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Proof of Evolutionary Psychology's Assumptions

Michael Shermer

My Op-Ed piece I threw out for fun has sparked some very insightful comments. One in particular, from Mark Spencer in the Department of Biological Anthropology and Anatomy at Duke University, makes a very good skeptical point regarding such speculations about the human paleolithic past. He writes:

"My question is, how do you know that this reconstruction is correct? As a human paleontologist I am very aware of the tools that are used in trying to inferthe lifeways of past humans, and I am certain that none of them allow us the kind of resolution that would be needed for the above claim. I am also certain that simple reference to the lifeways of ‘primitive’ peoples living today is unfounded, at least on the grand scale of assuming past people must have been the same. The truth is, we have very little idea what the social structure of past people was like, and we may never know.

I am not particularly opposed to your ideas - they may be right - and I fully acknowledge the important role of evolutionary theory in studies of human behavior. But, making claims about the number of people living in groups in the paleolithic, let alone the nature of their personal interactions, is really unfounded. I can’t see that this is in any way scientific, as you claim."

Precisely how a good skeptic should think. And I’m the first to admit that I could be wrong. I have tried to base my analysis on what I consider to be the best science available, mostly from anthropology, psychology, and evolutionary psychology. But if these areas turn out to be mistaken, then my analysis my go down with the ship.

I will address this question with two excerpts from two forthcoming books I have written. The first is from on on how we prove the Holocaust (or anything in the past) happened:

In August, 1996, NASA announced that it had discovered life on Mars. The evidence was the Allan Hills 84001 rock believed to have been ejected out of Mars by a meteor impact millions of years ago, which then struck the Earth. On the panel of NASA experts was paleobiologist William Schopf, a historical scientist specializing in ancient life. Schopf was skeptical of NASA’s claim because, he said, the four "lines of evidence" claimed to support the find did not converge toward a single conclusion. Instead, they pointed to several possible conclusions.

Schopf’s "lines of evidence" analysis reflects a method defined by the nineteenth-century philosopher of science, William Whewell, as a consilience of inductions. To prove a theory, Whewell believed, one must have more than one induction, or a single generalization drawn from specific facts. One must have multiple inductions that converge upon one another, independently but in conjunction. Whewell said that if these inductions "jump together" it strengthens the plausibility of a theory: "Accordingly the cases in which inductions from classes of facts altogether different have thus jumped together, belong only to the best established theories which the history of science contains. And, as I shall have occasion to refer to this particular feature in their evidence, I will take the liberty of describing it by a particular phrase; and will term it the Consilience of Inductions" (1840, 230).

We know about the past through a convergence of evidence. Cosmologists use evidence from astronomy, astrophysics, planetary geology, and physics to tell the history of the universe. Geologists reconstruct the history of the Earth through a convergence of evidence from geology and the related Earth sciences. Archeologists piece together the history of civilization using art work, written sources, and other site-specific artifacts. The historical theory of evolution is confirmed by the fact that so many independent lines of evidence converge to a single conclusion. Independent sets of data from geology, paleontology, botany, zoology, herpetology, entomology, biogeography, comparative anatomy, physiology, and many other sciences each point to the conclusion that life has evolved. This is a convergence of evidence. Creationists demand "just one fossil transitional form" that shows evolution. But evolution is not proved through a single fossil. It is proved through a convergence of fossils, and many other lines of evidence, such as DNA sequence comparisons across species. For creationists to disprove evolution they would need to unravel all these independent lines of evidence and find a rival theory that can explain them better than evolution.

In a similar way, there is an assumption by Holocaust deniers that if they can just find one tiny crack in the Holocaust structure, the entire edifice will come tumbling down. This is the fundamental flaw in their reasoning. The Holocaust is not a single event to be proved by a single fact. The Holocaust was 10,000 events in 10,000 places, and is proved by 10,000 pieces of data that converge into one conclusion. The Holocaust cannot be disproved by minor errors or inconsistencies here and there, for the simple reason that it was never proved by these lone bits of data in the first place.

