Timing of foetal growth spurts can explain sex ratio variation in polygynous mammals

The prediction from sex ratio theory that natural selection on sexually dim orphic mammals should favour an excess of male offspring only when mothers are in good condition, has been tested extensively but with little consiste ncy in results. Although recent studies have shown that environmental varia tions may cause some of the discrepancy, there have also been reports of co ntrasting sex ratios under similar environmental settings. Here it is sugge sted that variation in timing of environmental stress and sex-specific diff erences in foetal growth pattern in relation to maternal condition, may exp lain such seeming contradictions in sex ratio variation of polygynous mamma ls.