Perhaps the most important factor of all, in considering this question of man’s natural diet, is the anatomical argument—the argument, that is, which says that man must or should naturally eat certain foods, for the reason that he belongs to the class or genus of animals which lives upon that class of foods—and that, consequently, he should live upon them also. Comparative anatomy affords us one of the most tangible and at the same time one of the most forceful and convincing arguments that can be furnished in favour of man’s natural diet (whatever that may prove to be)—for the reason that its facts are so well-attested that they cannot be gainsaid by anyone who is in possession of them; and only the inferences drawn from these facts can be disputed—which is a question that will be considered later. As before stated, this line of argument is in many ways the most important with which we shall have to deal; it will tend either to condemn or to confirm my argument most strongly. From a scientific standpoint, the study of this subject is founded upon the fact that the diet of any animal, in its natural state, is always found to agree both with its anatomical structure and with its several digestive processes and general bodily functions. So clearly is this fact recognised, indeed, by comparative anatomists and scientists generally, that animals have been divided, according to their dietetic habits, into four great classes—herbivorous, frugivorous, carnivorous and omnivorous. There are various sub-and minor-divisions that can be and in fact are made—such as the gramnivora, or grain-eaters; the rodentia, or gnawers; the ruminants, or cud-chewers; and the edentata or creatures without teeth. These subdivisions need not concern us here, however; and I shall not discuss their anatomical structure or food-habits at any length. Their names sufficiently classify them—in a work of this nature, which deals with foods, and is not a natural history. For practical purposes, the gramnivora may be included in the class of frugivora—since most frugivorous animals eat grains to some extent. This understood, we can proceed to a consideration of the facts; and we shall see to which of these classes man belongs.

In order to classify an animal, and place him in his proper division, it is necessary first of all to make a careful examination of his physical structure, and examine his organs in turn and severally, with the utmost care; when, by a comparative study of his organs, and by comparing them with those of other animals, living upon other foods, we shall be enabled to classify man properly—at least, so far as the evidence afforded by comparative anatomy enables us to reach a decisive conclusion one way or the other. There are numerous other facts and arguments to be taken into consideration; but, as said before, the argument drawn from comparative anatomy is the most complete and convincing of all—since that alone practically settles the case for all other animals. Let us, therefore, consider the structure or anatomy of man, from this point of view; and see how far these arguments lead us, and to what class we should naturally assign man, from a study of these facts alone. I shall take up for discussion first of all the teeth.

The Teeth

The Herbivora.—Let us consider first the teeth of the herbivorous animal. The horse, the ox, and the sheep are typical of this class of animals—living, as they do, almost entirely upon grass and herbs. The character of their food is peculiar. It is bulky, coarse, and covered with sharp, cutting edges—ill suited for tender mouths and gums. It must be mashed and ground thoroughly between the teeth and in the mouth before it is fit to be swallowed; and teeth of a peculiar construction and mutual relation are necessary in order properly to perform this function. Just such teeth they possess. There are twenty-four molars, six on each side in each jaw; and in the lower jaw, in front, eight incisors, or cutting teeth, with none on the upper jaw. In place of any of these teeth on the upper jaw, there is simply a horny plate upon which the long incisors of the lower jaw impinge when the jaws are closed. This renders possible the tearing, grinding motions necessary for biting off and masticating the food upon which these animals live. Not only that. The actual structure of their teeth is peculiarly suited to their food and its mastication. Unlike our teeth, they are not covered with enamel, but are composed of alternate layers of enamel and dentine—a soft, bony substance lying between the layers of enamel, and wearing away more rapidly than it does. The result is that there is soon formed a series of jagged edges, which form cutting, grinding surfaces, and are especially adapted for the food which these animals feed upon. No such formation is present in any other class of animals, since their food is different from that of the herbivora. It is a wise provision of nature, precisely adapted to the desired ends.

The Insectivora.—The insect-eaters are more nearly related to the Rodentia than to the Carnivora. The form of teeth varies with the species. The incisors and canines are not especially prominent, but the molars are always serrated with numerous small-pointed eminences, or cusps, adapted to crushing insects. The three leading families of the Insectivora are the moles, the shrew-mice, and the hedgehogs. They are of small size, and are found in all countries, except in South America and Australia.

