The sun., 1889-12-08


Iect leads him to dissent from one OF Darwin's
conclusions by denying the transmissibility OF
OF acquired characters. We now proceed to in
dicate as clearly and concsely as we may. DR..
weismann's principal positions, though the
space at our disposal will not permit us to ade-
auately exhibit the array Of facts and argu-
msnts by which they are sustained.
The authors view OF the origin and signl6-
eance OF mortality. as distinguished from un-
limited longevity. Is set forth in two essays
published In 1881 and 1888. and respectively
entitled "The Duration OF Life" and Life
and Death" The question raised and answered
In these papers is: Why are organic bodies
porishable2 Why is 1t that while life main
tsins the appearance OF Immortality in the con-
slant succession Of individuals, the individuals
themselves pass awayH About the fact that
the life OF an individual has Its natural limit
there Is no dispnte, as regards at least those
animals and plants which are met with in
everyday life. 1t is equally indisputable that
the limits are very differently placed IN the va
rious species OF animals and plaDtR Some In
sects live but few hours and perish in tho act
Of reproduction. On the other hand. parrots
have in captivity attained the age OF upwards
OF a century; a falcon is said to have lived 162
years; elephants live 200 years, and swans are
paid to have lived 300 years. Certain trees in
the Cape Verde Islands (the Adansoniasl are al
legged to live 6000 years. There Is undoubtedly
some relation between the magnitude Of an
organism and longevity. but the length Of life
cannot be determined by the size OF body
alone. The crsyflsh lives as long as pig; the
toad us long as horse; the pike or carp as
long as an elephant There is also some rela-
tion between the duration OF the period Of
growth and the length OF life. DR.. Weisman
shows. however. that Flourens was mistaken In
asserting the length OF life to be always equiVa-
lent to i've times the duration Of the period Of
growth The ratio might be accepted in the case
Of man, but not In the case Of the horse, which
becomes mature In four years. yet lives from
forty to fifty years. A third factor which eX-
erts some influence on the duration Of life Is
the rate at which the animal lives. the rapidity
with which assimilation and other vital pro-
cesses take place. the rate OF metabollsm In o
word. It is not true, however. that intense
activity necessarily implies shortness Of life.
The most active birds have very long lives-no
less long and sometimes longer than the ma
jority OF amphibia which attain the same size.
From this point OF view DR.. Weismann would
have us regard an organism-not as q heap Of
combustible material which is completely re-
which is determined by size and by the rate at
which 1t burns-but rather as a fire to which
fresh fuel can be continually added. and which.
whether 1t burns quickly or slowly. can be kept
: burning as long as necessity demands,
There Is, finally a fourth factor which un-
QuestionablY exercises some influence upon
longevity, to wit, complexity Of structure.
Two organisms OF the same size. but belong
ing to different grades Of organization, will re-
auire different periods Of time for their devel-
opment. Thus under favorable circumstances
an AmGbs can divide into two animals in ten
minutes, whereas no insects egg can develop
into the young animal In a shorter period than
twenty -four hours. Hence We may say that the
peculiar constitution Of an animal does In
part determine the length of time which must
elapse before reproduction begins The period
before reproduction is. however. only part Of
the whole life OF an animal. which. Of course.
extends over the total period during which the
animal exists.
1t is. therefore, an erroneous assumption
that the duration Of the total period OF indi-
vidual life Is solely determined by the constitu-
ton Of the animals body. 1t is not true that
duration of life is exclusively regulated by the
size OF the animal. by the length OF time re-
quired to reach maturity. by the rate ofmetao-
olism. or by complexlty Of structure. Were
II tTue VIC buOulu uuu IL lI0pOSblDle TO explain
the fact that the queen ant and the working
ants live Tor many years. while the male ants
live for few weeks at most For In ants the
sexes are not distinguished by any great differ
ence in size. or in rate OF metabolism or In
complexity OF body. Yet there is an immense
difference between the lengths OF their lives.
DR.. Weismann. consequently, deems 1t proved
that physiological considerations alone cannot
determine the duration OF life. 1t follows that
the duration OF life must be forced upon the
organism by causes outside itself. DR.. Weis-
mann's explanation Of the phenomenon Is
briefly this: That duration Of life is dependent
upon adaptation to external conditions: that
It's length. uhether longer or shorter is governed
bp the needs Of the species. and that 1t is deter
mined by precisely the same mechanical pro-
cess OF regulation as that by which the struc-
ture and functions OF an organism are adapted
to Its environment
Before indicating the means by which adap-
tation is effected. DR.. Weismann dwells on tho
Rfflrmance that In regulating duration Of life
the advantage to the species. and not
to the individual. is alone OF any i'm
Dortance. This must, he says be OBJ
vlous to any one who has thoroughly
thought out the PROCESS Of natural selection.
1t is OF no Importance to the species whether
the individual lives longer or shorter. provided
IL lives long enough to do its work toward the
maintenance Of the species. AS soon as tho in
dividual has performed Its share In the work of
reproduction 1t ceases to be OF any value to the
species; 1t has fulfilled its duty. and may die.
But the individual may be OF advantage to the
species for longer period II it not only pro-
duces offspring. but tends them for a longer or
shorter time. either by protecting. feeding, or
instructing them. We should. therefore, ex-
pect to find that as rule life docs not greatly |
outlast the period OF reproduction except in |
those species which tend their young. and as a |
matter OF fact We find that this is tho case.
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