Paedomorphosis: a novel explanation of physical and behavioural differences in horses?

Goodwin, D., Levine, M. and McGreevy, P. (2007) Paedomorphosis: a novel explanation of physical and behavioural differences in horses? In Proceedings of the 3rd International Equitation Science Conference. International Society for Equitation Science. p.21 .

Abstract

Breeds and types of horses are generally acknowledged but their classification often lacks scientific rigour. Paedomorphosis, the retention of juvenile morphology at maturity, is important in generating evolutionary change through domestication. When dogs are compared with their ancestral species, the wolf, paedomorphosis manifests in different breeds through their physical and behavioural traits (Goodwin et al. 1997).
The current popularity of small heads and long legs in the selection of some performance horses (van Heel et al., 2006) is strongly suggestive of paedomorphism, a process that may influence communication, play, trainability, responsiveness and socialization. These qualities can directly influence the usefulness and therefore welfare of riding horses. However, examination of paedomorphic effects associated with the domestication of horses is thwarted because their ancestral species are extinct. Nevertheless, reports of breed differences in morphology (e.g., Evans & McGreevy 2006) and behavior of horses (Lindberg et al. 1999) are available in the literature. Combined with data from faunal records of ancient horses (Levine 1999), preliminary analysis of paedomorphic effects on extant breed differences in morphology and behavior is possible.
Using morphological and behavioural data, paedomorphic trends can be investigated in a range of breeds from northern (e.g. Exmoor ponies) to southern (e.g. Arabs) regions. Breed differences in social and ingestive behavior can be recorded from observations of adults kept in single-breed groups under controlled conditions including: open field tests; interactions with familiar and unfamiliar humans and horses; access to familiar and novel forage resources. These data can be correlated with morphological data including skull morphology; head:body ratio; long bones ratios; limb length:height ratio; gut length; and skeletal biometrics. This approach facilitates investigation of any relationship between physical and behavioural differences across the breeds and allows us to move beyond the current limits of typing horses as hot-bloods, cold-bloods and warm-bloods.

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