CHANGES WHICH THE JAWS AND TEETH OF MAN HAVE UNDERGONE DURING MAN’S
EVOLUTION FROM HIS ANTHROPOID ANCESTORS
During man’s progress upwards from the anthropoid his diet has
undergone a progressive change, and a parallel adaptation has taken
place in his jaws and teeth. Dietetically considered, we may divide
his evolutionary career into the following epochs[8]: (1) the
anthropoid stage; (2) the pre-cooking human stage; (3) the cooking
pre-agricultural stage; (4) the early agricultural stage; and (5) the
late agricultural stage.
1. _The anthropoid stage._--The diet of man’s anthropoid ancestors
was probably much the same as is that of existing anthropoid apes; it
consisted, namely, of raw vegetable and animal food, necessitating a
vigorous use of the maxillary apparatus. This latter, we may assume,
was of the type belonging to the anthropoids--_i. e._, the jaws were
massive and markedly prognathic; the denture was the same as it is in
existing man, but the teeth were larger, especially the upper canines,
which served as weapons of offence and defence; the third molars (the
wisdom teeth) were as large as the other molars and were provided with
three fangs, and there was an ample portion of alveolar ridge behind
them; there was no chin. No doubt the massiveness and the marked
prognathism, which characterised the jaws at this stage, served other
ends than that of mastication; it is obvious that projecting jaws and
teeth are much more effectual for seizing and lacerating prey than are
the orthognathic jaws of modern man.
2. _The pre-cooking human stage_ extends from the time man’s ancestors
first assumed the human form till they learned to apply fire in the
preparation of their food. During all this period the jaws and teeth
were probably used as much, or almost as much, for mastication as
during the anthropoid stage; raw animal food had to be torn from
the bones, the latter had to be crunched, while the bulk of the
raw vegetable food needed then no less than it needs now prolonged
and vigorous mastication in order to liberate the starch and other
nutritive ingredients from their undigestible cellulose envelopes.[9]
Nevertheless, the jaws and teeth underwent considerable change during
this period, for not only were they with every advance in intelligence
called less and less into requisition for purposes of offence and
defence, but the jaws, at least, became materially modified in
correlation with the expanding cranial cavity and in connection with
the assumption of the erect posture. It is, I think, rather for these
reasons than in consequence of alterations in the nature of the food
that the masticatory apparatus now gradually lost its more bestial
aspect and assumed an essentially human type, becoming towards the
close of the period much the same as may be observed among the most
primitive peoples now living.
3. _The pre-agricultural cooking period._--The characters of the
maxillary apparatus belonging to this period are still available for
study, the aboriginal Australians, the Bushmen, Negritos, and many
Esquimaux not having yet emerged from it. So far as mastication is
concerned, cooking influences vegetable far more than animal food, for
it not only softens it but by rupturing the undigestible cellulose
chambers and liberating their contents relieves mastication of one
of its essential functions. Wherefore, with the advent of cooking,
man’s jaws and teeth began to get smaller, and they have continued to
diminish in size up to the present time. No great diminution, however,
took place at first, inasmuch as the diet still continued to be largely
animal (and prior to the use of knives and forks such food had to be
torn by the teeth), while the coarse vegetable food of this date, even
when cooked, still needed laborious mastication. The chief differences
between the maxillary apparatus of this early cooking age as compared
with that of the present day are as follows: the jaws of the earlier
period--_e. g._, in the aboriginal Australian--are more massive, and
their sagittal diameter is greater, giving rise to decided prognathism,
the teeth for the most part are larger and stronger, the third molars
being nearly, if not quite, as big as the other molars, and provided
with three fangs, while there is a considerable portion of alveolar
ridge behind them. The third molars, however, show a decided tendency
to be smaller than the rest, and the alveolar ridge behind them is less
marked than in the previous period, features, I doubt not, attributable
to the influence of cooking in diminishing mastication. Dental caries
is rare and is chiefly met with in the third molars.
