This chapter provides a novel evolutionary scenario, one that contradicts several fundamental tenets of traditional social biology. For three decades a general assumption has been that genotype and phenotype can be equated for purposes of mathematical modeling. Another premise has been that selection arising from competition between groups is so feeble that it does not warrant serious consideration. For humans in the Late Paleolithic, neither of these assumptions can be taken for granted.
The Genetic Paradox of Altruism
My general hypothesis is that the spread of Paleolithic egalitarianism had a profound effect on basic mechanisms of natural selection. Specifically, selection at the between-group level was empowered at the expense of selection at the within-group level, a shift that profoundly affected human nature. This was the case because between-group selection supports the altruistic traits that have been so vigorously denied for three decades. I would not advocate this controversial hypothesis unless there was persuasive ethnographic evidence in its favor.
Like many evolutionary scenarios developed by paleoanthropologists, this behavioral hypothesis is not susceptible to disconfirmation with present archaeological evidence. But because it is critical to our understanding of human nature, that standard of scientific accuracy can be replaced by one of relative plausibility. The first assumption to be tested against that yardstick is fundamental. It concerns the availability of sufficient time for human nature to have been transformed under the aegis of egalitarianism. We are speaking about evolutionary time, which must be measured in generations.
It is extinction rates, along with variation, that determine the rate of evolution of a species. E. O. Wilson (1978:91) has the following to say about the rate of evolution for humans: “The theory of population genetics and experiments on other organisms show that substantial changes can occur in the span of less than 100 generations, which for man reaches back only to the time of the Roman Empire. Two thousand generations, roughly the time since typical Homo sapiens invaded Europe, is enough time to create new species and to mold their anatomy and behavior in major ways.”
I have quoted Wilson to show that if something were to have changed radically in the natural-selection scenario for humans, it certainly could have had significant effects in a thousand generations or so. A human generation is a relatively lengthy twenty-five years, so a thousand generations places us at 25,000 years ago, and two thousand generations would take us back 50,000 years.
Egalitarianism could be far more ancient than this (Knauft 1991). Indeed, later Homo erectus and Neanderthal apparently lived in smallish bands like those of extant mobile hunter-gatherers (Dunbar 1996; see also Mithen 1990). By inference their brain sizes might have provided them with the requisite political intelligence—and with the moral communities that were needed—to reverse their dominance hierarchies. A more conservative estimate (one that I prefer, given present evidence) is that about 100,000 years ago Anatomically Modern hunter-gatherers were fully egalitarian—or were about to become so. The assumption is that a fully modern brain made them as capable of maintaining an egalitarian order as their extant counterparts. An extremely conservative estimate would pair the invention of egalitarianism with the cultural emergence of realistic cave art, sculpture, and incised calendars, as described by Marshak (1989; see also 1992). Egalitarianism would still have had more than a thousand generations in which to do its work on human nature.
How such work was done is the subject of this chapter, and the selection scenario I describe is far from simple. Indeed, it involves a variety of hunter-gatherer behaviors and their combined effects on natural selection. The overall hypothesis is straightforward: basically, the advent of egalitarianism shifted the balance of forces within natural selection so that within-group selection was substantially debilitated and between-group selection was amplified. At the same time, egalitarian moral communities found themselves uniquely positioned to suppress free-riding (to be discussed shortly) at the level of phenotype. With respect to the natural selection of behavior genes, this mechanical formula clearly favors the retention of altruistic traits.
An altruistic gene can be defined simply and unambiguously: it is supported by between-group selection, and it is undercut by within-group selection (E. O. Wilson 1975; Wilson and Sober 1994). However, as Knauft (1989) points out, for well over twenty years evolutionary biologists, sociobiologically inclined anthropologists, and evolutionary psychologists have agreed—almost, but not quite unanimously—that natural selection can support nepotistic helpfulness but not altruistic helpfulness.
A wide variety of scholars have gone to ingenious lengths to show that for humans genetically altruistic behaviors—those that mitigate against inclusive fitness and appear to transfer reproductive resources to nonrelatives—somehow are bogus. It is held that such giveaways must be derived from kin selection or social coercion (for example, Wilson 1978), or else that they somehow are made possible by selfishly-motivated exchanges of service that take place over time (for instance, Trivers 1971; see also Alexander 1987). With humans, two problems arise with this approach. One is simply that many members of the species in question do not like to see themselves reduced to “total selfishness.” This is a problem of the heart, and I have done my best to set it aside. The second problem is one of facts—and theories—that challenge a powerful paradigm long in vogue, a paradigm which as I write is subject to serious scrutiny (Wilson and Sober 1994; Boehm 1996, 1997a, 1997b, 1999a, 1999b; Sober and Wilson 1998; see also Wilson’s 1997 edited American Naturalist supplement).
The factual problem is that extant hunter-gatherer nomads not only cooperate, in very generalized ways, as groups, but to a significant degree they may take care of nonrelatives in their bands—as described in the previous chapter and elsewhere (Kelly 1995; Wiessner 1996; see also Boehm 1999b). They also preach steadfastly and strongly in favor of altruism (Campbell 1972); while such preaching is of obvious importance, its ultimate, natural-selection basis remains little explored.
In my opinion, traditional approaches in social biology have been seriously out of touch with common sense when traits such as human cooperativeness and one-way helping behavior are explained wholly in terms of selfish desire for self-aggrandizement, innate nepotism, exact reciprocation, or third-party coercion. Sober and Wilson (1998) propose that the rejection of pre-1966 group-selection theories involved not only a set of deep biases, but also some technical misunderstandings that have become rigidly institutionalized. A number of evolutionary biologists have responded favorably to their earlier critical but constructive attack (see Wilson and Sober 1994), which called for a substantial paradigm shift, and the campaign continues as I write.
Altruism has always posed a special puzzle for philosophers, a puzzle that resonates strongly because we all know, introspectively, how powerful the forces of selfishness must be. Yet for readers unacquainted with the academic literature on altruism, the term as used by philosophers, biologists, and anthropologists can be ambiguous. A few general illustrations will be helpful before I present detailed arguments at the level of biology and culture.
With respect to reproductively self-sacrificial helping behavior, Lorenz’s (1963) study of the behavior of turkey hens and how they protect their offspring is highly instructive. These fowl viciously attack a dangerous predator such as a fox that comes near their nest, and in normal English usage this behavior could be called altruistic because the mother is risking her life to protect her offspring. Technically, biologists would call the behavior nepotism and contrast it with altruism. Reproductive success is their currency, and the hen’s investment in her own offspring provides her with net inclusive fitness gains rather than losses. If the same turkey hen were to defend another mother’s chicks, a biologist would call this altruism because it would reduce her ability to advance her genes into the gene pool and thereby damage her inclusive fitness. In fact, she would be reducing her relative fitness quite significantly, for this risky behavior would be advancing the inclusive fitness of her genetic competitor at the very time that her own fitness was being reduced.
