It is a treasure trove of photographs, manuscripts, field notes and sketches that up to now has mostly been the preserve of Darwin scholars. But now the Darwin Online project in Cambridge is making 90,000 new pages of material available to anyone on the web.

Darwin junkies will be in their element with gems that range from scientifically significant notes on his theory of evolution to touching correspondence written by his wife.

One highlight is Darwin's first draft of his theory of evolution (extract pictured above). A transcript of this document was published in 1909 by Darwin's son Francis in the book Foundations of the Origin of Species. But seeing Darwin's scrawl in the original manuscript gives a special thrill. The text is full of footnotes, second thoughts, corrections and crossings out.

Another important moment was Darwin's first doubts in print about the permanence of species. He expressed these doubts in his "Ornithological notes" from the trip around the world on the Beagle (the relevant page is "image 121"). Contrary to popular belief though he was not observing Galapagos finches at the time, but mockingbirds. "Such facts would undermine the stability of species," he wrote.

You can also gain a sense of conditions on the Beagle by looking at a plan of the poop cabin where Darwin worked. He labelled it with "My Seat" and "Book Cases".

For a more personal peek into Darwin's life there is a letter from his wife Emma on her concerns about Darwin's dwindling faith (Emma was much more religious than him). She wrote:

May not the habit in scientific pursuits of believing nothing till it is proved, influence your mind too much in other things which cannot be proved in the same way, & which if true are likely to be above our comprehension.

Later in the same letter she refers to Darwin as "my own dear Nigger". This is a strange term of affection to modern ears, but was probably an ironic reference to him being her "slave" - a phrase she uses in other letters. Darwin was a staunch abolitionist and wrote in several places that he abhorred slavery.

There are also notes and drafts for his book the Descent of Man, unpublished photos collected for the Expression of the Emotions, caricatures and cartoons of Darwin and drafts of his never-published magnum opus "Natural Selection".