The coprolites are being dug up from the floor of caves in Israel, along with sediment containing ancient DNA from people and animals.

Traces of both Cromagnons, a race of early modern humans, and Neanderthals have been found in the caves at Mount Carmel near Haifa.

Neanderthals, which became extinct about 40,000 years ago, were not the ancestors of modern humans, but for a time they co-existed alongside our forbears.

Some scientists believe they may have interbred, and contributed to the genetic make-up of people living today. Others insist they kept apart and lived far from harmonious lives - perhaps even practising cannibalism.

By examining the coprolites and sediment samples scientists hope to see if any Cromagnon DNA contains Neanderthal sequences. If so, it would suggest that interbreeding took place.

Coprolite DNA might also provide evidence of cannibalism.

Dr Hendrik Poinar, from McMaster University in Hamilton, Ontario, who is leading the research, said: "In theory from the coprolite you're going to find the DNA of the defecator and the DNA of the consumer. Unfortunately in that kind of case it's very difficult to determine who ate who."