NEW SPECIES

Evening Star, Issue 22367, 17 June 1936, Page 3

NEW SPECIES

COSMIC RAYS AND EVOLUTION Since Darwin expounded the evidence for the fact of evolution progress towards the discovery of the mechanism of evolution lias been slow. Many early evolutionists behoved that the changes by which organisms evolved into higher forms were due to natural selection.' The tenacity of this belief is an interesting example of the wish to believe, because it is impossible to see how natural selection could be an active principle that produced the changes that improved the qualities of an organism. Natural selection is a passive, principle and can only decide which among new softs ot organisms brought into existence by some other principle shall survive. Modern .students of evolution are searching tor this other principle which brings the new varieties into existence and provides natural selection with something to work upon. It is difficult to say whether an apparently new sort of organism is really new without a thorough study of heredity. Hence students of evolution now tend to concentrate on the problems of heredity. During recent cSecacles they have discovered how to distinguish between rare _ characteristics and new - characteristics that appear in animals and plants during cultivation through many generations. They have found that some organisms, such as the frnit-fly, Drosophila, arc particularly unstable in hereditary constitution, and are liable to throw rip new types, with _ characteristics certainly not inherited from ancestors. This occasional throvving-np of new types is named spontaneous mutation. It is clear that spontaneous mutation may be the active principle of evolution. But the mere observation of the occurrence of spontaneous mutations does not explain their mechanism. The word “ spontaneous ” is not more informative than “ special creation.” Evolutionists are therefore vrying to discover tthe mechanism of spontaneous mutation. X-RAYS AND FLIES. The most brilliant contribution to this research was made by H. J. Muller in 1921, when lie showed that mutations similar to the naturally occurring spontaneous mutations could be produced artificially in fruit-flies_ by treating them with X-rays. This is the most important biological discovery of the twentieth centurjf as it showed that new sorts of organisms could be produced by familiar agents, and therefore that the innumerable organisms that had appeared during the history of the world had probably _ been brought into existence by similar agents whose nature would not be beyond human comprehension. After Muller’s discovery that X-rays could modify the hereditary constitution of fruit flies so that their descendants were genetically _ different from their ancestors biologists considered whether such X-rays and swift electrons that occur naturally might be the agents that sometimes changed the hereditary constitution of organisms and made them bring forth definitely new types. Radium emits rays like X-rays, and has been proved to have a similar power of producing mutations. But there is far too little radium in the earth to produce spontaneous mutations at the rate at which they are observed to occur. There is another natural source ot swift electrons and X-rays—the cosmic rays. These fall on to the earth .from miter space. The intensity of the cosmic rays at the surface of the earth is very low. Assuming that they produce mutations at the same rate as X-rays of equal intensity, they are a^ thousand times too feeble at the earth s suriace to produce the rate of spontaneous mutations observed. They are much more intense at high altitudes, though even there they are still 10 times too feeble, assuming their potency is proportional to X-rays of equal intensity. The hope that the cosmic rays might be the instigator of evolution fell. Vavilov found that plants wore present in far greater variety in some districts than in others. He assumed that this indicated that the plants had been there an exceptionally long time to come into existence through the operation of spontaneous mutation. Hie presence of many varieties in a region indicated that the plant had -probably come into existence in that region. In this wav Vavilov concluded, for instance, that Abyssinia is the birthplace of the wheat plant. Though wheat has been cultivated for many centuries in Egypt, far fewer varieties are known : iir that low-lying country than in the highlands of Abyssinia. SEVEN CENTRES. Vavilov found that the origins of nearly all the cultivated plants were restricted to about seven centres on earth, and nearly all of these - centres are in mountainous regions, such as Afghanistan, Abyssinia, and Central America, from Chile to Mexico. Maize, beans, and potatoes are cultivated up to 12,000 ft in Pern. The herbaceous flowering plant primula occurs in about 19 species at lowaltitudes. and in about 330 species at liigh altitudes. Other botanical evidence of this kind suggests that wide variety in plants is associated with mountainous altitudes. The rich variety of alpine flowers is well known. There is evidence that those past geological periods which have left remains containing many varieties of fossil plants have been periods of mountainbuilding. There is considerable evidence that new plants are born in mountain regions. That is where the cosmic rays are most intense, though not intense enough to produce the observed number of varieties if they act in exactly the same way as X-rays. Recent observations show i that cosmic rays may have special biological properties at high altitudes. Professor P. M. S. Blackett has pointed out that the effects produced by cosmic rays and X-rays may not bo in proportion to their relative intensities. The cosmic rays contain bursts and showers consisting of millions of swift particles, -which occur in_ small areas, besides a diffuse collection of single rays. The frequency of these bursts and showers increases even more rapidly with altitude than the general intensity of the cosmic rays. The bursts and showers may he tar more efficient producers of plant mutations than diffuse beams of X-rays of greater total intensity. It is not impossible that the bursts and showers of particles in cosmic rays, acting on the germ cells of plants and animals, especially in mountainous regions, have an important part in the production of new species.