Towards the end of the time I was at Oxford, I met Tony Allison, Anthony C Allison, who was a... a research fellow at the Department of Biochemistry, also a 1925-er, born in the same year as I,  totally different background than I. He grew up in... grew up in the... in the White Highlands, so called, of... of Kenya during the colonial... his father was a planter and he'd raised in Africa and in a funny way, always thought of himself as an African, as many white-born Africans are. And he... but in any case, Tony had done a lot of fieldwork in natural history when he was younger. He’d seriously thought of becoming a lepidopterist and he had done a lot of important collecting in... in Kenya. But then he went to medical school in the Witwatersrand, that's the university in... in Johannesburg, and then came to Oxford to do a PhD, DPhil degree and that's when I... I met him, shortly afterwards. Well, he introduced me to the concept of polymorphisms, and polymorphisms are, as you know, the... the study of variation in the products of a gene, in which you can have multiple alleles at the same locus, which may differ by a single amino acid, all very small differences, but they have major functional differences based on that. And also the notion that these... if these alleles, you know,why do these alleles exist in the population, why isn't everybody the same? Again, getting back to this idea of variation, and the, I suppose the overall answer, is you have to make compromises. If you can  arrive at a kind of perfect genome, everybody would be the same, and it's exactly the opposite, because anything that's... that’s perfect is by definition not perfect, because that means it's not ready for the next change in the environment. So variation, lack of perfection, is the kind of hallmark of successful, of all species, in a sense, somehow more than others. Well, that was... that was kind of theoretical but what Tony was interested in, and what I became interested in was the relation of these polymorphisms to disease. And Tony Allison had done some of the very early epidemiologic studies and also lab studies on the relation of the heterozygote form of sickle cell; that is if you have one normal adult hemoglobin gene and one sickle cell gene, that protected you in a certain period of childhood against fatal infection with falciparum malaria, and as a consequence, the polymorphism was retained in the population. So that general principle: if you have that kind of variation, there has to be advantages and disadvantages, and I've carried that concept through to my understanding of viruses. You know, any virus, like hepatitis B, that infects a third of the world's population, a third of the people in the world have been infected with it, and it's lasted since pre-human times, almost certainly because there are similar viruses in lower species, of the species; it's got to have some advantages, it's got to have some non-pathological effects and actually I’ve, you know, you don’t... people tend, you know, we’re medical microbiologists, right? We don't think of positive effects. Microbiology started off with disease, so we’ve got a kind of dim view of what bacteria do, and viruses.