Do cells of offspring in mothers disrupt future pregnancies?

Haig, David. (2014). Interbirth intervals: intrafamilial, intragenomic, and intrasomatic conflict. Evolution, Medicine, and Public Health. doi: 10.1093/emph/eou002  

Background 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 paper 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.