The Rodentia.—The Rodentia is a peculiar order of animals, characterised by two very long and strong teeth in each jaw, which occupy the place of the incisors and canines in other animals. Back of these there is a toothless space, and then four or five molars, which, when they have a roughened crown, indicate a vegetable, but when pointed, an insectivorous, diet. Their principal foods are grains and seeds of all kinds, and with these, often, fruits, nuts and acorns. To this order belong the families of the squirrel, marmot, all species of mice, the beaver, porcupine, hare, and others.

An especial dietetic subdivision of the Rodentia is the Rhizophaga, or root-eaters, which includes some species of the Marsupials, and of mice. The food often consists exclusively of the roots of the beet, carrot, celery and onion.

The Edentata.—Occasionally, though rarely, animals of this class have rudimentary back teeth. Their food consists of leaves, blossoms, buds, and juicy stalks. Some also devour insects, especially ants. To this order belong the sloth, armadillo, pangolin, and great ant-eater.

The Omnivora.—Omnivorous animals have very distinctive teeth. The canines are markedly developed, forming regular tusks at the side of the mouth. These are used for attack and defence, and also to dig up roots, upon which these animals largely feed. The hog is typical of omnivorous animals of this character, and we all know his disposition no less than his anatomy! Animals of this class can live upon both animal and vegetable food, and man is supposed to be included in this category! The great argument brought forward by those who recommend a “mixed” diet (i.e. one composed of flesh, vegetables, fruits, roots, grains, etc.), is that man can live on all these foods, and retain life and some degree of health, and that therefore he is omnivorous. We shall come to consider this argument somewhat at length presently. For the moment, it is enough to say that (so far as his teeth are considered, at any rate) man is in no way similar to the hog, or to any omnivorous animal whatever, but totally different from all of them. The most casual glance at the mouth and teeth of the hog should convince us that we are not in that class! The other considerations we shall come to later.

The Carnivora.—The next great class that we must consider is the carnivora. Their teeth are very distinctive, and their shape and arrangement are entirely different from those of any of the other animals. There are the incisor teeth in front, and molars behind; but the most distinctive teeth are the canine, which especially distinguish this class of feeders. There are four of these—two in each jaw, placed upon the sides, and they are long, sharp, and pointed. The more nearly the animal is purely carnivorous, the more are these teeth developed, and the less meat the animal eats, the less are they developed. Thus, the feline species, which is perhaps the most typically carnivorous of all, have canine teeth very well developed; in them, they are most marked. In such animals, the canine teeth are also set considerably apart from other teeth. In the dog, however, the teeth are less prominent than they are in the cat; his claws, eyes, etc., are also less distinctly carnivorous, and it will be observed that his habits are decidedly less like those of the preying animal than are those of the cat: he sleeps at night instead of in the daytime; does not adopt the stealthy methods for catching birds, etc., which the cat follows. All this has its significance when it is remembered that dogs are much more easily weaned away from a flesh diet, on to one of milk, bread, biscuits, etc., than are cats, who are very difficult to wean from their carnivorous habits. This, however, is by the way.

In the bear family, again, the carnivorous characteristics are still less marked. The canine teeth are less and the molars and incisors more developed—the latter having a flat but roughened crown. All this indicates a still nearer approach to a vegetable and fruit diet—as is actually the case. The bear, as is well known, is fond of berries, fruits of all kinds, milk and honey.

Man, has, of course, two “eye teeth,” which are more or less pointed, and that I do not deny. But these teeth are comparatively so small, when compared with the corresponding canines of the real carnivora, as to be altogether insignificant. When we examine the mouth of a person with normal teeth, we find that the teeth are almost exactly similar in size and shape—so much so, in fact, that any person ignorant of the fact that we have “carnivorous teeth” in our heads (supposedly) cannot pick them out from the others! He does not experience any such difficulty in selecting the carnivorous teeth of the tiger or the cat! Strange, is it not? Even the omnivorous hog has teeth so much larger as to be totally dissimilar to those of man. Man’s teeth are so uniform that all traces of his carnivorous nature have entirely disappeared. The only reply that can be made to this criticism is that, although man’s carnivorous teeth are considerably smaller than those of the pure carnivora, they are still there, none the less, and consequently man is entitled to live upon a certain amount of meat—though not to make it his chief or exclusive diet, as do the pure carnivora. The very fact that he has such teeth in his head at all is proof positive, it will be urged, that man should, or at least can, without injury, live upon flesh to some extent. For otherwise how came these teeth into his head?

