We can now take up the evidence that nitrogen starvation has been chronic since life first appeared on earth, and that it has had a potent influence in modifying organisms to adjust themselves for the search for this element. Those which can get much, such as snakes and the carnivora, eat seldom and have small digestive organs, but those which must depend upon the small amounts in grasses - the herbivora - have an enormous digestive apparatus to dispose of the large quantities of useless material they must swallow. In some species of fruit-eating monkeys, survival has been possible because they secure nitrogen in other ways - insects, birds' eggs, etc.
* American Medical, April 1, 1905.
It is well known that monkeys in confinement require large quantities of nitrogenous food, and that when they are kept on a vegetable diet they perish* I have been astounded at the quickness with which monkeys will seize and swallow insects. This has become instinct, transmissible to descendants, and even the human infant shows this monkey characteristic, and for the first few years of life it eats flies and other insects with perfect composure, and it acts in obedience to an instinct now useless but transmitted for a million years. What a pitiful illustration of the awful struggle for existence our ancestors experienced. Australians are still in this anthropoid state and resort to reptiles, maggots and shellfish; "even insects are not despised, but seized with avidity wherever they are found." (Haberlandt's Ethnology).
Since human customs result from selection, there is ground for belief that cannibalism itself is a result of nitrogen starvation. It occurs only in countries and islands where there are few food animals and a deficiency of nitrogenous food. There was a survival of only those tribes who were able to get nitrogen in this way. The same change exists in certain fishes which survive as species because some eat their weaker relatives when food lessens each season. In other words, the difficulty is sometimes overcome by the smaller storing up nitrogen in times of plenty to be used by the larger and stronger individuals of the species in time of stress, * Nitrogen starvation has probably been the basis for the evolution of sex. The earliest organisms were minute particles of living substance like bacteria, and multiplied simply by budding off pieces or actually dividing into two. When food became scarce they were enfeebled, and the sole survivors were the cannibals who ate each other - that is, two organisms mutually absorbed each other, each receiving a complete body of an equal individual. They could do this as easily as absorbing any other digestible food, but what a tremendous advantage it was to get the food already in the right form, and such a mass of it, too. At that rate a man would absorb as much nourishment as he gets in several months of feeding. No wonder this "autophagy," as the biologists call it, "rejuvenated" the organism resulting from the coalescence of two. No wonder they were the only survivors, and that the process of mutual cannibalism is now universal.
* Wood Hutchinson has a very interesting article in McClure's Magazine for April, 1906, in which there is a wealth of data as to the necessity for nitrogen among lower animals.
* "Cannibalism and its origin has found an ingenious explanation from the pen of a Parisian doctor. This authority holds that in the primitive ages, when man was unprovided with weapons, he satisfied his carnivorous appetite with the weakest of his brethren, as being less capable of resistance than the beasts of the field. As civilization crept on members of a tribe ceased to eat their own people, but chose those of some different community of cells. Even yet certain species go on reproducing asexually many generations, plant lice for hundreds of generations, but eventually rejuvenation by autophagy of germ cells or sexual union is necessary in every case. Some species survived because the rejuvenated cell was nourished and protected by one organism, thus having the advantage in the struggle for existence. Hence, arose sexes, female and male. Yet there is not a particle of difference between the essential elements of the male and female germ cells. They are identical in any one species, that furnished by the female being surrounded by masses of food, and the autophagy is the same as ever. Our bodies are evolved simply because they have proved to be the best variations for caring for and raising the cannibals who are to eat each other at conception. We, ourselves, are mere incidents in the immortality of our germ plasm, and our sole end is to make its rejuvenescence periodically possible - every few thousand of generations of germ cells. As soon as we accomplish this end, we die as of no further use, the germ plasm being immortal, flowing on forever in the bodies of our posterity. What we now know as death is really a late invention of nature to insure perpetuity of life, for originally death was always an accident, and living things lucky enough to fall into the right environment, never died. Thus, autophagy is the only reasonable explanation for organic evolution, and has probably had its basis in the cannibalism resulting from nitrogen starvation.
The offspring has a double inheritance from two parents, and varies more and thus gives more varieties for natural selection to choose from. Hence, evolution was rapid. Later, when organisms banded together for self-protection and those survived which were best fitted by reason of specialization of individuals, certain cells still continued the procreation or reproduction; that is, they became the germ-cells and still continue their autophagy. The body built up around them was for the sole purpose of protecting them and nourishing them during their multiplications by division until they became so exhausted as to require rejuvenation by cannibalism again - or the sexual union whom they might have been able to overpower. By and by, when weapons of defense and attack came into use, men found their own race more difficult to overcome, and accordingly turned for their daily nourishment to animals as less capable of defending themselves by artificial assistance. From this M. Joulin argues that to kill one's own kind from hunger, and for the victor to eat the vanquished, was quite natural and excusable".