London, Jan 25 : Known for his theories on evolution, Charles Darwin conducted his famous research because he wanted to rid the world of slavery, according to a new book.

In the book, called Darwin''s Sacred Cause, science historians Adrian Desmond and James Moorehave gathered evidence that shows Darwin was passionately opposed to slavery and that was the prime reason he embarked on his famous research.

The pair uncovered private notes and letters, which reveal that Darwin''s opinions on slavery were far stronger than had previously been believed.

The scientist''s notebooks from his five year voyage on HMS Beagle, during which Darwin first began to form his famous theories on natural selection, reveal his disgust at the slavery in South America.

Desmond and Moore have also discovered letters written by Darwin''s sisters, cousins and aunts, which show that his family consisted of highly active abolitionists.

In fact, his grandfather and uncles were key members of the anti-slavery movement.

In the book they have claimed that one of the reasons that Darwin chose to highlight the common descent of man from apes, was to show that all races were equal.

He wanted to negate those who insisted black people were a different, and inferior, species from those with white skin.

The historians wanted sexual selection was responsible for differences in appearance between races of both animals and humans.

In the theory of sexual selection traits seen as desirable but which give no competitive advantage to a species are passed down through generations.

Moore, from the department of history of science at the Open University, said that initially Darwin was reluctant to tackle the origins of humans in his book ''On the Origin of Species'', which was published in 1859, as it was a controversial subject.

"We are not trying to explain away all of Darwin''s work as being due to his passion for emancipation, but our argument is that his passion for racial unity is what drove him to touch this untouchable and treacherous subject," The Telegraph quoted him as saying.

He added: "Darwin was finally goaded into starting his work on the origins of man in 1865 by a rising tide of scientific belief that the races were separate species."

The new book examines notes that Darwin made during his voyage on the Beagle, which include how he felt disgusted at the slavery he saw in Brazil.

In notebooks he used while drawing up his theory of natural selection, he made references to slavery.

Desmond, an honorary research fellow at University College London, said: "Darwin doesn''t overtly refer to slavery and racism as his motivation for writing Descent of Man and On the Origin of Species, but it is there lurking in the background. I don''t think anyone has really looked at how strong his belief in anti-slavery was, and this could be why it has been overlooked. What he was saying was that if you accept evolution, then you don''t accept the view that black people are a separate species. It is clear that he believed the same as his grandfathers - that slaves were men and brothers."

The two historians will present their new theory at a lecture and book launch at Imperial College London on February 9. (ANI)