The answer to this is very simple. The gorilla—a typical example of the frugivorous animal—has these teeth much more strongly and markedly developed than man; and yet he does not feed upon flesh to any appreciable extent; and in fact lives almost entirely upon fruits, nuts, roots, etc. If we were to argue that man must eat meat, because of the carnivorous teeth in his head, much more must we insist that the orang and the gorilla should live upon flesh-food—and yet we know that these animals in their natural state do not eat flesh-foods at all, or only when they cannot obtain their own food in abundance! They are clearly frugivorous by nature; and, inasmuch as their eye-teeth are far more developed than are the same teeth in man’s head, we must come to the conclusion that man is certainly not adapted to a flesh diet, on account of his teeth or because of them. He is more certainly frugivorous than the gorilla—were we to judge by the teeth alone! They are mere rudiments—atrophied relics of bygone ages. Their use has ceased to be. Orangs and gorillas have some need of their teeth for purposes of cracking nuts, for digging up roots, for attack and defence, and perhaps other purposes in extreme necessity. But we have no need of teeth for any of these reasons, and hence the teeth are not developed in us, to any such great extent. All reason and analogy, therefore, clearly indicate that our teeth are far more indicative of a frugivorous diet than any animal living.

Further, it is interesting in this connection to note that anthropoid apes, as soon as they are deprived of their natural food and their natural life, soon become diseased and die. Says Dr Hartmann:

This is interesting as an illustration of the effects of perverted living upon apes; and suggests that man cannot depart from his natural food to any great extent, either, without dire consequences to himself. The thousands of sick and dying in every part of the country, the well-filled hospitals and overflowing graveyards unfortunately prove this to be the case!

Moreover, the eye-teeth of the anthropoid apes are of a totally different character from the canine teeth of the carnivora. The former are small and stout, and somewhat triangular; while the latter are long, round and slender. It is a noteworthy fact that the anthropoid eye-tooth is rough and cartilaginous at the point of contact between the external tooth and the gum, while that of the carnivora at the same point is smooth and sharp. The eye-tooth of the anthropoids is adapted for use in cracking nuts and the like, while those of the carnivora are exclusively employed in seizing and tearing flesh. Professor Nicholson, in his “Manual of Zoology,” pp. 604-605, says of the anthropoid apes:

The teeth of man are inferior in strength to those of the anthropoid apes, but the cause of this is to be sought not so much in their original character as in the fact that they have been weakened and degenerated by the use of cooked food for thousands of years.

It may perhaps be objected that anthropoid apes, which have been cited as typical frugivorous animals, are not so much so as I have contended; that, while their chief food is doubtless fruits and nuts, they do occasionally feed upon all kinds of substances—roots, insects, small animals when they can catch them, etc. Thus Professor Robert Hartmann in his “Anthropoid Apes” p. 255 says:

Now, it will be noticed in the above connection that (1) these apes are, by reason of their peculiar anatomical and physiological construction, incapable of competing with the carnivora for food of that character—and hence naturally disqualified to live upon it; and (2) these animals do not naturally live upon this food by choice, when other and, to them, more natural food is forthcoming. Only in the last stages of hunger do they resort to food of this nature, which they are obviously driven to by extremity, and are disqualified to eat by reason of their peculiar construction. An animal can be driven to eat anything if he is hungry enough. That does not prove that what he eats is his natural food, nevertheless! Instinct, and other considerations, must determine that.

The Frugivora.—The orang and the gorilla are perhaps the best examples of this class of animals. Some bats and kangaroos may be included in it also. Animals belonging to this class have thirty-two teeth—sixteen in each jaw; four incisors or cutting teeth; two pointed teeth, known as cuspids, four small molars, known as bicuspids, and six molars. The eye-teeth project somewhat beyond the others and fit into a blank space in the lower row, the other teeth articulating uniformly. I have referred to the uses of this large eye-tooth elsewhere (p. 29).

