Are humans patrilocal or matrilocal? What determines variation in endogamy?

Global Patterns in Human Mitochodrial DNA and Y-Chromosome Variation Caused by Spatial Instabilityof the Local Cultural Processes
Vikrant Kumar, Banrida T. Langstieh, Komal V. Madhavi, Vegi M. Naidu, Hardeep Pal Singh, Silpak Biswas, Kumarasamy Thangaraj, Lalji Singh, B. Mohan Reddy

PLoS Genetics v. 2 April 2006

Synopsis: In most human societies, women traditionally move to their husband's home after marriage, and these societies are thus “patrilocal,” but in a few “matrilocal” societies, men move to their wife's home. These social customs are expected to influence the patterns of genetic variation. They should lead to a localization of male-specific Y-chromosomal variants and wide dispersal of female-specific mitochondrial DNA variants in patrilocal societies and vice versa in matrilocal societies. These predicted patterns have indeed been observed in previous studies of populations from Thailand. Indian societies, however, are endogamous, so marriage should always take place within a population, and these different patterns of genetic variation should not build up. The authors have now analyzed ten patrilocal and five matrilocal Indian populations, and find that there is indeed little difference between the patrilocal and matrilocal societies. The authors therefore conclude that patterns of genetic variation in humans are not universal, but depend on local cultural practices.

The authors assume that most human societies are patrilocal, but it seems that the jury is still out on this topic. See papers by Mark Shriver, Frank Marlowe, Wilder (cited in this paper).
Endogamy is quite strict in the Indian groups examined in this study. An equally important issue arises, namely, what determines variation in endogamy?