Michael Novacek, provost of science at the American Museum of Natural History, which mounted a huge Darwin exhibition in 2005, says "Charles Darwin was a creationist when he stepped onto the Beagle. And he was completely aware of how his new theory would be received when he got off." This is true, but his path had already been smoothed by geologists, who demonstrated that the world was much older than the Bible implied, and by scientists investigating extinctions and the fossil record.

A literal Bible makes the earth some 6,000 years old. James Hutton (1726-1797), often called the father of modern geology, believed that rock structures were formed by erosion, sedimentation and the cooling of molten rock, and that these processes were still observable, operating as they always had. He called this belief uniformitarianism. These processes would have taken vast ages to work. Hutton’s work was popularised by John Playfair (1748-1819), who said that when he stared at the rock formations that had convinced Hutton, "the mind seemed to grow giddy by looking so far into the abyss of time."

Some geologists still argued that all rocks were made of sediment precipitated by the Great Flood – but another Scot, Charles Lyell, dealt their ideas a hammer blow with his three-volume Principles Of Geology (1830-1833). Lyell’s book was subtitled, "An Attempt to Explain the Former Changes of the Earth’s Surface by Reference to Causes now in Operation". In 1863, he would publish The Antiquity Of Man, which used evidence such as flint implements from ancient rock strata in the Somme, to argue that man had been around for much longer than the Bible stated. The book went through three editions in a year. Darwin was to say that "I always feel as if my books came half out of Lyell's brain".

The fossil factor

Fossil evidence of extinctions was also a problem for Biblical literalists, many of whom believed that God, having created so many creatures, could not have allowed them to die out. One argument ran that fossils represented creatures as yet undiscovered. The French naturalist Baron Georges Cuvier (1769-1832) established extinction as a fact in the eyes of most scientists by, among other things, explaining how elephant jaws differed from those of mammoths. Cuvier claimed this showed the earth was immensely old, and that periodic "revolutions" had wiped out many species.

Believing in an ancient earth was not the same as believing in evolution, and Cuvier did not. But James Hutton, as far back as 1794, tantalisingly seemed to link uniformitarianism, evolution and natural selection by saying that if individuals within a species were infinitely varied, those which are furthest from the "best adapted constitution" will perish, while the best adapted will preserve themselves and multiply their race.

The thought of Hutton, Playfair and Lyell would all have been current in the Edinburgh where the young Darwin studied medicine. Even giants stand on the shoulders of giants.

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