The sun. [volume] (New York [N.Y.]) 1833-1916, 1892-07-10

What holds good for the individual as
whole also holds good for each
separate organ. inasmuoh rs tho ability OF
an animal to perform Its allotted functions de-
ponds on the efficiency OF each particular organ
hence By means OF this perpetual elimination
OF the unfit. evory organ is brought to periec-
ton. On this hypothesis. and on this only. is
II possible to explain the wonderful adapta-
bility OF the minutest details OF structure In
animals and plants and the development OF the
organic world through tho operation OF natural
forces. II. however. this view be the true one. II
adaptation in all the parts ofliving forms be tru-
ly tho result OF natural selection 1t follows that
the Same process which produced these adap-
tatons will tend to preserve them. and 1t also
follows that they will disappear when natural
selection ceases to act. These considerations
show why organs which have become super
huous and have fallen into disuse necessarily
degenerate and ultimately disappear.
As an example. Prof. Weismann takes one OF
tho nevis which are common In the German
swamps and pools In spring. II its eyes are
examined they are observed to be very highly
developed; their structure bears considerable
likeness to that OF the human eye, and they play
o very important part in the life OF the animal.
which is almost entirely dependent on keen
ness OF vision for finding Its prey. We're 1t not
for its eyes the newt would starve. These eyes
are extremely delicate and COMPLEX organs.
which have only very gradually. e..
In tho course OF countless generations
and Of almost endless time-made the
approach to perfection exhibited In tho living
newt. The slow but steady progress In do
velopment from stage to stage Is due. as Prof.
Weismann believes to tho fact that the eyes
OF these animals were never all exactly alike.
or equally keen. and only those individuals
survived In each generation In which the devel-
opment OF tho eyes was above the average.
This process OF natural selection would not
only produce a gradual improvement to the
eye. but would also tond to keep the improve
ment when gained, up to n certain standard.
Now suppose such species OF newt to have
been carried underground by water into q
dark cavern. 1t would only gradually adapt
itself to the new conditions SO as to be able to
thrive In the cave. but after tho lapse OF gener-
atoms some individuals would have learned to
live in complete darkness and to distinguish
and catch their prey without the aid Of sight:
this would be rendered possible by on
improvement In other organs. espe-
cially those OF touch and smell. Thus.
In course OF time. race OF nevis
would be produced perfectly adapted for
life in the dark. and for finding food by scent
alone and not by sight Directly. however.
such cave jewellers became able to exist with
out using their eyes. the degeneration Of these
organs would set in: as soon as they ceased
to be essential to the life Of the animal natural
selection would DO powerless to affect them.
for 1t would be immaterial whether the eyes
OF any animal were above or below tho stand
ard. Hence the individuals with weaker sight
would no longer be eliminated. but would
have an equal chance Of surviving and propa-
1T. at
take place between individuals with strong
eyes and those with weak eyes. and
the result would be a gradual de-
terloration Of the organs. Possibly the
process might BIO accelerated by the circum-
stance that small and degenerate eyes would
be rather an advantage. because their de-
crease would involve an increase In the powers
Of other and now more important organs.
such as those Of touch and smell. But even
Independently Of this the eye when 1t ceases
to be kept UP to certain standard Of develop
ment By natural selection. will gradually de-
teriorate. the process being very slow ut first.
but absolutely sure.
According to Prof. Weismann the same SIM
pie explanation sufflces for all cases Of retro
eressive development. whether Of organs or
species. Why. for example have most OF our
domestic animals lost their original color
ing Sie"f'S oeeauo0 ooiot oeea'ne VI
little or no importance TO tnem as soon
as they were sheitefeo under the protec-
ton OF man. whereas IN "iio state
IL was great sates unro asuihse oetectioh oy
their enemies. eimilariy' q marry covering
has ceaseo 10 DO OF importance 10 GER
tain OF the nam aiia' ana consequently
mas disappeared. mus Whaies ana DOL
rhins nave hakeo sKin' ior the most
part entlrciy oeVolo Oh mar. athouGh tney
are unquestionaoly oescenoeo iro" marry an
cestors. ana even no" ruolmentary MARS may
be detected IN certain parts Oh ehelr poiles oy
the aid OF microscope. Mani1estiV the dis
appearance OF the NARY covering cannot be
direct consequence OF aisuse. ior mar VIII
grow as well whether lts protective warmth be
useful or OF no importance 10 inc animal But
that It's disappearance Is an lndlrect conse-
quence OF disuse Is plain: Tor as soon as an
immense thickness OF biunber was developed
beneath the SKIN OF wha!e the warmth
OF an additional covering was unneces-
sary: the halr becoming superiluous.
natural selection ceased TO affect 1t and
degeneration at once set IN. II any one doubts
whether the direct actlon OF sea water should
"