In place of environmental determinism a new theory called environmental possibilism was expounded by Forde (1934). The followers of this school asserted that the environment does not directly cause specific cultural developments, but the presence or absence of specific environmental factors placed limits on such developments either by permitting or forbidding their occurrence. Toynbee (1955) is of the opinion that development of civilisations could be explained in terms of their response to environmental challenges. Possibilities do not ignore the influence of the physical environment, and they realize that the imprint of nature shows in many cultures. However the possibilists stressed that cultural heritage is at least as important as the physical environment in affecting human behaviour.
Most importantly, the general orientation of environmental explanation in anthropology shifted away from determinism toward possibilism in the 1920s and 1930s. Much of this shift was due to the personal influence of Franz Boas, a renowned German-American anthropologist who showed that the origin of specific cultural features and patterns was generally to be found in historical tradition rather than in environment. Boas emphasised upon specific cultural explanation which gave rise to the socalled school of “historical particularism”, a school that has often been chided for its antienvironmentalism. However, Boas did not completely ignore environment and stated that: ‘I shall always continue to consider (environmental variables) as relevant in limiting and modifying existing culture”( Harris,1968). He did consider it irrelevant to explain the origin of culture traits and that environment, plays an important role in explaining why they did occur. This belief is the hallmark of possibilism. Perhaps the most famous example of possibilistic explanation is that posited by Kroeber(1939) for the geographical distribution of maize cultivation. Kroeber gave data showing that the distribution of maize farming in aboriginal North America was restricted to climates with at least a four-month growing season, during which rainfall was sufficient and there were no killing frosts. A similar study was made by the archaeologist Waldo Wedl who proposed that on the aboriginal Great Plains the geographical boundary of farming was a function of rainfall. Farming was practiced only in areas where the mean annual rainfall was sufficiently high to assure the necessary growing season and in areas where drought was not frequent. In areas where the mean annual rainfall was high enough but in which killing droughts were frequent, mixed farming and foraging (hunting and gathering) were practiced. Finally, in areas with both frequent droughts and low average rainfall, only foragers were found.
Possibilism made significant contribution to the “culture area” concept. As early as 1896, Otis T. Mason suggested that the geographical distribution of material culture and technology is “molded” by the environment but is not caused by it. He defined 12 “ethnic” environments or culture areas based upon this assumption. Mason’s work was elaborated by Clark (1926) and Kroeber (1939). Both recognised a general correlation between culture areas and natural areas but viewed the correlation in terms of what cultural features a natural area would or would not permit. Thus farming was relevant to the eastern United States, not because of the temperature climate but because it permitted the necessary growing season. Likewise, big game hunting was permitted by the grasslands of the Great Plains, after the introduction of the horse and firearms, but was not caused by it. Finally, the limited cultural development in the Great Basin and other “marginal” areas was attributed to environmental limitations while the cultural “florescence” in the southeast United States was attributed to the absence of environmental limitations. Environment, however, could not be used to explain why one culture area was marked by patrilineal inheritance and another by matrilineal inheritance. This could only be explained by cultural history. Thus, Kroeber (1939) remarked that while it is true that cultures are rooted in nature, and can therefore never be completely understood except with reference to that piece of nature in which they occur, they are no more produced by that nature than a plant is produced or caused by the soil in which it is rooted. The immediate causes of cultural phenomena are other cultural phenomena. The culture area concept, therefore developed into a kind of compromise between determinism and the extreme diffusionists’ views of the “kulturkries” and related schools. The role of environment in cultural evolution is particularly clear in possibilists’ thought: environment places stringent limitations on the level of cultural development. Perhaps the most frequently cited example of this position is taken by the archaeologist Betty Meggers. In her 1954 paper “Environmental limitations on the Development of culture”, Meggers suggests that farming is necessary for advanced stages of cultural evolution and that areas suitability for farming is an accurate measure of its “potential” for cultural evolution. She defines four environment “types” from at least suitable for farming to the most suitable:
- 1. “Where agriculture is impossible because of temperature, aridity, soil consumption, altitude, topography, latitude, or some other natural factor which inhibits the growth or maturation of domesticated plants”.
- 2. “Where agricultural productivity is limited to a relatively low level by climate factors causing rapid depletion of soil fertility”.
- 3. “Where relatively high crop yields can be obtained indefinitely from the same plot of land with fertilization, fallowing, crop rotation, and other kinds of soil restorative measures, or in more arid regions by irrigation”.
- 4. “Where little or no specialized knowledge is required to achieve and maintain a stable level of agricultural productivity”.
These types are not to be constructed as causing cultural evolution. According to Meggers, types 3 and 4 may not reach a high level of development for cultural reasons, for example, the absence of appropriate diffusion. However, no amount of diffusion or other cultural factors can lead to advanced cultural development in a type 1 or type 2 environment. Furthermore, if an advanced culture expands into a type 1 or type 2 environment, it is deemed to failure. The most notable application of this model is in the lowland Maya, who occupied a type 2 environment, migrated into the tropical lowlands after achieving the roots of civilization elsewhere, probably in the highlands of southern Mexico and Guatemala. Reaching maturity in its new home, it suddenly surpassed the farming potential of the poor environment and collapsed.