Spatial dynamics of adaptive sex ratios

According to Fisherian seu allocation theory, parents that can adjust their offspring sex ratio in response to skews in population sex ratio will maxi mize their fitness over parents lacking this ability. There is good evidenc e that adaptive sex ratio adjustment occurs in many natural populations, bu t deviations from theoretical predictions have also been observed. These an omalies may be more apparent than real. When the spatial dimension of sex r atio variation is ignored, then a mismatch between empirical data and theor etical predictions based on panmictic mating is to be expected. We illustra te this with data on human ses ratio variation in 21 preindustrial populati ons, and with a cellular automaton model built re, obey Fisherian sex alloc ation rules. The results from the model generally match with the data. When information about the ambient sea ratio is limited, then the ses allocatio n decisions may appear locally maladaptive. In general, the results indicat e that Fisher's ses-ratio theory may have greater explanatory power than pr eviously thought.