Quirks & Quarks

Monkeys are 'naturally selecting' themselves for domestic cooperation and tranquility

Researchers found the marmosets' social development is tied to their white facial fur as part of their self-domestication process

Marmosets' social development is tied to their white facial fur as part of their self-domestication process

Professor Asif Ghazanfar led a team of scientists who determined that changing an infant marmoset monkey’s verbal development also changed a physical marker of domesticity: a patch of white fur on its forehead. (Rebecca Terrett / Lauren Kelly / Ghazanfar Lab / Princeton University)

Like humans, marmoset monkeys are social, cooperative and show physical characteristics associated with domestication. 

As humanity evolved, it's thought to be that we selected our mates to be more gentle, more patient and less spontaneously violent than our ape ancestors. 

We domesticated ourselves similar to the way we tamed animals like dogs, cows and horses to make them easier to live with than their wild relatives.

As a result, our skulls and brow ridges became smaller, males and females are more similar in size and we can now mate all year round.

When Asif Ghazanfar, a professor of neuroscience and psychology at Princeton University, learned that certain physical traits — like floppier ears in dogs and shorter horns in goats — are by-products of the domestication process, he recognized some of these features in the marmosets he had been studying.

Like domesticated horses, marmosets also develop white patches of facial fur, and males and females — that are also very similar in size — also mate all year round.

He decided to test out that link by studying the relationship between the white facial fur and the calls marmosets make to connect with other marmosets that are out of sight.

The research team discovered the size of the marmoset's white facial fur strongly correlated with how frequently they produced these contact calls.

They also drew a connection between the cells that give rise to the adrenal glands, pigment that produced white fur and their larynx that enables their contact calls. Reduced populations of these cells made the monkeys calmer, and produced the white patch of fur. 

This was the critical connection between social development, behaviour and appearance.

Ghazanfar also found a causal relationship by exposing one infant marmoset twin to more frequent parental contact calls, and the other infant less, and discovered the more vocal feedback the infant got, the faster the white patch of fur developed.

He thinks the selection pressure that led marmoset self-domestication is the same that led to ours: mothers that need a lot of help when their babies are born, resulting in more cooperative behaviour.

Produced and written by Sonya Buyting


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