In such analysis, the sole criterion is reproductive success. A biologist’s version of altruism or nepotism does not necessarily entail the empathy or selfless feelings of generosity that we think of when applying the term to humans who are selflessly helpful in the motivational sense (Wilson 1978; Boehm 1979; Sober and Wilson 1998). Lorenz discovered that turkey hens were programmed so “stupidly” that their self-endangering maternal instincts appear to be far from maternal concern as we see it in humans. The first clue came when a turkey hen that had been deafened immediately destroyed her own chicks, attacking them just as she would a predator.
Lorenz formed a hypothesis. He wanted to know if turkey hens would attack anything living that drew near to their nests, that is, anything that failed to give the high-pitched vocalizations turkey chicks are programmed to emit. He obtained a stuffed fox and brought it near the nest of a turkey hen that was not deafened, and predictably the hen attacked viciously. The second time, he hung a little machine around the fox’s neck, a tape recorder that emitted the cheeping sound of turkey chicks, and the mother ignored the fox entirely. In effect, the hen was acting on a hard-wired compulsion. We may never know her emotions and cognitive state, but this genetic compulsion appears to be quite different from what we mean by altruism when we refer to a socially sensitive psychological state—one that involves empathy, feelings of generosity, and a decision to help.
Human social behavior is seldom driven by anything approaching so-called blind instinct, even though, as Darwin himself noted in The Expression of Emotions in Animals and Man, a few of our facial expressions are hard-wired (see also Masters 1989) and linked to specific emotions. These surely include anger, grief, and fear, but not necessarily any emotions we would associate with altruism. This makes it still easier for traditionalist social biologists to deny innately-prepared altruism in humans, altruism that at the level of psychological motives we would call genuine.
To identify such emotions in humans is difficult because in any given instance of altruistic-seeming behavior, the motivational waters are likely to be muddied by other factors. A fireman may undertake a rescue mission because he was originally attracted by the pay, and now this is just his line of work. He knows that he would endure both shame and damage to his career if he failed to undertake a rescue where the risks were reasonable. Another fireman may wish to play the hero and receive accolades (or professional advancement) because he takes unusual risks. His motives, too, are patently selfish. Another fireman’s original attraction to his career may in fact have been based on genuinely wanting to help others, and an unusual degree of genuine altruism may still gear him to take unusual risks—above and beyond the call of duty. Still another fireman may take unusual risks partly because he likes the pay, partly because he selfishly seeks the esteem of his community, and partly also because he is driven by genuine altruism.
In some human instances of what appears to be self-sacrificial helping behavior, no altruistic feelings are likely; social pressure alone is responsible for the munificent action. For example, at work one grudgingly gives a few dollars to the United Way because one’s boss is known to be making a list of donors—and one knows the list will be circulated through the office. The same unwilling donor may identify strongly with animals, and give generously and anonymously to wildlife conservation. The difference is between socially influenced altruism and motivationally genuine altruism.
In other cases direct coercion may play a role, as when totally unwilling men submit to the draft. They may then fight for their country in what they consider to be unjust wars—simply because they do not want to invite court-martial. These examples suggest that if genuine altruism does exist, it can be mixed in countless ways with personal self-interest, and altruistic performance can be largely if not entirely influenced or forced socially. These motivational clouds have made it easy for many to claim that genuine human altruism can be dismissed (Wilson 1978; Alexander 1987)—that basically all altruistic-appearing behavior is reducible to individual genetic self-interest as represented by inclusive fitness.
If human altruism amounts to a definitional and motivational jumble, social biologists have sorted out the problem in a bizarre—if unambiguous—way. Guided by their own standard paradigm, they have arrived at the conclusion that the only self-sacrificial behaviors that can be supported by natural selection involve assistance directed to offspring or closer relatives. In terms of selection mechanisms, the name of this nepotistic game is kin selection (Hamilton 1964). As explained by E. O. Wilson (1975), kin selection derives from both the turkey-hen type of parental investment (Trivers 1972) and from broader types of nepotism that involve helping siblings, cousins, and the like.
As a major amendment, Wilson and Alexander also include long-term, exactly reciprocated exchanges between individuals as another sustainable type of genetically selfish helping behavior. For three decades now, the majority of evolutionary biologists have agreed that perfectly evened-out sacrifices and benefits, exchanged recurrently between a dyad over time, can be sustained because the cooperators have greater reproductive success than pairs of individuals who fail to cooperate. Such behavior has been labeled reciprocal altruism (Trivers 1971), which is confusing. By definition, there can be no net reproductive sacrifice—on either side.
That Darwinian selection is augmented by kin selection of various degrees is indisputable; inclusive fitness is a powerful factor in human evolution. However, the reciprocal-altruism argument seems far less convincing, given the fact that such exact reciprocation is required over time, with many repeated interactions. While it is true that pairs of cooperators tend to outclass noncooperators, it is in the reproductive interest of each cooperating partner to inconspicuously cheat, thereby gaining not only the advantages of mutual cooperation but a further selfish bonus as well.
This explanation is the best that sociobiology can do, and it does very well indeed in explaining why people help their closer relatives. When it comes to explaining helping behavior that extends beyond nepotism, a serious empirical problem is encountered: extant foragers often cooperate with nonkin spontaneously and with a spirit of generosity, rather than meting out their donations very carefully, and such cooperation extends far beyond the level of dyads. Even though certain individuals manage to do some moderate freeloading, people in bands tend to cooperate intensively, with apparent good will and with great benefit to group members in general. Or so it seems to me, as I read richly descriptive ethnographic reports on hunting bands (for instance, Balikci 1970; Lee 1979).
It is true that while some bands seem to cooperate smoothly, others do so only moderately effectively, with squabbling or cheating. I am referring to the equitable distribution of large-game meat. In effect, the entire band engages in this type of variance reduction, and it does so whenever sharing makes sense. Sharing is accomplished in spite of this squabbling, and even though an occasional social deviant may compromise the system somewhat by cheating when others will not be too disturbed (Boehm 1999b).
Psychologically, there appears to be a genuinely altruistic component in this cooperation. A precise “tit for tat” ideology is absent, and often sharing proceeds smoothly even though typical bands contain unrelated families. People seem to have readily internalized cooperative values they were taught as children (Goody 1991). This innately disposed “readiness” requires explanation at the level of human nature, for it certainly seems to involve genetic altruism as we have defined it.
