By Cameron Balbirnie
BBC Horizon Programme
In 1848, a strange skull was discovered on the military outpost of Gibraltar. It was undoubtedly human, but also had some of the heavy features of an ape - distinct brow ridges, and a forward projecting face.
Rebuilding the Neanderthal past
Just what was this ancient creature? And when had it lived?
As more remains were discovered one thing became clear: this creature had once lived right across Europe. The remains were named Homo neanderthalensis - or Neanderthal Man - an ancient and primitive form of human.
The archaeological evidence revealed that the earliest Neanderthals had lived in Europe about 200,000 years ago. But then, about 30,000 years ago, they disappeared - just at the time when the first "modern humans" appear in Europe.
The story is that our ancestors, those modern humans, spread out of Africa about 100,000 years ago with better brains and more sophisticated tools. As they spread into Neanderthal territory, they simply out-competed their primitive cousins.
But was Neanderthal really the brutish ape-man of legend, or an effective rival to our own species? And how exactly had he been driven to extinction?
This week's Horizon programme brings together a team of leading experts to see just what we could find out about this remarkable creature, from the bones themselves. But to begin we needed a skeleton, and no complete Neanderthal has ever been found.
However, Gary Sawyer, a reconstruction expert at the American Museum of Natural History in New York, US, realised that enough partial skeletons existed to create an entire composite skeleton from casts of the fragments.
So Sawyer combined and rebuilt broken parts to create the most complete Neanderthal the world had ever seen. Our Neanderthal stood no more than 1.6m (5ft 4in) tall, and yet he had a robust and powerful build - perfect for his ice-age environment.
But would he have really stood up to the cold better than us?
The popular image of the ice age is a period of unremitting freezing conditions.
But over nearly a million years, Europe has seen huge climate swings - warm and cold.
For much of the last 200,000 years, when Neanderthals were alive, the climate was mild, sometimes even warmer than that which we experience today. But they did also have to live through periods of intense cold.
Our body plan expert Professor Trenton Holliday, from Tulane University, US, revealed that our skeleton had comparatively short limbs and a deep, wide ribcage.
The theory is that this body plan minimises the body's surface area to retain heat, and to keep vital organs embedded deep within the body to insulate them from the cold.
Neanderthals would have had an advantage in cold conditions
To see if this would have helped Neanderthal to survive we brought anthropologist Professor Leslie Aiello, from University College London, UK, to Loughborough University to team up with Dr George Havenith, who runs a laboratory studying the way modern humans retain heat.
In an experiment, two modern humans with very different body shapes were subjected to cooling in an ice bath - one with the long limbed, athletic shape of a runner, the other with the stockier, heavily muscled body plan closer to that of a Neanderthal.
The heavily muscled person lasted longer in the ice bath, so Neanderthals would have had an advantage. His muscle would have acted as an insulator, and his deep chest did help to keep organs warm.
Even so, the advantage doesn't mean that Neanderthal could have survived the icy extremes - this was a polar wasteland and his heavily muscled body plan needed a lot of feeding: about twice as much as we need today.
The archaeological record suggests that Neanderthals lived around the edges of forests where they hunted large animals like red deer, horse, and wild cattle. The forests gave them firewood, and materials to construct shelters, and spears.
By studying Neanderthal stone spear points, Professor John Shea from Stony Brook University, New York, US, has found that the shafts of Neanderthal spears would have been thick and heavy. And if they hunted in woodland, then trying to throw these spears at animals would have been useless. So just how did Neanderthals hunt?
Professor Trenton Holliday can identify a clue in the BBC Neanderthal - he was much stronger on the right side than on the left, and his right forearm was particularly powerful, demonstrating a very powerful grip.
To see how this muscle development might have related to hunting, Professor Steve Churchill, from Duke University, US, carried out another experiment.
By fitting a metal pole with stress sensors, he could determine what force each arm was delivering when the pole was thrust into a pad. It turns out that this action could explain the muscle development identified in the skeleton.
