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Not Necessarily Lacking in Mental or Physical VigorNever
Absolutely Identical in Looks or Actiom-r-Often No More
Alike' Than Brothers and Sisters Born Many Years Apart
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These Ywin Sisters Are Very
Much Alike, but Science Finds
That a Great Many Brothers and Sisters Bora Years
Apart Would Show Just as Close a Resemblance If They
Could Be Viewed Side by Side at the Same Ages.
SCIENCE has recently- made some very
interesting and important discoveries
about twins, and as a result of these
we now know that a great many Ideas on
this subject which hare long been accept
ed as true are entirely incorrect.
Twins are not necessarily lacking in
mental or physical vigor; they are never
absolutely Identical in the way they look .
or act; they often differ from one another
as widely as brothers and sisters born
many years apart; the body of a twin is
likely to be more symmetrical than that of
one not a twin these are Just a few of
th things which are pretty well estab
lished toy the recent scientific investiga
tion. This Investigation was begun over a
year ago by the American Genetic Asso
ciation, an organization devoted to study
of the laws of heredity and their applica
tion to the Improvement of plants, ani
mals and human racial stocks. Appeals
were sent to all parts of the world for
detailed information concerning twins, to
gether with photographs of them at vari
ous ages. Responses were received from
more than 600 pairs of twins and their
parents, and with them came 160 photo
graphs of twins. With this mass of life
histories and pictures at their disposal the
scientists connected with, the association
have been able to. make a more exhaustive
study of the whole subject of twins than
has ever before been attempted.
From time immemorial many parents
have felt serious regrets over the arrival
of twins owing to the popular-belief that
such children were less vigorous than
others not likely to be long lived and not
so well equipped for success In life. It
was long supposed that there was strong
sclentiflo (basis for this belief, particu
larly in the case of what are known as
Identical twins.
These are children sprung from a single,
parent cell instead of being the . product
of two unions of two different mother and
father cells as what are called fraternal
twins are. Many scientists thought it
quite reasonable to suppose that a baby
having only half a cell from which to
draw its heredity would be less vigorous
than one springing from a whole cell.
But the recent investigation by the
genetic experts leaves no ground for be
lieving any such thing. On the contrary
It presents a great deal of evidence which
seems to show that It Is a highly fortu
nate thing for a child to be born a twin.
The record of the Grosvenor twins
Gilbert and Edwin Grosvenor would of
" itself be almost sufficient to shatter the
theory that identical wins are naturally
ill fitted for success In life. As students
at Amherst College these twin brothers
divided highest honors In the class room
and on the tennis court After graduation
oue, Ms uuuuer wu uircviur ot luo nsuumu
Geographic Society, and the other as as
assistant attorney-general and partner In
one of th country's greatest law firms,
have demonstrated, their abilities as
.. leaders. , ,
During their whole lives the two have
fiever varied more than a pound in weight
Prints of the Left Soles
of Twin Brothers,
Showing Great
Similarity in the
General Plan of the
Lines But Many
Differences in the -Minor
Detail. Similar
Differences Prevail
Throughout the Mental
and Physical Make-Up
of Twins and Prevent
Their Being; Absolutely
Identical.
In college their grades never varied more
than one-tenth of one per cent. Their
tailor says that one of the twins has a
short left arm and the other a short right
arm. Although absolutely dependent upon
glasses, each can wear the other's.
Their Illnesses have often coincided.
They have always been devoted friends,
and frequently their letters cross. Most
of their tastes are similar, hut there is
one striking exception they have never
agreed when it came to girls!
"They look enough alike to be twins,"
is an expression one often hears, but it is
a statement which ha9 no good Scientific
basis. As a matter of fact, while certain
twins show profound resemblances in
both mental and physical traits, others
show no such unusual similarity. Twins
that look and act alike attract our atten
tion more than the dissimilar ones and
this Is what has given rise to the idea that
all twins are very much like one, another.
