I don't know if randyrand has any statistics to support his statement and I don't see it as very similar to polygamy but http://www.ncbi.nlm.nih.gov/pmc/article

I don't know if randyrand has any statistics to support his statement and I don't see it as very similar to polygamy but http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4182921/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4182921/ says "Although the sample sizes for parents (especially those with two or more children) at younger ages are quite small and the magnitude of the differences is not large, the pattern nevertheless suggests that MPF (multiple-partner fertility) is likely to increase as younger cohorts age." I haven't seen any better estimates of this possible trend. 59% of African American mothers with two or more children have children by different fathers (http://ns.umich.edu/new/releases/8338-many-us-women-have-children-by-more-than-one-man http://ns.umich.edu/new/releases/8338-many-us-women-have-chi...).