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Atavistic human foot. Its developmental significance

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ATAVISTIC HUMAN FOOT
ITS DEVELOPMENTAL SIGNIFICANCE
GEORGE A. WILLIAMS
Atlanta, Georgia
EIGHT FIGURES
Atavistic phenomena claim the interest of t.he physician
frequently because they may occasion problems of altered
function, but more often because in them he sees incidents
in the developmental course of the individual and episodes in
the evolutional history of the species. I n the human foot
may be seen many features which remind us that we are still
within the gamut of evolutional change. No one has ever
delivered an infant and noted the peculiar configuration of
the lower extremities without realizing that vast changes
must occur before the adult type is attained. Considered
functionally, the foot, with its ever-present problem of static
disorder, must convince the orthopedist, at least, that he has
to deal with an organ none too perfectly adapted to its present
requirements.
I t may be accepted that the human foot in its present form
has been evolved from one which was prehensile in type, and
was used for grasping and climbing in a manner quite similar
to that of the anthropoid primates of to-day. I n no other
way may the peculiar structure of the foot and its adaptation
to function plausibly be explained. Certain features are
common to the entire primate order, and variation in the
structure of the feet of the several genera may be regarded
as a deviation from these. Indeed, the very presence of the
so-called normal variation within a given species serves to
* From the Department of Anatomy, Emory University School of Medicine.
1
AXCERICAN J O U R N 6 L OF PRYSICAL ANTHR0POU)GY. VOL. X V I , NO.
JULY-SEPTEMBER,
1931
1
2
GEORGE A. WILLIAMS
link closely its kinship in structure with other groups. The
peroneus tertius muscle, formerly thought to occur only in
man, and as such, often proclaimed an obstacle to the theory
of a n organic evolution, has recently been demonstrated by
Morton(1) in the feet of two individuals of the Kivu, or highland, gorilla, an animal which has largely discarded its
arboreal life. The incomplete separation of this muscle from
the extensor digitorum communis in man and its complete
absence in 8 per cent of human bodies(2) would lead u s to
believe that this structure was only recently differentiated
and serve to explain its occurrence as a sport in the gorilla.
It can easily be demonstrated that the evolution of the
human foot is the result of a gradual transition, and not
the product of sudden or spectacular mutation. The comparative anatomy of the primate order presents a striking
picture of a serial change in the structure, form, and function
of the lower extremity as we pass from the more primitive
species toward the anthropoid type (fig. I). This gradual
transition is still more interesting when we correlate the form
of the foot with the function demanded of it on account of
the size and habits of its possessor. Wolff’s law, “Characteristic structure and distinctive function go hand in hand, ” is
constantly affirmed.
The first primates of which we have evidence were small
creatures not unlike the Lemuridae of to-day, and we may
assume that primate life began when these small quadrupeds
adopted an aboreal existence. The typical mammalian foot
became altered for clinging and clutching by a wide divergence of the hallux, or great toe, from the outer digital elements (fig. la). These animals were, no doubt, slow and
deliberate in their progression because of limited adaptation
to function, as, indeed, are the lemurs of the present time.
The next stage in primate development was characterized
by the acquisition of a keen sense of equilibrium in small
pronograde monkeys who were enabled to discard to a large
extent the necessity of clutching and grasping the larger
branches and ran lightly and with great agility on the distal
3
ATAMSM IN FOOT
ends of their middle metatarsals. These bones were lengthened for their new function, the phalanges being shortened.
The hallux became less divergent, a s may be seen in living
representatives of this type, the well-known macaque monkey
W
F i g . 1 Skeletons of primate feet. A, marmoset; B, macaque; C, gibbon;
D, chimpanzee (Morton); E, nine-week human fetus (Schultz); F, adult gorilla
(Morton) ; G, author’s case; H, adult human (Cunningham).
of the laboratory and the smaller zoos (fig. 1B). These ani.
mals cannot be said t o walk erect ;their characteristic position
is that of squatting.
With the next group of primates we encounter what Keith
(2) considers as one of the most important factors in the
development of the human type of foot, an increase in size
4
GEORGE A. WILLIAMS
and weight which created a postural problem and necessitated
the ability to grasp large branches to sustain such bulk. I n
order to accomplish this, the foot became divided into a
supinated outer, or digital, portion, opposed by a less divergent hallux, greatly strengthened f o r this purpose. When
the orthograde, or upright, posture was assumed, it was no
longer possible to run on the tips of the metatarsals ; it became
necessary to apply the heel to the traction surface to secure
a proper balance. The importance of this change in size
and function of the tarsus may be seen in the gibbon (fig. 1C).
