Was it difficult playing such a famous man?

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It was a real honour and horribly frightening in equal measure. Often when I prepare I must scratch around for research, but with Darwin there is almost too much material. He was such a prolific writer and there has been so much written about him that no matter how much I read, I felt that I hadn't done enough.

Did your experience of playing the ship's surgeon in the 2003 film Master and Commander help you?

I found it really useful having spent time in the Galapagos Islands making that earlier movie. I was able to draw on a real place in my memory. Creation is set during the writing of On the Origin of Species 20 years after Darwin returned from the Galapagos. The film is about his procrastination and the reasons for it — his inability to write, it making him sick, the death of his daughter, the effect that had on his relationship with his wife, and their different means of dealing with it.

Scientists are often portrayed as being emotionless, so how did you draw out his intense grief following his daughter Annie's death?

People say he looked at his children like they were projects. But I think that this was a sign of the utmost love and respect. Science was his life. So of course he was going to involve his family. For him, science was an act of love, and study was an act of love. I don't think that science is a dry, dusty thing for scientists.

Paul Bettany as Charles Darwin in Creation. Credit: L. DANIEL/ICON FILM DISTRIBUTION

Was it easy playing opposite your wife, Jennifer Connelly, as Emma Darwin?

We got a lot for free in terms of the physicality that real married people have with each other. When you are trying to produce a relationship on screen that doesn't actually exist between the actors, there is a temptation to look at or touch each other more, whereas there is an absent-minded closeness between Jennifer and I in the movie.

How did you handle the conflict between Darwin's agnosticism and his wife's strong Christian beliefs?

Darwin was a social conservative who had a revolutionary idea, and it was very difficult for him. He couldn't help seeing how the idea fitted like a glove everywhere he looked, in the indifferent cruelty of nature. When their child died, he went to science and she went to religion. And the thing that he was working on was potentially going to take her solace away. So it is incredibly moving and dynamic to play.

How did they convey their feelings?

Charles and Emma had a fantastic system of writing. They were in the same house but would write each other letters to discuss things. They were brutally honest with each other about their feelings. Even so, Annie's death was very difficult for them to discuss.

Any plans to play him again?

I would love to play the old Darwin, simply to be able to say I've had the biggest beard in cinematic history.