a contemporary religion. There are other hypotheses and theories. According to a team of British researchers led by Mike Parker Pearson of the University of Sheffield, Stonehenge may have been built as a symbol of "peace and unity", indicated in part by the fact that at the time of its construction, Britain's Neolithic people were experiencing a period of cultural unification. Stonehenge megaliths include smaller bluestones and larger sarsens (a term for silicified sandstone boulders found in the chalk downs of southern England). The bluestones are composed of dolerite, tuff, rhyolite, or sandstone. The igneous bluestones appear to have originated in the Preseli hills of southwestern Wales about from the monument. The sandstone Altar Stone may have originated in east Wales. Recent analysis has indicated the sarsens originated from West Woods, about from the monument. Researchers from the Royal College of Art in London have discovered that the monument's igneous bluestones possess "unusual acoustic properties" – when struck they respond with a "loud clanging noise". Rocks with such acoustic properties are frequent in the Carn Melyn ridge of Presili; the Presili village of Maenclochog (Welsh for bell or ringing stones), used local bluestones as church bells until the 18th century. According to the team, these acoustic properties could explain why certain bluestones were hauled such a long distance, a major technical accomplishment at the time. In certain ancient cultures, rocks that ring out, known as lithophonic rocks, were believed to contain mystic or healing powers, and Stonehenge has a history of association with rituals. The presence of these "ringing rocks" seems to support the hypothesis that Stonehenge was a "place for healing" put forward by Darvill, who consulted with the researchers. DNA studies and historical context Researchers studying DNA extracted from Neolithic human remains across Britain determined that the ancestors of the people who built Stonehenge were early European farmers who came from the Eastern Mediterranean, travelling west from there, as well as Western hunter-gatherers from western Europe. DNA studies indicate that they had a predominantly Aegean ancestry, although their agricultural techniques seem to have come originally from Anatolia. These Aegean farmers then moved to Iberia before heading north, reaching Britain in about 4,000 BC. Neolithic individuals in the British Isles were close to Iberian and Central European Early and Middle Neolithic populations, modelled as having about 75% ancestry from Aegean farmers with the rest coming from Western Hunter-Gatherers in