As I got deeper and deeper into the history of biology, and in particularly in connection with my Darwin studies, I became more and more in contact with problems of philosophy. And, as I studied and I started to read the philosophic literature, the leading so-called philosophers of science, I began to subscribe to philosophical journals and I was dismayed and distressed that the real problems of biology were not mentioned by anybody, they were not treated by anybody. And what was called philosophy of science wasn't philosophy of science at all, it was philosophy of a mixture of physics, mathematics and logic, and much of it totally unsuitable for biology. And I finally got quite angry and I think it was in 1967 or thereabouts that I gave a lecture to the… at a AAAS [American Association for the Advancement of Science] meeting in Berkeley… no, it was in Los Angeles, in California, in which I lashed out against the philosophers – this was in a philosophical symposium – saying, ‘You're talking about philosophy of science and it's nothing but philosophy of physics’. And there was something rather amusing, the next speaker after me was a astronomer who constantly said, ‘Philosophy of science, I mean of physics’. He was sufficiently scared by my angry outburst that he didn't dare to use the word philosophy of science when he really meant philosophy of physics. Well, it took another two or three years before this paper of mine was published. In the meantime I continued to do more reading and more thinking about it and I gradually realized that I myself, already, had greatly contributed toward the development of a philosophy of biology.