THE EVOLUTION OF PATTERNS OF HAIR.
Some attention must here be given to the supposed mode of formation of
individual patterns of hair, that is to say, their evolution. So here
one has to move among the fields of hypothesis, without which detached
facts of nature are useless to science.
The simplest pattern consists of a reversed area of hair appearing
between two adjoining streams; the more complex are whorls, featherings
and crests. No detailed description nor illustration of the former
are required, but I have prepared a diagram to illustrate the latter
(see p. 51.) (A) shows a whorl by itself; (B) a whorl, feathering and
crest. The arrows at the sides indicate the direction of the adjoining
hair-streams, the arrow in the centre of (B) the direction of the
reversed flow of hair.
An understanding of the dynamics of a hair-whorl leads quite simply
to that of a feathering and crest, for the two latter are only the
results of the further extension of the battle of forces concerned
in the whorl itself, and the end of their conflict. A whorl marks a
point in the stream of hair where two contending forces have come
into collision; on the one hand the centrifugal force of growth from
each hair-papilla, the rate of which has been described, and on the
other a certain centripetal dynamic force which may be either that
of localised _friction_, _pressure_, _gravitation_, or _muscular
traction_, directly opposing or divergent. Thus conceived a whorl may
be looked at symbolically as a written treaty between two nations,
one of which has defeated the other, and actually as a proof that the
contending centrifugal and centripetal forces are in the state called
the balance of power. But when the centripetal force of some habitual
action prevails over that of the original force of growth in the
hair, a whorl becomes extended into a feathering, and the length of
this, metaphorically speaking, corresponds with the duration of open
fighting, and terminated by a sharp crest when another and a decisive
battle has been fought. A crest may again be looked upon as a “treaty.”
The whole process pictured here shows a battle followed by a treaty or
truce (W) again a retreat (F) and a counter-attack (C) with a final
treaty and peace.
This hypothetical treatment, with addition of some metaphors, does not
carry us far enough to leave it thus to the tender mercy of that class
of critic who relies too much on the “argument from ignorance.” He
tells us such a process as I have pictured may be true or not, and that
no one can do more than leave the case open, and treat it like that of
Jarndyce & Jarndyce where it would remain in Chancery till all of us
concerned in the inquiry have returned to our dust. The critic might
reasonably ask for experiments which will bear out the suggested views.
But verification by calculated experiments is impossible, for, _ex
hypothesi_, the variations or patterns which are described require long
periods of time for their production. Such experiments being ruled out,
the evidence in favour of the hypothesis must be sought in some region
of the hairy coat of mammals where whorls, featherings and crests can
be observed in all stages of their formation.
[Illustration: Fig. 2.--A. Diagram of a whorl. B. Diagram of a whorl (W)
a feathering (F) a crest (C).]
The Side of the Horse’s Neck.
The field chosen for observation is, from one point of view, the most
remarkable among all the numerous regions in the great series of
hair-clad mammals. The side of the neck in the domestic horse displays
all degrees and forms of whorls, featherings and crests in such variety
as to be almost bewildering. I must have examined many thousands of
specimens of this valuable large mammal in reference to this state
of things on the side of its neck, and can only regret that I have
not kept any record of them as to number or quality, and I fear the
opportunity for doing so will not return in this country. There are
three reasons for this choice of field. In the _first_ place there is
or was an extensive supply of the specimens for examination; in the
_second_, the side of a horse’s neck is a region where no extraneous
or artificial agents, such as harness, except a bridle, can operate,
and therefore Nature and the animal’s habits have free play; in the
_third_ the neck of a horse in its locomotive life is subject to
powerful mechanical forces which are _constant_, literally speaking,
while it walks, trots, canters or gallops. Here then, if anywhere, one
may read the records, in indelible characters of hair patterns, the
history of its active life and that of its ancestors, and here also one
may reasonably expect to find these patterns in every possible stage
of formation, from a mere rudiment to the most finished product in a
whorl, feathering and crest--_and this is precisely what is found to
exist_.
Even an observer not acquainted with the anatomy of this region who
watches closely a horse in action cannot fail to notice how at every
step taken there is a marked jolt of the neck produced in the neck by
the impact of its hoofs with the ground and in supporting its heavy
skull. I have computed several times the number of jolts that the neck
of a trotting horse sustains, in my numerous rides behind various
horses, during many hundreds of miles, and have reckoned the number
which occur in a horse trotting for an hour, at the usual rate at which
a doctor travels. This is on the average 6,000, and of course the
numbers of jolts in walking, cantering, and galloping vary according to
these different paces. But a great deal more of movement of the head
and neck is observed beside the jolt at every step. See how the animal
tosses up its head, twists it to this and that side for the mere _joie
de vivre_ when it is fresh, or, even when hindered by blinkers,[47] how
he turns his head to look at every passing object in the road with his
ancestral caution, how he will pass contemptuously a great horse-waggon
or even now a villainous-looking motor lorry, but will peer at a beggar
woman sitting beside the road, or a heap of stones, or a yapping cur!