Levels of Natural Selection
Cultural anthropologists may be only semiconversant with the nuances of natural-selection theory as promulgated by social biologists, and for that reason I shall err in favor of detail. Explanatory strategies begin with the fact that humans live in groups and that basically natural selection takes place within the group. The individual (with his or her inclusive fitness) is the fundamental “container” or unit, the essential vehicle of selection (Wilson and Sober 1994). Selection takes place either by individuals competing genetically on an indirect basis, as Darwin postulated, or sometimes by their competing on a direct basis, as when one hunter successfully steals another’s wife or is killed in the attempt. The expected behavioral result of within-group selection is selfishness and nepotism, never altruism.
Another level at which natural selection operates is the between-group level (E. O. Wilson 1975). In this case a group of individuals is the container that determines the fate of a given set of genes. If such units are subject to variation and extinction, they too can serve as (larger) vehicles of natural selection. Such selection does not require rigidly demarcated groups, or groups that remain in existence for a very long time, or outright group extinctions (Sober and Wilson 1998). What is needed is a population that somehow is structured into variable units that tend to replace one another, and it helps if the units are not too large (Wade 1978).
For the time being we are dealing with genes rather than with psychological motives. I have defined altruistic genes in terms of levels of selection. It is between-group selection that supports them, and it bears emphasizing that most biologists concede, in theory, that selection at this level could support genuinely altruistic traits on a straightforward basis (E. O. Wilson 1975). What they deny, often quite vehemently, is that natural conditions could ever lead to between-group selection’s approaching the power of within-group selection.
Realistic possibilities for group selection were first raised by Darwin. Recent efforts, referred to above, have tried to rescue the group-selection baby from the bathwater that was thrown out after 1966. As this book is published, a very large community of evolutionary biologists, anthropologists, psychologists, and others will be deciding whether a major paradigm adjustment is in order.
Selection Mechanisms and Altruism
The inclusive-fitness/reciprocal-altruism paradigm of social biology has profoundly influenced certain anthropologists (for example, see Chagnon and Irons 1979), ethologists and behavioral ecologists (Wrangham and Peterson 1996), psychologists (Campbell 1975; Tooby and Cosmides 1992), philosophers (Sober and Wilson 1998), political scientists (Corning 1984; Masters 1989; Arnhart 1998), and economists (Bergstrom and Stark 1993; Bowles and Gintis 1998). A full list would include hundreds of names.
The vast majority of these scholars have rejected group selection as a viable level of natural selection, and this decision automatically excludes the evolution of altruistic genes in any orthodox mammalian species, including our own. However, for more than two decades David Sloan Wilson has been a “voice in the wilderness” within the community of evolutionary biologists (D. S. Wilson 1975, 1977, 1980, 1983, 1989, 1990, 1991, 1992, 1997; Wilson and Sober 1994; Sober and Wilson 1998). His heretical and increasingly persuasive campaign on behalf of multilevel selection prominently features selection between groups, and it dates all the way back to the publication of Edward O. Wilson’s Sociobiology in 1975. It is an approach that applies to a wide variety of species, including humans.
For two decades I too have been pointing to mechanical possibilities for group selection mainly in humans (Boehm 1978, 1981, 1982a, 1986, 1991a, 1996, 1997a, 1997b, 1999a, 1999b). Here I shall detail a specific hypothesis involving between-group selection and effective free-rider suppression, a hypothesis that could go far toward resolving the natural-selection paradox of altruism for our own species. I shall accomplish this task by examining further the behavior of egalitarian hunter-gatherers in whose bands our genes were selected.
The relevant selection mechanics are as follows. Fundamentally, it is the balance of power between within-group selection and between-group selection that determines whether altruistic genes can reach equilibrium in a gene pool. When people perform altruistic acts that are beneficial to the group but costly to individual reproductive success, by definition such traits will be supported by between-group selection and opposed by within-group selection. Any population structure with phenotypically variable groupings that are positioned to replace one another is capable of generating selection forces that operate at the between-group level (Wilson and Sober 1994). Nevertheless, mathematical models show that between-group selection must become powerful indeed to overcome the free-rider problem defined by Hamilton (1964).
This problem needs to be further defined for humans, for free-riding plays a crucial role in the hypotheses I am about to develop. An example will help. Let us say that in sharing zebra kills I am genetically disposed to assist unrelated members of my band, and that many band members are not close kin of mine. In terms of selection at the within-group level, my altruistic genes would be quickly eliminated because some group members, lacking this gene, will take a free ride on my altruism by eating my zebra meat but not sharing theirs. Thus, their nonaltruistic genes will be forwarded into the gene pool at a higher rate than my altruistic ones. If born free-riders regularly outcompete born altruists, in the long run altruism cannot be supported unless group selection can somehow do the job.
If extremely robust selection is taking place between groups, the situation will change for these altruistic genes. At the same time that within-group selection is whittling away at a band’s altruistic genes and free-riders are taking their toll, between-group selection will be supporting such genes because groups with many altruists can succeed better than groups with few altruists. In theory, if the between-group level of selection becomes much more robust than usual, or if the within-group level is sufficiently debilitated, altruistic genes could stand a chance of reaching fixation in spite of free-riding.
There is one other way that altruistic genes could prevail. If, somehow, free-riding behavior could be eliminated or heavily suppressed at the level of phenotype, then the force of selection taking place between groups would not need to rise to nearly so high a level for altruistic genes to be supported.
What can we actually expect with humans? At first glance, selection taking place between individuals within the group should be operating very powerfully indeed, because humans, like any other mammalian species, exhibit a high rate of genetic variation. Furthermore, as individuals with finite life cycles they “go extinct” very predictably, if at much longer intervals than most mammals. By contrast, prehistoric bands did not tend to go extinct every thirty-five years or so, unless intensive warfare, or recurrent plagues, droughts, or epidemics, or radical changes in their environments were cutting down entire bands on an extremely frequent basis. Although the relevant facts are few, this scenario is at present considered unlikely. Furthermore, groups are likely to be much less genetically variable than individuals, for groups are composed of many individuals, and averaging effects make variation between nearby groups much less than variation among individuals within those groups.
For these reasons group selection has been rejected as a basis for altruistic behaviors that involve significant reproductive costs to the donors. According to advocates of the standard paradigm, even though Paleolithic humans lived in smallish bands (Dunbar 1996) that in size were quite appropriate as group vehicles of selection, the between-group effects were simply too feeble to have had any significant effect on human nature. This supposition has been basic and widespread for all social mammals, but I propose four solid reasons why humans should be exceptions to the rule. All have to do with the fact that people in the Late Paleolithic lived in small moral communities, nomadic bands that insisted on egalitarianism as a social and political way of life.
