[Drafts]

Date:
1972
Reference:
PP/CRI/H/5/7/1
Catalogue details

Licence: In copyright

Credit: [Drafts]. Source: Wellcome Collection.

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    Introduction It was not until the middle of the nineteenth century that Pasteur and Tyndall completed the demonstration that spontaneous 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 conditions were more favourable. A number of scientists, however, drew a quite different conclusion. They supposed that if life does not evolve from terrestrial non-living 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 and 1967) has shown that any known type of radiation-resistant extra-solar 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 sufficiently 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 extra-solar 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 earth. It is thus important to know whether primitive organisms evolved here or whether
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