4. _The early agricultural age._--All the existing primitive races
which have attained to the cultivation of the soil may be regarded as
belonging to this period. Previously to it man was mainly carnivorous,
owing to the comparatively limited quantity of vegetable food
available, so long as the supply was left to nature alone; but when by
cultivation this supply was increased and, at the same time, rendered
more constant and certain, he gradually became less carnivorous and
more vegetarian in his diet. The result of agriculture, however, is
not only to increase the supply of vegetable food, but to diminish its
fibrous, cellulosic ingredients, and thus to render it more easily
masticated. Hence at this stage we find the maxillary apparatus
becoming smaller than in the previous period, although the difference
as shown--_e. g._, by the examinations of the skulls of the African
negroes and the Melanesians--is less pronounced than we might perhaps
have anticipated; prognathism is not so decided, the jaws are smaller,
also the teeth, especially the third molars, which now for the first
time show a tendency to be furnished with two instead of three fangs,
while the alveolar ridge behind them is distinctly shorter than in
the preceding period. Dental caries, hitherto rare, now becomes more
frequent.
5. _The late agricultural period._--A mid-agricultural period might be
described, but I shall take no account of it here, but pass on to a
consideration of the late agricultural period--that, namely, in which
we ourselves live. The chief characteristic of the food of this period
is its softness. Cooked animal food requires, indeed, more mastication
than raw, but the vegetable food of to-day, owing to the combined
effects of improved agriculture, and skilful milling and cooking, is so
soft as to excite comparatively little mastication. The present may,
in fact, be described as the _age of pap_. Hence the jaws and teeth
are now called upon to perform far less work than in any earlier stage
of our evolution, and there has taken place in consequence a great
diminution in their size, more especially in the size of the jaws, so
that there is now often no room for the teeth to take up their normal
positions, and there is generally a complete absence of alveolar ridge
behind the last molars. The latter are, moreover, apt to be very small
or even absent, while dental caries is alarmingly frequent.
It will thus be seen that from the period of the anthropoids to the
present time, a progressive change in the size and shape of the jaws
and teeth has been taking place, a change which is to be explained
by (1) the cessation of the need for using them for offensive and
defensive purposes; (2) the growing capacity of the cranium and the
assumption of the erect position; (3) the progressive alteration in
man’s diet; and probably also (4) considerations of beauty. The first
three factors have operated through natural selection, the last through
sexual selection, which has come into play, I would suggest, chiefly
within recent times. Probably the most pronounced change which has
taken place in the jaws during the agricultural periods has been the
suppression of prognathism which, in the woman especially, is very
unsightly, and tends to diminish the likelihood of marriage.
INSTANCES OF THE VIGOROUS USE TO WHICH THE JAWS AND TEETH ARE PUT AMONG
EXISTING PRIMITIVE PEOPLES
A study of existing primitive peoples brings forcibly home to the
mind how laboriously the jaws and teeth of our primitive ancestors
were used. I have already shown how in pre-agricultural and early
agricultural times the nature of the food compelled a sustained and
vigorous exercise of these structures, and I wish here only to refer
to a few specific and peculiar instances of laborious mastication
exercised by primitive races now or recently living.[10] Among some
of these mastication has been promoted almost to the position of an
industrial art.
_The chewing of very tough substances in order to extract therefrom
liquid or nourishment._--The recently extinct Tasmanians included
among their articles of diet a species of sea-weed which, even when
cooked, was so tough as to require long-sustained mastication in order
to extract its nutrient elements. The Indians of North California chew
kelp, which is “as tough as white leather” (_i. e._, leather dressed
with alum). “A young fellow with good teeth will masticate a piece
of it a whole day.” Again Featherman[11] tells how when the Bushmen
are short of food in the winter they steep an old dried gnu-skin in
water and, having rubbed off the hair, boil it, and proceed to gnaw the
tough morsel until their very jaws ache. The Modoc Indians are said to
munch the raw kais root all day long.[12] Among the Esquimaux it is a
universal custom to chew the raw skin of the whale, the porpoise, and
the seal for the blubber it contains, and the skin being as tough as
india-rubber, it requires, as may be imagined, a good deal of chewing.
The Lower Californians also chew deer-skin and ox-skin (Bayert). The
more southern Esquimaux, according to Nansen, preserve the stalks of
_angelica_ by steeping them in a mixture of chewed blubber and saliva.
Finally, I may refer to the habit of chewing the sugar-cane, a practice
which is prevalent among the natives in all countries where the cane
grows, and affords, it need scarcely be said, abundant exercise for the
jaws and teeth.