Behaviors that Weaken Within-Group Selection
Elimination of Pronounced Dominance Hierarchies
When entire hunting bands began to form formidable, moralistically aggressive coalitions to keep their alpha-male types from dominating group life, individual variation was affected profoundly. In an orthodox primate social dominance hierarchy, the individuals at the top gain the advantage in accumulating reproductive benefits (Ellis 1995), while subordinates regularly are given short shrift. This direct competition heightens phenotypic variation among individuals. When an egalitarian band eliminates this type of power role and begins to share its large-game meat on a more or less equalized basis (Kelly 1995; Erdal and Whiten 1996; Wiessner 1996), the variation picture changes radically.
Keep in mind that Darwinian selection acts not on genotype, but on phenotype. In the final analysis, it is actual behavior that counts, not the genetic dispositions that underlie it. For most animals the disparity between the two is not large, and in their use of mathematical models to explain gene selection, social biologists properly simplify matters by assuming isomorphism. When the human moral community arose, however, public opinion and active moral sanctioning acted together to make people conform to social mores that often went against human nature (Campbell 1972, 1975; see also Boehm 1982a; Boyd and Richerson 1992).
Such conformity greatly reduced phenotypic variation among individuals, the same variation that drives natural selection taking place within groups. The potential camp bullies—individuals unusually aggressive by nature who let their hunting prowess go to their heads in a way that led to self-aggrandizement—were obliged to behave very much like everyone else. This leveling applied to acquiring spouses, to sharing meat, or to actively taking away the resources of others; all are important to reproductive success.
I must take care to say that egalitarianism did not eliminate all individual reproductive advantages within bands (Kaplan and Hill 1985; see also Fried 1967; Flanagan 1989). Far from it. But it did drive phenotypic variation to much lower levels. We can see this result if we try to imagine a hunting band in the absence of egalitarians who are continually suppressing the behavior of bullies. One need only compare the egalitarian !Kung with the despotic Kwakiutl to get the point: the presence of nobles, commoners, and slaves creates a substantial amount of phenotype variation that impacts on reproductive success. With certain literate societies, highly despotic by Vehrencamp’s ethological standard, the disparities become still greater (Betzig 1982, 1992). Egalitarians nip these tendencies in the bud.
The prehistoric result was a significant debilitation of within-group selection, a process that automatically allowed more scope for whatever between-group selection was present to support altruistic traits. I must emphasize that in the analysis so far, the behaviors we are talking about are not boosting the absolute power of between-group effects. The change is merely relative: in what amounts to a “horsepower race,” the strength of the much more powerful within-group engine is being significantly reduced, while the power of the between-group engine remains far, far weaker.
This diminution of within-group variation may have been substantial, but by itself it cannot explain the degrees of altruism and willing cooperation exhibited by our species in its forager manifestations. For such traits to evolve, some further reduction in the force of within-group selection would seem to be necessary, and also some absolute boosting of between-group effects. In addition, it would be extremely useful to have some drastic reduction of free-riding at the level of phenotype, for this diminution would all but neutralize the reproductive advantages of born cheaters as they compete with born altruists. As will be seen, the morally based “egalitarian syndrome” of Paleolithic hunter-gatherers made all of this possible (Boehm 1997b).
Consensual Decisions
Egalitarian foragers uniformly eschew strong, authoritative leadership. Yet they do not give up on making decisions at the band level. Consensus-seeking is a strong feature of all egalitarian societies (Boehm 1996) and of forager societies in particular (Mithen 1990; Knauft 1991); and consensus-seeking further reduces phenotypic variation within the group. In arriving at a consensus, foragers do not necessarily all meet in one place for discussion as tribesmen often do. They arrive at group decisions, nonetheless, because nomadic bands normally move around as units. Every adult has the right to contribute, as people in small or large groups discuss their migration options. We have seen that as consensus builds the majority is likely to pressure any dissenters to join with them.
There is nothing mandatory about forming a consensus; in an egalitarian band every family is free to go its own way. But the challenges that stimulate such discussions affect the entire group. Everyone understands that if they do not reach a consensus, they may no longer be able to function as a group. Hunter-gatherers make their group decisions principally about major migrations, a type of problem with which they cope up to a dozen times in a single year (Tanaka 1980). They have valid reasons to stay together when they move to a new camp. One is to share their large-game meat, and thereby reduce family-level variation in high-quality protein intake, or to share other foods that are subject to scarcity. Another may be to defend the resources they are exploiting against other groups. Another is simply to stay together because they are highly sociable and enjoy one another’s company.
From the standpoint of natural selection, the net effect of consensus-seeking is that phenotypic variation among individuals (or families) is reduced. Say that, as a household head, one hunter thinks it better to hunt eland than giraffe, and eland and giraffe are located in opposite directions. He goes along with the group’s strategy, migrating to where giraffe possibilities are maximized. Another hunter prefers buffalo, another zebra, but they all agree on giraffe because giraffe is preferred by the majority. At any given time, the habit of making migration decisions on a consensual basis renders every family’s basic subsistence strategy the same. This strategy can shift, obviously, if the entire band changes its mind. But the basic strategy remains uniform for a group that, if it atomized into families, would become far more variable in its behavior.
As long as the strategies are chosen unanimously, individual variation is being leveled drastically at the level of phenotype, a process that further weakens within-group selection. As a result, the relative power of between-group selection is further enhanced, which increases the mechanical possibility that altruistic genes can be maintained in the gene pool. This hypothesis must be judged in terms of relative plausibility. I know of no published data that permit a quantitative analysis of the degree to which potentially varying family strategies are being made uniform because people prefer to live and migrate as bands.
One major exception supports the rule. Several Australian desert groups, discussed by Gould (1982), live in an environment so marginal and so unpredictable that they cannot consistently stay in bands: to survive, each family needs to be ready to move expediently wherever it must, following its own basic subsistence strategy. Because these unusually harsh ecological conditions are chronic, band consensus is seldom in a position to equalize the subsistence strategies for these hard-pressed nomads. Such hunter-gatherers are exceptional, but with them the family seems to be the largest group on which natural selection is likely to operate.
I point out, parenthetically, that such families themselves are groups susceptible to between-group selection (see Sober and Wilson 1998; Smuts 1999). However, when family members help one another unselfishly, this generosity can be laid on the doorstep of nepotism, even though a group is assisted. By contrast, the genetic paradox of altruism arises unambiguously when groups contain people who are unrelated and group members help one another on a nonprecise basis. This sort of help is exactly what takes place in bands, rather than in families, so in probing the genetic-altruism paradox we properly focus our attention on bands as a test case.
Behaviors that Amplify Between-Group Selection
Consensus-seeking at the band level does more than diminish variation within groups; it also amplifies variation between groups. For example, one entire band may migrate to seek eland as its preferred prey, whereas its neighbor may unanimously opt for giraffe and move off in a different direction. In a given year, particularly in a difficult year, these varying commitments may lead to differential reproductive success for nearby groups that belong to the same breeding population. Because such groups are in a position to replace each other, between-group selection can operate.
