Tomasello et al. (2012) The interdependence hypothesis

Tomasello M, Melis AP, Tennie C, Wyman E, Herrmann E (2012) Two key steps in the evolution of human cooperation: The interdependence hypothesis. Current Anthropology 53: 673-692.

There are many good ideas in this paper.

The Main Idea

“At some point humans created lifeways in which collaborating with others was necessary for survival and procreation (and cheating was controlled by partner choice). This situation of interdependence led inevitably to altruism, as individuals naturally wanted to help the collaborative partners on whom they depended for, for example, foraging success. Moreover, interdependent collaboration also helps to explain humans’ unique forms of cognition and social organization, since it is collaboration, not altruism, that creates the many coordination problems that arise as individuals attempt to put their heads together in acts of shared intentionality to create and maintain the complex technologies, symbol systems, and cultural institutions of modern human societies.”

Two steps: (1) Obligate Collaborate Foraging, and (2) Group Mindedness

“First, small-scale collaboration involving cognitively complex coordination problems took place initially, we will argue, in the context of collaborative foraging…

Second, group-level collaboration followed as the entire social group needed to work together interdependently in order to compete with other social groups, leading to such things as group-created conventions, norms, and institutions.” (p. 674)

Step 1: Obligate Collaborative foraging

While acknowledging Hrdy’s emphasis on cooperative breeding, they downplay the role it had, and instead focus on collaborative foraging, which probably involved an emphasis on scavenging for large prey (Sterelny holds they don’t emphasize scavenging enough). They argue that collaborative foraging can be modeled as a Stag Hunt game, which comes with 3 main challenges

3 main challenges to the evolutionary Stag Hunt game:

1. Sharing the spoils – how to divide the spoils with no desctructive fighting, so to retain the incentive for future collaboration. 
2. Coordination – find a way to make a “group decision” about whether to go for the stag.
3. Temptations to free ride

1. Sharing the spoils

Chimpanzee’s do some group foraging, but this may be simple mutualism, and does not involve much coordination nor a democratic sharing of the spoils. There is a clear temptation to free ride, which is exploited.

“Chimpanzees’ predominant solution to food competition in general, namely, dominance, tends to destabilize collaborative foraging over time.” (p. 675)

Humans share spoils differently – they are more generous, and expect fairness in return. Portions of the hunt are also brought back to the encampment for future sharing.

Children (2 yr old) chose to pull food to themselves more often when that also meant food for their companion. Chimps “will in some situations help others to gain access to food, but only if the helper has no possibility of obtaining the food herself.” (p. 676).

NOTE: It seems like this could act as a preadaptation for further altruism and interdependence.

The big idea in what drove this shift in early hominins is climatic in nature, and depends on a shift to dependence on scavenging.

“Thus, as the genus Homo was emerging some 2 million years ago, a global cooling and drying trend created an expansion of open environments and a radiation in terrestrial monkeys, who would have competed with Homo for many plant foods. Scavenging large carcasses killed by other animals would have been one possible response. Such scavenging would have required multiple participants, as other carnivores would be competing for those carcasses as well.

Individuals would be especially well suited for scavenging if they were tolerant of conspecifics cofeeding on a carcass with them.” (p. 676)

NOTE: If this situation is plausible, then I think this makes a lot of sense. This kind of collaboration has fairly minimal requirements and is rife with opportunity for improvement. It is also reminiscent of the story I’ve heard for the evolution of the domestic cat. As human agricultural stores attracted rodents, this became a bounty for wild cats. The cats that were more willing to approach and tolerate humans were rewarded. Humans were then incentivized to keep cats around, including feeding them in times of rodent storage, which further drove cat evolution for tolerance of humans.

They bring Boehm’s ideas about “counter-dominance” (or “reverse dominance”), because “individuals who attempted to hog all of the food at a scavenged carcass would be actively repelled by others and perhaps shunned in other ways as well.” (p 676)

NOTE: This forces the question of why this kind of thing doesn’t happen in food sharing among other primates. One possibility is that large carcasses were big enough not to be taken away, so sharing was easily facilitated, and then encouraged. An explanation proposed by Tomasello et al is that this is related to the need to rive other predators away from the carcass, which requires coordination.

In sum, “our proposal is that in the context of scavenging, the individuals who did best were those who (1) were tolerant of others peacefully cofeeding on the same carcass and (2) did not attempt to hog the spoils and so be socially selected against by others for selfish behavior.”

2. Coordination

They note that coordination does not require the intention to coordinate. In chimpanzee group hunting, “each participant takes into account the position of the others and their behavior and how these might influence the monkey’s flight. The coordination is therefore an emergent property generated by individual decision making not aimed at that coordination.” (p 677)

In terms of the Stag Hunt game, they note that if chimps see a colobus monkey (which needs a group hunt for successful capture), they initiate it without looking, and others pretty much always join.

