ECOLOGICAL CONSTRAINTS ON MARRIAGE IN RURAL IRELAND

Behavioral ecological studies of cooperatively breeding birds suggest that delayed dispersal and reproduction are caused by ecological const raints on independent breeding opportunities. Here we use census data on marriage and reproduction among the 19th and 20th century rural Iri sh to determine if the ecological constraints hypothesis can be extend ed to humans and what modifications might be required. We focus specif ically on the following predictions: (1) marriage rates for farmers va ried directly with the availability of farms; (2) the incidence of cel ibacy among male heirs increased as size of farm decreased; (3) emigra tion increased as economic opportunities in rural Ireland decreased; ( 4) emigration rates were inversely related to farm size; and (5) emigr ants improved their chances for marriage by leaving Ireland. Despite i mportant differences between humans and other species, we conclude tha t the rural Irish fall within the scope of ecological constraints theo ry. Unmarried siblings who remained on the home farm potentially gaine d some indirect fitness benefits because (1) the labor of unmarried si blings probably enhanced farm wealth; and (2) heirs of wealthier farms had higher reproductive success. The latter prediction implies that i ncreased wealth, whether due to siblings or other causes, was reproduc tively valuable. (C) 1998 Elsevier Science Inc.