Does a cave beneath Pembroke Castle hold key to fate of early Britons?
A treasure trove of prehistoric material has been found beneath Pembroke Castle. Photograph: Drew Buckley
Pembroke Castle has been a seat of power for centuries. It was the birthplace of Henry Tudor, father of Henry VIII, and is one of the country’s best preserved medieval strongholds, containing a maze of passages, tunnels and stairways, as well as a vast gatehouse tower. Scientists have discovered that the fortress has also been concealing a startling secret. A cave, known as Wogan Cavern, which lies directly underneath Pembroke Castle, has been found to contain a treasure trove of prehistoric material, including ancient bones and stone tools left behind by early Homo sapiens and possibly by Neanderthals.
These remains will provide key information about the settling of Britain in prehistoric times, say scientists, who last week began their first major excavation of the year at Wogan. Work on the site over coming years should provide answers to major puzzles about prehistoric Britain, including the end of the Neanderthals’ occupation about 40,000 years ago.
Early finds at Wogan include a wide range of fossils including mammoth, reindeer, and woolly rhino, as well as the remains of a hippopotamus, a species that last wallowed in British waters 125,000 years ago. Archaeologists have also found that much of the cavern’s floor is covered with a layer of stalagmite which has preserved the soil, bones, proteins and DNA that lie below.
“The site has got fantastic potential,” said Prof Chris Stringer of the Natural History Museum, London. “It’s the best prospect that we have got in providing fresh material that can help us find out how Neanderthals lived in Britain and learn how they were replaced by Homo sapiens.”
One of the issues that scientists are seeking to resolve is the question of whether or not Neanderthals interbred with Homo sapiens in Britain, as they did in other parts of the world. For good measure, they also want to know if the two species lived alongside each other or whether they replaced each other in successive waves. “Wogan Cavern offers us the prospect of finding material that will give us clear answers to these questions,” added Stringer.
The excavation’s leader, Dr Rob Dinnis of Aberdeen University, said: “We have already shown that preserved layers of bone, stone tools, DNA and other material going back at least 40,000 years lie underneath Pembroke Castle, while the hippopotamus remains we have found suggest we might push this back to 125,000 years. If so, this is the perfect source for studying the transition between Neanderthals and modern humans which probably occurred around 45,000 years ago in Britain.”
Over the past few decades, scientists have struggled to explore this intriguing aspect of the settlement of Britain because they have faced a critical problem that affects many major prehistoric sites in the UK. In many cases, these have been stripped of all their sediment, rocks and other materials and so cannot be studied using the armoury of modern technologies that scientists have developed in the 20th century.
“In the past, when Victorian or Edwardian archaeologists had found remains of Neanderthal or early Homo sapiens at a site, it was usually stripped clear of all the sediment and bones it contained,” said Dinnis. “Every last scrap of archaeological material was either collected or, even worse, discarded. It has made modern research at these sites very difficult.”
A classic example of this fossil cleansing is provided by Gough’s cave, in Cheddar Gorge, where the remains of several ancient humans had been dug up in Victorian times before the cavern was stripped of all its sediment. “More than 500 tonnes were cleared out in a few weeks at the end of the 19th century because the owners of the cave were interested in exposing the stalagmite formations there and so turn it into tourist attraction,” said Stringer.
“So they just walked out with wheelbarrows full of stuff and no one knows where they dumped it. It was a tragic waste of critical important material that we could still exploit today – if only we knew where it was discarded.”
Other sites which have provided evidence of ancient occupation but which were subsequently emptied out include Kents Cavern, in Devon, and Paviland Cave in Wales. However, such a fate has not afflicted Wogan Cavern, say archaeologists. In medieval times, it was walled over and used as a storeroom for Pembroke Castle. Much of its floor has since remained intact and many of the wonders that lie below have been left undisturbed, it is believed.
Such pristine preservation will leave any finds made in Wogan Cavern ripe for exploitation using the tools of modern archaeology and palaeontology. The technology of sediment DNA analysis looks especially promising. It can be used to determine if an individual once lived or worked at a site simply from the genetic material that they left behind in the sediment there.
The technique was developed several years ago by scientists based at Germany’s Max Planck Institute for Evolutionary Anthropology and has already demonstrated its striking sensitivity in a cave system known as Galería de las Estatuas, in northern Spain. Each layer of sediment in the cave system had previously been analysed and dated precisely. Then, using sediment DNA analysis, researchers found that, about 100,000 years ago, the population of Neanderthals who had been living in the cave for millennia were supplanted by a completely different group of Neanderthal people.
It is unclear why this replacement occurred but the discovery clearly demonstrates the power of modern genetic analysis which, using DNA from blood and excrement left behind by the occupants of a cave, it was possible to reveal population movements 100,000 years later. The hope for Wogan Cavern is that similar analysis will shine a light on the interplay of modern humans and Neanderthals in our prehistoric past – simply from the sediments in which they left their DNA.
“This technology means that you don’t even need to find bones,” added Dinnis. “If you can just find DNA in samples you take of an archaeological layer that has been accurately dated, then you will find out who was living there and get a picture of when the cave was occupied and, more importantly, by whom it was occupied.
“We want to know the process of the replacement of Neanderthals that played out in Britain much better than we do now. Our understanding of it in this corner of Europe is a lot worse than elsewhere. That is, in part, due to the fact that we stripped out our best sites over a century ago. The crucial point is that Wogan Cavern should give us a chance to put that right.”
Stringer agrees. “Britain was right at the western edge of the inhabited world at this time. So you are really looking at individuals struggling to survive at the margins of existence, both Neanderthals and Homo sapiens. It is a fascinating period and we want to learn a lot more about it.”