1cavalli_sforza_luigi_luca_genes_peoples_and_languages

society democratic principles have established more complex political processes, although a small number of people from the political or business world continue to control an important number of daily decisions. The hierarchical structure of society can help a transition proceed, starting with the upper echelons of power and descending to the lower ones.

On the other hand, under the fourth transmission mechanism, which we have called."concerted" (where many people transmit the same cultural trait to a Single person, usually ofthe next generation, and do so in tum with each member of it), an innovation has a very small chance of success. A Single person sympathetic to the change would first meet resistance among the allies he needs. Unless the innovation is unusually useful, or the proposer prestigious, success is unlikely.

Most cultural characteristics are transmitted by a variety of means that often conflict. This conflict is common; for instance it occurs when one learns rules of behavior at school that differ from those taught at home, or when companions at school have very different opinions from school authorities and/or the family. The consequences of these conflicts vary Significantly among individuals and particular cultural traits.

Examples of Cultural Transmission

Cultural transmission comprises education received from both family and school. It also includes all the habits and customs that are not explicitly part of one's education. Certainly, an individual acquires these through personal experience, but here again, conscious or unconscious imitation must play an important part.

.It is not easy to distinguish between relative contributions. The similarity between two friends or between two individuals with a more intimate relationship, .like a husband and wife who have lived together for a very long period of time, are partly the expreSSion of what the two have learned from each other and what may have

187

attracted them in the first place. These forces are often vel)' strong, and we sought to examine them by surveying a group of students

about similarities between husbands and wives, parents and children, and between frie~ds. We asked about forty questions, and

queried the students about themselves and their parents, as well as the parents about the students and themselves. On average, the correlations (the similarities) between husbands and wives (the students' parents) were the greatest, followed by those between parents and children, and finally between friends. The characteristics studied addressed social activities, habits, leisure activities, superstitions, beliefs, and so on.

The most interesting result of this study is that the highest correlations were shown by characteristics of two categories-religion and politics. Both show the major role played by parents, that is, by vertical cultural transmission. In the first case, children resembled their mother to a remarkable degree, both in the choice of religion in mixed marriages, and in the frequency of prayer. The choice of religion is not surprising, since a child's religion is almost always chosen by his parents, or at least by one of them, at an age when the child cannot express his own preferences. Conversions do occur, but only rarely, and later in life. That a twenty-year-old should continue to pray to God, however, does seem to imply more than familial constraint. Unfortunately our data do not indicate whether prayer continues to be an important activity throughout the life of children raised to pray. If the mother's influence prevails in the choice of religion, the father appears to exercise influence only on the regularity with which a religion is practiced, which is a social rather than a spiritual decision-and even in this case, the mother's influence is as great as the father's. Both parents appear to contribute equally to a child's political outlook.

It is always possible that some part of the Similarity between parents and children has a genetic basis. The distinction between biological and cultural transmission is not always an obvious one. For example, it was long believed that the similarity between the IQ of parents and children was entirely genetic in origin. The famous British psycholOgist Sir Cyril Burt, undoubtedly carried

188

away by enthusiasm, even stooped so low as to publish false data to "proven a genetic basis for IQ. It is thanks to the American psychologist Leon Kamin that Burt's fraud was discovered.

At the beginning of work on IQ, the French government asked Alfred Binet to develop a method for identifying children with mental handicaps in order to provide them with special schooling at an early age. But it was primarily American psychologists who tried to change Binet's IQ scores into a measure of "puren intelligence-- independent of the culture or social milieu in which the tests were conducted. This misplaced enthusiasm led to several serious social mistakes, of which not all have been corrected. The study of adopted children was decisive in showing that cultural transmission exerts a strong influence on the determination of IQ. American studies in 1980 and 1981 established that only one-third of the vari- ation in IQ among individuals was due to biological heredity. Another third can be explained by cultural transmission, while the last third appears mostly due to other unspecified, mostly random differences in personal life experience. This is a far cry from the 80 or 90 percent genetic contribution suggested by Burt and his many American colleagues. Similarly, Arthur jensen's statement that the low IQ average of African Amelicans relative to Whites is genetic was contradicted by studies of Black children adopted by Whites in England and the United States.

