AN APOLOGY FOR YAWNING 
: 7 AWNING is commonly said to be 
a means of ventilating the lungs 
when they need it. Everyone 
knows that it is an involuntary 
act, and often excited by seeing some 
one else yawn; the real purpose of the 
act, however, has been very little 
studieds > Prot. _F., H. ~Pike, of “the 
College of Physicians and Surgeons, 
Columbia University, New York, was 
asked for his opinion in regard to the 
evolutionary origin of yawning, and has 
sent the following remarks, with a 
warning that they are partly fact and 
partly hypothesis. 
“Luciani in his Human Physiology, 
vol. 1, p. 438, speaks of a deep inspira- 
tion as a part of the general process of 
yawning. He regards it as the external 
expression of ennui, drowsiness, hunger, 
and the like, but it does not seem to me 
that the ventilation of the thorax is 
the primary object of yawning. On 
our present views of the nature of the 
stimulus to respiration, the ventilation 
of the thorax keeps pace with the chang- 
ing hydrogen ion content of the blood. 
An increase in the concentration of the 
hydrogen ions is accompanied by an 
immediate increase in the depth or 
rate of the respiratory movements. 
There is normally a deeper inspiration 
than usual occurring every few breaths, 
and it does not seem probable that there 
is a sufficient accumulation of carbon 
dioxide in the blood under any ordinary 
conditions to require any extreme 
effort such as yawning would indicate 
if its main purpose were to ventilate 
the lungs. A little vigorous exercise will 
remove the immediate cause of yawning, 
but it will also result in a greater 
ventilation of the thorax and lungs 
than occurred during yawning. 
MUSCULAR MOVEMENTS 
“Vawning, in a state of nature, 
involves certain attendant movements 
and sounds that are absent in the human 
subject, after a course in a young 
ladies’ finishing school or any similar 
institution. The dog gives a sort of 
whine and stretches his other muscles, 
particularly those of the fore legs, as 
well as those of the head and jaws. I 
am more and more inclined to regard 
yawning as an expression of a state of 
approaching fatigue, very much analo- 
gous to the other stretching movements 
of muscles in general. It may be a 
sort of involuntary exercise to keep one 
awake until a safe place for sleeping 
may be found. There is always a little 
quickening of the faculties after a deep 
yawn, and this is more pronounced if 
there is an attendant stretching of the 
muscles. One might imagine that the 
impulse to sleep might begin to come 
upon an animal while still out in the 
open, and that, if no warning sign were 
present, he might lie down in the open 
and go to sleep in a place exposed to 
attack from enemies. The continued 
yawning may be sufficient to keep him 
awake until he can reach a place of 
safety. This particular kind of utility 
may be lacking in civilized man, but 
the whole mechanism persists un- 
changed. To a certain limited extent, 
yawning might be regarded as a vesti- 
gal function if regarded from this point 
of view alone. But I am not sure that 
yawning has ceased to be useful to 
civilized man. The onset of yawning 
may interrupt a process which might 
otherwise be carried to a harmful degree. 
A student begins to yawn in the evening, 
and, unless he resorts to some measures 
to overcome his drowsiness, the inter- 
ruption to his work is likely to become 
so great that he seeks relief in sleep. 
If he employ measures to drive away 
his drowsiness, such as the use of strong 
coffee, a walk around the block, or 
other similar things, he may be able to 
_ go on working, but he is pretty certain 
later on to feel, more severely than ever, 
the effects of fatigue, and he may suffer 
great injury if he persists too long in dis- 
regarding these warning signs of nature. 
447 
