Evening star., 1940-11-09
Of Stors, Men
And Atoms
Notebook Of Science Progress
In Laboratory. Field
And Study
By Thomas r. Henry.

By Thomas r. Henry.
For the first time in history two species
have been crossed to produce fertile
hybrid.
This accomplishment, which demol-
ishes one of the last bulwarks of oppo-
nents of the evolution hypothesis, was
announced here today by DR.. H. j.
Muller, American biologist who has been
working for the past decade in Moscow
and Edinburgh. He returned to the
United States few weeks ago, bringing
80 cultures of a new kind of living ami
NAL he had created in the laboratories
of Edinburgh University
1t is a man-made species of fruit fly,
the type of insect generally used in
heredity experiments, because of the
possibility of studying several genera
tions in one season. About IL years ago
DR.. Muller, then at the University of
Texas, made one Of the fundamental
discoveries of the generation when he
found that the hereditary characters
of these creatures could be altered by
the use of X-rays.
In the past, he said, the definition of
species difference in plants and animals
has been that indefinable difference that
made it impossible for two individuals to
produce fertile crosses. Thus horse and
ass can be crossed to produce a mule,
but the mule itself is sterile and the line
can be continued no further. The same
is true of lions and tigers, and many
other apparently closely related animals.
If two individuals have been incapable
of producing fertile hybrids, DR.. Muller
said, this has been sufficient evidence in
itself that they belonged to different
species.
It has been known for a long time
that animal and plant lines change both
in nature and in the laboratory by the
use of various agents such as X-rays,
ultra violet rays, freezing, powerful drugs,
such as colchichine. etc. In the wild
the changes are brought about by means
of mutations, the mechanism of which
is not yet understood, and once produced
they are hereditary.
But, says DR.. Muller, all such changes
have been minor and restrained within
species limits An infinite number of
hereditary differences might arise in
man or rose-but there never could be
man-mouSe or a rose -marigold. The
best that could be done was TO produce
a different kind of one species.
This has led to the idea. DR.. Muller
said, that life is divided into alright
compartments between which there are
no connections.
1t is known that the heredity of any
species is controlled by the genes, infini-
tesimally minute bodies arranged in
strings, like strings of beads, in every
living cell The fundamental reason
why species cannot be crossed to get fer
tile hybrids is that these bead strings
in the two parents do not match. DR..
Muller took two clearly defined species
of fruit flies. Such thing as fertile
hybrid he said was unthinkable to or
thodox geneticists.
First he destroyed some of the strings
of the male parent. Then he took a varl-
art female from other species, which
had in each cell three instead of the
normal two rows of these chromosomes.
BY long process of manipulating, he
says, he finally got offspring which con-
tanned more than 90 per cent of the
genes of the mother. The remainder,
however. were from the father. These
offspring were vigorous and healthy, and
laid fertile eggs. He now has carried
them through many generations with no
signs of diminished vigor.
Il have shown for the first time" he
said. that unmixable populations can
be mixed Admittedly there would seem
to be insuperable difficulties to this in
any of the higher animals. The divi-
sions among them which exist in nature
presumably have been brought about by
long series of mutations with cunula-
tive effect"
But already it has been demonstrated,
DR.. Muller pointed out, that hereditary
changes can be brought about in mice
by means of X-rays and that the process
is even simpler than in the commonly
used fruit flies. What can be done to
mice may eventually be done to other
animals.
Any human population, DR.. Muller
said, must be considered al containing
an infinite number of mutations. With
the application of the rigid law of sur
yival of the fittest in the past, some of
these have been crystallized into heredi-
tary lines, but at present there seems to
be only random, chaotic mixture which
leads nowhere.
The genes in which the changes take
place, he said, are so minute that they
probably never will become visible under
any microscope. His latest estimate of
the size of one of them is about 5000 900
atoms-and there are probably million
times that number in the head of pin.
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