuil’s story about the origin of new human hierarchies is plausible, my concern is that Dubreuil’s explanation relies heavily on the role of the emotion of gratitude. The origin of this emotion is never really explained; nevertheless, it needs explaining because first, it appears unique to humans and second, it seems to impose (at least a group) fitness cost. Individuals motivated by the feeling of gratitude in the above way are permitting what are essentially free riders (powerful, even abusive leaders) into human societies. Without an explanation for the origin of these capacities Dubreuil’s explanation for the return of human hierarchies is incomplete.
Conclusion In conclusion, then, Dubreuil’s book is impressive in its ambition and scope. It does, however, have some significant problems—I’ve focused here on those related to Dubreuil’s discussion in the first three chapters. Dubreuil needs to make much clearer which cognitive capacities he thinks are necessary and sufficient to the loss of hierarchies; this would then allow him to do a better job of extracting a time for the loss of hierarchies from his discussion of the larger question of the evolution of human capacities for cooperation. His discussion of the evolution of cooperative capacities also needs to be reworked: the most plausible account for him is that early hominids, such as Homo erectus, evolved the capacity for joint attention to facilitate active scavenging; later in human history, more complex forms of large game hunting required the evolution of the capacity to follow norms of sharing. Finally, Dubreuil needs to give an account of the evolution of emotions such as gratitude since these have a very important role in his explanation for why humans ended up regaining their social hierarchies.
References Aichhorn M, Perner J, Kronbichler M, Staffen W, Ladurner G (2006) Do visual perspective tasks need theory of mind? NeuroImage 30:1059–1068 Astafiev SV, Shulman GL, Corbetta M (2006) Visuospatial reorienting signals in the human temporoparietal junction are independent of response selection. Eur J Neurosci 23:591–596 Brosnan SF, de Waal FBM (2003) Monkeys reject unequal pay. Nature 425:297–299 Brosnan SF, Schiff HC, de Waal FBM (2005) Tolerance for inequity may increase with social closeness in chimpanzees. Proc R Soc Lond B 272:253–258 de Waal FBM (1984) Sex differences in the formation of coalitions among chimpanzees. Ethol Sociobiol 5:239–255 Dean C (2007) Growing up slowly 160, 000 years ago. Proc Natl Acad Sci 104(15):6093–6094 Decety J, Lamm C (2007) The role of the right temporoparietal junction in social interaction: how lowlevel computational processes contribute to meta-cognition. Neuroscientist 13(6):580–593 Dominguez-Rodrigo M (2002) Hunting and scavenging by early humans: the state of the debate. J World Prehistory 16(1):1–54 Driscoll C (2009) Grandmothers, hunters and human life history. Biol Philos 24:665–686
123
Evolution and the loss of hierarchies
135
Gurven M (2004) To give and to give not: the behavioral ecology of human food transfers. Behav Brain Sci 27:543–583 Hawkes K (1991) Showing off: tests of an hypothesis about men’s foraging goals. Ethol Sociobiol 12:29–54 Hawkes K (1993) Why hunter gatherers work: an ancient version of the problem of public goods. Curr Anthropol 34(4):341–351 Hawkes K (2003) Grandmothers and the evolution of human longevity. Am J Hum Biol 15:380–400 Hill K, Hurtado AM (1996) Ache Life History. Aldine de Gruyter, New York Kaplan H (1994) Evolutionary and wealth flows theories of fertility: empirical tests and new models. Popul Dev Rev 20(4):753–791 Kaplan H, Hill K, Lancaster J, Hurtado AM (2000) A theory of human life history evolution: diet, intelligence, and longevity. Evol Anthropol 9:156–185 Kaplan HS, Gurven M, Lancaster JB (2007) Brain evolution and the human adaptive complex: an ecological and social theory. In: Gangstead SW, Simpson JA (eds) The evolution of mind: fundamental questions and controversies. Guildford Press, New York, pp 269–279 Klein RG (2000) Archaeology and the evolution of human behavior. Evol Anthropol 9:17–36 Marshall L (1976) The !Kung of Nyae Nyae. Harvard University Press, Cambridge Mitchell JP (2008) Activity in right temporo-parietal junction is not selective for theory-of-mind. Cereb Cortex 18:262–271 Nishida T (1983) Alpha status and agonistic alliance in wild chimpanzees (pan troglodytes schweinfurthii). Primates 24(3):318–336 O’Connell JF, Hawkes K, Blurton Jones N (1988) Hazda scavenging: implications for plio/pleistocene hominid subsistence. Curr Anthropol 29(2):356–363 O’Connell JF, Hawkes K, Lupo KD, Blurton Jones NG (2002) Male strategies and plio-pleistocene archaeology. J Hum Evol 43:831–872 Perner J, Aichhorn M (2008) Theory of mind, language and the temporoparietal junction mystery. Trends Cogn Sci 12(4):123–126 Scholz J, Triantafyllou C, Whitfield-Gabrieli S, Brown EN, Saxe R (2009) Distinct regions of right temporo-parietal junction are selective for theory of mind and exogenous attention. PLoS ONE 4(3):e4869 Smith TM, Toussaint M, Reid DJ, Olejniczak AJ, Hublin J-J (2007) Rapid dental development in a Middle Paleolithic Belgian Neanderthal. Proc Natl Acad Sci 104(51):20220–20225 Smith TM, Tafforeau P, Reid DJ, Pouech J, Lazzari V, Zermeno JP et al (2010) Dental evidence for ontogenetic differences between modern humans and Neanderthals. Proc Natl Acad Sci 107(49):20923–20928 Stanford CB (1996) The hunting ecology of wild chimpanzees: implications for the evolutionary ecology of pilocene hominids. Am Anthropol 98(1):96–113
123