Thomas John Jehu

“ The fact of organic evolution is no longer disputed; the many different lines of evidence so ably marshalled by Darwin in his great work were sufficient in themselves to bring most biologists to share his view that "species have been modified, during a long course of descent"; and since his day further proofs have accumulated. A general agreement on this matter now prevails. But no such unanimity yet exists concerning the means by which such modifications have been effected. ”

“ According to his theory of Heredity there is a great difference between acquired and congenital characters. The one can never pass into the other. It was in 1883 that Weismann first gave to the world his theory of the Continuity of Germ Plasm. This germ-plasm is taken to be the material basis of heredity and is handed down from generation to generation. Changes produced in the body are not transmitted for this germ-plasm occupies a sphere of its own and is uninfluenced by any environmental and functional changes which may appear in the some. ”

“ It is now realised that the causes of Variation must be understood and the laws of Heredity discovered before the problem of development can be fully solved. It is by the observation of what takes place at the earth's surface to-day, or that has taken place recently,that geologists have found the clue by means of which they can unravel the origin and history of the rocks which make up the crust. ”

“ The transmissability of acquired characters has been called in question and is totally denied by a great number of leading biologists at the present day.
Darwin took Variation and Heredity as his basis and upon these two pillars he built up his theory of the origin of species and the evolution of organic forms. Biologists are now pushing their enquiries further back; they are not content to take Variation and Heredity as facts which require no further explanation. ”

“ Mr.Bateson's work, entitled Materials for the Study of Variation, is an important contribution in this direction. He is not content with the knowledge that variability exists but seeks to find out by detailed investigations of particular cases what variations actually do occur in nature. He brings forward evidence to show that there are variations which cannot be arranged in a continuous series—that such variations are therefore discontinuous. ”

“ Another school, to which Herbert Spencer and Haeckel belong and which finds a large support in America especially amongst the paleontologists, while admitting that natural selection has played an important part in evolution, emphazises the relative importance of the environmental and functional changes produced in organisms and lays stress on the transmission of acquired character. Some even go so far as to throw the whole burden of evolution on the Lamarckian factors. ”

“ The appeal must be made to facts - the accumulation of observations and the performance of proper experiments will alone lead to their solution. A new school of experimental evolutionists has arisen whose avowed object is to eschew speculation and to find out what actually does occur in nature. It is important to find what part acquired characters play in the origin of species. Acquired characters form a large proportion of the characters of adults. How large it is not easy to determine. ”

“ A third school, represented by Nageli, Henslow, Eimiez
s and others, rejects the view that variations are haphazard, believing on the contrary that they occur in a determinate direction due to some force which is thought to be at work within the organism and prior to the operation of natural selection. The nature of this force is not very clear and the different writers probably do not always mean the same thing: it has been variously called "growth-force", "bathmism", "self-adaptation", etc. ”

“ It is questionable whether we are any longer justified in speaking of cells at all. The fully segmented ovum is a syncytium and it is probable that this syncytium is maintained throughout life. This seems to show that there is a closer connection between the reproductive elements and the soma than Weismann has been willing to allow. And it suggests to us a possible way by which influences might pass from the body to the reproductive organs. Indeed, evidence can be brought forward to show that influences do occasionally pass from the soma to the reproductive elements. ”

“ For the fact that these characters are now developed in the embryo before there is an opportunity for the modifications to occur through use and disuse of parts, proves that they are no longer produced in each individual independently as a result of functional changes in its own experience and that characters which were originally acquired by the ancestors of those birds have now through inheritance become congenital in the race. ”

“ Though much has been done already, more experimental evidence is still needed with a view of finding what characters depend upon the environment. Plants and animals require to be placed under new conditions and the results noted. And with rapidly breeding forms the observations can be continued for many generations. In carrying out such experiments it is of great importance to note not only the changes which occur in the organism when brought under new conditions but also, and this is too often forgotten, to find what happens to such organisms when transported back to the old conditions. ”

“ Another line of argument advanced by Spencer (Appendix to the Principles of Biology, Vol.1) and one which Weismann and his followers have failed to meet satisfactorily, is that derived from (illegible text)
Welia's experiments on the sense of touch. The unlikeness of tactual discriminativeness displayed by different parts of the body-surface can be expressed by actual measurements. It is very difficult to explain by natural selection how such a distribution of tactual perceptiveness as is found can have arisen. ”

“ If it could be taken as an absolute certainty that the modifications in the crop resulted originally from changes due to adaptation to new conditions of life and that the skeletal peculiarities have resulted from the alteration in the crop, then a case of this kind would be decisive. ”

“ In that case natural selection is not such an important factor in the origin of species as the Darwinians have supposed. Other naturalists, notably De Vries, have within recent years recognised the existence of discontinuous variations. Bateson confined himself for most part to the study of variations in the number, symmetry, and arrangement of parts ”

“ It also
^ makes it possible for us to understand how intelligence might become a factor in evolution. Intelligence often leads to the formation of new habits and thus to the development of acquired character. Any congenital variations which coincided in description with the modifications thus produced would be favoured and eventually preserved.
But it must not be supposed that biologists are yet agreed in throwing over the Lamarckian factors and in denying their transmissibility. ”

“ Poulton in his book on Colour in Animals gives an account of the changes or colour in butterflies caused by the differences of conditions of temperature and light under which the caterpillars and pupae are reared. Again changes are often seen in the colour of birds, caused by feeding them on different foods. ”

“ The only legitimate induction which can be drawn from these differences is therefore that the facets disappear in the adult European through disuse. There is no evidence to show that there is any transmission of acquired characters. ”

“ The microscopical examination of the tissues of plants and animals has during recent years resulted in the discovery of a state of things which tends to remove this difficulty. The cells composing the organisms have in numerous cases been found to have connections with each other by means of protoplasmic threads. ”

“ This bird has a peculiar alimentary canal, the gizzard is much reduced in size and strength and the function usually performed by it has been assumed by another organ, the Crop which has consequently also become modified in a peculiar fashion. The wide and thick-walled crop rests directly upon the breast-bone. ”

“ He points out that these
other influences must be brought to bear on the plant in early youth, otherwise the results are not shown. The keeping up of the new variety, also, depends upon its nutrition. ”