Being Well-Born: An Introduction to Eugenics

by Michael F. Guyer

Diagram of a cell showing various parts.

Unicellular Organisms.—While such a structure as a tree or a horse is composed of countless millions of cells, on the other hand numerous organisms, both plant and animal, exist which consist of only one cell. Yet this cell is just as characteristically a cell as are the components of a complex animal or plant. It has the necessary parts, the cell body and the nucleus. Moreover it exhibits all of the fundamental activities of life, though in a simplified form, that a complex higher organism does.

Importance of Cell-Theory.—This discovery that every living thing is a single cell or an aggregation of cooperating cells and cell-products is one of our most important biological generalizations because it has brought such a wide range of phenomena under a common point of view. In the first place, the structure of both plants and animals is reducible to a common fundamental unit of organization. Moreover, both physiological and pathological phenomena are more readily understood since we recognize that the functions of the body in health or disease are in large measure the result of the activities of the individual cells of the functioning part. Then again, the problems of embryological development have become much more sharply defined since it could be shown that the egg is a single cell and that it is through a series of divisions of this cell and subsequent changes in the new cells thus formed that the new organism is built up. And lastly, the problem of hereditary transmission has been rendered more definite and approachable by the discovery that the male germ is likewise a single cell, that fertilization of the egg is therefore the union of two cells, and that in consequence the mechanism of inheritance must be stowed away somehow in these two cells.

Heredity in Unicellular Forms.—In unicellular animals one can readily see how it is possible for an individual always to give rise to its own kind. One of the simplest of the single-celled animals is the Ameba (Fig. 4, [p. 24]).

The ameba eats and grows as do other animals. Sooner or later it reaches a size beyond which it can not increase advantageously, yet it is continuously taking in new food material which stimulates it to further growth. Here then is a problem. The ameba solves this difficulty by dividing to form two amebæ. Such a division is illustrated in Fig. 4, [p.24]. First the nucleus divides, then the cell-body. When the two new amebæ separate completely each renews the occupation of eating and growing. But what has become of the parent? Here, where once existed a large adult ameba are two young amebæ. The parent individual as such has disappeared, yet there has been no death, for we have simply two bits of living jelly in place of one. They will in turn repeat the same process, so will their offspring, and thus, barring accident, this growth and reproduction, or overgrowth as we may regard it, may go on forever, as far as we know. Here the problem of heredity, or the resemblance of offspring to parent, is not a very complicated one. The substance of the cell-body and cell-nucleus divides into two similar halves, so that each descendant has the substance of the parent in its own body, only it has but half as much. It differs from the parent, not in quality or kind, but in size.

Fig. 4

Six successive stages in the division of Ameba polypodia (after Schulze). The nucleus is seen as a dark spot in the interior.

Reproduction and Heredity in Colonial Protozoa.—There are enormous numbers of these single-celled animals existing in all parts of the world. Some are simple like the ameba, others are very complex in structure. Many, after division, move apart and pursue wholly independent courses of existence. On the other hand we find a modification appearing in some which is of the greatest importance. After division instead of moving apart the two cells may remain side by side and divide further to form two more, these in turn may divide and thus the process goes on until there is formed what is known as a colony. Each cell of such a colony resembles the original ancestral cell because each is a part of the actual substance of that cell. As in the ameba, the first two cells are the ancestral cell done up in two separate packets, and thus finally the full quota of cells must be so many separate packets of the same kind of material. Inasmuch as each is but a repetition of its original ancestor, it can, and at times does, produce a colony of the same kind as that ancestor produced.