This question has been hotly debated in recent years, and, despite very confident claims, particularly on behalf of the meteorite-catastrophe theory, is still not decisively resolved. There are in fact many theories which have attempted to explain a phenomenon which, both because of its spectacular appearance and because of its implications for the emergence of our own species, has captured the popular imagination in a unique way. Nevertheless, it is necessary to remind ourselves that this was not a unique event in the chain of evolution. It was not the only mass extinction, or the biggest, or necessarily the one with the most far-reaching evolutionary consequences.

The theory which currently enjoys most support and which certainly has been given the most sensational publicity is based on the assertion that the impact of a huge meteorite falling somewhere on the earth’s surface caused an effect rather similar to the “nuclear winter” which would follow a major nuclear war. If the impact were sufficiently large, it would throw great quantities of dust and debris into the atmosphere. The dense clouds thus formed would prevent the sun’s rays from reaching the earth’s surface, resulting in a prolonged period of darkness and falling temperatures.

There is empirical evidence to suggest that some kind of explosion took place, which may have been caused by a meteorite. The theory has gained ground in recent years with the discovery of a thin layer of clay amongst fossil remains, which would be consistent with the effect of dust produced by such a large impact. The idea has, for example, seemingly been accepted by Stephen J. Gould. Nevertheless, there are questions that have still to be answered. First of all, the dinosaurs did not disappear overnight, or even in a few years. In fact, the extinction occurred over several million years – a very short time in geological terms, but sufficiently long to cast some doubt on the idea of a meteoric catastrophe.

While the meteorite hypothesis cannot be ruled out, it has one major disadvantage. As we have pointed out, there have been many mass extinctions along the evolutionary road. How is this to be explained? Do we really have to resort to an external phenomenon such as a sudden meteor impact to do so? Or does the rise and fall of species have something to do with tendencies that are inherent within the process of evolution itself? Even at the present time, we can observe the phenomenon of the rise and fall of animal populations. Only recently have we come close to understanding the laws that govern this complex process. By looking for explanations that lie outside the given phenomenon, we run the risk of abandoning the search for a real understanding. Moreover, a solution that seems attractive because it removes all difficulties at a stroke can create even greater difficulties than the ones it was alleged to have solved.

Several other suggestions have been put forward. The period under consideration was characterised by widespread volcanic activity. This, and not a meteorite impact, could well have caused a change in the climate that the dinosaurs were unable to cope with. It has also been suggested that the disappearance of the dinosaurs was connected with competition from the mammals. There is a parallel here with the disappearance of most of the original marsupial population of South America under pressure from the mammals from the North. Indeed, it is possible that the extinction of these creatures was the result of a combination of these circumstances – volcanic activity, destruction of the existing environment, excessive specialisation, and competition for reduced food resources by a species better equipped to cope with the changed conditions. It is unlikely that this particular controversy will be resolved in the near future. What is not in dispute is that, at the end of the Mesozoic some fundamental change ended the domination of the dinosaurs. The main thing is that it is not necessary to introduce external factors to explain this phenomenon:

‘You don’t have to look for sunspots, climatic upheavals or any other weird explanation to account for the disappearance of the dinosaurs. They did fine as long as they had the world to themselves, as long as there was no better reproductive strategy around. They lasted more than a hundred million years; humans should as well. But once a breakthrough adaption was made, once dinosaurs were confronted by animals that could reproduce successfully three or four times as fast as they could, they were through’.[28]

  1. Quoted in Johanson, D. and Edey, M. Lucy, The Beginning of Humankind, p. 327.