A study has suggested that had it not been for the Neanderthals the human race would not have survived or developed a strong immune system.
Research by immunologist Peter Parham suggests that interbreeding with Neanderthals gave our ancestors a ready-made cocktail of DNA invaluable in fighting diseases common in northern climates.
In some parts of the world, up to 4 percent of people's DNA comes from the short, stocky cavemen, and now new research reveals how this DNA has benefited us.
Professor Parham, of the respected Stanford University in California, focused on a family of 200-plus genes called human leukocyte antigens that are key to the workings of the immune system.
He showed that some of our HLA genes are identical to those that were found in Neanderthals.
This includes one Neanderthal immune system gene called HLA-C 0702, which is also quite common in modern European and Asian populations but absent in modern Africans.
Experts believe that modern man and Neanderthals shared a common ancestor in Africa.
Around 400,000 years ago, early Neanderthals left Africa and headed for Europe and Asia. However, our ancestors stayed behind and evolved into modern humans.
Professor Parham's results could be explained by interbreeding between the two 'tribes' passing immunity to disease developed by the Neanderthals after they'd left Africa our way.
The professor told a meeting of the Royal Society in London that this interbreeding instilled modern man with a "hybrid vigour" that allowed it to go on and populate the world.
Matt Pope, a University College London expert in Neanderthal evolution told the Sunday Times that modern man benefited from the arrangement.
"Rather than having to evolve from scratch as they moved out of Africa and into Europe and Asia, this interaction would have provided a fast-track to adapting to new environments," the Daily Mail quoted him as saying.