We've never actually worked together on... on a problem. It's not been a deliberate decision, we've never said, 'We will not work together.' But I do think it would be tempting providence in a way. I mean, marriage is not the easiest of relationships, I mean, we've been married for 57, 58 years or something now, quite a while, anybody who could put up with either of us for that length of time, you know, it's not the easiest thing to do. But if you've known one, a really close research collaboration, it's very like a marriage. It has just the same kind of tensions and potential jealousies and potential feelings of being let down, all the things that can threaten a marriage can threaten a research collaboration. And I have seen several research collaborations between people whom I... I loved and whom I really liked to see the joint work, break up, rather as marriages could break up, in recrimination and mutual, sort of, distrust and so on. To try and bring both off in one relationship would, I think... I think it would be terribly hard. But on the other hand, it has been a great advantage to Sheila and me that we've... I mean, she worked as an engineer while I was engineering as well, and we married when we were students but... we went to the same place to work when we were working on aeroplanes.

[Q] She also made the switch from engineer to biologist then?

No, no, she's not an engineer - I'm not allowed to say she's a mathematician, because she's - actually, it's quite true, she's not a mathematician, but she took her first degree in mathematics. And if you took a degree in mathematics and it was wartime, you were employed as an engineer. And she sort of picked up the engineering on the way. And then she had a biggish break for producing kids, you know. Then, when, you know, the youngest was old enough to go to nursery to be looked after and so on, she wanted to get back into some sort of work and actually worked in human genetics, at University College, which was nice because... I mean, she wasn't working directly for Haldane but she was working for Haldane's colleague, Lionel Penrose, and we were all in the same department, so that was a good relationship. And then, when we came down here, there's no medical school, and there was no way she could go on being a human geneticist. You can't be a human geneticist without a medical school because you can't let blood out of people, even, you know, unless you've got a medical colleague. And I had this colleague, Neville Simons, who was working on bacterial genetics, and so Sheila decided to become a bacterial geneticist. If you can add and subtract, you can do anything in science, I believe. I mean, all the detail you can learn, but to have a mathematic... an ability to think logically and clearly, which you get if you're a mathematician, I think you can take it anywhere.

[Q] Do you talk shop a lot, even though not actually collaborating on particular research?

Oh yes, yes. We've always talked about the work we're doing. That... it may be one of the reasons why we've put up with one another for so long, I don't know.