_Mastication in the preparation of beverages._--I find that among
widely separated aboriginal peoples chewing is resorted to in the
preparation of beverages, both intoxicating and non-intoxicating.
The Gran Chaco Indians make an intoxicating drink by chewing the
algarroba bean and then spitting into a receptacle. In other parts of
South America berries are chewed with the same object. In some of the
Pacific Islands boys and girls with good teeth are selected to chew a
root (kava), from which they then prepare a drink. In New Guinea drinks
are similarly prepared from roots. Boiled cassava root is chewed by
the Indians of Nicaragua for the same purpose. In British Guiana the
natives make a drink by adding chewed maize and saliva to sweet potato,
maize, and sugar-cane. The Indians in Honduras, after steeping cassava
cake or carbonised bread in hot water, chew a portion and mix it with
the rest.
_Mastication in the industries._--Even among moderns teeth are used
for many purposes other than mastication--_e. g._, for holding pins
and needles and for severing cotton; also in some industries--_e.
g._, among diamond workers--where it is the custom for girls to hold
the diamond between their front teeth, which in consequence get much
worn away, as I have myself seen. It is only among primitive peoples,
however, that the jaws and teeth actually play the part of implements
for use in the arts. The Australian women make lines, nets, and bags
by chewing various kinds of fibre, a process which wears down their
teeth considerably and may cause them to be tender.[13] The Esquimaux
are still more dependent upon the use of their teeth as implements,
especially in the preparation of skins for their clothing, boats, and
lines. The teeth are used to hold the skins, while the latter are
being scraped, the mouth constituting, in fact, “a third hand;” and
the front teeth of Esquimaux women are often by this means worn away
to the merest stumps.[14] The garments of the Esquimaux, even to the
boots, are made up of skins which have been laboriously chewed for this
purpose by the women “inch by inch,” till they acquire a beautiful
softness and flexibility, and are often, indeed, chewed again after
having been dried. And we are told that the women have no objection
to the task, while the children are eager to help in it on account of
the blubber the skin contains; also, that in bad times the men do not
object to join in the work. The lines for harpooning are prepared in
a similar way from the skin of the bearded seal, and in very large
quantities.[15] When we think of the quantity of skins needed for these
lines, for their dress, including boots and gloves, and for their
boats (although for the latter some skins are used without having
first undergone chewing), it is clear that enormous quantities must be
chewed. The Esquimaux men also use their teeth considerably in other
work--_e. g._, in lashing the sledges together.[16] The Indians of
North California use their teeth for stripping the bark from the fresh
shoots employed in making their wickerwork utensils, and they also
employ their teeth in making strings, cords, and nets.
THE INSTINCT TO MASTICATE
Seeing that the maxillary apparatus of man has for long ages past been
put to vigorous use, it is not surprising that the need to exercise it
should express itself as a powerful instinct. This instinct manifests
itself in many and curious ways, some of which I will now consider.
During the early months of life the natural function of feeding at
the breast provides the infant’s jaws, tongue, and lips with all the
needful exercise. This bottle-feeding fails to do, and we frequently
find bottle-fed children seeking to satisfy the natural instinct by
sucking their thumb, fingers, or any convenient object to hand. The
teeth are a provision for biting hard foods, but even before they
actually appear we find the child seeking to exercise his toothless
gums on any hard substance he can lay hold of, and there can be no
doubt that exercise of this kind tends to facilitate the eruption of
the teeth, a truth, indeed, recognised universally, whether by the
primitive mother who strings the tooth of some wild animal round the
neck of her infant, or the up-to-date parent who provides her child
with a bejewelled ivory or coral bauble. When the teeth have erupted,
the masticatory instinct finds among primitive peoples abundant
satisfaction in the chewing of the coarse, hard foods which constitute
their dietary; but among us moderns, subsisting as we do mainly on soft
foods, affording but little exercise for the masticatory apparatus,
it does not find its proper expression, and thus tends to die out.
Nevertheless, it dies a hard death, and long continues to assert
itself; witness the tendency of children to bite their pencils and
pen-holders; I have known a child to gnaw through a bone pen-holder,
much in the same way as a carnivorous animal gnaws at a bone.
