It's pretty much accepted that the origin of the theory of natural selection lies in the writings of Charles Darwin. But it seems the long-known scientific theory on evolution was itself subject to survival of the fittest. Experts are now claiming that at least some of the credit for everything we believe about how species develop should have gone to someone else.

Alfred Russel Wallace, they say, was the first to write a paper on the theory, but his efforts were crushed by the greater fame of the "gentleman naturalist" Darwin.

Dr George Beccaloni, a curator at the Natural History Museum, said yesterday: "Wallace was the one who had the paper ready for publication, and if he'd sent it directly to a journal it would have been published and natural selection would have been Wallace's discovery."

The comedian Bill Bailey, who does a stage show about the plight of Wallace and whose two-part documentary for the BBC is to be shown in March, puts it more bluntly: "He was robbed – whatever way you look at it."

Debate over who deserves credit for the theory of evolution has been re-ignited by the approach of the 100th anniversary of Wallace's death. The unveiling on Thursday by Bailey of a portrait of the Welsh-born scientist at the Natural History Museum in London opens a year-long celebration of Wallace's life and work.

Dr Beccaloni said there was no better time to recognise that, while Darwin had been working on the theory of natural selection for many years, Wallace had also been toiling away on the same idea. The two men made breakthroughs independently but Wallace was the first to write an explanation down in an essay. According to Dr Beccaloni, however, Wallace's mistake was sending the essay from Indonesia –where he had been researching for eight years – to Darwin, in the course of a correspondence between the two men.

The curator says Wallace had no idea his scientific pen pal been working on the same theory. And Darwin was apparently "horrified" when he received the paper, and immediately passed it on to his friends, two of Victorian England's most eminent scientists, Sir Charles Lyell and Dr Joseph Hooker.

The two then decided to release a joint paper containing the essay and excerpts from the writings of the much more famous and respected Darwin on natural selection. But Dr Beccaloni says their crime was that they did this without Wallace's knowledge.

In a letter to the German anthropologist A B Meyer in 1869, Wallace himself bears out this claim: "I sat down, wrote out the article, copied it, and sent it off by the next post to Mr Darwin. It was printed without my knowledge, and of course without any correction of proofs."

Dr Beccaloni said the actions of Lyell and Hooker were "pretty morally reprehensible".