Part 7

With the vexed problem of heredity, which has been so much to the fore in science for the last twenty-four years, while many great thinkers have distinctly taken sides, it must be remembered that in many points of great importance, the only possible verdict on the contentions of either side, is one of “not proven.”

But although this controversy has split the evolutionists into two camps, it in no way compromises the evolution theory itself. The controversy is based on the admission of all the parties to it, that evolution is granted, and the question at issue involves only a difference as to how the acknowledged results are accomplished. Evolution is no longer merely a theory, it is an established fact, and is recognized as such by all who live in an intellectual atmosphere belonging to this side of 1859, the year of the publication of the “Origin of Species.”

Neither does the result of this discussion threaten, in any way, the validity of the Darwinian theory of “Natural Selection.” All the disputants are avowed Darwinians, and disagree only as to whether Darwin’s theory is alone sufficient to account for the origin of new species.

Professor Packard, Lamarck’s biographer, and one of his warmest admirers, at the close of his chapter devoted to the denial of “pure” Darwinism says: “We must never forget or under-estimate, however, the inestimable value of the services rendered by Darwin, who by his patience, industry, and rare genius for observation and experiment, and his powers of lucid exposition, convinced the world of the truth of evolution, with the result that it has transformed the philosophy of our day. We are all evolutionists, though we may differ as to the nature of the efficient causes.”

There are now three possible positions. (1) That of the Lamarckians, pure and simple, who maintain that Lamarck’s theory in itself explains all the phenomena, and that Darwin’s principle of selection is not only invalid but superfluous. This school is practically extinct, though Packard often sails to its very edge in his efforts to defend his subject, as is the manner of biographers. (2) The Neo- (New)- Lamarckians who develop Lamarck’s theory and add to it Darwin’s selective principle as of greater, equal, or secondary importance, according as they lean the more strongly to Darwin or Lamarck. This position held the field almost alone, until Weismann fired his opening gun in 1883. He founded (3) the Neo-Darwinian school which repudiates altogether the Lamarckian factor of the hereditary transmission of acquired characters, and maintains that Darwin’s theory is able to dispense with Lamarckian ideas of use and disuse.

As Weismann is the storm center of the controversy we will now examine his theory.

In 1883 Weismann became the pro-Rector of the University of Freiburg and in the hall of the University, in June of that year, he publicly delivered his inaugural lecture “On Heredity.” This lecture is generally regarded as the first broadside in that war which filled with its reverberations the scientific magazines of the world for the next thirteen years. As one writer aptly says, “The warring scientists splashed like irate cuttle-fishes in clouds of their own ink.” About 1896 however, the public grew tired of the never-ending flood of biological lore on what looked to the lay mind like an insoluble problem. The editors, with their fingers on the public pulse, cried, “A plague on both your houses,” and sent the savants to seek in their laboratories the victories denied to their pens.

As a matter of fact however, the coming struggle was foreshadowed in a paper read by Weismann at the meeting of the Association of the German Naturalists at Salzburg, two years earlier, in 1881.

This paper was entitled “The Duration of Life,” and the subject was still further developed in an academic lecture, in 1883, on “Life and Death.” These two biological contributions not only indicated the foundations of Weismann’s theory, but they threw a very brilliant light in certain very dark places. Weismann not only took up, but he solved the hitherto obscure question of the origin of death.

Johannes Muller had, as early as 1840, rejected the prevailing hypothesis which held the death of animals to be due to “the influences of the organic environment, which gradually wear away the life of the individual.” Muller argued that if this were so “the organic energy of an individual would steadily decrease from the beginning.” Everybody knows, however, that in spite of the wear and tear caused by the “environment,” be it organic or inorganic, the volume of life increases, until a certain stage is reached in all animals. But Muller had failed to fill the gap his criticism had created.

This problem Weismann solved by analysing the methods of reproduction among animals. These generally speaking are two; sexual, and non-sexual or, as it is sometimes termed, a-sexual. This latter form is the mode that prevails at the bottom of the organic scale--among the protozoa, animals consisting of a single cell. This method has a variety of forms which are classified by Haeckel as (1) self-division; (2) formation of buds; (3) the formation of germ-cells or spores. We shall here deal only with the first, self-division, or fission, which is the most universal of all methods of propagation, being the progress by which the individual cells which compose all the higher animals multiply themselves. This is the method vital to Weismann’s theory and the other two are no more than distinct modifications of fission.

When a Moneron or an Amoeba reaches a certain size, it begins to pinch in the middle like a tightly-laced corset. This increases until the creature divides into two equal halves. Each of these halves becomes a complete individual which continues to thrive until the next division takes place.

What Weismann observed as the most significant thing about this was that in this process and among these unicellular (single celled) organisms there is no such thing as natural death. Accidental death is wholesale in its proportions, but no Moneron ever dies of old age. Astounding as it may seem to the layman, the race-old, world-wide idea that death is “essential to the very nature of life itself” is here totally and indisputably overthrown.

“I pointed out,” says Weismann, in the second lecture and referring to the first “that we could not speak of natural death among unicellular animals, for their growth has no termination which is comparable with death. The origin of new individuals is not connected with the death of the old; but increase by division takes place in such a way that the two parts into which an organism separates are exactly equivalent to one another, and neither of them is older or younger than the other. In this way countless numbers of individuals arise, each of which is as old as the species itself, while each possesses the capability of living on indefinitely, by means of divisions.”

