Evening star., 1932-02-07
ARM-[EG LENGTH
MEASURE Of AGE
Mans Evolutionary Status
Shown by Study Reported
to AnthropoIogiStS.

AS child grows Older its legs grow
faster than its arms.
That's one reason why man and
gorilla look so different. The great apes
arms grow faster than his legs.
This popularity of the human race
may be the basis Of an important meas
ure of individual difTcrences-reheCtin
age. sex, physical constitution and he
redity-a study Of which has just been
reported to the American Association Of
Physical Anthropologists here.
The arm-lcg indeX--l00 times the
length Of the arm divided by the length
of the leg-iS q fairly reliable means of
telling a ChildS age between birth and
the twelfth year, according to the re-
port, published in the journal of the
association.
Baby Looks Like Ape.
A baby is born looking very much like
an ape, so far as this characteristic is
concerned. The arms are about as long
as the legs From birth on the annual
tncrementS of the leg are always greater
than the annual additions to the length
of the arm up to the eleventh year for
girls and the thirteenth year for boys.
This means that the arm-leg index will
decline steadily during this period. Up
to the third year it drops very rapidly,
the annual decrease becoming only about
one-fifth as great in the ninth or tenth
year Average indexes have been pre-
pared for different age levels during
childhood, for both girls and boys.
Between the thirteenth and sixteenth
year the process is reversed in girls and
the legs grow each year a little more
than the arms Boys, between 13 and
18, have approximately equal rates of
growth each year for both legs and
+Nirt the
index changes very little and so is
not an age measure
Difference in Sexes.
The sex difference is quite important,
according to the report made by Ruth
S Jones of the University Of Iowa.
There is a constant lower value for
girls compared With boys Of the same
age and height between the second
and the twelfth year. From 13 to II
the index for girls rises above that for
bows, because of the fact, aSCertained
from this study, that girls reach their
maximum height about a year earlier
than boys, while the length of the arm
continues to increase. There is some
evidence that the arm is shorter in
proportion to the leg among adult
women than among men. The differ
ence is considered evidence that the
The arm-leg index, the study shows,
tends to vary consistently according to
constitutional type, at least during
childhood The 5-year-old, who has
proportionately short legs and long
arms, is very likely to be similarly
proportioned at 9 or II. He cllngs
as closely to this measure of his in
oividuality as he does to his general
height pattern. There is also cOnSld-
cradle evidence that individual differ
enCes in this measure run in families.
Measure of Status.
The arm-leg index is considered, ac-
cording to the report, as a measure
of evolutionary status, if the point is
not carried too far. The long Crutch-
like arms and the short bent legs that
set off the gorilla or Chimpanzee from
the adult man are noe shared by the
lower members of the monkey family.
The length of the arms of all the an
thropOids. including the gibbons, is al
wayS greater than that Of the legs and
the difference between the two tends to
become greater with age-eXactly the
reverse Of the case with human beings.
The long arms of the ape are one OF
his most striking peculiaritieS.
It is pointed out in the report, how
ever. that the real difference is in the
human legs and not the ape arms Ac-
tiallv the ratio of a mans arm length
to the length of his trunk is about the
same as that Of ChlmpanZee. Inc
proportion between the length OF the
legs and that Of the trunk, however, IS
much greater for man than for any
of the apes.