Theories about the role IQ plays in social stratification have also been disproved. Some researchers have claimed, without real evidence, that the difference in IQ observed between high and low social classes was genetic, because people with a high IQ automatically became part of the high soCial classes. A French study on adoptions again showed that the difference was primarily sociocultural and not genetic.

There is probably still very widespread prejudice in America concerning the low IQ of Black Americans: the majority is likely to be still convinced that it is the result of a real genetic difference and not of a strong social handicap that cannot be reversed in a short time. Contrast the enthusiastic acceptance of the book The Bell Curve and its racist message with the response to the information

189

that the average Japanese IQ is greater than that of White Americans by 11 pOints, almost as much as the average difference between White Americans and Black Americans. Then, the response was: it is clear that American high schools are very bad.

Adoption studies provide the best guarantee against the confusion ofbiological and cultural transmissions, but these studies are dif- ficult and costly, largely because there are so few subjects. The most ambitious studies use ~dentical twins who have been raised separately. But these studies are hampered by small samples and because the very early environments oftwins, pairs, and their rearing is not always independent. But other methods exist that help limit confusion between cultural and biological inheritance. For example, in the case of religiOUS or political similarities between parents and children, we used published research data comparing identical twins, fraternal twins, and regular siblings. Fraternal twins should not resemble each other more than regular siblings if biolOgical heredity were the only important factor. In the case of religiOUS or political creeds, the similarity between fraternal pairs was almost the same as for identical twins, indicating that genetics plays no (or only a vel)' small part) in this trait. Family background does have a major effect. The purely or predominantly maternal transmission ofsome religiOUS characteristics would be difficult to explain in a strictly biological way. Maternal transmission exists for biolOgical characteristics determined by the mitochondrial genome. However, it would be very surprising iftl,ese cytoplasmic organelles, which supply the cell's energy, had any effect on individual religiOUS beliefs.

We can study cultural transmission directly, instead oftaking the indirect approach of twin studies. In this way we avoid confusing biological inheritance with other mechanisms. We can question people directly for certain characteristics, and the depth of memory revealed in subjects is often surprising. In collaboration, the anthropologist Barry Hewlett and I asked African Pygmies from whom they learned certain basic knowledge essential to their life: information about hunting, gathering, preparing food, building houses, and so on. They perfectly remembered learning these things and often they even remembered the time and place where

190

they were taught particular skills. The information collected could be verified by questioning also the teachers of this knowledge. From 80 to 90 percent ofthe time, parents were responsible for the transmission. Because some of the skills were known to only one sex, teaching usually occurred via the parent of the same sex. Only for important communal activities like dancing, singing, rules for dividing food; and other characteristics of Pygmy society did members ofthe wider community participate with the parents in educating children. The contribution of other African villagers with whom Pygmies associate during parts of the year is restricted mostly to farming, which Pygmies do in a very limited way, having been exclusively hunter-gatherers until recently. The Pygmies have also learned how to make and use certain hunting weapons, like the crosshow, from villagers. This knowledge has diffused very quickly among the Pygmies. Our notes show that several Pygmies learned how to make crossbows directly from a villagel; although we also observed one instance of a Pygmy father teaching his son. A traditional society like that ofthe African Pygmies that lacks leaders and schools, and is organized in very small social groups, tends to remain independent from nearby villagers, even when those villagers try to establish control over the Pygmies. Therefore, cultural transmission tends to be vertical within both groups, with very limited horizontal exchange between them. Vertical transmission and the social pressure exerted by the group's members tend to make Pygmy society very conservative. African farmers, on the other hand, have more contact with the exterior, missionaries, for instance, and have radios and schools.

C.ritical (Receptive/Susceptible) Periods and Their Importance

Most culturally determined characteristics are more easily changed than genetic ones. Even for clear-cut genetic diseases, onset can occur very late in life, with much variation from one individual to another. Huntington's chorea can strike individuals ranging from

191

two to eighty years old, although: most cases. manifest themselves around the age of forty. But the pattern of inheritance is very strict. Some genetic diseases disappear with age, as do certain types of allergy. But in general, genetically detennined characteristics are rather stable and rarely reversible. The same is not true of cultural characteristics. We have already observed that religious conversions take place. Political affiliations also change with appreciable frequency.

