Land inheritance establishes sibling competition for marriage and reproduction in rural Ethiopia.
Intergenerational transfer of wealth has been proposed as playing a pivotal role in the evolution of human sibling relationships. Sibling rivalry is assumed to be more marked when offspring compete for limited heritable resources, which are crucial for reproductive success (e.g., land and livestock); whereas in the absence of heritable wealth, related siblings may cooperate. To date, comparative studies undertaken to support this evolutionary assumption have been confounded by other socioecological factors, which vary across populations, e.g., food sharing and intergroup conflict. In this article we explore effects of sibling competition and cooperation for agricultural resources, marriage, and reproduction in one contemporary Ethiopian agropastoralist society. Here recent changes in land tenure policy, altering transfers of land from parents to offspring, present a unique framework to test the importance of intergenerational transfers of wealth in driving sibling competition, while controlling for socioeconomic biases. In households where land is inherited, the number of elder brothers reduces a man's agricultural productivity, marriage, and reproductive success, as resources diminish and competition increases with each additional sibling. Where land is not inherited (for males receiving land directly from the government and all females) older siblings do not have a competitive effect and in some instances may be beneficial. This study has wider implications for the evolution of human family sizes. Recent changes in wealth transfers, which have driven sibling competition, may be contributing to an increased desire for smaller family sizes.
Department of Archaeology and Anthropology, University of Bristol, Bristol BS8 1UU, United Kingdom. mhairi.gibson@bristol.ac.uk
Mhairi A
MA
Gibson
Eshetu
E
Gurmu
D000383:Agriculture; D005002:Ethiopia / Q000208:ethnology; D005260:Female; D006801:Humans; D008297:Male; D008393:Marriage / Q000208:ethnology*; D012098:Reproduction; D012424:Rural Population; D035781:Siblings / Q000208:ethnology*; D014918:Wills / Q000208:ethnology*
Proc Biol Sci. 2003 Aug 7;270 Suppl 1:S108-9
12952651
Philos Trans R Soc Lond B Biol Sci. 1998 Mar 29;353(1367):389-97
9569432
PLoS Med. 2006 Apr;3(4):e87
16464132
Behav Ecol Sociobiol. 1996 Feb;38(2):75-81
12292074
Anim Behav. 2000 Jan;59(1):1-10
10640361
Am J Hum Biol. 2008 May-Jun;20(3):325-36
18186514
Hum Nat. 2000 Jun;11(2):117-56
26193364
Demography. 2002 Feb;39(1):43-63
11852839
Proc Biol Sci. 2006 Apr 7;273(1588):835-41
16618677
Science. 2009 Oct 30;326(5953):682-8
19900925
Soc Sci Med. 2009 Jul;69(2):285-92
19505751
Proc Biol Sci. 2009 Nov 7;276(1674):3863-70
19692401
Hum Nat. 2008 Sep;19(3):263-76
26181617
J Biosoc Sci. 2007 Mar;39(2):287-300
16817989
Hum Nat. 1995 Mar;6(1):33-49
24202829
Demography. 2003 Aug;40(3):521-42
12962061
Hum Nat. 1998 Jun;9(2):119-61
26197443
Philos Trans R Soc Lond B Biol Sci. 2011 Feb 12;366(1563):333-43
21199838
Hum Nat. 1993 Mar;4(1):1-45
24214292