Sometimes band decisions can be critical to reproductive success in a very immediate way (Boehm 1996, 1997b). When bands in a given area are suffering prolonged drought, they may waver, between staying to ride it out versus investing what little energy they have in migrating to an area where rainfall might be greater. Under some circumstances, they may survive either way—or suffer disaster either way. Under others, if neighboring bands make different decisions, one small group may survive while the other suffers decimation or actually perishes (for example, Mirsky 1937).
Bands facing reduced resource levels or scattered resources do not always stay together. Foragers who normally operate as groups may temporarily fission into independently acting households and follow family rather than band strategies (for example, Balikci 1970). They may be faced with seasonal resource dispersion and routinely scatter until they can be together again. Selection thereby is temporarily reduced at the between-band level. When a major migration is in order, however, it is usually the entire band that deals with where to go next. As long as nearby bands sometimes arrive at varying strategies and then enact them as entire bands, variation between bands is amplified. Selection of altruistic traits at the between-band level thus becomes far more robust than it would be if the families primarily went their own way.
It has been argued that forager bands are so unstable that they might almost be considered non-groups (Palmer et al. 1998). It is true that most families can and do move back and forth between bands, particularly if a married couple has in-laws in two different bands (Kelly 1995). It is also true that published data are lacking to demonstrate how bands are replaced and what kind of propagules (Wade 1978) might be operative. Let me emphasize that the operation of between-group selection does not require permanent, perfectly bounded groups (Wilson and Sober 1994; Sober and Wilson 1998). The porous, far from permanent bands of nomadic hunter-gatherers seem to provide effective vehicles for group selection, but I leave to others the task of using mathematical modeling to evaluate group-selection possibilities on a more technical basis. My goal here is to provide a general outline of the probable selection paths, with ethnographic data to support it.
In the preceding arguments I have made the assumption that the environments of most prehistoric foragers were usually rich enough not only to permit bands to stay together, but to allow nearby bands to make their living by following subsistence strategies that differed. Obviously, some environments drastically constrain adaptive-strategic possibilities, as with the famines endured by the Netsilik. Even in such instances it is possible that crucial differences of strategic fine-tuning (see Boehm 1978) will cause differences in reproductive success at the between-band level. In more favorable environments, the possibilities for strategic variation will obviously increase. We must keep in mind that in Paleolithic times the planet’s best environments were available to foragers whose social and adaptive patterns varied across a very wide spectrum (Kelly 1995), and that often there were a variety of adaptive strategies that might succeed in the same rich environment.
Human Manipulation of the Free-Rider Problem
Surely the combined effects I have described are far from making selection at the between-group level as robust as selection that operates at the within-group level. Were this the case, humans would be so altruistic that it would stagger the imagination. However, these cultural influences on phenotypic variation do make the two competing engines more nearly even in their ratings; therefore, the group-selection engine is in a far better position to support altruistic traits. The remaining obstacle is the theoretically formidable problem of free-riders.
“Free-riders” may be defined as individuals who were born with fewer altruistic genes than other people or perhaps carry “opportunistic genes” that help them actively to take advantage of altruists. Such individuals were cited by Williams (1966) when, in effect, he blew the mathematically ill-founded group-selection theory of Wynne-Edwards (1962) out of the water. Free-riders obviously are important figments of mathematical modeling, but for foragers living in bands, the problem of free-riders is a real-life, social problem—as we saw in a mild form with the Utku studied by Briggs. Hyperbolically, the question is, How can cheerful, altruistic cooperators, people guided by generous feelings and positive expectations about cooperation, avoid being exploited by lazy slackers and outright cheaters, or by opportunistic bullies who take advantage of situations by force? To whatever degree the cooperating altruists in a group can be successful in circumventing such losses, it becomes far, far easier to explain the natural selection of altruistic traits.
Social control (see Black 1984) has powerful effects on human behavior. Wiessner provides an excellent description of sharing among hunter-gatherers, one that includes their negative response to free-riders:
Relationships that pool risk are ideally balanced over a lifetime, if constantly controlled for cheating. For example, those who have things of value but do not give are subject to social control through gossip, ridicule or ostracism. Those who feel that they are being exploited may cease to produce for a while and force others to do their share. However, it is recognized that unpredictable events will make some people unable to reciprocate adequately even in the best of times, and, accordingly, a wide range of reciprocal ties are maintained so that people will win some times, lose other times, and break even in most. (Wiessner 1996:186) It is clear that a multiplicity of sanctions is being used for the same purpose—to curb would-be free-riders whose motives are opportunistic.
By exercising their actuarial intelligence, foragers realize that an excess of free-riding will make their generalized systems of sharing ineffective. One way they can resolve this all-too-apparent social problem is by “legislating” altruism. As moral communities, humans try to stimulate, reward, and in some areas insist on altruistic behavior from group members (Campbell 1972). These actions facilitate the expression of whatever altruistic tendencies are inherent in the species, but are present variably in individuals who are basically egoistic. At the level of socialization, foragers prosocially manipulate children’s ambivalent genetic potential for selfishness and altruism, doing so in a direction that leads to helpfulness and cooperation (Goody 1991). They also praise their best adult altruists in everyday life, even as they frown at their worst free-riders. They can do more than praise or frown, of course. If the stakes are high, they can apply stern sanctions such as ostracism (Gruter and Masters 1986). Group members faced with severe individual breaches of their altruistic ethic can turn to effective punishment (Boyd and Richerson 1982, 1991, 1992). Surely it was hunter-gatherers who did this first as the inventors of morality. To this day they continue to promote altruism—and condemn undue selfishness—in ways that are similar on every continent.
Let me illustrate with a concrete area of behavior. We have seen that foragers are famous for their sharing of large-game meat, and that they can be quite inventive in making sure that accomplishment of a large kill is all but meaningless when it comes to individual control over the meat (Lee 1979; Kelly 1996; Erdal and Whiten 1996; Wiessner 1996). As a result, the best hunters cannot easily turn proprietary feelings into an excessive share or total control, and thereby gain political power to dominate others or monopolize women.
This situation amounts to socially enforced altruism, in that the hunter is virtually obliged to relinquish his product and hand it over to the group. Earlier, a kind of scientific mythology sprang up about nomadic hunters. It saw the sharing of kills as a virtually automatic behavior accompanied by beatific feelings of camaraderie. Sometimes it probably is that. For a forager-style system of cooperative sharing to work well, though, wholehearted generosity is far from necessary. Peterson (1993) has surveyed a number of foragers and finds that often group pressure is applied quite actively to ensure that altruistic rather than selfish impulses are acted on. Among the Hazda, the process of sharing meat has even been interpreted as tolerated theft, rather than socially facilitated giving away of resources (Blurton-Jones 1984), but the analogy to chimpanzee meat-sharing may be inexact (see de Waal 1996).
