Evening star. [volume] (Washington, D.C.) 1854-1972, 1908-08-22
NATURAL SELECTION THEORY
HOW NATURE LIMITS THE SUR.
vIvAL OF. THE FITTEsr.
Darwinian Doctrine overestimated.
Does Not Possess AL the Merit
Claimed for It.
From Current Literature.

the survival of the fittest-seems to that
eminent zoologist of Great Britain, DIR.
ID. Dewar who has spent years OF study
In the tropics. 10 be quite misunderstood
as factor in organic evolution He has
been led 10 wonder if nature does NOT
actually limit the survival of even those
fortunate individuals whose variations
render them the best equipped for life i'm
the environment in which they find them
selves. DIR. Dewar would not initiate
those by whom Darwin's theory of natural
selection was scoffed at when first pro-
pounded. but he says, i'm The Albany Re-
view Q-ondon). that the present tendency
Is TO value natural selection too highly.
to attribute to il powers that it does not
possess. TO i'm it the one and only
cause of the origin of species and OF or
ganic evolution" He insists that the doe
trine has yet to pass through the third
phase of its existence. 1T has to find its
own level, to take its proper place as q
factor in the making of Species
Simply because 1t is easy of enuncia-
ton and comprehension. logical and self
evident in a sense, the Darwinian theory
has gained rapid and widespread popu-
larity. mere child can perceive that
If kind of insect be preyed upon by fly
catching birds. the most rapid of wing
among these insects would possess better
opportunities of escape than the slow
ones. Consequently as like produces like.
the tendency would be for that species Of
insect to become more and more rapid i'm
flight through traits transmitted from one
generation to another.
Now things in this particular contends
Dr. Dewar, are not SO simple as all that.
The theory of natural selection, as thus
popularity stated. involves two assump-
lions, which. as DIR. Dewar tries to show,
are not warranted.
To begin with. the hypothesis neslects
what We may, for want of better word,
call the element OF luck
In the second place, 1t assumes that en-
cry slightest variation must tell No
matter how small the variation be, n
must help or hinder its possessor i'm the
struggle for existence
The Element of Luck.
When DR.. Dewar says the theory ne
elects the element of luck he means
that 1t assumes the race TO be al
ways to the swift, the battle
TO the strong. This is not necessarily
SO. A herd of antelope is fleeing for
dear life from a leopard. After n lonp.
rum the painting herd finds itself I'm a
trac- of unknown country, with the leo
pard still in pursuit. Suddenly the fc-e
most antelope-the swiftest OF the herd
finds himself I'm bog. His plight
acts as warning to the slower mem
pers of the herd, who change their course
ana escape. But the leader is caught.
TOT the leopard. having broader feet, is
able to negotiate the bog.
Two insects of the same species are
disport1ng themselves in the air when
fly catcher appears on the scene from
such direction that it catches sight
only of the faster flyer of the two in
sects. This 1T chases and devours. The
slower insect escape, because, thanks to
its position, it happens to escape obser--
walton: One of the most familiar sights
in India is that of little "myna" or an
egret stalking beside a cow, catching
the grasshoppers as they jump to avoid
being trodden upon by the quadruped.
AS the birds can not be on both sides
of the cow at the same time. il catches
only those grasshoppers that happen to
be on its side of the COW. Those on the
other side escape, rs do those in all parts
or the field not traversed by the bird
and its cow companion. In these cir
cumstances, it is obviously chance, pure
and simple, the accident of position that
determines which grasshoppers shall be
destroyed.
Again. take the case Of the birds that
perish in a cyclone, a fierce tropical
storm, a prolonged drought. an excep-
es ba ae s sgch the hnn
dred. the weak and the strong. the swift
and the slow alike. All the birds of one
locality succumb, while not one of those
in the neighboring locality is affected.
Luck Balances. Itself.
If it be urged that the cases cited do
not affect the fact that in the long run
the fittest survive, il it be pleaded that
i'm the long run luck balances itself, so
that 1T is. at the most, a disturbing fac
tor. DR.. Dewar has his reply ready. We
may grant this, he says, and still be con-
tent that the path of natural selection
is not SO smooth as some men Of science
would have the world suppose. But Dr.
Dewar passes to what he thinks perhaps
the greatest flaw in the theory of survi-
val of the fittest-namely, the assump-
ton that the balance Of nature is so
nicely adjusted that the least difference
in the length of a leg or wing is of vital
Importance to the individual.
When the beast of prey and its victim
are evenly matched as regards f1eetness
and power of endurance, then, doubtless,
the assumption is justified. But how
rarely in the rough and tumble of the
struggle for existence are the victim
end the foe well matched.
Mote the conSummate ease with
which the fycatcher captures its quarry.
Watch the effortIess sally, the elegant
sweep of the bird, and the sudden dis
appearance of the luckless insect. The
hycatcher will some times take three or
four insects in the course of one flight:
all are captured with the same ease.
although the length of wing i'm each
varies. SO great is the birds superiority
that it does not notice the differences i'm
the flying powers of its puny victims.
When overtiken by a mighty flood the
good swimmer and the man who cannot
swim at all are equally helpless.
Look at the swifts as they dash
through the air at speed or a hun
dred miles an hour, swallowing the
gnats and other tiny insects they meet
in their course, and consider the extent
to which small variations Will affect the
chance of escape of these insects.
Equally free from effort does the
capture of a crow. or other slow-fying
bird. by a Boneli's eagle (IIieraetus fas-
ciatus) appear to be. The eagle sits
waiting in "A tree. Presently a flight OF
crows passes. vending its way to The
trees i'm which it will pass the night.
The eagle makes a dash. and, In less
time than it takes to relate, seizes the
crow that happens to be nearest. regard
less of the fact that that particular
crow may be capable OF faster hight imam
many OIL it's companions.
Birds Prey on Locusts.
Watch, as DIR. Dewar has frequently
done i'm India, the progress Of a small
flight of locusts. The fluttering crea-
lures look like flakes of reddish snow.
Numbers of crows. kites and mynas are
always in attendance. feeding on the To-
Gusts They invariably catch the locusts
that happen to be nearest. Their SUI
periority in the air is SO great that