Evening star., 1938-04-16
STARS, MEN AND ATOMS
Notebook of Science Progress in Field,
Laboratory and Study.
BY THOMAS r. HENRY.

Instances of living things obviously in
the midst Of evolutionary change are
rare.
A superficial survey Of Nature might
give the impression that Nature has
reached a status quo-that the differ
entiation of genera and species Of plants
and animals has long since been COM
pleted job.
But every now and then Nature gives
the cards a quick shuttle. Such is the
case of Cochlostyla virgata, beautiful
tree-dwelling snail of the Philippines
described by Dr. Paul Bartsch in bull
letin just issued by the Smithsonian In
stitution. The little animal has ap-
peared under more than so different
scientific names during the past CEN
tury, each biologist believing that he was
describing an entirely new species.
In most instances says DR.. Bartsch,
"the field naturalist finds that organ
isms belonging to what We call species
reproduce themselves with their definite
characters so faithfully that they are
easily recognized as coins OF modern
realm. But he meets now and then with
an assemblage of specimens that occupy
a definite habitat but, while they have
certain characters in common present
such as enormous range OF variation
that it is difficult to find any two lndl-
vduals exactly alike"
Evolution in Nature. not as speeded up
by human mechanism. in the laboratory
such as irradiation of germ cells with
X-rays, the application of groWth-pro-
noting chemicals, or by cross-breedlng
is such a slow process that It's very
reality is difficult to prove by living ex-
amples Offspring for generation after
genera; ION are of the same genus and
species as the parents, and usually con-
crete examples Of the process must be
obtained from fossil remains preserving
records of millions of years.
Perhaps the best known exception to
this is the evening primrose cited by the
Dutch biologist De Vrees in propoundlng
the theory of evolution by mutation.
He showed that this plant-actually was
mutating today, that it's genes and
chromosomes were in condition OF un-
stable equilibrium. In this case the
formation of new species was not some
thing which had happened in the dis
tant past. 1t was something that was
happening before the eyes OF the OBJ
servers.
This particular tree snail found by DR..
Bartsch is perhaps an even better ex-
ample with the additional advantage
that the race seems to have frozen, like
a slowed-up moving picture, in one phase
of the process. It occupies limited area
in the Mindoro Province. 1t was first
described by an English naturalist in
1889. Since then it has reappeared in
scientific literature. under different
name and as a different species, every
two or three years.
Superficially the specimens bear only
a general resemblance to each other. It
is not at all surprising, says DIR. Bartsch,
that isolated specimens reaching mu-
set,ms should have been described as
altogether different animals. 1t was
only with q great mass of specimens be-
fore him, he points out, that their true
"inwardnesS" is revealed. There is now
no more excuse for holding them as dis
tinct species than there would be Justlt1-
cation for so separating all the horticul-
tural varieties of chrysanthemums or
dahlias in a flower show.
At least one of the processes OF evo-
luton from one species to another works
in five steps, DR.. Bartsch points out.
First there must be hybridization, the
crossing Of two strains. Then there must
be mutation. This, as DR.. Bartsch him
self has shown in breeding experiments
with other types of mollusks. occurs
usually in the second generation of off,
spring. The third stage is isolation. One
of the mutant forms must be shut off so
that it will not be in competition with
the rest, in which case it would be sub
ject to the law of survival of the fittest
and In all likelihood would perish.
Under such conditions, DR.. Bartsch