Orthodox scientific wisdom holds that humans evolved from apes, which had been forced to adapt to life on the ground as climate change turned dense jungles into open, dry savannah in Africa about two million years ago. However, Morgan's controversial hypothesis builds on a theory advanced by British marine biologist Alistair Hardy in 1960 that our ancestors abandoned life in trees and learned how to walk as a result of being forced to wade through wetter environments such as marshland in search of food.

While Brook-Fox has no training in paleontology or any related discipline, Morgan's book inspired him to read extensively on the subject. Ongoing debates in the academic world helped sustain a keen interest in the hypothesis. But the amateur paleoanthropologist has taken the concept even further: he suggests that early man appeared two to three million years earlier than generally supposed - in Tibet.

A former executive director of insurer Guardian Royal Assurance Asia, Brook-Fox can afford to indulge in what he describes as his hobby horse. He plans to divide his time between Hong Kong and Lijiang in Yunnan, which he sees as a convenient base from which to conduct a search for fossil evidence on the Tibetan Plateau, and has begun hunting for a house there. 'The locals I've been dealing with have been supportive of my project, including government officials,' he says.

Recently, he has spent up to six hours a day studying Putonghua in an effort to facilitate contact with mainland researchers; his exchanges so far have mainly been with European geologists.

'Many people don't believe man originated from Asia because until recently there had been no record that homonids or homonoids lived in that area four million years ago,' Brook-Fox says. But that's changing now, he says, with discoveries of fossils dating back one to two million years in regions such as Yunnan and Qinghai.

Brook-Fox's ideas rest partly on modern paleontology theory which says that the area now occupied by India, Indonesia and the Indian Ocean was once under a mass of water called the Tethys Ocean. While the movement of tectonic plates buried much of the seabed, part of it was pushed up to form the Indian continental shelf - hence the discovery of marine fossils in the Himalayas.

However, Brook-Fox had a brainwave while trekking in the Kali Gandaki Gorge in central Nepal. Instead of being carved by the movement of ice and water, he says, 'I suddenly had the idea, or realisation, that for that gorge to have been created would have required a much bigger volume of water than has been estimated, and there must have been a sea behind the Himalayas, which continued [to exist] a long time after the range started [to emerge].'

He suggests that it was around that body of water, which he calls the Tibetan Sea, where communities of island-dwelling apes would have eventually learned how to walk as the area dried up. It would have been an immense archipelago stretching from East Ladakh to Xinjiang, Gansu and Qinghai, he says.

Not surprisingly, most scholars have ignored Brook-Fox's postulations. 'I have had a difficult time trying to get a response from any academic establishment,' he says.

He argues that scientists' refusal to seriously consider an Asian theory on the origins of man is due to their focus on Africa. That's understandable when the weight of fossil evidence is concentrated there. Perhaps the most famous, Lucy - an almost complete skeleton estimated to be 3.18 million years old - was found in Ethiopia in 1974. Subsequent discoveries in Africa only reinforced convictions that the paleoanthropological community's focus was in the right place.

Still, Brook-Fox is not deterred. 'All I need is to make a discovery. As soon as I find a fossil that would be it, I would be home and dry,' he says. 'It's a matter of getting an idea of what area to look in.'

It's just as well that he recently purchased a global positioning system to help in his search. (Most maps were 'useless', he says, and it would be too unwieldy to take along detailed satellite photos.) However, when the ancient archipelago that Brook-Fox posits stretches from Ladakh to Qinghai, the amateur sleuth has his work cut out. Even if he were to find fossils, trained fieldworkers would be needed to ensure the findings were properly preserved.

Dennis Etler, a US anthropologist involved in research into human evolution in China, confirms fossils have been found on the mainland since the early 20th century, but doubts that any relate to our ancestry.

'Some Chinese continued to believe that a number of the fossils from various sites represent a true human ancestor, but this is a decidedly minority view among both Chinese and foreign scientists,' says Etler, who has worked with experts from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.

'The evidence for an African origin of the last common ancestor of apes and humans is very persuasive,' he says. 'Central Asia has not been a focus of human origins research since the 1930s and there seems little reason to pursue inquiries of that sort as no tenable evidence exists to support it.'

Some academics salute Brook-Fox's iconoclastic quest. 'It's good for someone to challenge existing beliefs,' says Max Holland, who teaches human evolution at the Chinese University of Hong Kong. '[But] he should try to publish something; otherwise no one in the scientific community will take him seriously.'

Holland concedes there are circumstantial reasons for a bias towards Africa in human fossil studies. 'It wasn't possible for westerners to do research in parts of China in much of the 20th century, so you could say it was easier to look in Africa, and western scientists have perhaps overlooked Chinese evidence.'

Brook-Fox's perseverance for what many view as a crackpot scheme may stem from a childhood lesson in failure to appreciate a legacy. When his family inherited two historical paintings from his grandmother, they threw out the canvas that had been damaged. They later learned that if restored, the pair would have been worth a fortune. Brook-Fox will return to Lijiang next month, determined not to make a similar mistake.