Of the 600 pairs of twins studied by the
American Genetic Association a large
number showed a remarkable degree of
resemblance, but on the other hand many
showed the most surprising dissimilarity.
And it is believed that the average re
semblance of all the twins in the world
Is considerably lower even than It was
found to be in this somewhat selected
group.
Exact correspondence In the height of
twins is not at all unusual, and a differ
ence of a quarter of an inch more or less
is common.
Yet variations of several Inches some
times occur, and considerable differences
are sometimes found between twins other
Wise very similar.
Complete identity in weight, or a differ
ence of only a pound or two, Is common.
The changes in weight of many twins, as
In the case of the Grosvenor brothers, are
always parallel, so that they never differ
from each other by more than a small
amount.
Perfect uniformity In color of hair and
eyes is the rule with twins. But, on the
other hand, twins one of whom has dark
eyes and the other light are rather fre
quent. In general, similarity with reference to
one trait Is correlated with reference to
most other traits. Rarely are there only a
few points In common. In other words,
either twins look very much alike or else
they show a wide difference in appearance.
The same general laws hold good ,for
gait, tone of toice, reaction to foods and
ate
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An American Mother and Her Two Pairs of Twin Who Were Among Tho
JVeighed, Measured and Carefully Studied by the Scientists in Making
the Discoveries Explained on This Page.
The Palm Prints of Twins Showing, as in the Case of the Soles, a Similarity in General
Pattern, but a Great Difference in the Way the Details Are Worked Out.
susceptibility to disease, as well as for
mental capacities, intellectual tastes and
likes and dislikes. One pair of twins state
that bananas make "both very sick." Two
little acrohats who are familiar figures In
the motion pictures always get hungry
and sleepy at exactly the same time.
Over and over again the two twins of a
pair are found to have virtually the same
preferences and aversions In their studies.
One twin and her sister commonly dream
about the same persons at the same time,
even when sleeping In widely separated
places. And not only thatthey actually
dream the same things about these per
sons! Rather a surprising number of the hun
dreds of pairs of twins studied were com
posed of one right and one left handed
individual. It has been suggested -that
perhaps one twin Is frequently the "mirror
Image of the other, left handed and with
heart and other organs reversed in their
symmetry. A further investigation is now
under way to determine If this Is true. .
Some who believe that right or left
handedness is an acquired characteristic
and not hereditary have still another ex
planation to offer.
Twin babies generally face each other in
their beds, and if care Is not taken to
change them about frequently their heads
become assymmetrical on opposite sides
Thi&j it is suggested, may possibly affect
(C) 1920. International Teatura Service, lac'
the hemispheres of their brains differently,
and thus influence the amount of use that
Is made of the left hand in one Infant and
the right in the other.
Do twins .like one another better than
anybody else? Yes, says science, as a
general rule they do. But It is noticeable
that this fondness Is usually strongest be
tween twins who are not only of the same
sex, but otherwise very) similar.
Right here it should be mentioned that
statistics based on thousands of cases show
that about one pair of twins in every three
born consists of a boy land ft girl. Tet of
160 pairs of twins whoso pictures were sub
mitted to the genetic- experts only 22 were
of both sexes. This small percentage is
accounted for by the fact that twins of dif
Terent sexes 'pigeon" twins are rarely
as fond of one another as those of the
same sex and. therefore, often drift apart
early In life.
Are twins ever so much alike that "even
their own mother can't tell them apart"?
No, says science, the resemblance between
similar pairs of individuals is never quite
complete, and practically every pair is
found to differ more or less widely in at
least one respect Although marked simi
larity is, with rare exception, the rule,
absolute identity is not attained.
Science, believes that the resemblances
found in Identical (wins twins derived
from a single parent cell are not super
exeat Britain &ihU Beaerrad.
flclal, but pervade their whole being. A
few dissections of Identical twins which
have been made reveal remarkable simi
larity in' the configuration of the brain
and in the structure of the muscles and -
blood vessels. The tendency of such twins
Is always to absolute
identity, but they never
quite attain it.
