Evening star. [volume] (Washington, D.C.) 1854-1972, 1938-08-21
Scientists

!. dominant animals on earth ut the
: time when the first fossils were pre-
q served in the rocks, and Of the monster
cephalopods, distantly related to the
fearsome octopuses Of today, who fol-
lowed them as masters Of the ancient
seas. Their stories, like those Of the
dinosaurs and OF many plant races,
are closed chapters in life's history.
The inside push, Prof. Trueman
said, apparently acts only over very
long periods so that it cannot be dis
tinguished in living races. The factor
is quite weak, but eventually grooves
path so deeply that a race cannot
deviate from 1t to avoid disaster and
is like a man caught on a railroad
bridge with fast express train ap-
preaching.
F.. Seems Mystical.
The inside push seems mystical, 1t
was pointed out, probably only be-
cause it is not yet understood and 1t
need not be interpreted as something
above nature. Evidence for it, Prof.
Trueman said, appears in four cate
gories. In many groups there ap-
pears to be definite variation con-
fined to q small number of trends
A few specific characters become
more and more pronounced while the
rest Of the organism remains sta
tionary, such as may be the case with
the brain of man or the tusks Of the
elephant. Another line of evidence
Is the strange phenomena Of paral-
lei evolution in which similar forms
are produced in entirely different
kinds Of animals. For example,
among the marsupiak of Australia
appear forms such as bear, rat and
cat, which specifically are very
similar to types found among the en-
tirely different placental mammals of
the rest OF the world. Looked at from
the perspective of vast, stretches of
time, Prof. Trueman said, some of
these changes appear entirely I'M
related to environmental conditions.
In other cases, however, they are
clearly responses to environment be-
ing the best forms with which a race
can cope with nature. In some cases,
especially in their latter stages, the
changes are clearly out of harmony
! with the environment, he said, and
are sure roads to extinction.
: Isolation Needed,
, One Of the requirements for the
production Of new species by evolu-
ton Is isolation 70 that there cannot
be continuous cross-breeding through
out an entire race. Otherwise there
could be no distinct dividing line
such as constitutes a species. In the
past such isolation generally has been
considered due to the physical en-
MISUNDERSTANDING on islands, or
separations by mountain ranges or
oceans.
An even more important part In
preventing inbreeding In nature, &C.
cording to a paper by DR.. c. d.
Darlington, may be played by Gin
side barriers" acting alphabetically
or mechanically but determined gene
tically. The process Is especially ap-
parent in plants. Thus 4 genetic
change may take place 50 that the
pollen grows more quickly on plants
having similar genes than on those
having those genes in q mutant form.
1t may act in similar way in ami
mails, he said, through the mating in
stincts or capabilities. However. DR..
Darlington stressed, the building up
OF such differential systems cannot
be achieved in one step by q gene
mutation. In nature it seems that
its action depends on simultaneous
change in a group of genes. Such
a group can be held together only
when associated with some sudden
change in the arrangement Of renes.