India, Feb. 28 -- Much of the chemical manipulation that trees practise on animals remains appropriate. The striking relationship between the cacao tree and monkeys, for example, appears to have been seamlessly transferred into humans and our love of chocolate, even though our genetic paths parted from the monkeys of South America 5 million years ago.

The debate still rages over the exact dates when humans first travelled to the continent of America, but new evidence suggests that they, like the cacao tree, were sheltering in small warmer patches of South America20,000 years ago. The cacao tree was the keystone species of many pre-Columbian South American cultures. Could it be that as the world warmed up cacao and humans expanded their r...