This animal has a small and poorly developed heel ; it cannot
walk slowly in the upright position, but finds it necessary
to run rapidly and, on reaching its destination, immediately
squats to preserve its equilibrium. A similar disability is
seen in patients with spastic extensor paralysis of the lower
extremity, who run on the ‘balls’ of their feet and, on reaching their destination, lose their balance unless the arms can
grasp some additional means of support.
When the heavy orthograde primate began to use his lower
limbs to sustain his weight upon the ground, further changes
in the structure of the foot became necessary. When the
weight of the body was placed upon the supinated foot, most
of the burden fell upon its outer, o r digital, as compared to
the inner, or hallucial, portion. The insertions of the postural
muscles of the leg are not all into the digital part of the
foot, however, and to give these muscles a firm base upon
which to act it became necessary to fix or stabilize the inner
border of the foot. This is accomplished in the adult male
gorilla, an animal often weighing over 400 pounds and far
too heavy for arboreal life, by clumsily adducting and extending his great toe and appressing it to the ground(2) (fig. 1F).
I n this position the foot becomes a tripod with a posterior
base at the tuberosity of the calcaneus, a lateral base along
the outer, or plantar, side of the foot, and a medial base at
the distal end of the metatarsal of the great toe. This was
the first step in the development of the longitudinal arch of
the foot-a feature which is essentially human and not found
5
ATAVISM IN FOOT
in the lower primates. The further development of the longitudinal arch was enhanced by the increased pull of the flexors
of the foot, especially the flexor hallucis longus, upon their
insertions, the heel acting as a fulcrum and the tense tendons
exerting a bowstring effect upon the components of the arch
as the bow(1).
Briefly, the bony structure of the human foot may be regarded a s having resulted from a gradual increase in size of
TABLE 1
~
-
I-
Man:
Eight-week fetus
Five-month fetus
Nine month fetus
Kewborn
Juvenile
Adult
,
I
Author's case
~
32.0
10.0
8.9
5.8
5.0
6.2
....
,
32.0
Anthropoids :
Orang-utan
Juvenile chimpanzee
Adult chimpanzee
Juvenile gorilla
Adult gorilla
Adult gibbon
--
~
I
I
i
1
46.8
42.0.
39.0
25.0
25.0
17.0
69.9
81.9
81.1
85.9
84.9
83.1
....
29.5
30.4
28.4
32.8
35.0
17.2
15.3
14.1
13.0
12.8
28.6
43.4
45.9
45.7
46.7
46.9
83.3
38.8
36.7
33.3
32.0
32.8
29.0
85.1
22.0
48.4
46.6
17.8
51.2
....
....
29.6
....
....
....
....
79.9
77.5
80.3
26.1
25.0
23.4
40.4
41.8
43.0
26.2
19.7
30.4
29.3
17.7
....
!
I
24.6
28.4
32.7
I ....
....
..
I
1
I
~~~~
The figures with which the atavistic foot is compared above a r e taken from
Straus ('27).
the primate tarsus, and a shortening of the metatarsals and
phalanges, especially the latter, together with a progressive
diminution in the angle formed by the divergence of the
hallucial metatarsal from that of the second toe (table 1).
The arches of the foot have resulted from the position of
supination for the outer, o r digital elements, opposed by a
well-developed great toe. It was but a short further step
t o the formation of the longitudinal arch of the foot when
the supinated sole was placed upon the ground.
6
GEORGE A. WILLIAMS
Of the living representatives of the higher primates, the
chimpanzee possesses the most generalized type of foot (fig.
1D). From this typical anthropoid foot man's lower extremity has pursued a definite evolutional course to accommodate his requirements for terrestrial life. The heavy
gorilla, closely related to the chimpanzee, but on account of
his great weight much less arboreal in habit, presents a foot
which shows a decided tendency to follow the human course
of development, but has not progressed nearly so far (fig. 1F).
I n this animal the divergence of the great toe has been decreased to about half of the difference (25") that distinguishes
the chimpanzee foot (40") from the human type (6") (fig.
1G). It is striking that the feet of the higher primates
resemble each other most closely in their early fetal stages.
From this state the hallucial element advances in length and
the digits fall back in the human, while the opposite is characteristic of the anthropoid apes. The hallux in the macaque
monkey forms 52 per cent of the length of the longest digit;
in the chimpanzee and gorilla this proportion has been
increased to nearly 70 per cent, while in man the great toe is
equal in length with the longest of the other toes. It is interesting to note that in the nine weeks' human fetus the hallucial
element is only 95 per cent of the length of the second toe,
while i n the chimpanzee fetus of the same age this percentage
is 85 ( 3 ) . The position of the hallux in the eighth-week human
fetus is markedly divergent (32") and closely resembles that
of the chimpanzee fetus (fig. 1E).
