The researchers said, in an article published in New Scientist magazine, their work provided powerful evidence of naturally occurring animal epidemics.
Dr Peter Simmonds, of Edinburgh University, said that crossover infection by the virus was likely to have triggered the pandemic which now claims 1m lives a year.
He was part of a team of British scientists who tested wild chimpanzees from Cameroon.
They tested positive for hepatitis B - and the virus matched a strain contracted by a chimp at London Zoo.
The researchers said, in an article published in New Scientist magazine, their work provided powerful evidence of naturally occurring animal epidemics.
That could dispel theories that the virus was spread from the Americas about 400 years ago, or that modern humans carried the virus out of Africa 100,000 years ago.
Dr Simmonds said the strains of the virus probably co-evolved with primates 10 to 35m years ago and different strains occurred when the virus was passed over to humans.
The researchers said they remained puzzled because the six major human strains of the virus were not very different although the virus could mutate quickly.
Virus mutations
If it did pass to humans tens of thousands of years ago there should be a greater genetic variation in the virus.
Dr Simmonds said: "It may be that initially the virus mutated rapidly, but beyond a certain point further mutation was not viable."
Carriers of the hepatitis B virus can develop cancer and cirrhosis later in life and can transmit the condition to other people.
The virus can be transmitted through sexual activity or through infected blood.