Despite their varied genetic origins, domesticated animals have a lot of traits in common, and it’s not entirely clear why. But a study by Australian and Swiss researchers has added another piece to the domestication puzzle, challenging a theory that tries to account for overarching similarities between animals.
“We see many different species that are not so closely related at all, from an evolutionary perspective, that start to show similar characteristics through their intensified relationship with humans,” says Laura Wilson, a senior lecturer in biological anthropology at the Australian National University, and lead author on a paper describing the research, published in Evolution Letters.
These traits include “things like smaller brain size, curly tails, and white patches on their fur”.
“And at the same time, we also see that this relationship has produced so much variation.”
One example is the vast differences between dog breeds. “This amount of variation is much greater than what we see in their wild relatives,” says Wilson.
Over the past decade, one theory has proposed that neural crest cells – which appear very early in the development of the embryo and eventually form a range of features including bone and cartilage – have a role to play in these physical similarities.
“This hypothesis has basically become the most popular explanation,” says Wilson. “It was very appealing, but it still remains hotly debated.”
To test it, Wilson and her colleagues from the University of Zurich examined the morphology of skull samples from six different domesticated animals – dogs, pigs, goats, llama, alpaca and horses. They looked specifically for skulls from animals that were starting to become domesticated, and compared the skulls to the animals’ wild counterparts (such as wolves and boar).
This required “looking at historical specimens from different museum collections around the world, searching out those populations where we know that they’re representing this early stage of domestication”, according to Wilson.
In total, the researchers collected cranial data from 539 different animals, from collections as far afield as Argentina and Russia. The data was analysed statistically, with each domesticate compared to its wild relative. Specific attention was paid to parts of the skull that were derived from neural crest cells, compared to parts that came from another embryonic source (the mesoderm).
While they found more cranial variation in domesticated animals compared to wild ones, their data did not back the neural crest hypothesis.
“We didn’t find strong support for it,” says Wilson. “Actually, we sort of reject this idea that domestication is this one-size-fits-all evolutionary process.”
She believes their research shows that more effort should be spent studying the domestication of individual animals. “We may need to start looking at each species separately, rather than [looking at] one explanation for everything.”
And which species will be the source of Wilson’s next inquiry? People. “I’m quite interested in the idea that humans were self-domesticated,” she says.