NOTE: Initiating the Stag Hunt is not particularly risky if players can take turns in decided what to do. If you KNOW I’m going to hunt Stag, then your optimal move is to hunt Stag.

“Humans, in contrast, coordinate and communicate about their decision making in such situations to form a joint goal. To form a joint goal, we must know together that each of us has the goal of working with the other. Knowing together means engaging in some form of recursive mind reading (we each know that the other knows, etc.), which is the basic cognitive ability that enables humans to engage in all forms of joint and collective intentionality.”

How did this ability evolve?

“How did early humans move from a chimpanzee mode of initiating and coordinating Stag Hunt activities—based either on a leader-follower strategy or on a kind of naive optimism about the other’s actions—to the modern human mode in which individuals coordinate their decision making through some kind of implicit or explicit communication, resulting in a joint commitment to follow through until everyone gets their reward, with a coordination of interchangeable, agent-neutral roles?”

“The hypothesis is that at some point their scavenging turned into active collaborative hunting and gathering (perhaps with the emergence of Homo heidelbergensis some 800 kya, with evidence for bringing large prey back to a home base from at least 400–200 kya. The key point in the transition from chimpanzees, from a psychological point of view, would have been when the decision making became more challenging, in particular when the risk became such that just optimistically leaving the hare in hand (as chimpanzees seemingly do) was no longer an effective strategy. That is to say, the situation was such that giving up the hare was no longer so cheap that one should just go for the stag without at- tempting to coordinate decisions with other potential hunters.” (p 678)

NOTE: There is some definite handwaving as to how this occurred. At some point, humans needed to collaborate for getting food, especially as they went from passive scavenging to more active collaborative foraging, and “were faced with ever more challenging coordination situations and decisions,… this provided the selective context for the evolution of ever greater skills of coordination and communication.” (p. 678)

This seems to me to be a key question: why did humans switch from scavenging to more active foraging? Did the scavenging facilitate increasing social cognition, allowing for it? That seems to be implied.

The final point here is that this collaboration led to social selection based on reputation. The emphasis was not on cooperation, i.e., “not for individuals who were tolerant around food and fair at sharing the spoils but rather for competent coordinators and communicators who would increase the likelihood of success.” (p 678)

3. Temptation to free ride

“The proposal is that the earliest manifestations of human collaborative foraging were not so vulnerable to free riding because they involved very small numbers of collaborators, each of whom believed their participation to be necessary.” (p 678)

NOTE: They basically just assert that this was the case, without justification. However, if we start with scavenging, then social selection helps form the group. If the main thing is to chosen for group membership in the first place, then reputation is paramount.

“When the collaboration is obligate, the stakes are raised to the degree that there may be even competition for partners, and in this case a concern for self-reputation would be especially important. Note that by this point, reputation means both (i) a more motivated collaborator who will not cheat either by monopolizing the food or by lagging and (ii) a more skillful collaborator who is better able to form joint goals and coordinate roles. What enables good collaborators to find one another is thus not reputation for altruism or anything else external, but simply reputation for being a good collaborator—which is, with actual partners and direct observers, impossible to fake.” (p 679)

Interdependence and altruistic helping

“Our proposal is that obligate collaborative foraging produces interdependence among members of a group, and this interdependence makes it in my direct interest to help others who might be my future partners.”

This involves mutualism, and what Clutton-Brock (2002) called group augmentation: “if my prosperity depends on my social group (for defense against predators, etc.), then it is in my interest to keep them alive and prosperous as well.”

On the roles of kinship and cooperative breeding:

“These kinds of processes, important as they are, would not help us to explain the more cognitive aspects of coordinating and communicating toward joint goals, nor would they explain humans’ tendency to socially select others with regard to their cooperative behaviors. To explain these, we need not just prosocial tendencies, but joint intentional skills and motivations for various kinds of collaboration.”

NOTE: Kristen Hawkes, in her commentary, takes serious issue with this. I think she has a point, but they also do. I think that some levels of coordination, communication, trust, and interdependence are necessary to get cooperative breeding between non-kin off the ground, as in humans. After it’s established, the two processes could reinforce one another in terms of shared intentionality and communication.

Limitations to Step 1:

“The collaboration we are talking about here was only small scale and ad hoc, in the sense that it existed only during the collaboration itself; when the foraging trip was over, so was the special “we” it had engendered. There was still some way to go to get to human large-group cooperation and its complex conventions, norms, and institutions.” (p 681)

Step 2: Group-Mindedness

The setup: “contemporary humans possess a whole other level of mechanisms for cooperation, including social conventions, norms (internalized into guilt and shame), and institutions, along with a strong in-group bias. Why did these become necessary?”

