Professor Mellanby said Dr Calhoun had suggested that by 1984 man was going to be as crowded as his mice and that this would have disastrous effects. Experiments had been going on for a long time with man. Man was not uniformly distributed. He lived in some communities just as crowded as Dr Calhoun's mice. Professor Mellanby had been very familiar with populations in parts of London forty years ago which were restricted communities. People seldom moved out of them. Until the children were taken to camps for holidays they had seldom been more than a quarter of a mile from their homes. They were living amidst extreme crowding and bred very successfully. Therefore, was it not possible to get an answer to this for human beings by examining such communities? Did crowded, enclosed communities behave like the mice? Or did this occur most obviously in those communities which had about the lowest population density in Sweden or the United States?
Dr Calhoun replied that 1984 was not the year in which ultimate density would be attained, but a date beyond which the opportunity for decision making and designing to avoid population catastrophe might be quickly lost. He stated, in any case, that density per se was not the major factor, that rate and quality of social interaction were paramount issues. Basic to his thesis was that despite the thousandfold increase in human numbers since the beginning of culture, some forty to fifty thousand years ago, there had been no change in effective density. The reason for this, alluded to by Professor Young, was that man had discovered a new kind of space, conceptual space, which enabled man to utilize ideas in order to mine resources and guide social relations. However, there was a breaking point for this process, at which time physical density might overwhelm man's ability to utilize conceptual space in order to cope with increasing numbers and it was that breaking point which we might be rapidly approaching. The fact that reproduction could be affected by density had been dealt with by Dr Thompson in Indianapolis (Thompson 1969). An older study for Scotland (Kincaid 1965) had shown that stillbirths and other parameters were density related. However, in terms of conceptual space, it might be the necessity for limitations to growth which might be the more difficult conceptual area for man to deal with. In that case a further increase in birth rate might be expected past the breaking point (Galle et al. 1972).