Animal Life and Intelligence

by C. Lloyd Morgan

Here the reduction of the characters b, c, and e has led to the enhancement of a, which thus stands at a higher level than in either parent.

On such an hypothesis we may, perhaps, explain the fact to which breeders of stock testify—that the organ strongly developed in both parents (a) is yet more strongly developed in some of their offspring, and that weakly parts (e) tend to become still weaker. I know not whether this way of putting the matter would commend itself to Professor Weismann or his followers; but some such additional hypothesis of transference of growth-force from one set of organs to another set of organs seems necessary to complete his hypothesis.

Professor Weismann's view, then, assumes (1) that the cell-division which gives rise to the ova in the ovary is so absolutely equal and similar that all ova have precisely the same characters; (2) that the first polar cell leaves the germinal matter unaffected, merely getting rid of formative body-plasm; (3) that the nuclear division giving rise to the second polar cell is unequal and dissimilar, effecting the differential reduction of ancestral germ-plasms. Concerning all of which one can only say that it may be so, but that there is not much evidence that it is so. And, without strong confirmatory evidence, it is questionable whether we are justified in assuming these three quite different modes of nuclear division.

There remains one more question for consideration, on the hypothesis that the germ-cells cannot in any special way be affected by the body-cells. In considering the union of ovum and sperm as a source of variation, we have taken for granted the existence of variations. We have been dealing with the mixture or combination of already existing variations. How were variations started in the first instance?

We have already seen that in the protozoa parent and offspring are still, in a certain sense, one and the same thing; the child is a part, and usually half, of the parent. If, therefore, the individuals of a unicellular species are acted upon by any of the various external influences, it is inevitable that hereditary individual differences will arise in them; and, as a matter of fact, it is indisputable that changes are thus produced in these organisms, and that the resulting characters are transmitted. Hereditary variability cannot, however, arise in the metazoa, in which the germ-plasm and the body-plasm are differentiated and kept distinct. It can only arise in the lowest unicellular organisms. But when once individual difference had been attained by these, it necessarily passed over into the higher organisms when they first appeared. Sexual reproduction coming into existence at the same time, the hereditary differences were increased and multiplied, and arranged in ever-changing combinations. Such is Professor Weismann's solution of the difficulty, told, for the most part, in his own words.

I do not know that Professor Weismann has anywhere distinctly stated what he conceives to be the relation of body-plasm and germ-plasm in the protozoa. Are the two as yet undifferentiated? This can hardly be so, seeing the fundamental distinction he draws between them. Is it the germ-plasm or the body-plasm that is influenced by external stresses? If the former, does it transfer its influence to the body-plasm during the life of the individual? If the latter, then the body-plasm must either directly influence the germ-plasm in unicellular organisms (it would seem that, according to Professor Weismann, it cannot do so in the metazoa), or the changed body-plasm, which shares in the fission of the protozoon, must participate in that so-called immortality which is often said to be the special prerogative of germinal matter.

These, however, are matters for Professor Weismann and his followers to settle. I regard the sharp distinction between body-plasm and germ-plasm as an interesting biological myth. For me, it is sufficient that the protoplasm of the protozoon is modified, and the modification handed on in fission. And it is clear that Professor Weismann is correct in saying that the commixture or combination of characters takes its origin among the protozoa. If the unicellular individuals are differently modified, however slightly, then, whenever conjugation occurs between two such individuals, there will be a commingling or combination of the different characters. The transmissible influence of the environment, however, ceases when the metazoon status is reached, and special cells are set apart for reproductive purposes—ceases, that is to say, in so far as the influence on the body is concerned. There may, of course, be still some direct[BU] influence on the germinal cells themselves. Except for this further influence, the metazoon starts with the stock of variations acquired by that particular group of protozoa—whatever it may be—from which it originated. All future variations in even the highest metazoa arise from these.

Now, it is obvious that no mere commingling and rearrangement of protozoan characters could conceivably give rise to the indefinitely more complex metazoan characters. But if there be a combination and recombination of these elements in ever-varying groups, the possibilities are no longer limited. Let us suppose that three simple protozoan characters were acquired. The mere commixture of these three could not give much scope for further variation. It would be like mixing carbon, oxygen, and hydrogen in varying proportions. But let them in some way combine, and you have, perhaps, such varied possibilities as are open to chemical combinations of oxygen, hydrogen, and carbon, whose name is legion, but whose character is determined by the laws of chemical combination.

Summing up now the origin of variations, apart from those which are merely individual, on the hypothesis that particular modifications of the body-cells cannot be transmitted to the germ-cells, we have—

1. In protozoa, the direct influence of the environment and the induced development of faculty.