Haig, David2014-03-112014Haig, David. 2014. “Interbirth intervals: Intrafamilial, intragenomic and intrasomatic conflict.” Evolution, Medicine, and Public Health 2014 (1): 12-17. doi:10.1093/emph/eou002. http://dx.doi.org/10.1093/emph/eou002.2050-6201http://nrs.harvard.edu/urn-3:HUL.InstRepos:11879808Background and objectives: Interbirth intervals (IBIs) mediate a trade-off between child number and child survival. Life history theory predicts that the evolutionarily optimal IBI differs for different individuals whose fitness is affected by how closely a mother spaces her children. The objective of the article is to clarify these conflicts and explore their implications for public health. Methodology: Simple models of inclusive fitness and kin conflict address the evolution of human birth-spacing. Results:: Genes of infants generally favor longer intervals than genes of mothers, and infant genes of paternal origin generally favor longer IBIs than genes of maternal origin. Conclusions and implications: The colonization of maternal bodies by offspring cells (fetal microchimerism) raises the possibility that cells of older offspring could extend IBIs by interfering with the implantation of subsequent embryos.en-USparent–offspring conflictinterbirth intervalgenomic imprintingmicrochimerismsecondary infertilityJournal Article2014-03-1110.1093/emph/eou002