of reasoning in the context of discovery. It is important to note that Crick was not doing quantifiable science; he was not testing or falsifying well-formed hypotheses. Directed Panspermia was not a hypothesis that could be tested as a finished research report in the context of justification; it was, nevertheless, a piece of reasoning that could be examined in the context of discovery, where the requirement for evidential support is less important than the need to indicate where new and even controversial claims might lead. The status of the actual thesis that Crick was proposing must be made clear, lest we fall into the errors made by his critics: Crick was defending the claim that Directed Panspermia is a plausible thesis, worthy of further pursuit, before it is either ruled out, adopted and possibly confirmed. To advance the case for plausibility of Directed Panspermia Crick, together with L.E. Orgel (1980: 35), appealed to the theorem of detailed cosmic reversibility: ‘If we are capable of infecting an as yet lifeless extrasolar planet, then, given that the time was available, another technological society might well have infected our planet when it was still lifeless.’ The authors stress that this theorem establishes a case for the possibility, not the probability, of Directed Panspermia.
Nevertheless, there are arguments in its favour. When contrasted with ortho-dox theories which postulated that life got started on Earth on its own – theories which have not yet been supported with satisfactory models or satisfactory experimental evidence – Directed Panspermia provides an extension of the timescale and suggests that the origin of life may require a very different environment to those where life can survive. Thus it not merely transfers the problem of the origins of life further back in time, it could resolve the mystery surrounding its origins, as the other place might be more suitable for its early development. Suppose, for example, we discover that life could never have started here, that there is some, as yet, unknown mineral or compound of crucial catalytic importance that is not found on Earth. This is not inconceivable, given the problems in finding a model for life’s origin.
The claim that Directed Panspermia provides an extension of the time required for life to get started has, however, been criticized on the grounds that it violates the Copernican principle which is one of SETI’s guiding beliefs. The Copernican principle states that our portion of the universe is fairly typical, and this yields the belief that if life can occur once, then in an infinite universe it can occur an infinite number of times. Paul Davies (1995) employs this argument against proponents of Directed Panspermia. There is, however, a twofold response: first, the Copernican principle has not been decisively verified, and, second, the scope of the concept ‘typical’ is undetermined. How typical is typical? How typical is our portion of the universe? In what respects is it typical? Mars and Earth are typical planets sharing a similar portion of the universe, but life is abundant on one and probably does not exist on the other. A consideration of Directed Panspermia may well be the way forward, thus generating alternative models to those which are restricted to analogies with conditions in the young Earth. Directed Panspermia thus offers an opportunity to generate
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alternative plausible hypotheses, which is an excellent example of reasoning in the context of scientific discovery.
In recent years, panspermia – if not Directed Panspermia – has gained in plausibility over the rival de novo theory. Perhaps the way forward for de novo theorists would be to abandon the assumption that complex forms of life developed as a result of a series of random chemical reactions. Paul Davies (1995) who supports explanations of life in terms of natural processes, rather than Directed Panspermia, maintains that life did not emerge as the result of accidents in the soup, but through more refined processes of self-organization which are found in chemistry and biology in ways that challenge neo-Darwinism. While Davies’ theory has considerable merit, it is neither incompatible with Directed Panspermia nor strong enough to rule it out. The emergence of complex forms of life by principles of self-organization could very well be co-existent with non-natural means of disseminating life. Techniques of genetic engineering on Earth already supplement natural evolutionary processes. Crick’s postulation of an advanced civilization which exports micro-organisms is by no means incompatible with a theory which appeals to more universal principles for the emergence of life.
The rebirth of the ‘seeding’ hypothesis
When Hoyle and Wickramasinghe first voiced their theory in the 1950s, that simple prebiotic chemicals existed in outer space and consequently ‘seeded’ potentially habitable planets like Earth, there were few members of the scientific community who were sympathetic. Yet during the past ten years the ‘seeding hypothesis’ has returned to a position of respectability. The main difference between the old panspermia hypothesis, represented by Arrhenius (and to a certain extent by Hoyle and Crick) and the new versions, is that for the latter it is not life that is being conveyed through space, but prebiotic chemicals. Nevertheless, the recognition that the essential chemistry of life exists in space and that the Earth was probably bombarded with organic chemicals in its early stages of development is a validation of Hoyle which was unthinkable several decades ago. Astronomers have discovered over 100 organic molecules in space, many of which are fairly complex. Hoyle and Wickramasinghe’s thesis was given further support in 1994 when Lewis Snyder and his group of radio astronomers at the University of Illinois claimed to have found fundamental building blocks of life in a dense cloud of gas and dust near the centre of the galaxy. A report in the New Scientist of June 1994 indicated that Snyder et al. had detected ‘spectral lines characteristic of many large molecules in the cloud, called Sagittarius B2, as well as glycine, the simplest of the amino acids which link up to form proteins’ (Hecht, 1994: 4).
John Gribbin (1994: 66) cites estimates that soon after the Earth was formed the amount of organic matter raining down on it from space must have been as much as 10,000 tonnes each year. He concludes that the notion that life started
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