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Though behavioural selection is likely at the forefront of the domestication process 7, 13, 14, understanding how domestication influences behaviours in animals represents a particular challenge, since archaeological records of behaviours do not exist. Hence, disentangling the observation of correlated traits in contemporary domesticated species from the selective processes that drove divergence from wild progenitors remains a major challenge when studying domestication.

Correlations among traits may imply a common mechanism underlying trait expression 8, or alternatively result from sequential, and not simultaneous, trait changes during domestication 12. While the mechanistic basis of the domestication syndrome remains a source of controversy 8, 10, the notion of correlated changes in traits is now embedded as a standard paradigm for studying domestication 7, 11. For example, domestication in mammalian species is commonly associated with reductions in brain size, depigmentation, increased tameness and changes in hormone and neurotransmitter levels 1, 10. Domesticated species typically display a ‘domestication syndrome’, exhibiting similar patterns of simultaneous alterations in physiology and morphology, and for animals, behaviour compared with their wild counterparts 5, 9. Domesticated species are selected to live in environments shaped and controlled by humans 2, 3, 4, often affecting the same traits across a wide range of species 5, 6, 7, 8. The domestication of plants and animals provides an ideal framework for studying evolutionary responses to selection 1. Our results suggest that suites of correlated behaviours have been temporally decoupled during dog domestication and that recent shifts in selection pressures in modern dog breeds affect the expression of domestication-related behaviours independently.

However, correlational strength varied between dog breeds representing early (ancient) and late (modern) stages of domestication, with ancient breeds exhibiting exaggerated correlations compared to modern breeds across prosocial and reactive behaviours. Consistent with the domestication syndrome hypothesis, behavioural correlations within prosocial and reactive categories demonstrated the expected direction-specificity across dogs. Here we evaluate the strength and direction of behavioural correlations among key prosocial (sociability, playfulness) and reactive (fearfulness, aggression) behaviours implicated in the domestication syndrome in 76,158 dogs representing 78 registered breeds. However, we currently lack quantitative confirmation that suites of behaviours are correlated during domestication.

Domestication is hypothesized to drive correlated responses in animal morphology, physiology and behaviour, a phenomenon known as the domestication syndrome.