Evolution and the pulmonary circulation.

We were sitting, I recall, in the canteen of the Medical School at Birmingham. It must have been 1958. I had just returned from a year and a half at the Bellevue Hospital, New York, my mind still reeling from the experience of working in the cardiopulmonary laboratory of Andre Cournand. Donald Heath had returned from the Mayo Clinic where he had coolly reshaped the face of pulmonary vascular pathology. And it was there, in the canteen, that we planned to write a book on the pulmonary circulation. It was the beginning of a collaboration and friendship which was to last to this day and through which I came to appreciate, among many other things, those imaginative intellectual processes whereby static anatomical images of dead tissue under the microscope can be transfigured into dynamic concepts of living pathological processes. During the succeeding 30 years our mutual interests led us on a series ofexpeditions to high altitudes which, in unexpected ways, added a depth of understanding and insight into common diseases back home. We were concerned, not with the short term problems of acclimatisation encountered by the occasional visitor to the mountains, but with the evidence for genetic adaptation in populations of humans and animals that have, for generations, been fated to spend their entire lives there. Such studies have, inevitably, prompted wider considerations of the way in which genetic influences have fashioned the lungs and, in the following review, I shall try to give a more general background ofthe evolution ofthe lungs and to show how important evolutionary influences may be in understanding the pulmonary circulation.