Scientists bent on finding the ‘missing link’ have seized on the discovery of bones in South Africa as the “Rosetta Stone” of human evolution. Palaeontologist, Lee Berger believes it will map the human species move from the trees to the ground.

Archaeologists in South Africa have discovered a previously unknown species of human ancestor in the form of the 1.9 million-year-old partial skeletons of an adult female and a young male hidden deep in an underground cave outside Johannesburg.

They’re thought to represent a key period of evolutionary transition between ape and man.

Not everyone agrees on the significance of the find and an earlier find in Siberia has used human genome mapping to isolate yet another unique species. Are they evolutionary ancestors or did they coexist and interbreed with modern man?

Some experts have voiced skepticism about the importance of Australopithecus sediba, however, because it shares such prominent anatomical features with both early humans from the genus Homo (long legs and a pelvis well adapted to walking upright), and their ancient predecessors the Australopithecines or southern apes (long arms like orang-utans).

“The transition to Homo continues to be almost totally confusing,” Donald Johanson of Arizona State University in Tempe – an opponent of Berger’s theory – told Science magazine. “It’s Homo,” he concluded.

Svante Paabo, of the Max Planck Institute and the inspiration for the scientists in Jurassic Park, has determined a unique DNA sequence sharing no resemblance to Neanderthals or early modern humans. But it has left a trace and its existence may have throughout Asia.

This discovery is extraordinary on many levels. Perhaps the most important is that one small group of modern humans who live far away from Siberia—the Melanesian islanders of the Pacific Ocean—have picked up a block of genes from the newly discovered species on their (or, rather, their ancestors’) travels. Genetic evidence of the Melanesians’ journey from the African cradle of Homo sapiens, which started (like that of all non-African people) about 60,000 years ago when a band of adventurers crossed the straits of Bab el Mandeb, from modern Djibouti to modern Yemen, suggests they then continued along the south coast of Asia, never going far inland. For the necessary interbreeding to have happened, Dr Paabo’s new species would thus have to have been spread over a vast area of Asia. Yet it has left no previously identified traces.

Biological evolutionary changes can and do occur sometimes in short order. Take for example the oxidative DNA damage of coal miners and some chemical workers that shows their offspring suffering higher incidents of leukemia and down’s syndrome. Long, slow evolutionary changes are much harder to track and isolate, particularly if science is determined to make the assumption modern man first lived in trees before stepping foot on the ground.

Why couldn’t these unique human species have evolved side by side their tree dwelling relatives?