WE have seen that the body of scientific research which has to do with what is popularly termed artificial life takes on two distinct phases. * The first has to do with the creation of an artificial system or machine which behaves more or less like a living . body, or like the living substance called protoplasm The second has to do with causing eggs to develop without being fertilized-"artificial parthenogenesis Before the discovery of the sperm in the seventeenth century, the nature of fertilization was absolutely unknown. It was in 1677 that the Dutch scientist Lieuwenhoek first saw the sperms of certain animals, but these swimming cells were at first regarded as parasite s. The aslumption among men of science was that the essential thing in fertilization was the fluid in which the sperms . foat. But the Italian m 0 n k Spallan-zani, who was :n some ways ahead of his time in hi, methods, filtered some spermaiIe fuid and showed that the sperms were the essential factors. This was more than a hundred years after the little animalcules had been discovered, and still nothing could be known of the nature of fertilization because nothing was known of the nature of the. egg. After the establishment of the cell theory of the strueture of living things in 1838-39, it w,tS possible to get the notion that the egg is a cell; and a few years later (1845) the actual union of sperm and egg cells was dIrectly observed, a I tho ugh the sperm was not yet recognized as being also a cell until t wen t y years later. During all these years, however, the r e was an a b u n d ance of speculation. This concerned itself with two major problems, which overlap in parts. The first is, how does a hen's egg, for example, become metamorphosed into a chick? The second is, what is the share of each parent in the developing egg? The first of these questions could not be answered in the latter part of the eighteenth century, when speculation probably reached the high-water mark. There were -two leading theories, with endless argu-ment and debat; According to one theory the egg contained within itself a minute duplicate of the parent, and that this simply grew and developed. The extreme exponent of this “preformation theory” was the French naturalist, Charles Bonnet, at whose hands ' developed into the absurdity that the parent bore these eggs with their preformed minute embryos while she was still herself in the egg, and so on indefinitely to the beginning of life. This doctrine was later abandoned by Bonnet, and had very few adherents. But, as we shall see, there was more in it than its strongest advocates ever suspected. The alternative view was that the egg s-tarted as a body without any definite structure, and developed the complex structure gradually. This idea of “epigenesis” was forwarded by Caspar Friedrich Wolff, who had the sense to abandon speculation and resorted to observing what could actually be seen in the developing hen's egg. But this doctrine did not carry satisfactory conviction. The second question above referred to, that of the share of each parent in the developing egg, was also chiefly the subject for speculation and dispute. According to one school, the essential thing is the egb; the sperm serves merely as a stimulus for development. According to the other, the sperm is the essential thing; the egg merely supplies the nutriment for its development. Since 1875, however, we know that both elements enter into the make-up of the develo]ing cells. In this year Oscar Hertwig and other biologists were able to observe directly the union of elements from the egg nucleus with elements from the sperm nucleus (Fig. 2). The debate between preformation and epigenesis has now no real meaning. Epigenesis is true in the sense that the fertilized egg from which the organism develops does not contain any preformed structure corresponding to the anatomy of the plant or animal into which it is to develop. On the other hand, the preformation theory was true in this sense: the fertilized egg cell contains elements that were present in the parents, which in turn derived them from their parents and so on indefinitely. In other words, the question that these speculations attempted to answer is in reality two questions: one has to do with the mechanics of development, the other has to do with heredity. The fact of feTtilization has also this double aspect: it introduces into the egg the elements that make up the heredity from the male parent; and it starts the activity of the egg that leads to development. These two aspects of fertilization have been experimentally demonstrated in a number of ways. The relation to heredity is shown by the fact of hybridization; indeed, it is through the study of hybrids that we have in recent years gathered the bulk of what we know abont heredity. T hat the e I e men t > which “bear the heredity,” or determine in so:ne way the character of the organism, are carried by the nucleus was shown in an e x p e r i ment by Boveri. He cut the eggs (unfertn-ized) of sea-nrchins, so that some pieces were without nuclear matter. The s e pieces he placed in sea water con-taining the sper!S of anothpr s p e c i e s of sea-urchin; -the sperms fused with pieces of egg protoplasm. The egg began to develop, and when it got far enough along to be identified, it turned out to have the characters of only its male parent. As the nucleus cannot be removed from a sperm-cell without killing it (since the sperm is practically all n ueleus) the reciprocal experiment cannot be performed. But the same results are obtained if an egg is made to develop without fertilization. There are many animals and plants whose eggs normally develop without fertilization-ither reg'l-larly, or under special conditions. For example, plaut lice produce during the warm weather large numbers of eggs which develop into organisms like the !oth.3f without being fertilized, although another series of eggs, produced in the fall, cannot develop without fertilization. The same is true of certain species of “water fleas.” The queen bee sometimes lays eggs that develop without being fertilized; these always develop into drones, and occasionally a worker-bee lays eggs which also develop without fertilization. This' phenomenon is called parthenogenesis, and attempts to produce parthenogenetic development artificially have been made for a long time as it was expected that by this means we could get a clue to the physico-chemical-(Contnued 011 1U(e 28/).)
This article was originally published with the title "Artificial Life"