Among the Metazoa, i. e., multicellular or many celled animals, this immortality of the individual disappears. “Here, also,” says Weismann, “reproduction takes place by means of cell-division, but every cell does not possess the power of reproducing the whole organism. The cells of the organism are differentiated into two essentially different groups, the reproductive cells--ova or spermatozoa--and the somatic cells, or cells of the body. The immortality of the unicellular organism has passed over to the former--the reproductive cells--the others must die, and since the body of the individual is chiefly composed of them, it must die also.”

And so death came into the world, not by sin, as the Genesis legend reports, but through sex; a most astonishing conclusion, it may be, but one from which there is apparently no escape. Immortality still remains, it is true, but it is not the immortality of the conscious self. Positive science, nothwithstanding all its glorious gifts, has dealt a terrible blow to those gorgeous dreams of primitive men and modern mystics; those hopes and longings which have sustained millions of our race in hours of supreme sorrow; a blow which not even the bravest has been able to receive without flinching. The only immortality of which science has any surety is that of these unconscious single cells, which make possible the reproduction of the species.

Weismann, then, divides the cells which compose the bodies of the higher animals, including man, into two distinct kinds; the somatic, or body cells and the germ, or reproductive cells. These germ cells are, so to speak, batteries in which are stored a substance which Weismann calls germ-plasm. A minutely small portion of this germ-plasm from an individual of one sex, mixed with a similar portion from an individual of the other will produce a new individual. But--and here comes the keystone of Weismann’s arch--only a portion of the mixed germ-plasm is used up in the composition of the new individual; the rest is stored away in the germ-cells of the new individual for further reproduction when the time arrives. The only relation that this reserved germ-plasm has with the body cells of the new individual is that it is provided by them with room and board.

Thus, according to Weismann, from generation to generation, there is an unbroken stream of germ-plasm, and this constitutes his celebrated theory of “The Continuity of Germ-Plasm.” Granted this theory as a premise, and Weismann’s conclusions cannot be gainsaid. This germ-plasm being the sole “carrier of heredity,” nothing that happens to the somatic or body cells can be transmitted to the progeny.

Darwin had put forward a theory of heredity which he called “Pangenesis,” which made out a good case for the admission of the Lamarckian factor. According to this theory all the somatic or body cells give forth still smaller cells which he calls “gemmules.” These gemmules are collected, by some process not explained, in the reproductive organs. Here they are in packets, and these “packets of gemmules” are “the carriers of heredity.” One can easily see how by this process the effects of use and disuse would be transmissible for an organ shrunk by disuse would not be capably represented by an efficient delegation of gemmules at the reproductive headquarters.

Speaking of this theory, Grant Allen in his biography of Darwin says, “Let not the love of the biographer deceive us. Not to mince matters, it was his one conspicuous failure, and is now pretty universally admitted as such.” It must be remembered however, that Darwin was fully aware of its purely speculative character and with his usual caution entitled it the “Provisional Hypothesis of Pangenesis.”

Romanes, one of Weismann’s ablest critics, compares Weismann’s theory with Darwin’s, and while he refuses to defend Pangenesis against Weismann’s charge that it is a wholly unsupported speculation, he replies by contending that the germ-plasm theory lives in precisely the same kind of a glass house.

However that may be, it is quite clear that the germ-plasm theory completely shuts out the Lamarckian factor of evolution in all cases where propagation is sexual.

“But,” say the Neo-Lamarckians, “Darwinism in itself, merely assumes variations without attempting to explain their origin. Natural selection only explains the survival of the fittest; it tells us nothing of what Prof. Cope calls the ‘Origin of the Fittest.’ There must be variation before selection, whence then, comes this variation?” To this question Weismann has a ready reply. “Variation is due to the blending of two wholly different kinds of germ-plasm at conception, producing at birth a result that is not, and cannot be, wholly like the contributor of either.”

And now, at last, the great German is in a corner. If all variations are due to congenital characters only, and these, of course, are only possible because of the combinations secured by sexual reproduction, how do variations arise among non-sexual organisms where such combinations cannot exist?

This is indeed, a poser. But any rejoicing by Weismann’s opponents is quite premature. The sagacity which set those opponents by the ears is still available. There is no attempt to untie that knot; Weismann cuts it with a knife. He empties his antagonist’s sails by a smiling and gracious surrender. Below the sexually reproducing animals, he concedes the operation of the Lamarckian factor. In that unicellular world it is not a special cell that is passed on but the individual itself is continued, and of course any character acquired by the individual will be preserved along with the individual.

Thus then the region of controversy is limited to sexually reproducing organisms and we come to the field where the fiercest fight was made. Do these organisms transmit by heredity those characters or peculiarities acquired by the individual during its own life-time? To this question the Neo-Lamarckians gave a positive affirmative, which Weismann met with an unwavering denial.

Weismann challenged his opponents to produce a single demonstration of such a transmission. Here let us be clear as to what is meant by an acquired character. For illustration, let us suppose a father leaves his son an estate of a thousand acres. That is inheritance. If the son leaves his son the same one thousand acres, that is still inheritance. But if that son increases the estate, during his life-time to two thousand, the second thousand is an “acquired character” of a property nature. There the analogy ceases for there is no dispute as to his ability to transmit both thousands to his heirs by inheritance.

But with “acquired characters” of a biological nature, Weismann maintains this to be impossible. Many specific instances were put forward in refutation of this contention. Herbert Spencer cited the case of the supposed degeneration of the little toe in civilized man as a result of the shoe wearing habit. This it was urged could only have occurred through the transmission of acquired characters and not by natural selection as this diminished toe could not be of any value in the struggle for existence.