Two (essentially demographic) factors:

1.     Population growth within groups

2.     Competition between groups.

Two new challenges:

• Large-scale group coordination: “as groups became larger, at least partly in competition with other groups, individuals needed to be able to coordinate with relative strangers—while still knowing that they were from within the group (and so had the requisite skills and trustworthiness).”
• Large-group social selection: “as groups became larger, again due partly to competition with other groups, incentives for cooperation diminished (each individual was less needed, and reputational information was more difficult to obtain; Olson 1965), so free riding—and even active cheating—proliferated and needed to be controlled.”

1. Large-Group Cooperation: Cultural Practices and Group Identification

“The problem for the individual is to know who has the requisite skills and trust- worthiness and, reciprocally, to make sure that others know that I myself possess these qualities.” (p. 681)

NOTE: This is an argument for group markers, and it makes sense (ala McElreath et al 2003). BUT, it doesn’t account for social identity complexity. Once groups get very larger, i.e., after the demographic transition, they will have to cooperate in small groups again. These groups, as before, may be ad hoc. There is also an ecology of games – we participate in many collaborative ventures simultaneously. This requires not just group markers/ group identity, but a complexity of social identities which can be expressed depending on the situation.

There is an appeal to Lewis’ ideas on conventions:

“Conventions thus require some kind of recursive mindreading or common ground as the basis of the agreement, and this basic ability evolved initially, as argued above, as a skill for forming joint goals and joint attention in collaborative activities.

…

Conventions generate the conformity characteristic of cultural practices because it is in the individual’s interest to do things the way that others do them so that they can effectively coordinate—and this is especially important if one wishes to be able to coordinate with anyone in the larger society, including strangers.” (p 682)

NOTE: This is a focus on cooperation. They discuss more complex coordination and collaboration, but the discussion betrays a less subtle view. This is about solving general coordination problems. I.e., we’ve decided to cooperate, now we need to know how. It would be best if we have the same goals and practices.

Another reason for cultural practices is inter-group competition.

“Competition with other groups helped to engender group identification…. To compete, the society as a whole—especially as population increased and there was increasing division of labor—had to scale up its small-scale collaboration to form collective, society-wide goals, plans, and collective knowledge of things in the face of outside threats. And individuals again had to help their collaborative partners for these group enterprises—who at this point comprised essentially everyone in the society, including some strangers.”

NOTE: This is fine, but it conflates large-group identity with small-group cooperation problems. You need to coordinate with strangers, but also to have a group mind. There are small-scale coordination problems. This requires social identity complexity. This is also supported by social psych research on mere exposure paradigms and the like. We are very willing to form a group identity with a group of strangers around some common thread. Social identity complexity helps us do this.

Social psychologists often distinguish between two broad types of group formation in humans: interpersonal interdependence and shared identity (see Lickel, Schmader, and Spanovic 2007)

2. Large–Group Social Selection: Social Norms and Institutions

“Social norms are mutual expectations in common ground that people behave in certain ways, where the expectations are not just statistical but rather normative, as in you are expected to do your part (or else!).” p 683)

They argue that social norms will be inherently cooperative:

“In our view, because of humans’ already existing cooperative lifeways and interdependence as evolved in step 1, social norms could not have emerged as directionally arbitrary, but only as encouraging collaboration and helping and as discouraging their opposites—since, to repeat, social norms are nothing more than conventionalizations of the more particular acts of social selection for cooperative behavior (and against uncooperative behavior) of step 1 individuals. Under conditions of group competition, social norms may be scaled up to the level of societal life in general.” (p 683)

NOTE: This ignores the inherent power disparities in a large-scale society. Leadership? Slavery? The question is: who benefits? There is likely some cultural group selection for these kinds of norms. I get that the argument here is for early hominin evolution, so we can assume that we are talking mostly about hunter-gatherers. Even so, though, there needs to be stronger selection on egalitarianism than this argument implies.

“In practice, enforcing social norms is mostly not necessary because individuals have already internalized them and naturally want to conform to them. And if individuals do violate a norm, they often punish themselves [e.g., through guilt and shame]” (p 684)

NOTE: This highlights the importance of norm-relevant emotions in human evolution, which likely coevolved with strong group identities.

There is a pretty minimal treatment of institutions. They basically tack on a paragraph about how they allow for diversification of roles. It’s a smart discussion, but pretty cursory.

“Pretty much all of the cooperative mechanisms characteristic of humans at this second step in our evolutionary story come together in the creation of social institutions. Social institutions are collaborative cultural practices with joint goals and standardized roles, with social norms governing how rewards are dispensed, how cheaters and free riders are treated, and so on. What is new about institutions is that they create new statuses for individuals playing particular roles that everyone must respect” (p 684)