The Teeth of Man.—Now when we come to consider the teeth of man, we are at once struck by the fact that they correspond, in almost every particular, with the teeth of the gorilla and other frugivorous animals; and the fact they do not at all resemble or correspond to the teeth of any other animal! To the teeth of the herbivora, the carnivora, the omnivora, etc., they bear but the slightest resemblance, while they agree in almost every respect with the teeth of frugivorous animals. If we compare the teeth of man with those of the orang, the gorilla, or other frugivorous animal, we find that the number, the arrangement, the structure, the nature, and the size of the teeth are almost identical; while they bear but the smallest resemblances to the teeth of any other animal or genera. The complete absence of intervening spaces between the human teeth characterises man as the highest and purest example of the frugivorous animal. Man possesses no long, canine tooth, capable of catching and holding a captured prey; he possesses no tusks, like the omnivorous animals, and in every other way bears no resemblance whatever to any other animal—while his teeth do bear the very greatest and most detailed resemblance to the teeth of the apes and frugivorous animals generally. Bearing all these facts in mind, then, we surely can have no hesitation in classifying man as a frugivorous animal—so far as his teeth are concerned. Considered from that point of view, man must be classed with the pure frugivora.

Not only in the number and structure of the teeth, but also in the manner of masticating the food—in the movements of the teeth and jaws themselves—there is a distinct resemblance between man and the apes and other frugivora, and a radical distinction between him and all other animals. In herbivorous animals the jaws have three distinct motions—a vertical, or up-and-down motion; lateral or sidewise; and forward and backward. These movements are frequent and free, the result being that food eaten by these animals undergoes a thorough grinding process well suited to the nature of their food. In the carnivorous animals, on the other hand, the movements of the jaws are in one direction only—they open and shut “like a pair of scissors,” as one author said, and are well adapted for tearing and biting off food that is to be swallowed more or less en masse, to be acted upon by the powerful gastric juices of the stomach. No such limited action is the case with man. With him also the jaws can move in three directions—as in the case of the herbivora—but the extent of such motion is much more limited. In other words, the jaws of man are adapted to a diet necessitating more or less grinding, and he may be classed with the herbivora on that account. Whatever might be said, however, by way of associating man with the herbivora, he is certainly as distinct as possible from the carnivora, and resembles other animals far more than he resembles them. He is certainly not carnivorous, whatever else he may be!

Having thus passed in review the evidence presented by the teeth for the naturally frugivorous nature of man, we must now turn and examine the evidence afforded by the other organs of the body; and see how far comparative anatomy affords proof of the nature of man’s diet—as derived from a study of the other portions of his bodily frame. I shall review these in turn. First let us consider the extremities.

The Extremities.—According to Huxley, there are three great divisions in the animal kingdom, as regards the extremities—viz. those which possess hoofs, those possessing claws, and those possessing hands. To the first division belong the herbivora and the omnivora. Almost all animals possessing claws are carnivorous, while animals possessing hands are almost invariably frugivorous. To this rule there are very few exceptions. Since man certainly belongs to the class possessed of hands, he is certainly frugivorous by nature. The reason for this becomes apparent when we stop to consider the habits of the various animals. The herbivora have no need for hands; they have merely to walk about the grassy plains, and partake of what nature has offered to them in abundance. The carnivorous animal, on the other hand, takes his food by violence—suddenly springing upon some defenceless and unresisting animal, and tearing it to pieces with its sharp teeth and claws. For this reason they are developed to the size and extent we see—capable of inflicting such terrible injuries. And here I would again call attention to what I said before—as to the carnivorous traits and characteristics of the cat as compared with those of the dog. The teeth and claws are far more developed in the former than in the latter. In man, of course, his teeth and claws are entirely unfitted for any such office. The soft, yielding nails are absolutely unlike the long, sharp claws of the carnivora: nothing could be more dissimilar. But if we compare the hands and extremities of man with those of other frugivorous animals, there is a very close similarity between them. The reason for this is that man (like the apes) can and should go out into the open fields and forests and pick his food off the trees. The human hand is eminently adapted to this end and for this purpose; but is quite unadapted for any such purposes as the claws of the carnivora are adapted for. I may remark here, incidentally, that all carnivorous animals drink by lapping up the water or other liquid with their tongues; while man, and all vegetarian animals, drink by suction—by drawing up the fluid directly into the mouth. This is a very distinguishing characteristic, to which there are few if any exceptions. Needless to say, since man drinks by suction, he is eminently a vegetarian animal, and is quite distinct from the carnivora in this respect, as in all others.