The external appearance of the primate foot in its various
stages of development is characterized by the gradual disappearance of the lines which denote the separation and independence of the various elements of the foot, especially the
cleft which marks the divergence of the great toe (fig. 2 ) .
In the chimpanzee there is a well-defined cleft which separates
the thenar from the hypothenar sole pads. The gorilla shows
a tendency toward the obliteration of this cleft, together with
a greater development of the thenar sole pad. I n the newborn human infant the distinct cleft demarking the great toe
ATAVISM I N FOOT
7
is represented by faint creases in the sole of the foot, but
in the adult these lines almost completely disappear. The
progressive development of the longitudinal arch and the
growth of the tarsus are, of course, strikingly portrayed in
the external appearance of the foot in the various species.
CASE REPORT
A native white school girl, seven years of age, was observed
to have numerous congenital malformations; among others :
Fig. 2 Plantar surfaces of primate feet. A, chimpanzee (Emory University
Laboratory of Anatomy) ; B, gorilla (Keith) j C, author’s case.
polydactylism, syndactylism, asymmetry of the skull, divergent strabismus, and marked malocclusion of the jaws. The
family history was of no importance except for the presence
of polydactylism and syndactylism in the paternal line. A
further investigation of the child revealed a foot of unusual
appearance and remarkable mobility, although she had always
worn shoes to conceal her deformity.
8
GEORGE A. WILLIAMS
The foot was short and broad (length-width index, 46.6)
and, on account of syndactylism, the phalanges appeared to
be shorter than usual. The general shape was that of a triangle, the apex of which was formed by the narrow heel. The
great toe was widely divergent from its fellows, the divergence occurring at the tarsometatarsal articulation and forming a n angle of 20.6" in the attitude of rest as compared with
the 6" usually found in the human adult (fig. 3). In the
attitude of rest the longitudinal arch was strikingly flat
(fig. 4 ) .
The independence of the hallux was marked by a cleft which
on the dorsum of the foot extended proximally to beyond
the metatarsophalangeal articulation (fig. 3 ) . On the plantar
surface this cleft was even more pronounced, being continued
a s a well-marked depression as far as the tarsometatarsal
joint, where it faded into the depression of the sole (figs. 2C,
5 ) . Sbduction of the hallux almost obliterated this groove,
but on adduction it became a deep crease separating the
hypothenar sole pad from that of the ball of the great toe.
On the sole of the foot were also seen flexion lines characteristic of the lower primates and distinguishable in the newborn human. These lines were much more pronounced than
in the normal infant, however, even after seven years of
weight bearing.
The characteristic position of the foot was moderate supination and inversion, but there was no tendency toward clubbing, complete eversion being possible without appreciable
effort (fig. 6). A remarkable feature was that the child could
supinate and invert the foot so that its plantar surface lay
parallel to the medial surface of the leg (fig. 8). Eversion
was present only within normal limits. Plantar flexion at
the tarsometatarsal and metatarsophalangeal joints was much
more pronounced than normal, but on the contrary, dorsal
flexion seemed to be slightly more limited than is usually the
case.
The most striking feature of the entire foot was the marked
divergence and excessive mobility of the hallux. When
ATAVISM IN FOOT
9
n~ishodand at rest, the characteristic position of the great toe
was midabduction to 22.6" and moderate extension, the longitudinal arch being very flat (fig. 4). When bearing weight
upon the foot, the hallux was held in a similar position except
that the head of the metatarsal was appressed to the ground,
Fig.3 Dorsum of foot (author's case).
Fig.4 Medial border of foot (author's case).
10
GEORGE A. WILLIAMS
increasing to a certain extent the height of the longitudinal
arch. The great toe, however, was capable of hyperabduction to a n angle of 32" and could be adducted to within 13" of
the long axis of the second toe (fig. 7B). It i s rather strange
that abduction was much more powerful than adduction, the
latter action being even weaker than is present in the normal
foot. The hallux was highly independent of its fellows in
Fig. 5
Fig. 6
Plantar surface of foot (author's case)
Lateral border of foot (author's case).
ATAVISM I N FOOT
11
A
8
Fig. 7 Tracings illustrating mobility of feet. A, armless Japanese boy;
B, author's case.
Fig. 8 Tracings of roentgenograms, illustrating ankle and intertarsal mobility
(author 's case).