Nevertheless, some cultural traits change less readily than others. Stability of celtairl behaviors may be favored by biological factors that render changes more or less likely at certain ages. In other words, there may be sensitive or critical periods in life, the phenomenon sometimes called "imprinting.»

The most obvious critical period, although inadequately studied, is undoubtedly the one governing our ability to learn a first and a second language. The first language must be acquired in the first years of life. One can learn other languages after the first, but rarely, if ever, as well; it is particularly difficult to learn proper pronunciation of a foreign language after puberty.

The time before puberty is· also a sensitive period for acquiring the incest taboo. The psychologist Edward Westermarck has suggested that the cohabitation of brothers and sisters before puberty could diminish sexual interest and explain why incest between brothers and sisters is as rare for humans as it is for other mammals. There have been notable exceptions in some ancient dynasties such as those in Egypt and Persia, where the marriage of Siblings was encouraged, but this custom quickly-disappeared. In some communities, especially in the Middle East and India, marriages between close relatives (e.g., uncle and niece, first cousins) are still frequent, but this is a different phenomenon.

Westermarck's hypothesis was tested by Arthur Wolf (1980) in Taiwan, where marriages have occurred between a boy and an adopted sister of similar age. The daughter would be adopted by the boy's parents after his birth. In a society where spouses are bought, adoption at a very young age guaranteed a lower buying price. This custom also afforded the mother the opportunity to

192

instruct the future daughter-in-law ill the art of serving he.r husband. Wolf showed that these marriages were less successful than others; they ended more often in divorce and produced fewer children on average. This result is consistent with data from Israeli kibbutzim where children are raised together in a SOlt of communal nurselY, and have little contact with their parents. These children essentially have a very large family of adoptive brothers and sisters, and very few marriages occur between children from the same kibbutz. It is harder to fall in love with someone whom you are used to seeing on the potty.

TIlere are celtainly many other Clitical peIiOds in the fonnation of human societies, about which we don't currently lmow much. Even those tllat I've just cited have not been studied in sufficient detail. I could mention just two other areas deserving further inquiry. Gianna Zei, Paola Astolfi, and Suresh Jayakar have shown that daughters of an older father tend to marry men considerably older tllan themselves. TIm may be palt of a more general phenomenon, which deselve5 to be investigated in great detail: it is likely that we llave a tendency to choose spouses who share some physical resemblance (and perllaps behavior) with our opposite-sex parents. This phenomenon could explain tlle pronounced physical resemblance obselVed among individuals of the same social group-especially obvious in the small and isolated ones. The same phenomenon broadens differences between groups.

In another investigation aided by psychologists, we studied the propensity of our Stanford students to identify with a pruticulru· region or physical habitat. Our preference for mountains, plains, seashores, lakes, big cities, or small towns is probably set at an early age. I became interested in this when I realized that I had no particular preference. The desert, countryside, or city were all the same to me, so long as the humidity was not too high. I thought this might be due to my parents' frequent changes of residence before I was four years old. In AmeIica the importance· of the environment in which one lives can be seen in the frequency with which immigrants establish themselves in areas that resemble those they have left. Our studies of Stanford students confirmed that those who

193

moved frequently during childhood had trouble identifying with a

.particular environment and adapted more easily to all environments. Our data did not allow us to determine the most sensitive age, but the study did succeed h, showing that a nomadic tendency can be culturally inherited, and that a psychological imprint received while young is difficult to erase later in life. Governments or countries with large nomadic populations (e.g., Gypsies, Bedouins, Berbers, Tuaregs, Pygmies) have difficulty changing their nomadic habits. This poses serious problems for the schooling of their children. Moreover, the freedom of nomadism is fascinating, and if that is the way in which one was raised, it must be very difficult to settle down.

