I was deeply flattered to be asked by Dr Jessica Gardener, Cambridge University Librarian, to open their new exhibition, Darwin in Conversation. Also part of the Library’s celebration of the Darwin Correspondence Project is their commission of eight magnificent photographs by artist Leonora Saunders that represent and recreate eight collaborators with Darwin whom history has overlooked (one of whom, Camilla Ludwig, is embodied by me). This post has been lightly edited lightly to reflect what I actually said that evening.

If you would like to find out more about my work as a writer, speaker and mentor, click here.

For more about me and my relationship to Charles and Emma Darwin, click here.

I hope it’s not bad manners, at such a special occasion for the Cambridge University Library, to mention another library, almost as distinguished as this one, though much younger – and the headcount of Nobel Prize-winning members is I think slightly lower too. But my scholarly duty to show my sources and my working means that I must tell you a story about how it was in the London Library – the subscription library in St James’s Square in London – that what I want to talk about tonight actually began.

It was established in 1841 and Erasmus Darwin, Charles’s older brother, was a founder member; Charles himself joined a few months later, and later still several of his sons and daughters did too. Recently, the London Library’s archivist, Nathalie Belkin, discovered the library’s original lending records; I was lucky enough to be invited to see them.

They’re not huge ledgers, but they’re fat, and they’re organised alphabetically by member’s name. The librarian would have turned the pages of the ledger till he found the right member, dipped a pen, and written down the book’s title, author and date borrowed – the librarian’s handwriting quite literally embodying the record of what until then had only been an idea in the head of Charles Darwin – or Thackeray, or John Stewart Mill or Gladstone: what he wanted to read next.

The handwriting shows that members borrowed each others’ books and donated their own. Sometimes they had books posted to the country, or borrowed copies for friends, or requested that particular new books be acquired. But of course most of what they borrowed was written by people they would never know and could never meet – but which they needed or wanted to learn from and draw on.

You’ll be glad to know that, for safety’s sake, I’d quickly swallowed the last of my glass of wine before I approached these treasures. So maybe that was why I could almost hear the tendrils of thought and feelings reaching out from those orderly pages, as if David Attenborough’s most brilliant plant sound-recordist had somehow captured the noise of ideas living, growing, reproducing and evolving.

In correspondence, of course, those implicit, indirect reachings-out become explicit, directly seeking connections and starting conversations, consciously sharing facts and narratives and understanding, trying to make friends or change behaviours, to help or ask for help, to collaborate or compete. And the handwriting doesn’t just embody thought, it’s actively directing that thought towards someone who will – with luck – actively receive it.

In the best epistolarly novels – such as Laclos’ Les Liaisons Dangereuses – the letters don’t just transmit the events of the plot, they are the plot: each letter sent is the cause of the next event in the story. As in fiction, so in real life. The Darwin Correspondence Project has spent decades mapping the vast network of letters, the many and complex chains of cause and effect, that formed Charles Darwin’s life and his work.

Here at Darwin in Conversation we can see some of the links in those chains laid out, but we can also feel them. While the letters of the text are merely symbols that represent the words the writer would speak if they could, the ink-marks on the paper are indexical – if you’ll forgive a bit of semiotics jargon. With the archivist's permission, we could pick up these pages and feel where Charles’s hand, Emma’s pen, Huxley’s pencil, embodied the next part of their conversations.

I’ve just been privileged to be shown round the exhibition by Dr Alison Pearn and Dr Mark Purcell, and there’s a letter from Charles but written by Emma, because he was ill, and you can’t use a dip pen when you’re lying in bed. But Charles must have got a bit better before the letter had to catch the post, because on the back of the page is a note in his own handwriting, in pencil. We could run our thumb along the folds they made, and though even I know that you can’t create a dinosaur from a fly trapped in amber – I’m looking round nervously as practically every person in this room knows more about DNA than I do – we could perhaps imagine that a scrap of their DNA lingers where they licked the glue of the flap and the stamp.

And so, as directly as a letter consigned to the Penny Post, their voices travel to through time to us and are gathered here at the Library. What noisy places libraries are! How endless in time and space the conversations are inside them! It’s just as well that the mythical symbol of the library – the bespectacled, cardiganned librarian – only has to ask the humans to hush: if she had to keep asking the books and documents to be quiet too she’d have lost her voice long ago.

Today, we’re celebrating a particular network of conversations which has caused change out of all proportion to even its own, very considerable size. The way we in our century see ourselves and our planet, our place in the universe, is the product of that change; we are the effects, if you like, of which these letters are the cause.

But we’re not only an effect. In recognising that we are all Darwin’s heirs – and the strictly biological meaning of the word is the least important here – we are also trying to understand what we have inherited, and work with that understanding to create new knowledge. And so we have become yet another node in the constantly extending network of these conversations. And it’s a great honour, as well as a pleasure, to open the doors on where it all began.