All this vivid muscular work of a horse’s head and neck hardly ceases
while he is in action and at any rate not till he is dead beat, and
the higher the courage and breeding of the horse the more frequent and
brisk are his movements. Is it possible to conceive a region of the
body of any large mammal where more numerous, varied, and powerful
action of underlying muscles can be found playing their ceaseless
tricks on the sober normal slope of hair in the skin which covers them?
If there be any region approaching this I have not found it.
[47] Blinkers ought long ago to have gone the way of bearing-reins
for draught horses. If a riding horse does not need them, no more
need a draught horse be thus insulted, for very little intelligence
and patience on the part of their drivers would have educated their
excellent brains into indifference towards startling objects.
[Illustration: Fig. 3.--Superficial muscles concerned in the movements
of the head and neck of the horse.]
[Illustration: Fig. 4.--Deeper layer of the muscles concerned in the
movements of the head and neck of the horse; the scapula removed.]
The main facts of the anatomy of the horse’s neck must be referred
to here, so that a better picture may be obtained as to the powerful
forces which are found in conflict during the locomotive life of the
animal. Fig. 3 shows the superficial layer of muscles concerned in
the actions of its head and neck, and the manner in which adjoining
muscles diverge from one another should be noted. Fig. 4 gives the
deepest layer of neck-muscles, the shoulder-blade having been removed,
and Fig. 5 the immensely strong _ligamentum nuchae_, of yellow
elastic tissue, which extends from the base of the skull to the great
projecting spinous process of the lowest cervical and second and third
dorsal vertebræ.
[Illustration: Fig. 5.--Ligaments and tendons supporting the head and
neck of the horse.]
There are here indeed great forces for conflict--_first_ a layer of
strong superficial muscles, _second_ a layer of smaller muscles which
has not been figured, _third_ a deep layer of muscles, and _fourth_ a
powerful, widely-spread and strongly-attached mass of dense elastic
tissue, adapted for supporting the head without muscular exertion, but
by its elasticity allowing a downward jerk of the head and neck at
every step. It is an exceedingly important structure for a domestic
horse.
The Normal Arrangement of Hair.
So much for the active part played by a horse’s neck and head, and for
the simpler anatomical facts of the region involved. Before proceeding
to describe the results of these as seen in the hair, it is well to
make sure of a point which a critic might raise. “How do you know,”
says he, “that some of the variations in this highly variable region
of the hair are not normal. What is the normal type here?” A very easy
answer to this is found by studying, not only any Ungulate known,
except the Gnu, but more particularly all wild Equidæ; and this reveals
the fact that in all this series the normal slope of hair prevails
here, that is to say, an even trend from head to shoulder. Variations
in others, indeed, hardly exist, and I may add that the absence of
variations here is a strong piece of negative evidence in my favour,
for no Ungulate comes near the domestic horse for amount and activity
of locomotion, which is indeed his _raison d’être_. He is the only
one that has invented new patterns. But a little direct evidence
can be brought which clinches this argument from inference based on
ancestry. I made an examination, at the stables of Messrs. Tilling,
at Peckham, of 100 consecutive specimens of hackney, for the purpose
of ascertaining the proportion in that group of those that showed the
normal slope on the neck to those with variations. In 62 of these the
normal existed on both sides of the neck, 18 Normal on one side, and in
the remaining 20 there were variations on both sides. If 100 specimens
of horses contain 80 with one side and 62 with both normal the previous
inference requires no further support.
Fourteen Varieties.
I have put together here, and described, fourteen out of a much larger
number of the most instructive varieties of pattern that I have been
able to collect during the course of many years and examination of
several thousand horses. They comprise examples the mostly likely, as
I think, to convey to the reader an adequate picture of the results of
the strength, number and variety of mechanical forces in our present
battle-field of hair. The diagrams almost speak for themselves, but a
short written description will help to emphasise the salient points.
[Illustration: Fig. 6.--Side of Neck of Horse.
Normal type, hair-stream passing evenly in line of neck.--Bay hackney,
examined 3rd May, 1904.]
[Illustration: Fig. 7.--Side of Neck of Horse.
Complete whorl with wide feathering which extends from base of the neck
to the ear where it ends in a crest.--W.F.C.
Brown hackney, examined 12th January, 1904.]
[Illustration: Fig. 8.--Side of Neck of Horse.
Offside, anterior portion of neck showing line of division, B to A,
along upper border of sterno-mastoid muscle, normal arrangement from A
to C.
Grey pony, examined 15th December, 1903.]
[Illustration: Fig 9.--Side of Neck in Horse.
