Have your pets inherited a cuteness gene?

Domesticated animals tend to share physical characteristics that make them look more appealing than their wild cousins. Charles Darwin puzzled over why this happened, but now scientists may have the answer. Dyani Lewis reports.

The familiar pattern of floppy ears, baby face, and patches of white fur is seen in many domesticated animals. – iStock

Ever wondered why the dog wagging its tail at your feet is so incredibly cute? Floppy ears, baby face, and patches of white fur – it’s a combination that’s hard to resist. But it's not just dogs that possess this winning suite of features, seen in domesticated animals from bunnies to cows. Charles Darwin first puzzled over this “domestication syndrome” more than 140 years ago. Now Adam Wilkins from Humboldt University in Berlin and his colleagues may have stumbled on the answer in a patch of embryonic cells that help shape an animal’s skull, colour and behaviour.

To domesticate animals breeders historically selected the tamest animals from the wild – those with less “fight-or-flight” response common to wild animals. So why did the critters end up cute as well? In the 1950s Russian fox fur breeder and geneticist Dmitri Belyaev confirmed this was no quirk by repeating thousands of years' domestication – in a few decades. Starting with wild silver foxes he bred from the tamest foxes in each generation. To his surprise he not only ended up with friendly foxes but foxes with floppy ears and patches of white in their coat.

In the July issue of the journal Genetics, Wilkins and colleagues suggest that neural crest cells could explain why these traits are linked. These multi-purpose cells form near the developing spinal cord of vertebrates. They then begin to migrate through the developing embryo seeding different types of tissue as they go. Some of those seeds give rise to the pigment-producing melanocytes that decide fur colour. Others form bone, cartilage and teeth in the skull. Yet others contribute to the adrenal gland, which releases the hormone adrenalin responsible for the fight-or-flight response.

Wilkins proposes that during domestication breeders selected variants of genes that interfere with how these cells move. Not only would such genes be likely to affect the fight-or-flight response, they would also cause changes to the animals’ appearance.

Anna Kukekova from the University of Illinois, who has also worked on the still-running Russian silver fox experiment, has some reservations. While she agrees that movement of neural crest cells could explain some of the cuteness of domestic animals she suspects these traits have come about through what’s known as “genetic linkage”. Genes located close together on a chromosome tend to be inherited together. So a gene for floppy ears could be inherited together with a gene for tameness simply because it tags along, not because there’s a single biological cause for both floppy ears and tameness as Wilkins proposes. This could also explain why these cute traits aren’t always inherited as a single package. Floppy ears and white fur patches can frequently be separated out through breeding.

The crucial next step is to test the hypothesis. Researchers can artificially tinker with how neural crest cells move and see if they reproduce the features of domestic animals. Or they could compare the cells in domestic animals and their wild counterparts. “We're throwing this idea out to the community and saying, ‘look, we think this is an interesting idea, we hope that some of you will look into it’,” says Wilkins.

According to Kukekova the final answer is likely to come from studies looking into the genomes of wild and tame species to see which genes have actually been tweaked during domestication. “When we have that we'll see if this hypothesis is correct or not.”

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