It has become evident that vigilant sharing (Erdal and Whiten 1994, 1996), rather than automatic, unambivalent, totally altruistic sharing, is at the heart of the matter. This is the way people who carry the more altruistic traits protect themselves from those who are more disposed to act as free-riders. By manipulating behavior in the direction of conformity in matters of sharing and cooperation, moralistically aggressive group members not only reduce phenotypic variation at the within-group level, but do so strategically when it comes to selection possibilities for altruistic genes. They go out of their way to all but neutralize the potential advantage of those who strike them as being opportunistically exploitative, people who very likely carry free-riding genes.
I define such people broadly, to include camp bullies as well as free-loaders and cheaters. Bullying free-riders are taken care of by egalitarian sanctioning, as described in Chapter 4. Other free-riders take advantage of altruists by being lazy, by feigning injury, by selfishly wolfing down meat they have killed secretly, and so on. Such people are not necessarily bullies. Members of the band are sensitive to these deceptive opportunists too, and usually can deal with them quite effectively.
Very little reproductive effort is expended in so doing. Much of the investment involves gossiping, and as a general phenomenon gossiping brings individual reproductive benefits through rewarding social interaction (Dunbar 1994) and through exchange of information about subsistence. In terms of physical risk, stress, extra energy expended, and time subtracted from the subsistence quest, little further investment is required if active sanctioning merely involves offering criticism, engaging in ridicule, or establishing some social distance. Most social control is accomplished in this way, and the psychological stress is likely to be far greater for the deviant than for those who exert the pressure.
Band members are in a position to pursue flagrant free-riders effectively, for when it comes to cheating on a band’s cooperative system, relatively little can be hidden in such a small group. If someone begins to emerge as a serious repeat offender, people may move from covert gossiping to active sanctioning, as noted by Wiessner, Balikci, and Briggs. We saw earlier, with the socially distanced Utku family and its particularly controversial member Niqi, that one approach is simply to keep such people at arm’s length. A certain aloofness that sets up some social or spatial distance can either change the behavior of such a readily identified deviant, or at least keep down the losses due to sharing with that person by reducing the degree of social contact. In the case of more serious free-riders, it may be necessary to escalate the sanctioning to criticism, ridicule, ostracism, even expulsion from the group—or execution.
Of course, minor transgressions are rife in the flow of hunter-gatherer affairs and human affairs. Indigenously, they tend to be overlooked or, more likely, set aside for future reference. But in important matters, forager communities can be quick to unite in manipulating deviants or getting rid of them—unless they are greatly feared. Whenever resources are scarce, freeloading or cheating becomes a far more serious matter, which foragers with their well-developed actuarial acumen thoroughly understand. Few foragers have been carefully studied in situations of prolonged scarcity, aside from Turnbull’s (1972) ethnographically dubious work on the geographically and ecologically dislocated Ik. Yet the sanctions we encountered in Chapter 4 are always available, whenever the group becomes aroused enough to use them.
Foragers do tolerate some moderate free-riding, as with Niqi, but it is safe to say that such behavior tends to be observed when food is relatively abundant, and that should not be taken as the norm for hard times. Furthermore, tolerance for free-riders presumably varies with the ratio of active free-riders to altruists. Predictably, the cooperators will become less responsive to questionable requests or demands to share food as the number of freeloaders in the band increases (Boehm 1999b).
I emphasize that foragers do not insist that all hunters perform equally—not by any means. But they do expect every adult male to produce willingly according to his ability. To summarize, while the data are mostly anecdotal, foragers seem to be quite astute when it comes to calculating the costs and benefits of behaviors related to hunting and food-sharing. We may assume, therefore, that they not only recognize free-riding behavior, but are intellectually equipped to deal with it on a cost-benefit basis. If the costs become significant, mere resentment will change to active sanctioning.
Free-riders do have a powerful tool at their disposal. Among foragers there is an ethic that one should always share according to the rules when it comes to large-game kills, and also that one should accede helpfully to direct requests of others to share food of any kind (Kelly 1995). That is why the Utku for a time shared their plentiful fish heads with Niqi, even though she habitually avoided doing her share in boiling them. An overall system of this sort helps everyone over the long run, as long as not too many people take free rides—and as long as free-riding can be dealt with decisively if need be. In one instance, reported for the Netsilik by Balikci (1970), when a man left home his food cache was destroyed by the children of a family to whom he had failed to reciprocate in the past. Although we may never have a great deal of data of this type, I suggest that the average band’s tolerance for lazy free-loading or outright cheating is low enough that the reproductive burden created by these social parasites is not high.
What are the consequences for altruistic genes and their retention? Negative sanctioning of free-riding, applied strongly just when the reproductive losses of altruists would otherwise be high, powerfully enhances the natural selection of altruistic traits because the advantages of free-riding largely disappear. Indeed, if a free-rider carries things too far and his deviance leads to really serious action such as ostracism, exile, or execution, he may experience a major reproductive loss in comparison with the altruists who invested limited energy in punishing him.
As a result, much of the evolutionary biologist’s free-rider problem is resolved at the level of phenotype, on a deliberate basis, by a moral community that wants everyone to do their part. Foragers in bands are not afraid to be unresponsive to flagrantly unjustified requests for food when serious scarcity looms, and they know how to punish outrageous cheaters if they must, and punish them rather severely. By means of this actuarily sophisticated group behavior, an enormous obstacle is removed when it comes to the retention of altruistic genes by what is probably a moderate degree of between-group selection.
All the same, in a forager band not everyone is equally altruistic to everyone else all of the time. The same moral communities that are so quick to suppress opportunistic free-riding do tolerate people taking legitimate free rides (Boehm 1999b). There are always willing but far less talented hunters whose families receive virtually the same share of meat as families of proficient hunters. There are individuals who fall on hard times because they are incapacitated and are helped by nonrelatives. There are those who by bad luck have no family to support them in old age and are cared for by nonrelatives. Such problems arise randomly with respect to the behavior genes people carry, and therefore these asymmetrical donations do not affect the natural selection of altruistic or free-rider genes.
It is when people who are innately disposed to cheat or dissemble actually succeed in doing so, that within-group selection can operate decisively against the retention of altruistic genes. At the level of phenotypic consequences, hunter-gatherers seem quite adept at calculating most of the potential losses and are in a position to drastically reduce them if necessary. In doing so, they create a nearly level playing field, on which born altruists play with little genetic disadvantage relative to the born free-riders.