So Neanderthal was an ambush hunter; waiting in a forest for his prey to stray close, and then attacking with a thrusting spear. Neanderthal was possibly the most carnivorous form of human ever to have lived.
What else could the skeleton tell us? Professor Ralph Holloway, from Columbia University, New York, US, is an expert on ancient brains. By taking casts of the inside of ancient skulls, he looks for details that might offer clues to the anatomy of the brain that was once inside.
His assessment of our skull was startling: 20% larger than the average size of a modern human's brain, and anatomically identical. He could tell that this Neanderthal was right-handed and that that the areas of brain responsible for complex thought were just as advanced. He should have had the ability to think like us.
But one of the ways we use our brains is very particular: we talk. This ability makes us unique in the world today, and ultimately human. So was it possible to tell if Neanderthal could have spoken?
A tiny bone in the throat, called the hyoid, offered a clue. This bone supports the soft tissue of the throat, and several groups of scientists are attempting to model that soft tissue from the bones and discover what Neanderthal might have sounded like.
Neanderthal was possibly the most carnivorous form of human ever to have lived
Professor Bob Franciscus, from Iowa University, US, is one of a multi-national group attempting to do just this. By making scans of modern humans, he can see how the soft tissue of the vocal tracts depends on the position of the hyoid bone and the anchoring sites on the skull.
Computer predictions can then be made that can determine the shape of the modern human vocal tract from bone data alone. The same equations can then be used with data from a Neanderthal skull to predict the shape of a Neanderthal vocal tract.
The Neanderthal vocal tract seems to have been shorter and wider than a modern male human, closer to that found today in modern human females. It's possible, then, that Neanderthal males had higher pitched voices than we might have expected.
Together with a big chest, mouth, and huge nasal cavity, a big, harsh, high, sound might have resulted. But, crucially, the anatomy of the vocal tract is close enough to that of modern humans to indicate that anatomically there was no reason why Neanderthal could not have produced the complex range of sounds needed for speech.
Powerful, better adapted to the cold, and perhaps just as intelligent - Neanderthal should have been invincible. So just how are we here, and why is Neanderthal extinct?
It seems that something much more random could have played a significant role. About 45,000 years ago, the climate of Europe went through a burst of very sudden switches between warm and cold conditions that would have transformed the Neanderthals' environment.
The forests on which they depended began to recede, giving way to open plains. Here, Professor John Shea believes, the Neanderthal thrusting spear and ambush strategy did not work. Neanderthals retreated with the forests, their population falling as their hunting grounds shrank.
By comparison, modern humans made lighter stone points that could be fitted on to lighter spear shafts. These could be thrown, enabling our ancestors to hunt more effectively in an open landscape.
Hunting in an open landscape also required high levels of mobility to follow migrating herds, and the agility to throw the spears themselves. So the question for our team was: how did Neanderthal stand up to our ancestors in agility?
Analysing the inner ear of a Neanderthal, Professor Fred Spoor, from UCL, has discovered clues to Neanderthal's agility.
The semi-circular canals of the inner ear provide us with our sense of balance, and by studying a range of animals, Spoor, has found a high correlation between the size of the canals and agility. Throughout human evolution, our canals seem to have increased in size as our agility has increased.
But Neanderthals have smaller canals than modern humans, and even earlier ancestors suggesting they were less agile.
Returning to the skeleton, Professor Trenton Holliday found an explanation for this - that the short limbs and wide pelvis of our Neanderthal would have resulted in less efficient locomotion than modern humans.
The energy costs in travelling would have been higher, and this would have been a serious evolutionary disadvantage.
For Neanderthal, it was an ironic end - the very body plan that had made Neanderthal so well adapted to the ice age had locked him into an evolutionary cul-de-sac.
He might have been better adapted to the cold than the first modern humans, but as the landscape changed, it was our ancestors who could take better advantage of the more open environment.
Neanderthal died and we survived to tell the tale.
Horizon is broadcast on BBC Two on Thursday, 10 February, at 2100GMT