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But if Darwin's idea of variations as a cause of evolution stands discredited, de Vries' theory has fared no better. His mutations have been demonstrated to be caused mainly by a peculiar type of Mendelian segregation, and others to be the result, mostly unstable, of an irregular method of germ cell formation. Oenothera lamarckiana shows unmistakable evidence of being a hybrid. It breeds true ordinarily because other combinations of genes are incompatible. Most of the 'mutations' de Vries observed, appear with predictable frequency as the result of 'crossing-over' of genes from one chromosome to the other of the pair, thus producing, now and then, other combinations which may live. The irregularities of germ cell formation are also characteristic of a hybrid. Are forms of life then really in a static condition permitting only of the shuffling within each species of its stock of characteristics? Are no new characters coming into existence?
These questions may be answered in the negative. New characters are coming into existence and have been recorded in very many and very different plants and animals. Such instances as the seedless orange and grape, and the appearance of albinism in animals, are known to everyone. They are believed to be due to a change in a gene, a gene mutation, which is the present signification of the expression of de Vries. Such mutations are occurring frequently, but it is doubtful if they could result in the formation of distinct new species. Moreover, nearly all that have been observed are deleterious. Of course to-day most forms of life are so specialized that changes would be more likely to hinder than assist normal function, and many would prevent some vital process from taking place. These latter are the 'lethal' genes which, when present in double dose to the exclusion of the normal gene, cause the early death of the fertilized egg.
Recently Jones has produced evidence from work on maize and tomato that, when opportunities are equal for cross- and self-fertilization, the latter occurs in the majority of cases, and that in maize the superior efficiency of the plant's own pollen in effecting fertilization is greater as the general differences increase. He points out that similar results have been obtained in two other distinct kinds of plants and that
assortative mating is the rule in animals. He concludes: "There is thus exhibited a tendency which when carried far enough, may erect an impassable physiological barrier between different groups that were once compatible. It is an indication that sterility between species is the result of the accumulation of genetic differences, however these differences may arise. Although the reasons for this predilection for inbreeding is unknown, the fact is illuminating, although numerous instances of plants sterile to their own pollen would indicate that it is not of absolutely general application. Moreover, if it does supply an indication as to how sterility between species arose, it still leaves us with the problem of the genesis of progressive, useful variations.
Irregularities in egg and sperm formation sometimes result in unequal distribution of the chromosomes with resultant heritable differences in the progeny. These 'chromosome aberrations' would appear to be probable causes of species formation, as the chromosomes of the species in a genus very frequently bear a simple numerical ratio to each other, such as 7, 14, 21, and 35 pair in the poppies, for instance. But when we cross species with different chromosome numbers and thus try to produce new forms, either they will not hybridize, or the hybrid is sterile, as in the case of the mule, or it is unstable. Some few new forms have thus been obtained, however, which breed true, and conform to the definition of a species.
And so to-day we are in doubt as to the method of evolution. We could not be more sure than we are that life has attained its present diversity and complexity in that way, but we do not know how it has come about. We observe frequent mutation but we do not know any general method by which individuals may arise with those definite associated characters which breed true, and which conform to the criterion of a new species.
The mutations which have been observed have no evident cause in the environment, and while doubtless they are so due, as they must have a cause, they are usually not adaptive in nature and are probably the result of chemical change in the gene. Adaptive changes in the organism, held by La
marck to be inherited, have since been largely discredited, but recently evidence has been produced which proves that in some cases at least acquired characters may be inherited. Such instances are the work of Guyer on rabbits' eyes, of Griffith on rotated rats, and of other workers on the effects of radium and X-rays on rats, mice, the fruit-fly and the thorn-apple.
Guyer found that injection of eye lens extract into pregnant rabbits caused destruction of the eye lenses of the young embryos, this being a character acquired by the young and interpreted as caused by the same phenomena as help to produce immunity to disease. Mature rabbits' eyes were unaffected by this injection because at that age their lenses have no blood supply. The rabbits with defective eyes have produced young similarly affected, although there has been no subsequent treatment, and this has continued for several generations, being transmitted as a Mendelian recessive through the male as well as the female. This defect is therefore definitely an inherited character, although of the nature of a loss. Rotation of rats produces results on the sense of equilibrium that have been transmitted several generations since rotation was discontinued. In this case, the effects are related to the direction of rotation so that they may here be interpreted as an acquisition or gain, although one that interferes sadly with normal conditions. Radium and X-rays have been found to induce heritable abnormalities in offspring. This is of great interest in view of the possible effects of exposure of persons to these rays. So this great subject is reopened.
It remains to mention that a consideration of the geological record and of the numerous degrees of expression of characters apparent in living creatures lends colour to the idea that variation is due to a definite force acting in a certain direction throughout long periods of time, as though there were a gradual approach towards equilibrium. This is the theory of Orthogenesis. Although the variations referred to have apparently not been related to the environment, their independence might be more apparent than real, in which case this contentious idea of the inheritance of acquired characters
might be used as an explanation. But it seems impossible to reconcile orthogenesis with what we know of mutations and of heredity.
We, therefore, see evolution in progress to-day through the occurrence of variations, for the most part not evidently the result of the environment, but also, as shown in a few cases, sometimes directly induced thereby. These are almost altogether within species. We have little evidence, however, that useful progressive changes occur. The great problem of the origin of species is still with us.
R. O. EARL.
Bateson, William, Evolutionary Faith and Modern Doubts, Science, vol. LV, No. 1412 (Jan. 20, 1922).
Conklin, E. G., Heredity and Environment, 1922.
East, E. M. and Jones, D. F., Inbreeding and Outbreeding, 1919.
Griffith, C. R., Are Permanent Disturbances of Equilibration Inherited? Science, vol.LVI, No. 1459 (Dec. 15, 1922).
Jones, D. F., Selective Fertilization and the Rate of Pollen-Tube Growth. Biological Bulletin, vol. XLIII, No. 3, September, 1922.
Newman, H. H., Readings in Evolution, Genetics and Eugenics, 1921.
THE HOROSCOPE OF MARS
O have been done properly, the horoscope of Mars, the god of war, should have been cast when the babe was born, but then there were no bold astrologers upon the scene. However, he is not yet dead, and the great question which many are asking to-day is, 'Will he continue his vigorous life, or will he wither away to a ghastly memory that would fain be forgotten?' There are reasons for believing that it is impossible for him to die, and there are reasons for believing that he is like his victims, mortal.
The first group of reasons is brought out by an examination of the attempt to find substitutes or palliatives for war, an attempt which has been particularly marked in the last century. The gain has been, to a considerable extent, illusory, and the obstacles encountered have been fundamental. The growth of arbitration has been an illusory gain. It has increased more than twenty-fold, and this has been acclaimed as tremendous progress in the direction of the abolition of war. But is it? The removal of many causes of friction has been undoubtedly an excellent thing. This, however, is not the point. Has it meant the prevention of war? Many serious students of international affairs affirm that no war has ever been avoided by arbitration, that the settlements effected have been settlements of convenience only, not of vital clashes of interest. According to this interpretation, the sole conclusion that can be drawn from the growth of arbitration is that there has been a corresponding growth of entangling problems of minor importance which, if left unsettled, would not of themselves have led to war.
The endeavour to solve international problems has not been confined to the field of arbitration, but has extended to more permanent and organized co-operation of the various states of Europe. Here also something has been achieved. The powers in conference have more than once settled political problems which might have led to war. By the same method, in the Geneva and Hague conferences, international law has