Proc. Natl. Acad. Sci. USA Vol. 92, pp. 7585-7589, August 1995 Anthropology Cultural variation in Africa: Role of mechanisms of transmission and adaptation (cultural transmission/demic diffusion/environmental adaptation/cultural diffusion) C. R. GUGLIELMINO*, C. VIGANOTt, B. HEWLETT4, AND L. L. CAVALLI-SFORZA§ *Dipartimento di Genetica e Microbiologia, Universita di Pavia and Istituto di Genetica Biochimica ed Evoluzionistica, Consiglio Nazionale delle Ricerche, 27100 Pavia, Italy; tlstituto di Analisi Numerica del Consiglio Nazionale delle Ricerche, 27100 Pavia, Italy; tDepartment of Anthropology, Washington State University, Pullman, WA 99164; and §Department of Genetics, Stanford University, Stanford, CA 94305 Contributed by L. L. Cavalli-Sforza, January 17, 1995 ABSTRACT Cultural inheritance can be considered as a Table 1. Major mechanisms of sociocultural transmission and mechanism of adaptation made possible by communication, theoretical expectation of their dynamics in ref 1 which has reached its greatest development in humans and can Type of Culture allow long-term conservation or rapid change of culturally mechanism Description change Comments transmissible traits depending on circumstances and needs. Conservativeness/flexibility is largely modulated by mecha- Vertical Parent-to-child or Unlikely Conservative nisms ofsociocultural transmission. An analysis was carried out through family and by testing the fit of three models to 47 cultural traits (classified slow in six groups) in 277African societies. Model A (demic diffusion) Group Concerted effort Very Highly is conservation over generations, as shown by correlations of pressure of many (older) slow conservative cultural traits with language, used as a measure of historical people on each connection. Model B (enviroumental adaptation) is measured by person correlation to the natural environment. Model C (cultural dif- Horizontal Person-to-person Can be Frequent route fusion) is the spread to neighbors by social contact in an (unrelated) rapid of innovation epidemic-like fashion and was tested by measuring the tightness One-to-many Teacher or leader Most Prevalent route of geographic clustering of the traits. Most traits examined, in to group rapid of innovation particular those affecting family structure and kinship, showed Mathematical treatment (1) has shown that cultural traits are highly great conservation over generations, as shown by the fit ofmodel conserved when parents transmit culture to children. Actions of A. They are most probably transmitted by family members. This parents and extended family members on children take place when is in they are young and more easily influenced. Even more conservative is agreement with the theoretical demonstration that cultural the action of a homogeneous social group (also social, political, and transmission in the family (vertical) is the most conservative one. religious groups) exercising pressure on all (usually younger) individ- Some traits show environmental effects, indicating the impor- uals one by one (e.g., during initiation). Since under these conditions tance ofadaptation to physical environment. Only a few ofthe 47 innovations have little chance of acceptance, we call these mechanisms traits showed tight geographic clustering indicating that their oftransmission "conservative." Innovations may affect an entire group spread to nearest neighbors follows model C, as is usually the through contact with unrelated individuals, which we called "horizon- case for transmission among unrelated people (called horizontal tal" transmission. They often originate from outside social groups. transmission). Their spread through teachers, powerful authority, or high-prestige individuals has been called "one-to-many" or "teacher/leader- directed" mechanisms [including that called "imposition" by Durham It is known that cultural behaviors, practices, and beliefs (2)]. (cultural traits) in human societies are variable in space and time. We are interested in the forces involved in cultural Is It Possible to Dissect, on the Basis of Synchronic Spatial conservation and change. A theoretical treatment of the Variation of Cultural Traits, the Action of the Above dynamics of conservation and change was given by Cavalli- Different Forces Affecting Cultural Evolution? Sforza and Feldman (1). Conservation is the result of trans- Appropriate data would be necessary for a satisfactory analysis mission over generations. Change involves (i) the occurrence of cultural variation in space and time. But while detailed of an innovation-usually an event sparked by an individual- diachronic data on culture seldom exist, cultural variation in often in response to a challenge caused by a