Adding Up the Effects
First, let us consider the division of labor between within-group and between-group selection. The former favors individualistic selfishness (egoism) and helping of kin (nepotism), and I deem it likely that selection at that level has remained by far the predominant mode of selection for egalitarian bands. This is because the egalitarian syndrome has little effect on the high extinction rates that prevail at the individual level. With variation, however, things are quite different. I judge that with egalitarians variation between groups has approached—but surely not equaled—variation within groups. Remember that we are concerned with phenotypic variation and that within-group competition has merely been debilitated, not eliminated. Male hunters are still competing for females, as partners in both marriage and adultery, and some will do better than others. Females also compete for breeding partners (see Shostak 1981). Egalitarianism does not wholly eliminate this type of competition, for occasional polygyny is prevalent (Kelly 1995), but a single alpha-bully no longer has the chance to monopolize many of the females.
On the matter of between-group selection, I have emphasized emergency decisions as contexts in which bands arrive at varying subsistence strategies, strategies that can quickly alter the relative sizes of nearby bands. Routine decisions also play their part (Boehm 1996). At the level of relative band size, group differences that emerge in the course of routinized migration patterns could add up substantially over time, but such differences are not analyzed in the ethnographic reports of which I am aware. Wherever environmental possibilities permit local variations in subsistence pattern, hunter-gatherers can be expected to probe some of the possibilities; and when their strategies vary, reproductive consequences can result. Even where environmental constraints allow a relatively narrow range of alternatives, bands are free to experiment with alternative strategies at their own peril, or to attempt migrations to different environments.
There is a further consideration. Emergency decisions that lead to more rapid evolution probably were more frequent prehistorically than with foragers we can observe today. Potentially, Pleistocene foragers were as variable in their subsistence strategies as their extant nomadic counterparts (Kelly 1995), but climatic fluctuations surely increased their need to experiment. People faced protracted and recurrent periods of stress (Potts 1996) when bands became desperate enough to improvise radically.
The general paleoanthropological view, based on precious little information, is that major climatic perturbations stimulated so-called migrations. One tends to think of large populations streaming more or less safely from cool to warm environments, a view corrected by Potts (1996). What seems more likely (Boehm 1999b) is that locally things became fraught with peril and chaotic. Faced with scarcity, our foraging actuaries began to modify their usual local migration patterns, moving in new directions that were not necessarily adaptive. The trials would have been many, and some of the errors fatal.
I suggest this scenario because the direction taken by slow-moving, glacier-driven cold fronts probably was difficult to discern most of the time, except by following migrations of prey. As a result, many bands surely perished or had to change their subsistence strategy radically because they stayed in place or moved in the wrong direction; those who moved experimentally in the right direction still had to compete with other bands that were becoming similarly stressed.
What I envisage, then, instead of a stream of people methodically moving in one direction, is a gradually moving climatic broom that swept a fortunate few before it and forced those left behind to experiment radically as they either succeeded or perished. How did such recurrent long-term periods of crisis affect interband variation? Certainly they led to greater differences of strategy as bands faced unaccustomed adaptive challenges, and therefore led to both higher variation and higher extinction rates. Selection at the between-group level became especially robust at times of extended emergency, as one band perished or was cut in half and had to grow again while another band, shrewder or in any event pursuing a different strategy, survived intact. The mechanical opportunities for selection at the between-group level (Sober and Wilson 1998) apparently were abundant at such times. Indeed, it could have been the more altruistic group members, as superior cooperators, who best survived such decimations and served as propagules to found new bands.
These are the conditions that prevailed during the Late Paleolithic. Extreme fluctuations of climate were quite frequent over the preceding million years (Potts 1996), and the past 500,000 years have seen several major oscillations between warmth and cold. The period from 128,000 to 78,000 years ago is generally considered an interglacial period, but from oxygen isotope curves Potts identifies ten radical climate reversals within that period. These shifts lasted as much as ten thousand years, with the amplitude of change being extreme, and Potts (1996:158) says, “I find it interesting … that the appearance of modern Homo sapiens and the oldest developments of symbolic activity, which are the foundation of modern culture, occurred during this span of high amplitude.”
If we assume that the egalitarian syndrome arose at the latest with Anatomically Modern Humans, there are convincing reasons to believe that between-group selection was significantly amplified during this highly unstable interglacial period. “Environmental change was expressed in different ways in different regions of the world, and each ice age or meltdown worked somewhat differently from the one before. Each major zig or zag in the isotope proxy of global change is a signal of new topographies and mosaics of vegetation never seen before. Each major shift in global climate created unfamiliar rearrangements of water, food, and other resources” (Potts 1996:159).
Rather than resulting in orderly migrations of entire populations, such conditions, I have suggested, would have mixed people around and disturbed existing territorial equilibria (Boehm 1999b). But one must resist the idea that it was just advancing cold fronts that stimulated human inventiveness and raised between-group variation. In windows of opportunity during warming cycles, people also had to experiment in the face of favorable new climates and biomes that were opening up as populations expanded. The result was further amplification of between-group selection as the strategies of some bands succeeded better than the strategies of others.
Other Possible Routes to Altruism
Pleiotropic Support of Helping Behaviors
I must mention briefly the possibility that natural selection could be helping to support altruistic behavior (that is, reproductive donations to non-kin), even in the absence of altruistic genes (Boehm 1981, 1999b; see also Simon 1990). This obviously is not a group-selection theory. The hypothesis is that genes based on kin selection could in effect be subsidizing the altruistic behavior by which nonkin are assisted. For example, an individually costly behavior that is extremely beneficial to inclusive fitness (such as intervening in the fights of one’s own offspring) is extended to nonkin with whom similar social bonds exist—even though this approach contradicts what is assumed sociobiologically about the operation of natural selection (Boehm 1981).
This type of general hypothesis is far from new (Boehm 1999b). It began with Aristotle and was mentioned by Darwin, while at the level of phenotype Eibl-Eibesfeldt (1989, 1996) and J. Q. Wilson (1993) have elaborated at length the ways that a parental type of nurturance can be extended to unrelated group members. The facts about behavior are indisputable; but a theory is badly needed to explain how natural selection could permit such an apparent misdirection of reproductive effort.
My thought is that normal methods of mathematical modeling in social biology may be getting in the way of understanding this phenomenon: specifically, consider the simplifying assumption that one gene prepares only one behavior. I believe the possibility of pleiotropy must be entertained, in the sense that a single gene can have multiple phenotypic effects. Thus, the same gene that makes for parental investment and helping of other very close kin has a second effect: it also allows nonkin, at least those with whom strong social bonds exist, to be treated generously. The further assumption is that the reproductive benefits from frequently helping close kin are so powerful that any moderate losses that may accrue from occasionally helping nonkin can be readily sustained—even though they constitute a drain on the reproductive success of the donors. I call this a pleiotropic subsidy (Boehm 1999b).