This instinct to chew for chewing’s sake manifests itself all over
the world. In our own country not only do children bite pencils and
pen-holders, but they will chew small pieces of india-rubber for hours
together. The practice of gum-chewing, so common among our American
cousins, evidently comes down from far-off times, for the primitive
Australians chew several kinds of gum, attributing to them nutrient
qualities,[17] and the Patagonians are said to keep their teeth white
and clean by chewing _matri_, a gum which exudes from the incense bush,
and is carefully collected by the women and children.[18]
A widespread custom in the East is betel-chewing, which is met with in
India, Malay, Melanesia, and Polynesia, and even among the primitive
Veddahs of Ceylon. This article is composed of the pungent leaf of
the betel plant, the areca nut and lime rolled together, and when
chewed yields a reddish juice which stains the mouth and teeth. The
Veddahs, failing to get the genuine article, manufacture a quid from
the leaves of an aromatic plant, the barks of one or two kinds of tree,
and calcined small shells.[19] The compound must possess some strange
attraction, for otherwise such pains would not be taken to secure it.
What is the attraction? Doubtless betel has stimulating properties,
and it must, moreover, be remembered that the mere mechanical act
of mastication stimulates the circulation, a fact which helps to
explain the tendency for man, all the world over, to chew non-nutrient
substances. Tobacco-chewing is common in many parts of the world, and
here, again, the effect for the time is stimulating. Pitcherie is
extensively chewed among the aboriginal Australians; it consists of
twigs of about the thickness of rye-grass stems, which are first chewed
into a mass, then mixed with the ash of gum trees, and made into a
paste, which is chewed for its stimulating and narcotic effects.[20]
I may allude in passing to the grinding of the teeth, which takes
place during sleep in disturbed states of the nervous system. It is
a true masticatory act, in which the normal lateral movement of the
mandible is well marked, and it may thus be regarded as a perverted
manifestation of the masticatory instinct.
THE CAUSATION OF INEFFICIENT MASTICATION
The effects for good upon the organism of efficient mastication being
profound and far-reaching, it follows that inefficient mastication must
lead to many evils. What these are we have now to consider; but first
it will be well to inquire into the causes of the defective mastication
which prevails among moderns.
1. _Softness of food._--By far the most important of these lies
in the nature of the food taken. The food of to-day--of the late
agricultural age period, as I have termed it--is for the most part
soft and pappy, of a kind which does not compel thorough mastication;
so much so, indeed, that, as I have already said, we may speak of this
as the age of pap. This feature is especially noticeable in the case
of children’s diet: under the modern system children are kept on a
liquid, or semi-liquid, diet, not merely during the first months, but
during the first years of life, and at the seventh or eighth month all
kinds of artificial saccharide foods in liquid or semi-liquid form are
poured into the child’s stomach; thereafter he is fed on such viands
as mashed potatoes and gravy, rusks soaked in milk, milk puddings,
bread dipped in bacon fat, pounded mutton, thin bread-and-butter,
and the like; and we are told that this is the kind of diet best
suited to the young human, from the time of weaning to the end of the
second year! The same pernicious methods are adopted subsequently.
“Perhaps the great majority of children after they have got their
complete set of temporary teeth have,” writes Dr. Sim Wallace,[21]
“a dietary such as the following. Breakfast: bread-and-milk or
porridge, milk, tea, coffee, or cocoa, bread-and-butter, perhaps an
egg. Dinner: potatoes and gravy, or meat, milk pudding. Tea: milk
or tea with bread-and-butter, jam, cakes. Supper: bread or biscuit
and milk.” Now food of this kind does not invite mastication, and it
finds its way into the stomach all too readily. Hence the instinct to
masticate has little opportunity of exercise and, not being properly
exercised, tends, as I have said, to die out. Small wonder that the
child nourished on such pappy food acquires the habit of bolting
it, and learns to reject hard, coarse foods in favour of the softer
kinds; everything nowadays must be tender, pultaceous, or “short.”
Given a choice between a food compelling little or no mastication
and one necessitating prolonged mastication--as between, say, fresh
Vienna bread and an Abernethy biscuit--and in nineteen cases out of
twenty the one which gives the least trouble in eating will be chosen.
