Look familiar? Scientists reveal what Neanderthals and Denisovans would look like TODAY if they hadn't gone extinct

For the last 40,000 years, Homo sapiens have been the only human species walking the Earth.

Our ancient ancestors died out thousands of years ago, leaving behind nothing but fossils, a few scattered artefacts, and lingering traces in our DNA.

But what if things had turned out differently?

MailOnline has asked the experts to find out what the world might look like if the Neanderthals and Denisovans hadn't gone extinct.

Surprisingly, they say that our distant evolutionary cousins might not be all that different to modern humans today.

However, they might have had a hard time fitting in with our fast-paced, highly social societies.

Dr April Noel, a palaeolithic archaeologist from the University of Victoria, told MailOnline: 'The idea that Neanderthals were hunched over, dim-witted individuals with no thought beyond their next meal is no longer tenable.

'At the same time, the idea that you could just slap a hat on a Neanderthal and you would not think twice about sitting next to him on the tube is also out the window.'

What would they look like?

Neanderthals and Denisovans are our closest ancient human relatives.

The Neanderthals emerged around 400,000 years ago when they branched off from our common ancestors.

Denisovans, meanwhile, are a far more elusive species of ancient humans who split from the Neanderthal evolutionary line around 430,000 years ago.

If they had remained as separate species rather than going extinct, Neanderthals and Denisovans might look much the same as they did in the distant past.

From the abundant fossil records, we know that Neanderthals were a little shorter than us on average, with shorter legs and wider hips.

Neanderthals were very muscular and rugged, with large bodies and even larger heads.

Their skulls show that they have room for a bigger brain than modern humans and would have been distinguished by a massive brow ridge and small foreheads.

However, experts say they still would be clearly recognisable as fellow humans.

Professor John Hawks, an anthropologist from the University of Wisconsin-Madison, told MailOnline: 'We don’t know of any physiological traits that make Neanderthals distinct, that is, traits that don’t overlap.

'Almost every physical trait in Neanderthals overlaps in its variation with ours today, at least to some extent.'

That means they wouldn't look like lumbering cavemen or women, but rather like a slightly different variation of humans.

Denisovans, meanwhile, are a little more of a mystery.

It was only this month that scientists identified the first Denisovan skull, and besides this, there are only small fragments of bone to go on.

Based on the newly identified skull, experts believe that Denisovans would have had a wide face with heavy, flat cheeks, a wide mouth, and a large nose.

These bones also show that Denisovans would have been exceptionally large and muscular people, much stronger than more slender Homo sapiens.

Not all that different

However, experts say that Homo sapiens, Denisovans, and Neanderthals might not have remained that distinct for long.

These human species interbred widely during the periods they overlapped, and many modern humans carry at least some Neanderthal and Denisovan DNA.

If these species hadn't vanished, they might have continued to interbreed and further intermix our genes.

Dr Hugo Zeberg, an expert on gene flow from Neanderthals and Denisovans into modern humans from the Karolinska Institutet in Sweden, told MailOnline: 'In a way they never went extinct. We merged!'

'Probably the relatively low amount of Neanderthal and Denisovan DNA in present humans reflects the fact that modern humans [Homo sapiens] were more numerous.

'But with more chances of encounters, we might have more archaic DNA present in the gene pool of modern humans.'

We're still learning about how ancient genes influence modern humans, so it's hard to say what effects this mixing might produce.

But Dr Zeberg points out that Denisovan genes are responsible for 'high altitude adaptation for Tibetans and some influence on lip shape in Latin American populations.'

Similarly, Neanderthal and Homo Sapiens hybrids would likely have a mixture of the traits of both species such as larger heads, longer limbs, and narrower hips.

Over time, some scientists believe Denisovans, Neanderthals and Homo Sapiens might have merged into a single human species with a mixture of all the traits.

Dr Bence Viola, a paleoanthropologist at the University of Toronto, told MailOnline: 'I think it would have been impossible for Denisovans and Neanderthals to retain sufficient genetic isolation to remain a separate population. 

'We know that they interbred with modern humans whenever they came into contact, and so the more contact there is, the more mixing happens – so they would have become a part of us.'

Would they fit in?

We don't currently know very much about how Denisovans lived, but research now shows Neanderthals might have struggled to fit in with modern society.

One of the leading theories for why Homo sapiens survived while other species dropped off is that modern humans essentially 'tamed' ourselves.

Modern humans developed genes that allowed us to become more sociable, develop larger social networks, and work with our fellow humans.

Dr Noel says: 'Unlike their modern human contemporaries, Neanderthals lived in small, fairly isolated groups.

'If there was an accident that killed a number of their hunters or some other crisis occurred, they did not always have others to reach out to. As a result, their numbers would drop below what you need to be sustainable.'

Dr Noel points out that research into Neanderthal genes suggests they were less cognitively flexible, had greater difficulties processing language, and lacked genes related to self-awareness, creativity, and behaviours intended to benefit others.

'In the highly connected world we all live in, I think Neanderthals would have been left behind, or at least, left out,' says Dr Noel.

In a world where Neanderthals lived alongside other human species, this could really change the way society was structured.

Professor Spikins says that while modern humans became 'tamer, more playful and more friendly to each other,' those changes came alongside 'being a bit easily led'.

She adds: 'If Neanderthals were better at not "following the herd" and more of those tendencies were present, I bet much of our world would be different; they might not be easily swayed by social media!'

How would the world be different?

If Neanderthals and Denisovans hadn't gone extinct thousands of years ago, the world might be a very different place.

From the evidence we have of these ancient species, we know that they lived in much smaller communities and had a far more limited impact on the land.

In fact, Dr Zeberg points out that modern humans appear to be unique in the way that we modify the world around us through agriculture and large cities.

One strange consequence of this is that a world where Homo sapiens are not dominant might mean a world without pets.

There is no evidence that Neanderthals and Denisovans attempted to nurture relationships with animals through domestication - that means no horses, cats, dogs or even modern agricultural species like cattle and sheep.

But with more of our relative anti-social genes, humanity may also have avoided some of its more destructive tendencies.

Professor Spikins says: 'If Neanderthals had been the ones to survive, we might not have the problem we have with climate change, as their tendency to be more isolated within their separate groups might have limited how technology spread and got used, and how much the environment got exploited.'