The Stomach.—The position and form of the stomach are also of significance. In the carnivora, it is only a small roundish sack, exceedingly simple in structure; while in the vegetable feeders it is oblong, lies transversely across the abdomen, and is more or less complicated with ringlike convolutions—according to the nature of the food. This appears conspicuously in the primates, which include man, in the Rodentia, Edentata, Marsupials, and, above all, in the Ruminants. In the latter, it presents a series of from four to seven wide, adjoining and communicating sacks.

At a first superficial glance at the exteriors of the stomachs of the carnivora and that of man, we apparently perceive a far closer resemblance than between man’s stomach and that of a herbivorous animal. In one sense, there can be no question that there is a closer similarity; in another sense, it is not so. In man this organ is simple, but is divided into a cardiac and pyloric portion—thus occupying, as in many other anatomical respects, a middle line between the carnivorous and herbivorous mammalia. The inner surface of the stomach is covered with rugÆ, or wrinkles, formed by the mucous membrane, which lines the whole intestinal canal, and which forms valvular folds; while in the carnivora the stomach is a simple globular sac, without these corrugations. As Dr Trall observed[7]:

The Liver.—Dr John Smith, in calling attention to the many distinctions between the bodily structure of man and that of the carnivora, pointed out the following differences among others:—

This author also says elsewhere (p. 79):

The Placenta.—Let us now turn to another important distinction between the carnivorous and non-carnivorous animals. Of these, perhaps the most important is the character of the placenta—one of the most distinguishing marks or characteristics of any species of animal. This subject has been so well and ably summed up by Professor Schlickeysen, in his “Fruit and Bread” (pp. 48-57), that I cannot do better than quote the main portion of the argument, as stated by this learned and able author. He says:

Relations between placental forms and Individual Characteristics.—From our entire knowledge of the development of races and of individuals, we may conclude, upon the basis of Huxley’s classification, that an intimate relation exists between the form and character of the placenta and the entire nature of the individual. We find among the non-deciduata, besides the toothless sloths, only the Ungulata, or hoofed quadrupeds, and others developed from them. The arrangement of their teeth, as of their entire digestive apparatus, marks them as belonging to a single family—namely, the herbivora.

The zonary placenta characterises a very large family of animals whose peculiarities are distinctly marked, especially with regard to their teeth and digestive apparatus. These belong to the widely diffused and numerous orders of the carnivora. But the most interesting and important group, with reference to our present study, is that characterised by the discoidal placenta; for, since it includes man and the fruit-eating apes, it gives occasion for the comparison between these and other placental animals from the standpoint of dietetics.

We observe here at once that the majority of animals having a discoidal placenta subsist chiefly upon fruits and grains, and that the typical representatives of this class, namely, those whose plactental formation is most distinctly discoidal, are also the most exclusively frugivorous.

Here, as elsewhere in nature, an exact line cannot be drawn. Transitional forms exist everywhere, and to this the placenta is no exception. The most striking accordance, however, exists between the placenta of man and that of the tailless apes—namely, the gorilla, orang, chimpanzee and gibbon. Between other discoidal species, the differentiation, though minute, is clearly marked; but between man and these apes the resemblance is so exact as to stamp them plainly as members of the same family.