To such absurd lengths has this harmful custom been pushed that
even bread crust is avoided by many. Witness the fashion of eating
bread-and-butter with a minimum of crust; order bread-and-butter at
any place of refreshment, and the last thing you will be served with
is a plateful of crusts of bread. Many establishments, indeed, make
a regular practice of giving away their crusts as unsaleable. Thus,
the rectangular loaves used for bread-and-butter in the “Aërated
bread-shops” are cut transversely into slices, each loaf thus yielding
two end crusts which are put into baskets for the poor, only the soft
crumby pieces being reserved for the customers, to be, in due course,
no doubt washed down by copious libations of tea and coffee.
When we trace the diet of the modern from childhood upwards we find the
same story: it tends to remain soft and pappy to the end. Animal food,
especially as it comes to the tables of the well-to-do, necessitates
very little mastication. It is the coarser varieties of vegetable food
alone which call out the full functional activity of the masticatory
apparatus, but the vegetable food of to-day is rarely of a kind to do
this; cooked vegetables, such as potatoes, greens, peas, and beans,
can be, and generally are, swallowed after little or no preliminary
mastication, and our flour is so carefully deprived of its fibrous
portions and so cunningly dealt with in the bakehouse and kitchen in
the making of bread, cakes, and pastry which shall eat light and short
that these articles get very little chewing; while such vegetable
products as rice, vermicelli, tapioca, and macaroni are, as served at
table, so soft that they slip down into the stomach almost as readily
as simple milk. Let any one run through his dietary of any one day,
and he will realise how very little work his masticatory apparatus is
called upon to perform. It will read something like the following.
Breakfast: porridge and milk, eggs, bacon, bread, and marmalade. Lunch:
fish, tender meat, boiled vegetables, bread, some “sweet,” and cheese.
Tea: bread, butter, and cake. Dinner: much the same as lunch. What
opportunity, I ask, does such a bill-of-fare afford for the development
of teeth and jaws, and for the proper functional activity of the
salivary glands?
2. _Defective masticatory apparatus._--Another potent cause of
inefficient mastication is some defect in the masticatory apparatus,
and defects of this kind are very common in those who have not been
accustomed to masticate thoroughly in early life. Foremost among these
are irregularities of the teeth leading to faulty “bite” and caries of
the teeth which causes them to be tender or to break away, if it does
not lead to their actual extraction. Mastication cannot be thorough
where the bite is defective, for this not only leads to imperfect
opposition of the upper and lower teeth, but renders the lower ones
incapable of that ample lateral movement, against the upper which is
needful to normal mastication.
3. _Idiosyncrasy._--Some are temperamentally more disposed to hurry
over their meals than others. The katabolic, restless, nervous
individual is more apt to swallow his food hastily than is his more
deliberate and phlegmatic brother. Individual differences in this
respect are even observed among the lower animals. Thus, one of a pair
of horses of about the same age and build is nervous and excitable
and inclined to bolt its food, while its companion of more stolid
temperament is a thorough and efficient masticator. The former shows
comparatively little wearing down of the teeth, and often suffers
from indigestion, a large portion of corn grains passing through
his digestive canal intact; in the latter the teeth are well worn,
indigestion never occurs, and but very few grains pass through the
digestive tract unchanged. It may be objected here that we cannot
help temperament, and to a large extent this is true; but much can be
done towards modifying it, and it is something to know where dangers,
temperamental dangers, among others, lie.
4. _Circumstances of life._--Again, in this hurrying, strenuous age
people are much less deliberate than in the easy, slow-going days of
long ago. A meal is too often regarded as something to be got through
quickly, as taking up time which might be devoted to something more
profitable. Especially is this true of breakfast and lunch; it is no
uncommon thing for a business man to hurry through his breakfast in a
few minutes, preparatory to rushing off to his train, and his lunch
as likely as not is as hastily swallowed in his office or at a bar.
Tradesmen are apt to take their meals in mere snatches; apprentices,
shop girls, and other “hands” are often not allowed sufficient time
for their meals; while, to come to the professions, we all know how
the busy medical man, for instance, is often obliged to take a hurried
snack in the short intervals between seeing his patients. No wonder
that thus circumstanced people acquire the habit of bolting their food.
A meal should be regarded as an end, and an important end, in itself.
It should be taken at leisure, body and mind being, for the time being,
given up to it, and to agreeable social intercourse. If this rule were
always observed a most important source of inefficient mastication
would be removed.