How Humans created our Best Friends

It’s no secret that we love our fluffy friends. Studies have even shown that humans have evolved to release oxytocin (the love hormone) just from gazing into the eyes of our four-legged pals.

But have you ever wondered how we created such lovable companions? What was the process that created our best friends?

One fox, two fox, nice fox, mean fox

Since 1959, Dmitry Belyaev and his student Lyudmila Trut have been running a continuous genetic experiment. Put simply, they have been raising a population of foxes and splitting them into separate groups of friendly and mean.

“Why?” You ask.

Belyaev wanted to replicate the domestication of dogs to prove that domestication has a genetic basis. He also wanted to link the ‘tameness’ trait to other traits commonly found in domestic species but not in their wild ancestors (more on that later).

Belyaev was meticulous in ensuring that all his results were due to genetics alone. Contact with humans was kept to a minimum and the foxes were never trained. At seven months old, pups were tested for their friendliness to humans and then categorised into one of three levels of ‘tameness’.

By 1964, the fourth generation of foxes were already so friendly that they would wag their tails whenever they saw humans approach. This far exceeded researchers’ expectations and by the sixth generation a new ‘elite’ category was created to define the hyper-friendly foxes who actively sought out human attention. By the 1970's the foxes were essentially pets.

This is Zoya; her hobbies include walkies and cuddles. Image credit: Kaydewa (Wikimedia Commons)

The friendly nature of the fox population continued to grow over successive generations. Researchers also noticed that physical changes had begun occurring in the fox population, linking these foxes to other domestic animals and confirming Belyaev’s suspicions about domestication traits.

Floppy ears = Friendly dog

Floppy ears are found in almost every domesticated species, and yet in the wild this trait is only found in elephants. 

So what's the deal? Did early humans have a fetish for floppy eared pets?

No! They just liked friendly animals. 

As Belyaev's experiment showed, genes for friendliness are intrinsically linked to many other traits. This is known as domestication syndrome, the traits which just come along for the ride when we breed for tameness. These traits include floppy ears, patchy colouring and a longer juvenile period, among many others.

Floppy ears = give me pats. Image credit: Rich Herrmann (Flickr)

What do any of those traits have to do with tameness?

When Trut succeeded Belyaev and took over the experiment, she discovered that domesticated foxes have a reduced level of glucocorticoids in their blood. These are the hormones which tell cells to stop dividing and start maturing. Reduced levels of these hormones give domestic animals a longer juvenile period, increasing the time for them to bond with humans before they become mistrustful.

Why the floppy ears and patchy colours?

When we’re still in early development we have a very important cell type known as neural crest cells. One of their responsibilities is forming parts of the hypothalamic-pituitary-adrenal axis (try saying that ten times quickly). This is essentially the command-centre for our fight-or-flight response. So, by picking animals that didn’t fight, we inadvertently chose the animals with fewer neural crest cells.

Now take a guess what else these cells are responsible for? 

That’s right, they also control pigmentation and ear stiffness. Some neural crest cells develop into melanocytes, cells responsible for creating pigment colour. By reducing the amount of these cells we’ve created animals that lack colour in small patches. Other neural crest cells develop into facial cartilage, and so animals with fewer crest cells often lack the structural support to hold up their ears, hence floppy ears.

 Domesticating humans… wait what?

After the domestication syndrome was discovered, scientists started noticing some similarities between some of these traits and features in humans. Look at our faces, they don’t protrude out like the other great apes, our teeth are also much smaller. Now compare a dog to a wolf, this pattern of facial features is found across many domestic species.

The next step was to find the evidence. Scientists sequenced the DNA of domesticated animals and compared it to their wild ancestors. They found very key differences that were common in all the domesticated species. This was compared to humans and amazingly we carried similar genes.

So maybe we just made them more primate-like?

Nope. Scientists checked that too by sequencing the DNA of Neanderthals, our closest relatives, and trying to find similar genes. By doing this, they found that these 'domestication' genes were unique to humans and animals we have domesticated (and Bonobos but that’s a story for another day).

Humans: The first species we domesticated. Image credit: Locutus Borg (Wikimedia Commons)

So it seems like humans are domesticated.

But how?

The essence of domestication is that it promotes cooperative communication and pro-social behaviours. This was critical in the evolution of early Homo sapiens as it gave us an advantage over competing species by allowing us to work in teams and eventually form communities. So of course, these humans had an advantage over their less cooperative brethren in survival.

And you probably thought I was just going to tell you how we created dogs.