A new study by anthropologists calls into question the widely held belief that, of all the ways in which subsistence-level communities get their food, those who farm have the most children and those who forage have the least.
The invention of agriculture by prehistoric societies was associated with rapid population growth, and various previous studies have suggested that the driving factor behind this was fertility. Farming made more food energy available, those studies argued, which led to mothers having a greater number of live births. And the same assumption is often applied nowadays to communities of different subsistence types: that fertility is higher in farming populations and lower in foraging populations.
A new analysis of more than 10,000 women from 27 societies from around the globe, published in the Proceedings of the National Academy of Sciences (PNAS), has concluded that a woman’s fertility cannot be predicted solely by their subsistence type – that context matters.
The researchers delved into the data that they and other anthropologists had gathered on societies over a large geographical spread: from the Choyeros in Mexico to the Agta in the Philippines, and from the Dolgan in Siberia to the Himba in Namibia.
The data included the numbers of live births each woman had had over their reproductive years. The anthropologists had noted the subsistence types in each community: agriculturalists and horticulturalists, collectively known as farmers; fishers and hunter-gatherers, both foragers; and wage labourers and pastoralists. There were also measurements of the market integration of each community – for example, the extent to which fishers not only fed themselves but also sold some of their catch in a local market.
“Almost all contemporary subsistence-level communities, in which individuals still produce their own food, engage to some degree in the monetary economy,” said Dr Abbey Page, a biological anthropologist at 明星八卦. “By analysing individual-level data from the 10,000 women who had been studied, we were able to investigate how well farming traits, foraging traits and measures of market integration could predict a woman’s fertility – and also how much variation there was within and between each population.”
Dr Page and her colleagues – from universities including the London School of Hygiene and Tropical Medicine and the University of Zürich – discovered a large amount of individual-level variation in fertility within populations, and that this variation didn’t map on to the different subsistence types within each community. So some farmer women in Kenya’s Kipsigis were among the most fertile, but rural Polish farmers were among the least.
When looking at individuals and comparing across cultures, some correlations emerged. The researchers found moderate evidence that foragers have lower fertility, and strong evidence that farmers have higher fertility. Individuals who engage more in market activities were found to have lower fertility. However, these results were not consistent across societies. So the amount of farmed food individuals ate in Guyana’s Makushi was strongly associated with higher fertility, but no such relationship was present in the Mosuo in China.
“When we looked at the population level – looking at all members of a community collectively, rather than at individuals – societies labelled as farmers did not have higher fertility than others, while those labelled as foragers did not have lower fertility,” Dr Page said. “The strongest association was that communities which engaged more in market activities have lower fertility. However, while what individuals did – regardless of their community’s subsistence type – is predictive of fertility, its relationship is complex”.
So the researchers concluded that the classic subsistence types poorly predict fertility. Dr Page explained: “There are so many other factors that can come into play: socio-ecological contexts such as wealth, inheritance, marriage patterns, political structures, and so on, all of which have implications for fertility. This means that the broader environment, cultural norms and local dynamics play a pivotal role in fertility, even when individuals engage in similar subsistence strategies.
“All this highlights the considerable variation present in the relationship between fertility and subsistence. In other words, context matters.
“Our findings caution against oversimplifying the relationship between subsistence and fertility, and underscore the importance of context in understanding human reproductive behaviour.”
, by Abigail Page, Erik Ringer, Rebecca Sear et al., is published in the Proceedings of the National Academy of Sciences (PNAS).
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