The explanation of the
fact that twins are never
actually Identical Is prob
ably to be found in the
same causes which pro
duce variations between
the two sides of the body
in a single Individual.
But Professor H. H. Wil
der holds that while the
variation between two
twins may be as great or
greater than it is be
tween the two sides of
an ordinary individual's
body, it is far less in the
body of each twin. In
other words the body of
a twin generally shows
greater symmetry than
that of the ordinary in
dividual Fraternal twins those
derived from two unions
of two different mother
and father cells are
never so, much alike as
those of the Identical variety. In fact their
resemblance to each other Is only about
equal to the average for all children of
the same family. Brothers and sisters
born many years apart would doubtless
look as much alike as fraternal twins, if It
were possible to see them together at the
same ages. Of course, the resemblance
between fraternal twins tends to Increase
If they grow up together, owing to their
being subjected to the same environmental
Influences.
But the most interesting Question In
connection with the study of twins is
whether a degree of difference similar to
that which keeps twins from being abso
lutely identical-: and often makes them
quite unlike in mental and physical traits
can also "manifest itself in their moral
natures.
Is It possible for one twin to become the
worst of criminals while the other becomes
an honest, useful member of society? Can
we have In a single pair of twins indi
viduals as different in character as Dr.
Jekyii and Mr. Hyde?
Science's latest discoveries lead to the
belief that the moral natures of twins may
show as great if -not greater differences
than their physical and mental traits. We
twins shows that while the lines tend to be
closely similar in their general pattern
there are always numerous minor points of
difference.
Similar small points of difference In the
development of the brain cells might easily
result in moral natures that would be as
different as right is from wrong.
Environment also plays an Important
part in making the moral as well as the
mental and physical natures of twins alike
or unlike. Twins living together under
precisely similar conditions naturally tend
to become more and more alike, but wide
differences in them would probably result
if they were separated and forced to live
under conditions not at all the same.
Take the case of two middle-aged twins
whose life histories were among those
studied by the genetic experts. In height,
weight, tastes,, dispositions and t talent
these men are the same. They have lived
and worked together continuously for
twenty-five years, and have never been
separated. Nine persons out of ten can
not tell them apart.
How far could different environments
have forced these men apart In character?
Supposing that one had grown up in
China, speaking only Chinese, and the
other in Spain, speaking only Spanish,
would they still look as much alike as they
do, and when we came to know them
would they Beem as-much alike? Is it not
possible that if one bad been subjected for
years to evil Influences ana the other only
to good they would have become quite
different in character)
These questions are most Interesting,
and it is hoped that further study of twins
will enable science to answer them.
The importance of twins in furnishing
science with evidence of the limitations of
Environment cannot be exaggerated. Iden
tical twins are the only human beings In
'.he world who have exactly the same
heredity. If we can find out the character-
ietic ways In which, they remain the same
throughout life, the qualities and habits
and mannerisms which persist unchanged
In them both. In spite of their living in
entirely different surroundings, we shall
know much more than we do at present
about what attributes are hereditary and
fixed and what are those which We can
hope to modify by environment and edu
cation. ' -
Any exact knowledge we can gain by &
t study of two identical twlns who -were
separated from each other as babies and
brought up in different towns under en
tirely different circumstances, scarcely
knowing each other, will give us a clearer
Idea than we appear to have now of what
changes ' in our bodies, and, perhaps, too
in some of our mental and moral charao
rs, are clearly due to the things we eat.
me exercise we take, the associations we
have seen how even the way twins lie fac- nake. and the work we do to onr m.
lug each other in their crib may make tironment, as it is call and what changes,
their bodily mechanisms different. A or failures to change, can fce correctly
study of the palm and foot print of various xaced to the very beginnings of our lives.
It . f