LONDON, Jan 23 (Reuters) - A new book on Charles Darwin says a passionate hatred of slavery was fundamental to his theory of evolution, which challenged the assumption held by many at the time that blacks and whites were separate species.

“Darwin’s Sacred Cause” is among the first of dozens of works about the 19th century scientist to appear in 2009, the bicentenary of his birth and 150th anniversary of the publication of his groundbreaking “On the Origin of Species”.

Its authors, Adrian Desmond and James Moore, also expect it to be one of the most controversial, because it explores what they call Darwin’s humanitarianism and challenges the notion that his conclusions were the result of pure scientific pursuit. “There’s got to be reasons why he came to common descent images of evolution when there was no precedent for that in the zoological science of his day,” Desmond told Reuters. “It comes out of anti-slavery.

“No one doubts that the Galapagos Islands, mockingbirds, the giant ground sloths and the giant tortoises were absolutely fundamental to his views and what he was interested in.

“But you have to look at some sort of marshalling principle. Every ship carried more than one naturalist generally in those days -- why did none of them come to this kind of common descent view and yet most of them had seen exactly the same evidence?”

Moore said the book did not seek to reduce the argument to “I’m against slavery therefore I’m an evolutionist”, adding:

“This is not a reductionist argument. We are making the case that it was necessary for Darwin to believe in ‘brotherhood science’ in order to see common descent. We can’t figure out where else he got it from.”

Desmond and Moore return to the naturalist 18 years after “Darwin”, their acclaimed biography of the man who concluded all species evolved from common ancestors.

As he himself was aware, his theories were revolutionary.

They knocked humans from their perch by suggesting they shared ancestors with monkeys and slugs, undermined the latest scientific research claiming whites were a superior species to blacks and challenged creationist assumptions.

FOREFATHERS, FIRST-HAND EXPERIENCE Desmond and Moore argue that their view is important, because it shows Darwin was driven by human desires and needs, and throws new light on works that are still attacked today for being morally subversive.

The authors sifted through thousands of letters and other archive material from the Darwin family correspondence and Cambridge University Library and related Darwin to the key racial literature of his day.

The National Archives also contained the logbooks of HMS Beagle, the ship aboard which Darwin travelled the world and gathered evidence that provided the basis of his theories.

Darwin’s Sacred Cause traces the naturalist’s abolitionism to his grandfathers’ opposition to slavery and to his friends and upbringing in Edinburgh and Cambridge at the height of the anti-slavery movement.

Crucially, he also had first-hand experience of slavery on the Beagle. During his five-year voyage Darwin saw evidence of thumbscrews, beatings, the result of armed clashes with white “masters” and heard of slavemasters threatening to sell the children of their slaves.

“Darwin came home from the Beagle voyage and in months he plumped for the common descent view of evolution,” said Desmond.

Moore said that while many scientists see politics and morals as “polluting” factors in research, Darwin is an example of someone who successfully combined the two.

“We know Darwin ‘got it right’. At one and the same time, Darwin could see something as a moral position and as scientifically relevant.”

Darwin’s Sacred Cause is published by Penguin imprint Allen Lane and hits the shelves in Britain on Jan. 29.