Linguistic Evolution as an Example of Cultural Evolution

Amazingly, linguistic evolution has not been studied much. There is great potential for rigorous quantitative analysis, and research is not very expensive. Interest in language evolution began in the second half ofthe nineteenth century, by applying the methods of evolutionary trees to the history of language differentiation-especially the Indo-European languages. I have already mentioned that August Schleicher constructed a tree ofthis family tha,t resembled one based on a recent study. Even though the phenomenon ofborrowing words from other languages, especially from neighbors, is well established, the most studied evolutionary trees give the impression that a language changes in ways that are largely independent ofchanges taking place in other languages. This is a prerequisite for the applicability of tree analysis. We know that languages are often spread over large areas with different varieties (or dialects) developing locally. We are aware that a language changes slightly even within an individual lifetime, but knowledge of old languages is limited, making variation in time somewhat less easy to study than variation in space. Nevertheless, variation in time almost automatically implies variation in space, and the basic rules are the same for both.

194

What precisely is linguistic variation? There are several aspects. Phonological variation is easily perceived. In any European country, and even in the United States, significant differences in accent occur between north and south, east and west. With a little experience, we can .easily guess someone's native region. The pronunciation of words changes in time and space----often significantly.

Another aspect of phonological variation is the richness or poverty of sounds in differ~ntlanguages. Polynesian languages have

among the fewest sounds. They have only three vowels: a, i, and u. English is at the opposite extreme with twenty or so vowel sounds (including diphthongs), which are different from those found in all other languages, making the acquisition of English very difficult for foreigners. The speed with which vowel sounds change is particularly astonishing. To paraphrase Voltaire: if the consonants are not very useful for etymolOgical reconstruction, the vowels are completely useless.

Semantic variation is the change of word meanings. For example, the French word femme has acquired a second meaning, to include both "woman" and "wife." In Italian, the word donna (originally denved from the Latin word domina meaning "household master") means "woman," but Italians use moglie (from another Latin word, mulier) for "wife." Italian also uses femmina (from the same root asfemme in French) to mean only "woman" and not "wife."

Although grammar is the most stable part of a language, it too can change with time. In English, as in French and Italian, the normal word order in a sentence is subject (S), verb (V), and object

(0)--<>r SVO. But all eight possible word orders exist in various languages, even if SVO and SOy languages are much more common. The rarest are OVS and Osv. In the film Return ofthe Jedi, Yoda, the master ofthe Jedi, uses the OSV style: "Your father he is."

For each of these three modes of linguistic variation (phonological, semantic, and grammatical), change in space is more obvious and easier to study than change in time. We can illustrate on a geographic map the variation a word experiences by drawing a curve delimiting the areas where the word has a particular pronunciation. This curve,

195

which separates one homogeneous region from another, is called all "isogloss." By tracing the isoglosses of many words, we notice that most words display a unique pattern: the limits of pronunciation eliffer for every word. Where, then, is the region where a single and eliscrete language or elialect is spoken? The representation of languages with a tree-like monolith, where languages are differentiated from each other in a totally regular malmer without being influenced by other languages, is ollly an approximation.

Five years after Schleicher's work, in 1872, one of his students, Johannes Schmidt, emphasized the importance of local linguistic variation and proposed a theory that in some ways opposed Schleicher's. According to Schmidt, each new fonn ofa word spreads over a geographic area like the waves spreading from a rock thrown into a pond, influencing neighbOring speakers to various degrees. This metaphor is particularly apt; it sets itself apart from the model of a tree, which presents completely isolated languages. Can these two views be reconciled?

TIleories of biolOgical variation in space, developed in the middle of the twentieth century by several different mathematicians, resulted in very sinlilar models. They have the generic name of "isolation by distance" and show that genes vary randomly in geographiC space, follOwing exact rules derived from statistics and probability. TIle most Significant regularity is the relation between genetic distance (calculated from averaging a number of genes) and geographic distance. We have seen that genetic distance increases regularly (but always more slowly) as geographic distance increases, until it reaches a maximum. The shape of the theoretical and empirical CUlves is determined by two measurable variables: the mutation rate, which increases genetiC differences between two places, and the rate of genetiC exchange between neighbors due to migration, which tends to increase genetic similarity between them-so these forces are opposed, to a certain extent, and balance each other.

The same mathematical theory can be applied to linguistiC evolution: the equivalent of mutation (which produces new forms of genes, or alleles) is innovation, which in linguistics is the generation of new sound, meaning, or grammar. Migration propagates these

196