We are used to thinking about natural selection as though its winnowing capacity were all-powerful. In this instance, however, proximate mechanisms of social bonding could be generating a problem that natural selection cannot solve. By this I mean that humans bond not specifically to kin, but to individuals with whom they interact positively, for whatever reason (see Fox 1989). In a small band, the closest bonding will take place between nurturant parents and offspring, between siblings, and between other close kin who stay in close proximity because of social ties. Lesser degrees of bonding will also take place among nonkin who, because of their life circumstances, have frequent social intercourse. In a small hunting band, this applies to virtually everyone.
To summarize, the hypothesis is that natural selection cannot solve the mechanical problem of eliminating moderate degrees of reproductive generosity that extend beyond nepotism. Precisely the same genes are supporting generosity toward close kin and generosity toward nonkin, and for the individual donors these genes are producing a net reproductive benefit that is large. If this hypothesis has merit, the process involved can be seen as being independent of the group-selection arguments made above (Boehm 1999b), even though ultimately the two types of argument may be combined.
A Warfare Hypothesis
This second hypothesis does look to group selection, and it is readily combined with the previous hypotheses, based on the egalitarian syndrome (Boehm 1999b). In theory, warfare could have made a straightforward contribution to the retention of altruistic traits by upping the extinction rates between groups (Alexander and Tinkle 1968; see also Alexander 1974; E. O. Wilson 1975), and it could have done so independently of egalitarianism. But for how many generations have humans been subject to warfare?
Keeley’s (1996) careful search of the archaeological record reveals no definitive evidence of massacres before the Neolithic (see also Daly and Wilson 1988). Keeley does document pre-Mesolithic cemeteries, in which over time many people died, apparently one at a time, of wounds inflicted by weapons. The cause could have been improbably high levels of conflict within the group, or gradual group attrition due to raiding or low-level territorial conflict. Given the Wilson and Sober (1994) theory of multilevel selection, absolute or near extinction of bands would not have been necessary for lesser degrees of warfare such as small raids to raise extinction rates at the between-group level. Occasional incremental decimations, comparable to those inflicted by chimpanzees on neighboring communities (Nishida 1979; Goodall 1986), could have had significant cumulative effects. But we are left with too few data from the Late Paleolithic.
Extant hunter-gatherers do not often seem to pursue all-out, intensive warfare, even though many exhibit perimeter defense or social boundary defense (Cashdan 1983). Today hunter-gatherers frequently are socially encapsulated, and their environments have been reasonably stable over the brief time we have known them. Yet if we hark back to Potts’s (1996) description of an ever-changing Late Pleistocene environment that was alternatively dangerous and full of opportunity, environmental stimulation of territorial conflict could have been extensive if periodic.
Times of environmental stability may have created far more territorial competition than we see in most foragers today, because Paleolithic foragers had the pick of our planet’s finest habitats. Eventually, population growth was likely to have increased territorial tensions as bands were subject to crowding. During times of sharp climatic perturbation, some of which were relatively immediate in reducing the resources available to Paleolithic hunter-gatherers, the pervasive and prolonged dislocations discussed in the previous section (and also possibly straight-line migrations in pursuit of prey) could have exacerbated intergroup competition as discussed by Kelly (1995). Thus, the issue of pre-Neolithic warfare may require further consideration (see Boehm 1999b).
The term “warfare” requires careful definition in this context, for intergroup conflict varies substantially in its scale and intensity. Raiding tends to be based on selfish incentives: normally just a few raiders go out, and the fact that they cautiously take some risks is compensated by the fact that they personally enjoy the spoils. A species that is not innately altruistic could easily engage in raiding as a reproductively selfish cooperative enterprise. By contrast, intensive warfare calls for substantial altruistic sacrifices from males, because in such warfare the men are fighting for their groups: indeed, they run a high risk of losing their lives in the process (Campbell 1975).
As the egalitarian syndrome helped to reshape human nature in the direction of altruism over hundreds or thousands of generations, the probability of intensive warfare rose precisely because this risky activity is predicated on a strong capacity for patriotic self-sacrifice—and therefore on altruistic genes. Intensive warfare with genocide may not have been affecting our species much during the early development of innate altruism, but once altruistic genes had time to become well established in human gene pools it was far more likely that intergroup conflict would rise to an intensive level, with territorial displacements and massacres.
One way to explain the massacres that rather suddenly appeared in the Mesolithic-Neolithic transition (Keeley 1996) would be to suggest that the selection of altruistic patriotic genes, induced by the egalitarian syndrome, was reaching fixation at about that time. A less precise hypothesis would be that at some earlier point tendencies to patriotic altruism reached a potential that could support intensive warfare, but it took changes in environment, technology, population density, and degree of sedentary living to strongly stimulate this behavioral potential.
Thus, the warfare hypothesis has two dimensions. First, it may have been necessary for the egalitarian syndrome to work on human nature for many generations to prepare the way for highly altruistic patriotic warfare. (Selfishly oriented raiding might have contributed to this preparatory process by raising the extinction rates between groups.) Second, once intensive warfare was in place, selection at the between-group level was in a still better position to support all altruistic traits. In developing my main arguments I have set the warfare question aside. Like pleiotropic subsidies, it does deserve some consideration (Boehm 1999b) as a potentially independent factor.
This chapter proposes, and elaborates, a new genetic theory of altruism in human beings. Aside from some possible help from pleiotropic subsidies, it is based squarely on mechanisms of natural selection as these have been defined by the majority of contemporary evolutionary biologists. On the assumption that extant foragers may be used as reasonably accurate proxies for their predecessors, the analysis applies directly to the Late Paleolithic humans in whose bands many of our genes were evolved. In recreating Paleolithic band life with its egalitarian syndrome, I have taken not only extant central tendencies but certain rarer extant responses to special environmental exigencies, and I have tried to adapt them to the extremely varied conditions experienced by our predecessors in the Late Pleistocene.
My main theory of altruism does not apply wholesale to all social mammals, for it depends on moral communities that manipulate behavior according to complicated cognitive blueprints—normatively-based plans that can radically restructure social organizations and patterns of personal interaction. The selection-mechanics approach I have used may have wider application where an animal species by some other means tends to equalize individual differences within groups, or to amplify differences between groups, or somehow to police its free-riders.
In considering humans as a special case, I have focused mainly on phenotypic variation, as opposed to extinction rates. Such variation is equally important in considering how strongly selection can operate at various levels. Yet it has been little considered by evolutionary biologists, because they prefer to model variation at the level of genes (Wilson and Kniffen 1999). I have all but eschewed mathematical modeling here, to focus on ethnography as a key to the overall outline of phenotypic behavior as it affects variation. This approach makes sense when dealing with a species that, through morality, can radically manipulate its own behavior. As will be seen in the next and final chapter, the effects of the egalitarian syndrome on phenotype, and ultimately on genotype, brought formidable changes to human nature itself.