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Domesticated animals often show the same collection of changed features when compared to their wild ancestors, an effect known as ‘domestication syndrome’.

But, over recent years, there’s been much debate among scientists about the validity of the domestication syndrome, and the mechanisms proposed to explain it.

Researchers at the Australian National University (ANU) have evaluated competing scientific explanations for what caused common changes in ancient domesticated animals.

Their findings could improve our understanding of animal domestication, and have wider implications for evolutionary theory.

The authors argue two currently popular theories give an oversimplified picture of evolutionary factors involved in animal domestication.

According to lead author and PhD researcher, Ben Gleeson , “it’s not that the idea of domestication syndrome is wrong, it’s just that we’ve had the wrong idea of how it works.”

Scientists have often assumed ‘selection for tameness’, by itself, caused traits to emerge, but according to the new study, multiple forms of selection are at play when wild animals enter domesticated environments.

”It shouldn’t be surprising that similar changes in selection would often provoke similar changes in the animals themselves, even across different species,” Mr Gleeson said.

“In fact, it would be more surprising if this didn’t happen to some extent.

“Domesticated animals usually have more reliable access to food, experience less natural competition for mating partners, and are protected from predators,” study co-author Associate Professor Laura Wilson said.

These shared changes should often lead to similar changes in metabolism and growth; would reduce wild reproductive features and behaviours; and would lead to fewer traits, like camouflage, that help wild animals avoid being eaten.

The study has implications for wider evolutionary theory because domestication syndrome sometimes appears in wild animals, most commonly among isolated sub-populations, like those living on islands.

Some scientists argue these animals have ‘self-domesticated’ suggesting the same processes occurring under domestication must also sometimes happen in the wild.

Bonobos (a relative of the chimpanzee) are a famous example of this, but there are others, like urban foxes, and island rats.

It’s also been suggested that humans themselves show evidence of domestication syndrome, so this new work may help reveal some influences affecting human evolution too.

The authors highlight four main ways in which evolutionary selection is often changed when wild animals become domesticated. These involve factors like male competition and maternal stress.

They call their new explanation of domestication syndrome the ‘reproductive disruption’ hypothesis because these four selective influences maintain important reproductive functions and behaviours in most animal species.

This research has been published in Proceedings of the Royal Society B.