John W. Sheets

Explaining Biased Sex Ratios in Human Populations: A Critique of Recent Studies [and Comments and Reply]

DANIELA F. SIEFF is a graduate student in human ecology at the University of California, Davis (Davis, Calif. 956I6, U.S.A.). Born in I965, she received a B.A. from Oxford University in I987 and an M.A. in anthropology and psychology from the University of Michigan in I989. Her research interests are parental-investment strategies and the costs of children in traditional societies. She is currently engaged in a study of the interaction of womens work, polygyny, fertility, and child care among the Dotoga pastoralists of northern Tanzania. The present paper was submitted in final form 30 vi 89.

Population structure of depreciated communities: I. the 1977 genetic demographies of colonsay and Jura Islands, the Scottish Inner Hebrides

Abstract This report compares the 1977 genetic demographies of Colonsay and Jura, adjacent yet isolated islands of the Scottish Inner Hebrides. Completed family analyses demonstrated that the residents of Colonsay have higher fertility, shorter generation length, and longer female reproduction span than those of Jura. Based on oral genealogies of five to six generations, the natives of Jura had a higher inbreeding coefficient (f= 0.0044) than did those of Colonsay (f= 0.0023). Each set of natives mainly derives from small groups of “founding” ancestors. Founder effects in the populations are transitory phenomena dependent upon population decline and the periodic emigration of native families. With their small sizes, the maximum sampling errors due to random genetic drift are ±0.063 for Colonsay and ±0.059 for Jura per generation. An unusual finding was that the effective sizes of Colonsay and Jura exceed their respective breeding sizes. Today Colonsay and Jura are former geographical isolates in dissoluti...

Nonleptokurtic Marriage Distances on Colonsay and Jura

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Excessive Twinning in a Rural American Genealogy: The Demographic Pedigree

Excessive twinning in an extended family of rural Missouri concentrates in the isolated generations of 1874-1930s. Moderate inbreeding, larger sibships to older mothers, and access to local doctors may have combined to enhance this familial twinning. These biosocial factors are similar to an isolated case of excessive twinning in Scotland.

Excessive twinning in a rural American genealogy.

A family record of 1693 descendants in rural Missouri exhibits a twinning rate of 2 X 2%. Weinbergs Differential Rule estimates the level of monozygosity in this twin sample at 61-83%, unlike previous results dominated by dizygosity . These historical data cannot directly support a genetic basis for monozygosity though. Clinical studies seem the best solution to the genetics of twinning.

A triplet maternity in a reduced population with excessive twinning

In 1991 a triplet maternity of same-sex (FFF) occurred in a depopulated community of Argyll, Scotland, with a history of excessive, same-sex twinning. Due to a stillbirth and its confidentiality, the maternity was recorded as a twin birth. Using public registers may result in underestimation of rates for higher multiple conceptions and births in local districts.