About 7,000 to 12,000 years ago, a dramatic change in the climate of Africa increased temperatures and humidity, creating sunlit pools of water in which mosquitos could breed.
At about the same time, agriculture in the Middle East and northeast Africa led to forest clearing in the Mediterranean region and the creation of mosquito-breeding pools. With a growing population of people living in villages, the conditions were ripe for a more lethal form of malaria to spread fast.
Tishkoff believes the second mutation arose in the Mediterranean area as a result of the emergence of a deadlier form of malaria, which may have been introduced by Greek farmers and spread throughout Asia by the army of Alexander the Great.
"By studying how nature copes with malaria, we may be able to design more effective treatments," she said.
(C) 2001 The Independent (London)