In a swirl of snowflakes, the bronze bust of Peking Man is an unflinching sentinel in front of the main entrance of the museum in Zhoukoudian Caves on a bitingly cold morning.

It must have been a similar day on December 2, 1929, when Chinese paleontologist Pei Wenzhong made his discovery -- the first complete skull of Peking Man, or Homo erectus -- at the Zhoukoudian excavation site.

The investigation started in 1921 when Swedish geologist John Gunnar Anderson came to search for animal fossils. Under the guidance of Austrian Otto Zdansky, the first excavations started and two hominid teeth were found in 1926.

They continued when Davidson Black, a Canadian pale anthropologist working at Zhoukoudian, applied for financial support from the Rockefeller Foundation in 1927. He defined a new species called Sinanthropus pekinensis which was later changed to Homo erectus pekinensis. By 1937 researchers had found 200 human fossils from about 40 individual specimens.

Left of the bronze sculpture is a sign pointing to the "Do-it-yourself area", where visitors can glue plastic bones together to replicate the Peking Man skeleton.

The plastic bones are basically all that is left of Peking Man.

German researcher Franz Weidenreich made imprints of the original bones before the Japanese invasion. But the original bones have been missing since 1941. During the war against the Japanese invasion from 1937 to 1945, the team of researchers in Zhoukoudian decided to send the skulls and other fossils to safety in the United States.

But the fossils disappeared. "I do not believe that they are lost, so it must be possible to find them," says Zhou Guoxing, 74,a former researcher at the Beijing Natural History Museum.

He is a member of the Committee to Search for the Peking Man, launched by the Chinese government in 2005. He has already been searching for the fossils for about 40 years.

First he thought that he would find the bones in Beijing.

A friend working for the US marines told him that Americans buried the cases with the bones below the former US embassy in downtown Beijing before the Japanese attacked Pearl Harbor on December 7, 1941.

But when Zhou went to the site he found nothing. The place had been turned into a hotel. So Zhou followed other leads.