>From my forthcoming book WHY PEOPLE BELIEVE IN GOD (W. H. Freeman), from a chapter entitled "THE STORY TELLING ANIMAL," this section follows a discussion on the evolution of language, from which we became story telling animals:

Paleoanthropologists believe that we evolved in small hunter-gatherer (and and possibly scavenging) communities operating out of a home base and utilizing considerable cooperation and communication. The late archeologist Glynn Isaac (1978) proffered the "home base hypothesis" from which hunting and gathering would have been conducted, with food substances brought back to a specific place where it was shared. Archaeologist Lewis Binford (1981) pushes for a "scavenging" model, where ancient hominids would have more likely taken what they could find from the remains of already hunted animals, rather than hunted themselves. (See Matt Cartmill’s 1993 A View to a Death in the Morning for an excellent summary of the hunting debate and how the various theories are influenced by cultural preferences.) Either way, anthropologist Robert Bettinger demonstrates how, compared with individuals, "groups may often be more efficient" not only "in finding and taking prey, particularly large prey," but also in coordinating the activities of individuals, who might otherwise unduly interfere with each other. Finally, as in the case of resource storage, foraging groups that pool and share resources have the effect of ‘smoothing’ the variation in daily capture rates between individuals" (1991, 158). That is, as the group grows larger, "lucky" individuals share their take with "unlucky" individuals, and everyone benefits. Cooperation would have been as powerful, if not more powerful, a drive in human evolution as competition. And communication is an essential tool of cooperation, so it makes sense that Paleolithic hunter-gatherers, as well as their modern counterparts, would have employed language to tell stories and solve problems.

How large were these communities? Most modern hunter-gatherer groups range in size from 50-400 residents, with a medium range of 100-200 people. Anthropologist Napoleon Chagnon, in his extensive studies of the Yanomamo people in the Amazon found the typical group to be roughly 100 people in size, with 40-80 living together in the rugged mountain regions, and 300-400 members living together in the largest lowland villages. He has also noted that when groups get excessively large for the carrying capacity of their local ecosystem (given their level of technology), they fission into smaller groups (1992, 80-86). Psychologist Robin Dunbar, in his compelling book Grooming, Gossip and the Evolution of Language, argues that the figure of 150 people in a typical group has a deeper evolutionary basis (1996, 61-79). The research on this subject is fascinating. It turns out that 150 is roughly the number of living descendants (wives, husbands, and children) a Paleolithic couple would produce in four generations at the birthrate of hunter-gatherer peoples—this is how many people they knew in their immediate and extended family. Archaeologists conclude that early agricultural communities in the Near East 7,000 years ago typically numbered about 150 people. Even modern farming communities, like the Hutterites in Europe (and now Dakota and Canada), average about 150 people. When the groups get larger they split into smaller groups like the Yamomamo. Why? According to the Hutterites, it is because shunning does not work as well in large groups, and shunning is a primary means of social control. Sociologists know that once groups exceed 200 people a hierarchical structure is needed to enforce the rules of cooperation and to deal with offenders, who in the smaller group could be dealt with through informal personal contracts. Still larger groups need chiefs and a police force, and rule enforcement involves more violence or the threat of violence.

So why 150 and not some other number? Remember the early 1990’s party game "six degrees of separation," based on the film of the same name? In six steps or less you can connect any person in the world to any other person in the world, including, as was the joke, Kevin Bacon. (The "six degrees of Kevin Bacon" is easy to play: one of my cycling partners, Rick Denman, was a cycling cameraman in the film American Flyers, starring Kevin Bacon—two degrees of separation. Another friend of mine, Michael Coles, ran for Congress against Newt Gingrich, who knows President Clinton, who knows Monica Lewinsky—four degrees of separation. You get the idea.) Something similar to this is actually used by sociologists to determine the social network of individuals, by having a subject send a message through a chain of connections to see how far it will go. Since this requires the subject asking a favor of their friends, the number of people in the network is limited by those whom are known fairly well. Two "small world" experiments (as these are known) in several American cities produced networks of about 135 people, close to Dunbar’s magic number 150. In the Second World War the average size company in the British Army was 130 men, in the United States Army it was 223 men. The 150 average also fits for the size of small businesses, of departments in large corporations, and of efficiently-run factories. A Church of England study, conducted in an attempt to balance the financial support provided by a large group and the intimacy of a small group, concluded that the ideal size for congregations was 200 or less. The average number of people in any given person’s address book also turns out to be about 150 people.

