Does the Domestication Syndrome Apply to the Domestic Pig? Not Completely

Abstract

Simple SummaryAn interesting anthropological question is whether, over the last 10,000 years, humans have domesticated animals by actually selecting the tamest and least aggressive individuals. These characteristics—known as ‘domestication syndrome’—should be present from the very early stages of life of domesticated animals. Because social play is the most important ‘friendly’ contact between very young individuals, we verified whether piglets (with both domestic pig parents) were more playful and less aggressive than hybrid pups (with wild boar father and domestic pig mother). To this purpose, we investigated three litters of piglets and three litters of wild boar hybrids, all raised in northern Italy (Parva Domus farm, Cavagnolo, Torino) in the same grassland/woodland environment and under similar farming conditions. We found that piglets played more and in a ‘less chaotic’ way than wild boar hybrids, especially after the first three weeks of life but also that piglets were more aggressive than hybrids, with piglet aggression being more frequently unbalanced in favour of one individual. Thus, the domestication syndrome does not fully apply to either social play or aggression, possibly because artificial selection may have produced greater tameness of pigs towards humans than towards other pigs.The ‘domestication syndrome’ defines a suite of features that domesticated animals possess as the result of the artificial selection operated by Homo sapiens since the Neolithic. An interesting anthropological question is whether such features, including increased tameness and reduced aggression, apply to all domesticated forms. We investigated this issue in the domestic pig (Sus scrofa). We video-recorded and analysed aggression and social play (mostly play-fighting) sessions from piglets (three litters; n = 24) and wild boar hybrids (domestic pig mother x wild boar father; three litters; n = 27) from 6–50 days of age, raised in the same woodland/grassland habitat and extensive farming management (ethical farm ‘Parva Domus’, Cavagnolo, Torino). Play and aggression session structure was assessed via Asymmetry (AI; offensive/defensive pattern balance), Shannon (H′; pattern variability), and Pielou (J; pattern evenness) indices. We found that piglets played more (especially after the 20th day of life) and engaged in less variable and uniform sessions than wild boar hybrids. Compared to hybrids, piglets showed less variable but more frequent (especially when approaching weaning) and asymmetrical aggressive events. Thus, the domestication syndrome does not seem to fully apply to either social play or aggression, possibly because artificial selection has produced greater tameness of pigs towards humans than towards conspecifics.