Near side, winter coat, showing normal arrangement from B to A, where a
division begins and extends along upper border of sterno-mastoid muscle
to base of neck.
Brown hackney, examined 28th December, 1903.]
[Illustration: Fig. 10.--Side of Neck of Horse.
Line of division of streams curving upwards to the mane near the base
of the neck.
Chestnut cart horse, examined 9th December, 1903.]
[Illustration: Fig. 11.--Side of Neck of Horse.
Near side, line of division along the upper border of sterno-mastoid
muscle diverted at C towards the mane.
Bay cart horse, examined 11th December, 1903.]
[Illustration: Fig. 12.--Side of Neck of Horse.
Near side, at C upward curve towards mane.
Brownish-yellow hackney, examined 18th August, 1903.
The same horse as appears in Fig. 13.]
[Illustration: Fig. 13.--Side of Neck of Horse--same specimen as in
Fig. 12.
Offside, fully developed whorl, feathering and crest W, F, C, lying
along upper border of sterno-mastoid muscle. Two stages of formation of
this form of pattern in one specimen.
Brownish-yellow hackney, examined 18th August, 1903.]
[Illustration: Fig. 14.--Side of Neck of Horse.
Near side, whorl (W) in place of common line of division, with wide
forward feathering to A, where the hair streams diverge sharply.
Brown hackney, examined 19th November, 1903.]
[Illustration: Fig. 15.--Side of Neck of Horse.
Near side, showing (B to C^1) diversion of hair stream towards mane
(W^1F^1C^1) whorl, feathering and crest; W^1 to W^2 stream in normal
direction W^2 a second whorl.
Chestnut cart horse, examined 1st January, 1904.]
[Illustration: Fig. 16.--Side of Neck of Horse.
Near side (W^1F^1C^1) showing whorl, feathering and crest along upper
line of division (W^2F^2C^2) a second fully-formed whorl, feathering
and crest, crossing both upper and lower lines of division, and
ending at W^1. Grey pony, examined 23rd May, 1903.]
[Illustration: Fig. 17.--Side of Neck of Horse.
Near side (W^1F^1C^1) whorl, feathering and crest, fully-formed,
cutting upper line of division at obtuse angle and a second whorl,
feathering and crest (W^2F^2C^2) along anterior part of common line
of division. Roan hackney, examined 7th November, 1903.]
[Illustration: Fig. 18.--Side of Neck of Horse.
Off side, simple whorl, behind ear at edge of mane.]
[Illustration: Fig. 19.--Side of Neck of Horse.
Simple whorl (W) at edge of mane midway between ears and base of neck.]
There are pictured here the normal type, divergent hair-streams
partially reversed, simple whorls in different regions, a whorl and
feathering, whorls, featherings and crests, and these in several areas.
It is a veritable portrait gallery in which is portrayed the earliest
and latest stages of this family of fashions in hair on the horse’s
neck. They are grouped mostly in pairs.
Fig. 6 shows the normal slope and by its side Fig. 7 gives a view of
the best specimen of a completed whorl, feathering and crest I have
been able to examine, _the whole length of the neck being occupied by
it_. So in this pair the normal and most extensive departure from it
lie side by side.
Fig. 8 shows the way in which two streams of hair close up to the ears
begin to diverge. Fig. 9 a similar divergence towards the base of the
neck.
Fig. 10 gives not only a divergence, but a well-marked turn in the
upper hair-stream and Fig. 11 the way in which this divergent turn of
hair is being converted into a feathering.
Fig. 12 presents a stream of hair still more twisted from its course
than that of Fig. 10, and Fig. 13 a whorl going on to a feathering
which loses itself, without coming to an abrupt stop in a crest which
is the more usual course.
Fig. 14 is a common type of whorl, feathering and crest in the most
usual situation. Fig. 15 a rarer and more complicated instance of a
simple whorl, a gap and then a whorl, feathering and crest in the same
“critical area.”
Fig. 16 and Fig. 17 are rare cases of irregularly placed double whorls,
featherings and crests, and give evidence of unusually complicated
traction of adjoining muscles underneath this battle-field of hair.
Figs. 18 and 19 show a simple whorl, situated at the very edge of the
mane, a very “critical” area because this looser and heavy part of the
neck is very much subject to jolting during the horse’s action.
I have little to add to the graphic evidence afforded by these
pictures, each of which I observed noted and sketched as the bearers
of them came before me during many years of a “Captain-Cuttle-like”
disposal of some of my leisure. No clearer proof can be desired of
the view here advanced, that habit or habitual muscular action, and
jolting, is the cause of the varied patterns in this field, and that
according to the Law of Parcimony no other is required, this canon
of Occam being expressed more succinctly--_Neither more, nor more
onerous causes are to be assumed than are necessary to account for the
phenomena_.