Scientists reveal exactly what a neanderthal human hybrid would look like

It has been over 40,000 years since the last of the Neanderthals, our ancient human cousins, disappeared from the Earth.

But from the shape of your nose to whether someone is an early riser, Neanderthal genes are still shaping many of our lives today.

Starting from around 250,000 years ago, ancient homo sapiens and Neanderthals met, lived alongside each other, and often had children together.

Now, MailOnline has asked leading paleoanthropologists to reveal what those hybrid children would have looked like.

Scientists believe that hybrid children would inherit traits from both of their parents.

That means hybrids might have a Neanderthal's long arms and short legs with the smaller skull of a Homo sapiens.

Likewise, some of the hybrid children may have had strong Neanderthal facial features but the upright posture and long legs of a modern human.

In some cases, this hybridisation process could even lead to the formation of unusual, new traits, not found in either parent.

What would a hybrid look like?

In a new research paper published this month, scientists revealed that a 5-year-old girl who lived 140,000 years ago was likely a Neanderthal-Homo sapiens hybrid.

The girl's skull had been found in the Skhul Cave on Mount Carmel, Israel, in 1929 in the earliest known human cemetery alongside seven adults, two other children, and the bones of 16 other hominins.

Originally, anthropologists classified the girl and all the bodies in the cemetery as Homo sapiens.

However, when researchers re-examined the skull with CT scanning, they found that it had a mixture of both neanderthal and homo sapiens traits.

Anne Dambricourt-Malassé, a paleoanthropologist at the French National Centre for Scientific Research and co-author of the study, told MailOnline that this girl's skeleton tells us what hybrids might have looked like.

Dr Dambricourt-Malassé says that the girl had 'a powerful neck, a little higher than Homo sapiens, her forehead was less bulging.'

The girl also showed a 'slight subnasal prognathism', meaning that her jaw would have jutted out much like the famous 'Habsburg chin'.

'Her smile showed a dental arch with the canines and incisors aligned and end-to-end, the upper and lower teeth touched,' says Dr Dambricourt-Malassé.

Her spine shows that she would have had a more upright position than a Neanderthal, who typically walked with a curved back.

However, the girl's jaw, spine, and pelvis all bear features that appear to be more Neanderthal in their origin.

Overall, the girl might not look radically different to a modern human, but there would be noticeable differences in their features.

New facial features

In addition to having a mixture of traits from both parents, some researchers believe that interbreeding might have given rise to entirely new characteristics.

In animals, hybrids often pick up new features that aren't present in either parent.

For example, hybrids between Russian and Chinese mice often have huge heads, while coyote-wolf hybrids grow strange extra teeth or unusual 'gaps' in their bones.

Likewise, Professor Israel Hershkovitz, an anthropologist from Tel Aviv University and a leading expert on human interbreeding, told MailOnline that this happens with humans as well.

Professor Hershkovitz says: 'A good example is the bony ridge above the orbits [the eye socket], which is unique to the Skhul people.'

This was 'not rounded but straight and continuous, protruding forward like a visor.'

What would a hybrid look like after multiple generations?

The so-called 'Skhul 1 Child' is extremely rare because Dr Dambricourt-Malassé and her co-authors believe she is the direct offspring of a Neanderthal and Homo sapiens.

However, most examples of interbreeding show evidence of a gradual mixing over a much longer period of time.

Professor Hershkovitz says: 'You have to distinguish between first-generation hybrid and long-running process.

In the first case, Professor Hershkovitz says the hybrid will look much like their father or mother, with a few traits from the other parent.

Hybrids formed over potentially thousands of years of inbreeding, meanwhile, will 'generally possess the shape of either the Neanderthal or Homo sapiens but will still show some traits of the other population.'

According to many researchers, this is why we find examples of hybrids that exhibit a mosaic of traits from both human species.

These hybrids would usually have some mixture of traits from both lineages.

João Zilhão, a paleoanthropologist at the University of Barcelona, told MailOnline: 'Based on the fossils we have, in some cases it was body proportions, in other cases it was the morphology of bones in the cranium, in other cases it was the shape of the mandible, in still others the shape or the tissue composition of the dentition [teeth].

One example of such a hybrid is the 'Lapedo child', whose remains were found in Portugal's Lapedo valley in 1998.

The child’s heavy limbs and stocky build resembled those of a Neanderthal, but their chin and other features were unmistakably from Homo sapiens.

Using novel dating methods, subsequent research has shown that this child probably died sometime between 27,780 and 28,550 years ago.

This was extremely unusual since Neanderthals were supposed to have died out 40,000 years ago.

That means this hybrid population was keeping Homo sapiens and Neanderthal genes alive over 10,000 years after the last 'pure' Neanderthals had vanished.

Two separate species?

According to Dr Zilhão, a co-author on the study, this shows that the two species must have been interbreeding far more frequently than most scientists were ready to consider.

Dr Zilhão says: 'All the genetically “modern” specimens from the time of contact that have been genomically sequenced have been shown to have “pure” Neandertals in their family history dating back no more than four to six generations.

'At least 45 per cent of the specifically “Neandertal” part of the Neandertals’ genome is still found among present-day humans.

'You can compute yourself what the odds are that such facts can be explained other than by interbreeding being the rule rather than the exception.'

Scientists believe that Homo sapiens and Neanderthals had two major periods of overlap and interbreeding.

The first occurred around 250,000 years ago in what is now the modern-day Levant and lasted nearly 200,000 years.

Followed by a second, shorter period of overlap of a few thousand years from about 45,000 years ago when Homo sapiens arrived in Europe.

Over that time, some scientists think that the two species became extremely interconnected.

Professor Hershkovitz believes that in the Levant, there were no 'pure' populations, only a population that looked like Neanderthals but had some Homo sapiens genes and a population that looked like Homo sapiens but retained some Neanderthal genes.

Perhaps more controversially, Dr Zilhão and a few other scientists now argue that Homo sapiens and Neanderthals were not really distinct species all along.

Dr Zilhão says: 'This shows that Neanderthals were Homo sapiens too. They were a West Eurasian variety, or race if you wish, of Homo sapiens.'