sciencetech-blog

comments

It is a mystery that has gone unsolved for more than 140 years since Charles Darwin noticed something peculiar about domesticated mammals.

But now scientists think they know why domestic species tend to have certain characteristics that accompany their tameness, such as floppier ears, patches of white fur, and more juvenile faces with smaller jaws.

Geneticists believe that a group of embryonic stem cells called the neural crest, link all these traits, which are seen in many people's pet cats and dogs.

Domestic science: Scientists think they know why domestic species tend to have certain characteristics that accompany their tameness, such as floppier ears, patches of white fur, and more juvenile faces with smaller jaws (illustrated by this spaniel) - and it's because of a group of embryonic stem cells called the neural crest

Although the experts' proposal has not yet been tested, it is the first hypothesis that connects several components of the 'domestication syndrome.'

It not only applies to mammals like dogs, foxes, pigs, horses, sheep and rabbits, but it may even explain similar changes in domesticated birds and fish, according to the study published in the journal Genetics.

'Because Darwin made his observations just as the science of genetics was beginning, the domestication syndrome is one of the oldest problems in the field. So it was tremendously exciting when we realised that the neural crest hypothesis neatly ties together this hodgepodge of traits,' said Adam Wilkins, from the Humboldt University of Berlin, who is one of the paper's authors.

Neural crest cells are formed near the developing spinal cord of early vertebrate embryos.

As the embryo matures, the cells migrate to different parts of the body and give rise to many tissue types.

Charles Darwin (pictured left) noticed tame mammals share certain characteristics and scientists have struggled to understand why they share certain characteristics ever since. Wild dogs and wolves, (pictured right) which evolved from a common ancestor of the modern dog, tend to have large jaws and erect ears

These tissues include pigment cells and parts of the skull, jaws, teeth and ears, as well as the adrenal glands, which are the centre of the 'fight-or-flight' response. Neural crest cells also indirectly affect brain development.

In the hypothesis proposed by Dr Wilkins and scientists at Harvard University and the University of Vienna, domesticated mammals may show impaired development or migration of neural crest cells compared to their wild ancestors.

'When humans bred these animals for tameness, they may have inadvertently selected those with mild neural crest deficits, resulting in smaller or slow-maturing adrenal glands. So, these animals were less fearful,' he explained.

Although the experts' proposal has not yet been tested, it is the first hypothesis that connects several components of the 'domestication syndrome'. It not only applies to mammals like dogs, foxes, pigs, horses, sheep and rabbits (pictured) but it may even explain similar changes in domesticated birds and fish

The neural crest influences more than adrenal glands. Among other effects, neural crest deficits can cause white patches of skin and fur, floppy ears, tooth anomalies, and jaw development changes, all of which are seen in the domestication syndrome.

The authors also suggest that the reduced forebrain size of most domestic mammals could be an indirect effect of neural crest changes, because a chemical signal sent by these cells is critical for proper brain development.

'This interesting idea based in developmental biology brings us closer to solving a riddle that's been with us a long time. It provides a unifying hypothesis to test and brings valuable insight into the biology of domestication,' said Mark Johnston, editor-in-chief of the journal.

Tests of the neural crest hypothesis may not be far off, as other scientists are rapidly mapping the genes that have been altered by domestication in the rat, fox, and dog. The hypothesis predicts that some of these genes will influence neural crest cell biology.

If so, experts will have a much deeper understanding of the biology underlying a significant evolutionary event, Dr Wilkins explained.

'Animal domestication was a crucial step in the development of human civilisations. Without these animals, it's hard to imagine that human societies would have thrived in the way they have,' he added.