12
GEORGE A. WILLIAMS
flexion and extension, these movements occurring a t the
tarsometatarsal joint a s well as those distal to it. When
the movements of flexion and abduction of the hallux were
combined, there occurred a medial rotation of the metatarsal
through a n a r c of about 22", which, with a counter movement
of supination (lateral rotation) and flexion of the outer four
metat,arsals, gave the appearance of slight opposition of the
great toe. It should be borne in mind, however, that this
movement was more apparent than real and was as dependent
upon supination of the digits a s upon any action of the great
toe itself. This tendency toward opposability was best demonstrated when the hallux was forcibly adducted against a n
object of proper size held between it and the second toe.
Measurement of roentgenograms of the foot showed the hallux
to be about 95 per cent of the length of the second toe.
Except f o r the movement of supination, the lateral toes
were not unusually mobile ; indeed, on account of syndactylism
and the fact that the child had always worn shoes, there was
probably even less independence in this group than is ordinarily found in the average barefoot child of her age.
DISCUSSION
The atavistic nature of the foot described can hardly be
disputed. I t s outstanding feat.ures : 1) arrested tarsal development; 2) a divergent, highly independent hallux, 95 per
cent of the length of the second toe; 3 ) the presence of
external markings denoting independence of the component
parts of the foot, especially the hallux; 4) retention of intertarsal and tarsometatarsal mobility so that the foot may be
supinated to bring the sole into the midsagittal plane (fig. 8)
- c e r t a i n l y resemble the fetal or generalized anthropoid type
of foot as closely as they approach the adult human type.
It is interesting to observe that the r61e of the hallux in
the formation of the longitudinal arch in this case serves
to support Keith's contention as to the evolution of this
essentially human feature(2).
ATAVISM I N F O O T
13
Much has been said about the excessive mobility in human
feet of normal structure in the barefoot races, but WoodJones ( 3 ) has reminded us that Wolff 's law will not be denied
even in the most spectacular of these cases. I n a congenitally
armless Japanese boy who became very dextrous with his
feet, employing them f o r writing, drawing, etc., he found
adduction and abduction of the toes to be slightly increased,
but definitely limited to the metatarsophalangeal articulations
by the transverse metatarsal ligament, which in the human
extends to include the great toe. The most excessive mobility
was produced by extension and flexion of the great toe, these
movements, too, being limited largely to the joints distal to
the metatarsal bone. A comparison of tracings illustrating
the range of motion in this abnormally active, normal foot
with similar tracings of the abnormal foot described herein
graphically illustrates that distinctive function must be concomitant with specialized st,ructure (fig. 7). It should be
remembered that the possessor of the abnormally formed
foot had always worn shoes and had never been trained to
employ her feet except in the usual way. The contrast between these two cases serves only to emphasize the atavistic
nature of the maldeveloped foot.
SUMMARY
The developmental history of the human foot is briefly
reviewed and an abnormal condition in a seven-year-old child
is described. Her foot was short and broad and triangular
in shape, the apex formed by a narrow heel. The hallux was
widely divergent from the second toe, forming with it an
angle of 20.6" in the position of rest, this angle being increased on voluntary abduction to 32". The presence of
external markings denoting flexibility was explained in the
retention of abnormal mobility of the various joints. The
hallux was highly independent of the rest of the foot and
capable of slight opposition to the outer toes when these were
supinated. Supination of the foot to bring the soles into
the midsagittal plane of the body was possible, but there was
14
GEORGE A. WILLIAMS
no tendency toward clubbing. A comparison of the structure
and function of this foot with the normal adult human type,
on one hand, and the fetal or generalized primate type, on the
other, leaves little room for doubt as to the atavistic nature
of the phenomena involved.
BIBLIOGRAPHY
1 MORTON,D. J. 1922-1924 The evolution of the human foot. Am. J.
Phys. Anthrop., V, 1922; V I I , 1, 1924.
1924 The evolution of the longitudinal arch of the foot. J. Bone
and Joint Surg., VI, 56.
1927 Human origin. Am. J. Phys. Anthrop., X, 173.
2 KEITH,SIRARTHUR1923 Hunterian lectures on man’s posture. Brit. Med.
J., I, 451, 499, 545, 587, 624, 669.
1926 The gorilla and man ae contrasted forms. Lancet, I, 490.
3 WOOD-JONES,
F. 1929 The distinction of the human hallux. J. Anat.,
L X I I , 408.
4 S~~~A
W.UL.,
S , JR. 1927 The growth of the human foot a n d i t s evolutionary
significance. Contrib. Embr. (Carneg. Inst. Wash.), no. 101, X I X ,
93.
5 SCHULTZ,
A. H. 1926 Fetal growth of man a n d other primates. Quart.
Rev. Biol., I, 465.
TEXTBOOK
OP ANATQMY 1926 5th ed. N. Y.
6 CUNNINGHAM’S
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