The Genetic Side of Gene-Culture Coevolution: Internalization of Norms and Prosocial Emotions
Herbert Gintis
May 23, 2016
Joseph Henrich’s “Cultural Group Selection, Coevolutionary Processes and Large-scale Cooperation” is an insightful exposition of a very important research agenta in the theory of human cooperation, to which he has made important con- tributions. In these remarks, I will attempt to add to Henrich’s argument for con- formist cultural transmission, to weaken the group selection requirements for gene- cultural coevolution, and to strengthen the argument for the genetic side of the evolutionary dynamic. My analysis has three stages. First, as Boyd and Richerson (1990) stressed in a related context, the evolutionary stability of altruism does not necessarily involve a within-group fitness deficit for the altruistic trait. Cultural group selection can take the unproblematic form of groups with higher expected payoffs for all agents displacing groups with lower expected payoffs. Price’s equa- tion and the thorny issues surrounding classical group selection theory can thereby be avoided. Second, the analysisof conformist cultural transmissioncan be strengthenedby recognizing the uniquely human capacity to internalize norms, which then become goals (arguments in the agent’s objective function) rather than techniques—means of attainingother goals—or beliefs—factual statements concerning states of affairs and causal relations. Third, human beings have prosocial emotions, including shame, guilt, and em- pathy, that equip the individual with rewards for altruistic behavior and penalties for self-regarding behavior. Prosocial emotions are predicated upon highly de- veloped, physiologically-based, genetically-grounded, arousal systems. Prosocial emotions heighten the subjective utility associated with internal norm compliance. To see this, note that when a self-regarding goal is not achieved we feel ‘disap- pointed,’ ‘frustrated,’ or ‘angry,’—emotions we share with many vertebrates—but when an other-regarding (altruistic) goal is not realized, we feel ‘guilty,’ ‘ashamed,’, or ‘remorseful.’ Prosocial emotions also predispose us to internalize some norms rather than others. For instance, as Adam Smith (1759/2000) long ago noted, we
1 1 A MODEL OF CULTURAL EQUILIBRIUM WITH ALTRUISM are predisposed to experience empathy for other members of our social group, unless they have specifically acted to harm us. Which individuals and types of in- dividuals count as members of “our social group” is highly culturally specific, but the expression of empathy for members of one’s own group is probably a human universal. Gene-culture coevolution, then, includes the following mechanism. Cultural complexity and the rapidity of cultural change (Boyd and Richerson 2004) ren- der the internalization of norms fitness-enhancing, so the genetic predisposition to internalize norms is an evolutionary adaptation. Moreover, agents who inter- nalize norms tend to punish norm violators. Thus conformity to social norms be- comes fitness-enhancing, which renders the genes for prosocial emotions fitness- enhancing adaptations. The internalization of norms and the prosocial emotions permit large-scale cooperation among non-kin, setting the stage for the technolog- ical and cultural evolution characteristic of modern civilization.
1 A Model of Cultural Equilibrium with Altruism
Consider a group in which members can adopt either altruistic cultural norm A, or fail to adopt, in which case they are self-interested.1 Self-interested types (we shall call them type B) have baseline fitness g.˛/, where ˛ is the fraction of altruists in the group, while altruistic types (those who have trait A) have fitness .1 s/g.˛/, where 0community and community institutions promoting altruistic values, a fraction ˛ of such offspring becoming altruists. We call this oblique transmission (Cavalli-Sforza and Feldman 1981, Boyd and Richerson 1985). First, agents pair off randomly, form families, mate, and have children. Sup- pose there are n males and n females at the beginning of the period. If the fraction of altruists is ˛, there will be n˛2 AA-families, who will produce n˛2.1 s/2ˇ offspring, all of whom are altruists, where we choose ˇ so that population grows at rate g.˛/. There will also be 2n˛.1 ˛/ AB-families, who will have 2n˛.1 ˛/.1 s/ˇ offspring, half of whom are altruists. Finally there will be n.1 ˛/2 BB-families who will have 2n.1 ˛/2ˇ offspring. Adding up the number of off- spring, we see that we must have ˇ D g.˛/=.1 s˛/2. The frequencies of AA,
1For a deeper analysis of this and related models, see Gintis (2003a,b).
2 1 A MODEL OF CULTURAL EQUILIBRIUM WITH ALTRUISM
AB, and BB offspring are thus given by
˛2.1 s/2 2˛.1 ˛/.1 s/ .1 ˛/2 fAA D ; fAB D ; fBB D : (1) .1 ˛s/2 .1 ˛s/2 .1 ˛s/2 Second, a fraction ˛ of offspring of AB- and BB-families who are self- interested types switch to being altruists under the influence of the oblique trans- mission of the altruistic norm A. It is easy to check that the change in the fraction of altruists in the next generation is given by a.1 ˛/. s/ ˛P D f.˛/ D : (2) 1 s˛ Third, suppose in every time period, each group member i learns the fitness and the type of a randomly chosen other member j , and changes to j ’s type if j ’s fitness is perceived as higher. However, information concerning the difference in fitnesses of the two strategies is imperfect, so the larger the difference in the payoffs, the more likely the agent is to perceive it and change. Specifically, we assume the probability p that an altruistic agent shift to being self-interested is proportional to the fitness difference of the two types, so p D s for some proportionalityconstant >0. Then it is easy to show (Gintis,2009) that the fraction ˛ of altruists follows the replicator dynamic ˛P D ˛.1 ˛/s: (3) We now combine the cultural transmission and replicator sources of change in the fraction of altruists, giving ˛P D f.˛/ ˛.1 ˛/s, which reduces to ˛.1 ˛/ ˛P D . s s.1 s˛//; (4) 1 s˛ where now represents the relative speed of the socialization and biologically adaptive processes. We call the situation ˛P D 0, ˛ 2 Œ0; 1 a cultural equilibrium of the dynamical system. We then have the following theorem.
Theorem 1. (a) If
0extinction.
(b) If 1 2 smin