The cave of Altamira in northern Spain contains some of the world's finest examples of Palaeolithic art - bisons, horses and mysterious signs painted and carved into the limestone as much as 22,000 years ago.
     In 2002, when algae-like mould started to appear on some paintings, the cave was closed to the public, but this year Altamira has been partially reopened. Since late February, five random visitors per week, clad in protective suits, have been allowed inside the cave. However, some scientists who studied Altamira and supported its closure have been upset by this experiment and the possibility of the cave's reopening, regarding both as politically motivated.
     Altamira was first discovered in 1879 by an amateur botanist and archaeologist, Marcelino Sanz de Sautuola, during an exploratory visit with his daughter. For decades, his find was mostly dismissed as fake. But in 1902 a French study confirmed that its striking black-and-red paintings were prehistoric, turning the cave into a major tourism destination. By the 1970s, Altamira was attracting more than 150,000 people per year.
     The site was closed in 1979, and later reopened to just 8,500 visitors per year. In 2002, the cave was completely closed, and visitors sent to a nearby museum containing an exact replica of part of the cave, including its main chamber. In 2013, the replica cave welcomed 250,000 visitors.
     The scientists who oppose any kind of reopening argue that the presence of people alters temperature, humidity and carbon dioxide levels, helping spread microbial colonisation on the walls and ceiling, while the added air currents erode wall and sediment surfaces.
     Lascaux, in southwestern France, was long ago closed to the public after suffering serious fungal damage. Muriel Mauriac, the curator of Lascaux, said she was following developments at Altamira. "I trust the Spanish authorities will ultimately take the right decision," she said.
     Both Altamira and Lascaux are on Unesco's list of World Heritage sites.

Edited from The New York Times (30 July 2014)