Pupils forced to choose are going for geography rather than history.
History teachers are calling for tougher exams in geography because they believe their own subject's "difficult" reputation is deterring pupils.
Historians have been alarmed by this year's 5 per cent fall in the numbers taking GCSE history, and believe pupils see geography as a safer bet.
Entries for geography at GCSE rose this year by 2.4 per cent, while those for history went down from 240,000 to 227,000, a drop of 5.3 per cent.
Neither subject is compulsory after the age of 14, so timetables often require pupils to choose between the two humanities subjects. The pressure is set to increase with this autumn's introduction of compulsory technology.
"Geography is perceived to be easier," said Christine Counsell, chair of the Historical Association's secondary committee. "I don't think that the way forward is to make history somehow easier. I think the answer really lies in calibrating subjects for difficulty more effectively. And to some extent the geography exam should be made more difficult.
"Pupils are required to do more fully developed work in history. In particular there's an explicit requirement for extended writing, which the lower attainers find so hard," she said.
An analysis of A-level results, she said, had shown history to be a comparatively difficult subject. "That kind of monitoring needs to be done at GCSE."
Michael Riley, another member of the Historical Association and an adviser with Somerset County Council, said: "I believe this problem is going to become worse over the next few years."
"Once it was confirmed that history was no longer compulsory, some schools made a fundamental change to the whole key stage 4 timetable. A lot of schools used to have a consistent option block in the humanities. But now they are moving away from that model. The humanities are having to compete with such things as a second modern foreign language and, in particular, a range of vocational options.
"History is often perceived as more difficult; and in fact if you look at the exam papers, it is more difficult. A lot of the geography GCSE papers demand simple factual recall. The history papers never demand that. They all ask pupils to think very seriously and very hard."
Martin Roberts, head of the Cherwell School in Oxford and a past vice-president of the Historical Association, said that history was in danger of becoming a "mandarin subject" with damaging consequences for the state of British democracy. He blamed the "utilitarian" approach of the School Curriculum and Assessment Authority for marginalising the humanities.
"The reason geography's doing better than history is partly for the technical reasons outlined by Christine Counsell. But it's partly because geography's seen to be relevant; geographers have an easier case arguing the relevance of geography in straightforward economic terms. History is not part of Great Britain plc."
A SCAA spokeswoman said that the drop in history was unlikely to be repeated. Entry patterns for geography and history have tended to be similar, she said.
* A Gallup survey has confirmed what most people already know: that British children are more familiar with television shows than with leading figures of history.
More than a quarter of 16 to 24-year-olds questioned could not produce the correct date for the Battle of Hastings. Fewer than half knew that Henry VIII had six wives, or knew who was reigning at the time of the Spanish Armada. However, all the teenagers identified without trouble the roles of Barbara Windsor and Bruce Forsyth.