The completely developed placenta is in the form of a circular disc, about eight inches broad, one inch thick and weighing about two pounds. Its manner of development is identical in the human subject and that of the above-named anthropoid apes. Its exact formation is thus described by Huxley:

The foetus thus united to the mother is nourished by means of numerous arterial and venous trunks, which traverse the deeper substance of the uterine mucous membrane, in the region of the placenta. These are connected with the placenta by means of the umbilical cord, which consists of two arteries and two veins. The length of this cord is greater in the case of man and the anthropoid apes than in any other animals, reaching in them a length of about two feet. The strict accordance which thus appears between the placental structure of man and the ape indicates, upon the basis of Huxley’s principles of classification, the same physiological functions and the same dietetic character. There exists a complete similarity between the corresponding organs in each: Their extremities end in hands and feet. Their teeth and digestive apparatus indicates a frugivorous diet. Their breasts and manner of nursing suggest the same tender care of the new-born creature; while the brain and mental capacity are also of a like character—differing only in degree; indeed, the difference between the ape and animals of the next lower grade is much greater than between the ape and man; there being in the latter case really no essential anatomical or physiological differences.

The fact that man has four cuspid teeth affords no evidence whatever that he is either partially or wholly carnivorous as regards his dietary. If in diet he is naturally omnivorous, his teeth should have the structure and arrangement of those of omnivorous animals—as exhibited in the hog, for example.

That the cuspid teeth do not indicate a flesh dietary, either in whole or in part, is shown by the presence of the so-called cuspids in purely herbivorous animals—as in the stag, the camel and the so-called “bridle-teeth” of the horse.

I am convinced that no animals were created to eat flesh, but that so-called carnivorous animals were originally nut-eating animals (see p. 55). The squirrel eats birds as well as nuts, which closely resemble meat in composition. This view readily explains the close resemblance in many particulars existing between the human digestive apparatus and that of the so-called carnivorous animals. It is reasonable to suppose that these nut-eating animals were at some remote time forced by starvation to slay, and eat, by the failure of their ordinary food supply—just as the horses of the Norwegian coast have been known to plunge into the sea and catch fish, when driven to this extremity by starvation. Suppose the carnivorous animal’s natural diet to be nuts, in the absence of his normal food he would find nothing else so closely resembling his ordinary food as the flesh of animals, since the two have about the same proteid percentages.

Dr Kellogg, in his excellent little book, entitled “Shall We Slay to Eat?” (pp. 30-32), sums up a number of remarkable facts in favour of a fruitarian diet, or at least in favour of a non-flesh diet, as follows:—

“In carnivorous, herbivorous and omnivorous animals, the mammary glands are located upon the abdomen, while in the higher apes and man they are located on the chest. This is an interesting anatomical fact to which there is no exception.

“In carnivorous animals the colon is smooth and non-sacculated. In the higher apes and man the colon is sacculated. In herbivorous animals the colon is sacculated, as in man.” (The great importance and significance of this fact will be apparent presently, when we come to consider the physiological arguments against flesh-eating.)

“In carnivorous animals the tongue is very rough, producing a rasping sensation when coming in contact with the flesh. In the higher apes and man the tongue is smooth.

“In carnivorous animals the skin is not provided with perspiratory ducts—hence the skin does not perspire in the dog, the cat, and allied animals. In the ape, the skin is provided with millions of these glands, and in man they are so numerous that if spread out, their walls would cover a surface of eleven thousand square feet. In the pig, an omnivorous animal, only the snout sweats. In horses, cows and other vegetable-eating animals, the whole skin sweats, as it does in man.” (The great importance of this fact will be apparent when we come to consider the physiological arguments against a flesh-diet: see p. 55.)

“Carnivorous, herbivorous and omnivorous animals are all supplied with an extension of the backbone—a tail. In the higher apes, as well as in man, the tail is wanting.

“Carnivorous, herbivorous and omnivorous animals go on all fours, and their eyes look on either side, while many of the higher apes walk nearly or entirely upright, as does man, and their eyes look forward.[9]

“Carnivorous animals have claws, herbivorous and omnivorous have hoofs, while apes and men have flat nails, not found in any other animal. Carnivorous, herbivorous and omnivorous animals are all quadrupeds, or four-footed, while the higher apes and man are provided with two hands and two feet. The hinder or lower extremities of the ape are sometimes erroneously called hands; according to Dr Huxley, they are, from both bony and muscular structure, properly classified as feet, and not as hands.

“In carnivorous animals, the salivary glands are small, and the saliva which they secrete has little effect upon starch, while in the apes and man the glands are well developed and the saliva is active” (see pp. 47-48).