Identifying cases of social contagion using memetic isolation--论文代写范文精选

在一个微不足道的层面上,文化隔离可以定义为人类文化所包围。地理文化分离如山脉、河流等，可以允许先前同质文化的一个主要因素。另外,地理障碍可能有助于防止集成的两种文化不同的起源。下面的essay代写范文进行详述。

Abstract
A simulation is presented of a grid of connected societies of reproducing agents. These agents are capable of horizontal and vertical transmission of non-genetic cultural traits (memes). This simulation exhibits the theoretically predicted effect that horizontally transmitted memes are less likely, overall, to be encountered in geographical isolation than strictly vertically transmitted ones. Furthermore, when horizontal memes are under cultural selection, and thus behave 'contagiously', their likelihood of geographical isolation is virtually eliminated. By contrast, natural selection has far weaker effects than cultural selection in reducing geographical isolation. Thus it should be possible to identify contagious memes by an examination of their geographical distribution. The degree of geographical isolation of 17 categories of postulated cultural traits in an ethnographic data set of 863 societies is then examined, and compared with the simulations, using z-tests. Using this method, the empirical data can be sorted into four broad categories, each with a different spectrum of probabilities of mode of transmission and contagion.
Keywords:Allomeme; Axelrod's Cultural Model; Contagion; Cultural Evolution; Cultural Selection; Cultural Trait; Evolutionary Epidemiology Of Culture; Meme

Introduction
On a trivial level, cultural isolates may be defined as human cultures surrounded by rather different human cultures. Geographical separation of cultures by physical obstacles such as mountain ranges, rivers or seas can be a major factor allowing a previously homogeneous culture, perhaps of common ancestry, to drift apart into two genetically and culturally distinct groups (e.g. Gonzalez Jose et al. 2002). Alternatively, geographical obstacles may serve to prevent the integration of two cultures that are of different origin but located in close proximity, that might otherwise be expected to gradually homogenize (e.g. De Silvestri and Guglielmino 2000). 

Once achieved, cultural isolation may reinforce genetic isolation, if cultural differences can impose barriers to gene flow as effective as those of geographical obstacles (Sokal et al. 1989; Barbujani and Sokal 1990). For instance, in Bali, an Hindu culture exists in the midst of the Islamic culture that spread to the rest of the Indonesian archipelago in the Middle Ages. However, genetically, both the Balinese population and the surrounding Javanese and other Indonesian populations are descended from a common Austronesian ancestor originating possibly in Taiwan in Neolithic times (Gray and Jordan 2000). Although many aspects of Balinese and Javanese cultures are now different, the populations are still linguistically similar. By contrast, Vona et al. (1996) have shown how a southern Sardinian immigrant population is both culturally and genetically isolated from surrounding populations. These examples serve to illustrate how different aspects of culture may evolve in ways that are essentially independent.

This paper examines memetic isolation, that is the situation in which any cultural trait of a society is different to the corresponding mutually exclusive cultural trait, the 'allomeme' (Durham 1991), of any of its surrounding cultures. For each cultural trait under consideration, one may partition the totality of the world's cultures into those that are memetic isolates for that trait, and those that are not. Thus, a culture that is not sufficiently isolated to be considered a true cultural isolate, may nevertheless exhibit memetic isolation for several cultural traits.

The subject of memetic isolates is of relevance to the study of social contagion. Cavalli-Sforza and Feldman (1981) define 'horizontal transmission' as the process of cultural exchange between non-familial individuals. This contrasts with 'vertical transmission' and 'oblique transmission', which are forms of memetic interaction between related individuals. Horizontal transmission permits the sharing of culture between different societies, whereas exclusively vertical and/or oblique transmission will confine cultural traits within groups of related individuals in the same society, unless individuals migrate out of their society and become members of another. 

A strictly vertically transmitted trait will behave in a manner essentially identical to that of a gene in a haploid organism (i.e. an organism with only a single allele at each genetic locus). When a horizontal trait has more than one allomeme, and one of the allomemes has more likelihood than the others of being transmitted, the trait is said to be under 'cultural selection'. Similarly when one allomeme confers a survival or reproductive advantage on the individual exhibiting that behaviour, the trait is said to be under 'natural selection' (Cavalli-Sforza and Feldman 1981). Cultural selection, even when slight, results in the spread of a meme to fixation in the population, provided the cultural selection pressure is maintained for a sufficient time. The meme is then said to be 'contagious' (Rashevsky 1949). Gatherer (2002) provides diagrams of the dynamics of meme incidence in a single population under conditions of no selection (a 'random walk': Gatherer 2002: Fig. 2) and conditions of cultural selection (a sigmoid curve, the 'contagionist paradigm': Gatherer 2002: Fig. 1).

Classic mathematical memetic theory demonstrates that traits with more than one means of transmission have a greater tendency to homogeneity within populations, and also that horizontally transmitted traits are more likely to be spatially clustered (Cavalli-Sforza and Feldman 1973, Uyenoyama et al. 1979, reviewed by Cavalli-Sforza 1979). This theory provides the basis of part of Guglielmino et al. 's (1995) analysis of Sub-Saharan African culture. These authors examined the distribution of 47 groups of cultural traits in 277 sub-Saharan African populations, deriving correlations for their co-distribution with climate and language and also measuring their tendency to memetic isolation.（essay代写)

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