Omaha daily bee., 1916-05-30
Two Kinds of Twins
Literary Digest.


EEW persons know that If present biological
l. theories are correct, there are two fundamen-
tally different kinds Of twins In one kind, where
each individual develops from separate egg
cell there is more intimate connection imam
between any two children Of the same parent IN
the other the twins really one individual split
in two, being products OF single divided egg
cell Twins Of the first type may have little re-
semblance and may be of different sexes. WINS
OF the SECOND type are always OF the same sex
and are often so much alike that only their CLOS
est friends can tell them apart These facts are
brought out by a discussion in The Journal OF
Heredity. in which DR.. {. r. Danforth OF the
Washington University Medical school, St.
Louis, inquiries whether or not twinning runs N
families He gives on this point the results OF
Investigations in 81. Louis;
"The kind of evidence that one gets as to the
heredity Of twinning may be indicated by refer
ence TO group Of fifty st. Louis families The
investigator had no knowledge Of any Of these
families until in each case, the birth OF twins was
reported to the bureau OF vital statistics On
looking into the family histories, It was Learned
that these fifty newborn pairs OF twins had NJ
elder brothers and sisters born singX ana
twenty (ten psirs) who were TWINS Inc ire
anency OF twins among the brothers and SIS.
tiers Of twins then is about :l8. In the mothers
fraternties (groups Of brothers and sisters there
had been 3l8 single births and ten pairs Of twins
q 32), and in the fathers, 2l9 single and eieht
pairs OF twins lls0). comparing lHeee nkullCa
with the normal incidence for ST. Louis l90o)
one is justified, especially since essentially sm-
lar figures arc obtained from more extensive
data in concluding that twin-production is ire
quenty family PECULIARLY
"Anayzing the individual families, evidence is
found that what seems to be biovular twinning
is hereditary in the direct female line. Whether
there is any relation at all between the two types
is an open question. While some OF these fami-
lies furnish beautiful charts indicative OF he
reditary tendency for twinnng, others are ire
ouently met with in which while there may be a
record OF many individuals in several genera
tions, only one pair OF twins appears. In these
instances the twins sometimes seem 10 be bioyu-
lar, sometimes unovular. Such family histories
may indicate that while twinning Is IN some way
hereditary in most instances, il may nevertheless
at times appear sporadcally. The most prob
able inference 20 be drawn from this tact would
seem 70 be that the ability 10 produce twins Is
possibly common 10 all strains and that the ire
duency OF twin-birth in different lines is merely
relative. II is not likely, on the one hand that
strains will be found in which twins never occur,
nor, on the other hand, in which there is nothing
but twins. But that such causes as may tend
toward twin-production are more constant or
react more cffectually in some lines than in
Others seems evident. That one OF the factors
commonly involved in the case OF both unovular
and bocular twinnng is hereditary seems TO be
we'll established The obstacles that are met N
attempting to solve this problem are found TO be
OF such nature as 10 prevent quick arrival at
final conclusions. but they are not such as TO
discourage the hope that definite solution Of
the problem may be obtained