This latitudinal span shows diversity in subsistence modes across time and space, ranging from Andean agro-pastoralists in the north to Patagonian hunter-gatherers in the south.
In the industrialized world, few of us live in a subsistence mode, so shadow work is ubiquitous: shopping, paying bills, housework.
In 16 samples, the subsistence mode could not be reliably inferred because of a lack of information on the precise ethnic origin or ethnic composition of the sample (e.g. Iranians, Emirati, Nicaraguans, etc).
Significant genetic structure was also detected with a classification according to subsistence strategy, but under this categorization criterion and for each of the three datasets, the ΦCT index is lower than the ΦSC index, thereby meaning that more differentiation is found among populations in groups with matching subsistence mode than between those groups, even if only slightly more so.
Among the 110 samples included in the correlation analysis of NAT2 polymorphism with subsistence mode, 37 include less than 30 individuals and many of these samples belong, unfortunately, to the hunter-gatherer or pastoralist categories.
Multi-factor ANOVAs further showed that no significant interaction between subsistence mode and ecoregion explained the observed differences in predicted mean slow acetylation frequency (Additional file 15: Table S5).
The specific pattern of NAT2 haplotype frequencies in Northeast Asian populations can hardly be explained by a distinctive subsistence mode since these populations share, with those of Europe and many other parts of Asia, the same mode based primarily on agriculture.
Actually, crossing the information on subsistence mode with that on biome suggests higher slow acetylation in agricultural and hunter-gatherer populations living in the seasonally dry zones (Sahel, Savanna) than in those living in the humid tropical and equatorial zones.
Moreover, ecoregion and subsistence mode were shown to be independently associated with differences in mean predicted slow acetylation frequency by multi-factor ANOVAs, as no significant interaction between these two factors (categorization groups) was found.
First, in our analysis, there is no spatial clustering of samples sharing a same subsistence mode (Figure S1): the populations are widely distributed throughout the world, making unlikely that the greater similarity in acetylation profiles between populations with a same subsistence strategy can arise from greater gene flow between them due to shorter geographic distances.
