SMILES were developed by ancient humans as a way to attract less-aggressive mates, according to a new study.

A team of scientists is claiming that the kindness humans can show via facial expressions was a key factor in our evolution.

2 Smiling Neanderthals may have been more likely to mate Credit: Alamy

The study was conducted by researchers from the University of Milan.

They focused on genetic samples from Neanderthals, which showed that gene mutations may have led humans to “self-select less aggressive mating partners”.

They added that this led to 'self domestication'.

This term is usually used to describe the process of wild animals adapting to life living with humans without direct selective breeding.

2 Homo sapiens are thought to have more expressive faces than the Neanderthals had Credit: PA:Press Association

Genetic data was gathered from human stem cells taken from the remains of two Neanderthals and one Denisovan.

These two groups of prehistoric ancestors lived around the same time and there is even evidence to suggest they interbred.

They are thought to have lived somewhere around 130,000 to 40,000 years ago.

The specific genes studied are known as ‘BAZ1B’, which is said to be highly influential on human facial expressions and is the gene that allows dogs to make their eyes expressive in a way wolves cannot.

Mutations in BAZ1B that are linked to parts of the brain for controlling facial expression were absent from the Neanderthal and Denisovan samples.

However, it is thought that selected breeding patterns of some Neanderthals led to the BAZ1B gene and could have contributed to Homo sapiens developing distinctively expressive faces.

The researchers concluded from this that humans were selecting mates with “I probably won’t kill you” facial expressions more commonly than their ancestors.

This then led to the prominence of the gene mutation in Homo sapiens.

They also theorised that this mating pattern led to a condition called Williams-Beuren syndrome.

Williams-Beuren syndrome causes humans to have what same people perceive as a welcoming expression with a wide mouth and a small nose.

It has long been suspected that humans developed smiles to enhance mating options but this is thought to be the study with the first evidence for the self-domestication hypothesis.

The study has been published in Science Advances.

A timeline of life on Earth The history of the planet in years... 4.6billion years ago – the origin of Earth

3.8billion years ago – first life appears on Earth

2.1billion years ago – lifeforms made up of multiple cells evolve

1.5billion years ago – eukaryotes, which are cells that contain a nucleus inside of their membranes, emerge

550million years ago – first arthropods evolve

530million years ago – first fish appear

470million years ago – first land plants appear

380million years ago – forests emerge on Earth

370million years ago – first amphibians emerge from the water onto land

320million years ago – earliest reptiles evolve

230million years ago – dinosaurs evolve

200million years ago – mammals appear

150million years ago – earliest birds evolve

130million years ago – first flowering plants

100million years ago – earliest bees

55million years ago – hares and rabbits appear

30million years ago – first cats evolve

20million years ago – great apes evolve

7million years ago –first human ancestors appear

2million years ago – Homo erectus appears

300,000 years ago – Homo sapiens evolves

50,000 years ago – Eurasia and Oceania colonised

40,000 years ago – Neandethal extinction

Prehistoric Neanderthal humans could have survived 3,000 years later than we previously thought

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