The problem becomes clear the moment we pose the question in the following way: very well, let’s accept that the extinction of the dinosaurs was caused by an accident in the form of a sudden meteorite impact. How do we explain all the other mass extinctions? Were they all caused by meteorites? The question is not as pointless as it might seem. Attempts have indeed been made to show that all the large-scale extinctions were the result of periodic storms of meteorites from the asteroid belt. This is the substance of the so-called Nemesis theory put forward by Richard Muller of the University of California.

Certain palaeontologists (David Raup and Jack Sepkoski) have claimed that mass extinctions occur at regular intervals of approximately 26 million years. However, others basing themselves on the same evidence have found no such regularity in this phenomenon. There is a similar disagreement among geologists, some of whom claim to see evidence of regular periodicity in the occurrence of big craters, while others disagree. In short, there is no conclusive evidence either for the idea of regular intervals between mass exterminations or of regular bombardment of the earth by comets or meteorites.

Such a field lends itself easily to the most arbitrary and senseless speculations. Moreover, it is precisely such sensational “theories” which tend to get most publicity, irrespective of their scientific merit. The “Nemesis” theory is a case in point. If we accept, as Muller does, that mass exterminations occur regularly every 26 million years, and if we further accept, as he does, that mass extinctions are caused by meteorite storms, then it must follow that the earth must have been visited by meteorites every 26 million years, as regular as the clock.

The difficulty in such a notion is quite clear – even to Muller, who writes:

I found it incredible that an asteroid would hit precisely every 26 million years. In the vastness of space, even the Earth is a very small target. An asteroid passing close to the sun has only slightly better than one chance in a billion of hitting our planet. The impacts that do occur should be randomly spaced, not evenly strung out in time. What could make them hit on a regular schedule? Perhaps some cosmic terrorist was taking aim with an asteroid gun. Ludicrous results require ludicrous theories.

And Muller went on to make up precisely such a ludicrous theory, in order to justify the preconceived idea that all mass extinctions were indeed caused by meteorite impacts, and that these happen regularly every 26 million years. He describes a heated argument with Luis Alvarez, the originator of the original theory that the dinosaurs were wiped out by an asteroid crashing into the earth, who was sceptical about Muller’s ideas. The following extract from this dialogue gives us an interesting insight into the methodology whereby certain hypotheses are born:

‘Suppose someday we found a way to make an asteroid hit the Earth every 26 million years. Then wouldn’t you have to admit that you were wrong, and that all the data should have been used?’

‘What is your model?’ he demanded. I thought he was evading my question.

‘It doesn’t matter! It’s the possibility of such a model that makes your logic wrong, not the existence of any particular model’.

There was a slight quiver in Alvarez’s voice. He, too, seemed to be getting angry. ‘Look, Rich,’ he retorted, ‘I’ve been in the data-analysis business a long time, and most people consider me quite an expert. You just can’t take a no-think approach and ignore something you know’.

He was claiming authority! Scientists aren’t allowed to do that. Hold your temper, Rich, I said to myself. Don’t show him you’re getting annoyed.

‘The burden of proof is on you,’ I continued, in an artificially calm voice. ‘I don’t have to come up with a model. Unless you can demonstrate that no such models are possible, your logic is wrong’.

‘How could asteroids hit the Earth periodically? What is your model?’ he demanded again. My frustration brought me close to the breaking point. Why couldn’t Alvarez understand what I was saying? He was my scientific hero. How could he be so stupid?

Damn it! I thought. If I have to, I’ll win this argument on his terms. I’ll invent a model. Now my adrenaline was flowing. After another moment’s thought, I said: ‘Suppose there is a companion star that orbits the sun. Every 26 million years it comes close to the Earth and does something, I’m not sure what, but it makes asteroids hit the Earth. Maybe it brings the asteroids with it’.

The completely arbitrary nature of the method used to arrive at a hypothesis without the slightest basis in fact is glaringly obvious. With such an approach, we really leave the realm of science and enter that of science fiction, where, in the words of the old song, “anything goes”. In fact, Muller himself is honest enough to confess that “I hadn’t meant my model to be taken that seriously, although I had felt that my point would be made if the model could withstand assault for at least a few minutes.”[29] But we live in an age of credulity. The “Nemesis” theory, which is quite clearly not a scientific model, but an arbitrary guess, is now being taken with the utmost seriousness by many astronomers who are sweeping the skies, busily searching for clues of the existence of this invisible “death-star”, this cosmic terrorist who, having made short work of the dinosaurs, will one day return to the scene of the crime, and finish us all off!

The problem here is one of method. When Napoleon asked Laplace where God fitted into his mechanical scheme of the universe, he gave the famous reply: “Sire, je n’ai pas besoin de cette hypothèse.” (“Sire, I have no need for that hypothesis”). Dialectical materialism sets out to discover the inherent laws of motion of nature. Whereas accident plays a role in all natural processes, and it cannot, in principle be excluded that, for example, the extinction of the dinosaurs was caused by a stray asteroid, it is completely misleading and counterproductive to seek the causes of mass exterminations in general in external phenomena, wholly unrelated to the processes under consideration. The laws which govern the evolution of the species must be sought for and found in the process of evolution itself, which includes both long periods of slow change, but also other periods where change is enormously accelerated, giving rise both to mass exterminations of some species and the emergence and strengthening of new ones.

It is the lack of ability to grasp the process as a whole, to understand its contradictory, complex, non-linear character – that is to say, the lack of a dialectical approach – which leads to these arbitrary attempts to solve problems by recourse to extraneous factors, like a deus ex machina, the proverbial rabbit pulled out of a conjurer’s hat. Along this road lies only the deadest of dead-ends. Moreover, the extraordinary propensity for the acceptance of the wildest scenarios – almost all involving the idea of some impending cosmic catastrophe, signifying, at the very least, the end of the world – is something which tells us a lot about the general psychological make-up of society in the last decade of the 20th century.

  1. Quoted in Ferris, T. op. cit., pp. 262-3, 265 and 266.