It would appear that 150 is the number of people each of us knows fairly well. Dunbar claims that this figure fits a ratio of primate group size to their neocortex ratio (the volume of the neocortex—evolutionarily the most recent regions of the cerebral cortex—to the rest of the brain). That is to say, extremely social primates need big brains to handle living in big groups, because there is only so much brain power to keep track of the complex relationships needed to live in relative peaceful cooperation. (Figure 9-1 shows how Dunbar arrived at his prediction of 150 based on human versus nonhuman primate neocortex ratio.) Dunbar concludes that these groupings "are a consequence of the fact that the human brain cannot sustain more than a certain number of relationships of a given strength at any one time. The figure of 150 seems to represent the maximum number of individuals with whom we can have a genuine social relationship, the kind of relationship that goes with knowing who they are and how they relate to us. Putting it another way, it’s the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar" (77).

Morality most likely evolved in these tiny bands of 100-200 people as a form of reciprocal altruism, or I’ll scratch your back if you’ll scratch mine. But as Lincoln noted, men are not angels. There are cheaters. Individuals defect from informal contracts. Reciprocal altruism, in the long run, only works when you know who will cooperate and who will defect. In these small groups cooperation is regulated through a complex feedback loop of communication between members of the community. (This also helps to explain why people in big cities can get away with being rude, inconsiderate, and uncooperative—they are anonymous and thus not subject to the normal checks and balances that come with knowing people and seeing them every day.) In order to play the game of reciprocation you need to know whose back needs scratching and who you will trust to scratch yours. This information is gathered through telling stories abou other people, better known as gossip. According to anthropologist Jerome Barkow (1992, 627-628):

If no one tells you the gossip, you are an outsider. Gossip from an anthropologist’s perspective is a means of social control, a sanction that forces one to adhere more closely to social norms than one would otherwise be inclined. Reputation is determined by gossip, and the casual conversations of others affect one’s relative standing and one’s acceptability as a mate or as a partner in social exchange. In Euro-American society, gossiping may at times be publicly disvalued and disowned, but it remains a favorite pastime, as it no doubt is in all human societies.

The etymology of the word "gossip," in fact, is enlightening. The root stems are "god" and "sib" and meant "akin or related." Its early use included "one who has contracted spiritual affinity with another," "a godfather or godmother," "a sponsor," and "applied to a woman’s female friends invited to be present at a birth" (where they would gossip). The word then mutates into talk surrounding those who are akin or related to us (Oxford English Dictionary). Not surprising, we are especially interested in gossiping about the activities of others that most effects our inclusive fitness, that is, our reproductive success, the reproductive success of our relatives, and the reciprocation of those around us. In the Bio-Cultural Evolutionary Pyramid from the previous chapter, gossip and storytelling are most common and effectual in the middle levels of the family, extended family, and community. It is here where we find our favorite subjects of gossip—sex, generosity, cheating, aggression, violence, social status and standings, births and deaths, political and religious commitments, physical and psychological health, and the various nuances of human relations, particularly friendships and alliances. Normal gossip, then, is about relatives, close friends, and those in our immediate sphere of influence in the community, plus members of the community or society that are high ranking or have high social status. Gossip is the stuff of which not only soap operas, but grand operas are made. But why, in our culture, do we gossip about total strangers, namely celebrities? The probable reason is that the mass media makes these figures so familiar to us that they seem like our relatives, friends, and members of the community. This is true even for fictional characters on television. "Who shot JR?" was a topic of much conversation in the 1980s. If we do not have Cinderella, we create one in people like Diana Spencer. Why would anyone care who Princess Diana slept with or what her status was within the Royal Family? Because our Pleistocene brains are being tricked into thinking that Princess Diana is someone we personally know and someone we should care about.

Michael Shermer

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Michael Shermer is the Publisher of Skeptic magazine and the author of Why People Believe Weird Things (1997, W. H. Freeman). His ideas on gossip, storytelling, mythmaking, and religion will be presented in his next book, Why People Believe in God.


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Ian Pitchford and Robert M. Young - Last updated: 28 May, 2005 02:29 PM

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