The Ulster Museum in Belfast faces a legal challenge unless it stages a creationist exhibition as a counter to its forthcoming series on Charles Darwin, a Democratic Unionist member of the Northern Ireland assembly warned today.

Forty-eight hours after the DUP's Northern Ireland environment minister, Sammy Wilson, railed against the idea that climate change is man-made, his party colleague Mervyn Storey has threatened legal action against the museum over its promotion of Darwin's theory of evolution.

The North Antrim DUP assembly member called this morning for an "alternative exhibition" promoting creationism to be staged alongside one planned for the Ulster Museum in Belfast this year.

Storey, a born-again Christian advocate of creationism and so-called intelligent design, said that as the museum in Belfast's university district was publicly funded it should be subject to the province's equality legislation.

Speaking to the Guardian at Stormont, he said: "In the past, when I have written to the museum about necessity to show the public an alternative to Darwin's theory (and let's stress it is still only a theory), they have been quite dismissive.

"They could be subject to a legal challenge under equality legislation within Northern Ireland if they chose to ignore alternative views that many people here in the Province believe in," he said.

He also described Charles Darwin as a "racist" over his description of aboriginal peoples in his other classic tome The Descent of Man. "In this politically correct society we live in today, if Darwin expressed those views about other peoples of the world now he would not be put on any pedestal."

Asked if humans evolved from monkeys, Storey said: "Certainly not, and there are plenty of other people in this society who don't believe it either."

The chairman of the education committee at the Northern Ireland Assembly said: "I am not against the museum or anywhere else promoting Darwin's theory, but I think it would be in the public's interest to give them an alternative theory as well.

"We are currently because of the anniversary being bombarded with Darwin's theory but there are others in the scientific world who question that thesis and their voices should be heard in publicly funded institutions like the museum."

Storey confirmed he has written to the National Trust complaining about information on display around Ireland's most famous landmark, the Giant's Causeway in his North Antrim constituency. The DUP assembly member said he had objected to notices informing the public that the rock formation was about 550m years old. Storey believes in the literal truth of the Bible and that the earth was created only several thousand years before Christ's birth.

The former school teacher is also campaigning to have creationism and intelligent design theory taught in Northern Ireland's schools. However the Sinn Fein education minister, Catriona Ruane, insisted they would not form any part of the schools' curriculum.

The backbone of the DUP – the largest party in the Stormont assembly – is made up of evangelical Christians, many of whom have been members of Ian Paisley's Free Presbyterian church. It has left the more secular wing of the party to have to deal with maverick statements from the DUP evangelicals.

Last year Iris Robinson, a DUP MP and wife of Northern Ireland's first minister, caused controversy when she condemned homosexuality as an "abomination" that could be "cured" with psychiatry. Her remarks are the subject of a police investigation after complaints that the comments allegedly incited hatred against the local gay community.

Earlier this month, Wilson used his powers to ban a government-paid climate change TV advertisement. Wilson, a climate-change sceptic, claimed the ad was "insidious New Labour propaganda."