"Directed panspermia"

Date:
1973
Reference:
PP/CRI/I/1/27
Catalogue details

Licence: In copyright

Credit: "Directed panspermia". Source: Wellcome Collection.

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    ICAHUS 19, 341-346 (1973) Directed Panspermia F. H. C. CRICK Medical Research Council, Laboratory of Molecular Biology, Hills Road, Cambridge, England and L. E. ORGEL TheSalk Institute for Biological Studies, P.O. Box 1809, San Diego, California 92112 Received June 22, 1972; revised December 20, 1972 It now seems unlikely that extraterrestrial living organisms could have reached the earth either as spores driven by the radiation pressure from another star or as living organisms imbedded in a meteorite. As an alternative to these nineteenth-century mechanisms, we have considered Directed Panspermia, the theory that organisms were deliberately transmitted to the earth by intelligent beings on another planet. We conclude that it is possible that life reached the earth in this way, but that the scientific evidence is inadequate at the present time to say anything about the probability. We draw attention to the kinds of evidence that might throw additional light on the topic. Introduction It was not until the middle of the nine teenth century that Pasteur and Tyndall completed the demonstration that spon taneous generation is not occurring on the Earth nowadays. Darwin and a number of other biologists concluded that life must have evolved here long ago when condi tions were more favourable. A number of scientists, however, drew a quite different conclusion. They supposed that if life does not evolve from terrestrial nonliving matter nowadays, it may never have done so. Hence, they argued, life reached the earth as an infection from another planet (Oparin, 1957). Arrhenius (1908) proposed that spores had been driven here by the pressure of the light from the central star of another planetary system. His theory is known as Panspermia. Kelvin suggested that the first organisms reached the Earth in a meteorite. Neither of these theories is absurd, but both can be subjected to severe criticism. Sagan (Shklovski and Sagan, 1966; Sagan and Whitehall, 1973) has shown that any known type of radiation- copyright © 1973 by Academic Press, Inc. o All rights of reproduction in any form reserved. Printed in Great Britain. resistant spore would receive so large a dose of radiation during its journey to the Earth from another Solar System that it would be extremely unlikely to remain viable. The probability that suf ficiently massive objects escape from a Solar System and arrive on the planet of another one is considered to be so small that it is unlikely that a single meteorite of extrasolar origin has ever reached the surface of the Earth (Sagan, private communication). These arguments may not be conclusive, but they argue against the infective theories of the origins of life that were proposed in the nineteenth century. It has also been argued that infective theories of the origins of terrestrial life should be rejected because they do no more than transfer the problem of origins to another planet. This view is mistaken ; the historical facts are important in their own right. For all we know there may be other types of planet on which the origin of life ab initio is greatly more probable than on our own. For example, such a planet may possess a mineral, or compound, of crucial catalytic importance, which is rare on