new situation in space is documented by several collections of data, among the social or physical environment that is spontaneous or is due which those of Murdock's early Ethnographic Atlas (5), al- to migration and resettlement in other regions or other events; though imperfect, have been chosen for the present prelimi- (ii) transmission of the innovation to other individuals of the nary analysis. Three models of spatial cultural variation are social group, first through communication and then through first defined (Fig. 1) and then tested with a collection of acceptance, which usually is conditioned by its function (its statistical approaches to interpret the geographic distribution perceived or real adaptive value) and other factors [prestige, of cultural diversity in sub-Saharan Africa. This approach is imposition (2), etc.]; and (iii) possible transmission of the new different - from, but in a sense is complementary to, that behavioral trait over future generations. This is the least suggested by Mace and Pagel (9). It does not try to reconstruct studied part ofthe process, which is essential for understanding the history of the origins of innovations in the tree of descent; long-term conservation. Major mechanisms of cultural trans- this is sometimes a difficult proposition, given that the spread mission summarized in Table 1 have a profound influence on of a group in a new area rarely can be represented by a tree the rate of cultural change and resulting spatial variation branching without reciprocal connections. Methods to test the within and between groups (1, 3, 4). above models are described briefly below. Cultural Trait Analysis, Classification, and Correlation The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in We consider the nature and sources of variation of 47 cultural accordance with 18 U.S.C. §1734 solely to indicate this fact. traits (given in ref. 5), which are ordered in six groups (see 7585 Downloaded by guest on September 27, 2021 7586 Anthropology: Guglielmino et at Proc. Natl. Acad. Sci. USA 92 (1995) Time 7) Origin between the six groups are given. We tested the significance of correlations in contingency tables of all possible pairs of traits by means of G2 (11). We also calculated the distribution of G2 from 100 contingency tables, each obtained from resampling Genreacttlseyto| with replacement of the original data (bootstrap analysis) (12). (~~~~~ae so,>3fa Significance levels in the right upper part of Table 3 are based on the standard deviation of the distribution of bootstrapped G2 values. Since this procedure generated a lower number of significant values than the normal procedure using the x2 distribution, further analyses are referred to these more con- servative results. Table 2 summarizes the correlations signif- icant at the 5% level from Table 3. The traits within four groups-Family and Kinship, Economy, Social Stratification, and House-are correlated to each other in 67%, 79%, 67%, and 60% of trait pairs, respectively. This high correlation is expected (13). The two other trait groups (labor division by sex and various others) are less compact (24% and 7% of associ- ation within the groups, respectively). Thus, a sexual division of labor in one task is almost uncorrelated with that in another task. The "various others" group of traits shows no correlation Duk Ecological Cultural between members of the group and with traits from other dlfaulon adaptation dlfuion groups. This is expected, as this group is a collection of miscellaneous traits remaining after forming the first five groups and has no a priori internal coherence. Fewer asso- 5 1 2 3 4 5 1 2 3 4 ciations (30% on average) occur between traits of different xxx Y Y XXyY x Y XXX Y groups than within groups. Even though this occurrence is FIG. 1. Models of evolutions of a cultural trait (X) undergoing more frequent than expected (5%), it is clear that the grouping change X -- Y. (Model A) Radiation of people and the accompanying made is confirmed to be useful by this correlational analysis. spread of their cultural practices and beliefs. This model is called "demic diffusion" and is usually the result of repeated expansion due Demic Diffusion and Environmental Adaptation: to population growth and migration after local saturation (6, 7). with Similarities in cultural traits may exist even though the cultures may Correlation of Cultural Traits Language and Ecology live at great distances from one another because the two groups share a common history. In this case cultural similarities may be maintained To try to determine which cultural traits in Africa were by the two highly conservative sociocultural transmission mechanisms consequences of demic diffusion (see legend