Maternal fitness should be maximized by the optimal division of reproductive investment between offspring number and offspring quality…We used a dataset of humans spanning three generations from pre-industrial Finland to test how increases in maternal fecundity affect offspring quality and maternal fitness in contrasting socio-economic conditions. For ‘resource-poor’ landless families, but not ‘resource-rich’ landowning families, maternal fitness returns diminished with increased maternal fecundity. This was because the average offspring contribution to maternal fitness declined with increased maternal fecundity for landless but not landowning families. This decline was due to reduced offspring recruitment with increased maternal fecundity. However, in landowning families, recruited offspring fecundity increased with increased maternal fecundity. This suggests that despite decreased offspring recruitment, maternal fitness is not reduced in favourable socio-economic conditions due to an increase in subsequent offspring fecundity. These results provide evidence consistent with an offspring quantity-quality trade-off in the lifetime reproduction of humans from poor socio-economic conditions. The results also highlight the importance of measuring offspring quality across their whole lifespan to estimate reliably the fitness consequences of increased maternal fecundity.
Remember the fecund upper classes in Farewell to Alms? In any case, one thing that I have assumed is that this sort of model might explain the success of the Neolithic lifestyle despite its decreases of average quality of life. When populations first take up farming, or migrate to a new area, they are well below the Malthusian limit. In contrast resident hunter-gatherers, who aren’t as efficient at extracting productivity per unit area, would already be at their Malthusian limit. One can imagine that a Neolithic deme would rapidly expand and demographically surpass the hunter-gatherers around them. During the initial phases of expansion there would be enough land so that all farmers might be prosperous on a absolute scale. Consider the fitness, both reproductively and physiologically, of Americans on the frontier in comparison to their European ancestors. Of course, within a few generations the land would be “filled up” and a stagnant stationary state would be reached…at which point health decreases and the social pathologies characteristic of down-trodden peasantry would manifest themselves.
Labels: Evolutionary Psychology