By Ishbel Matheson
BBC correspondent in Nairobi
International experts in early human art are calling for greater protection to save many of these ancient paintings from destruction.
The rock art survived the harsh climate but is now under threat from people
They say rock paintings by early man in Africa are particularly at risk, as human populations grow, and expose sites to vandalism and graffiti.
Near Nairobi this week, experts saw for themselves the problem facing rock art.
On a rocky outcrop, an hour's drive out of the Kenyan capital, Dr Steven Ambrose drew people's attention to some faded white-and-red lines, just visible on a stone-overhang.
http://news.bbc.co.uk/1/hi/world/africa/3993819.stm