302 
evolution, which has also been felt and combated by Darwin, 
was very often advanced against it, especially in the beginning. 
Cuvier had already reminded Lamarck that the absolute identity 
between the Egyptian animals, as they were embalmed three 
thousand years ago, with those inhabiting the same provinces in 
the present day, rendered untenable his ideas about gradual 
change and perfection of organic beings. 
Huxley, to whose close reasoning powers and untiring reedi- 
ness for batile the rapid progress of evolution is in a great 
measure due, has devoted several pages to the refutation of this 
objection, His argument runsas follows ? :— 
The two chief factors in the process of evolution are : the one 
the tendency to vary, the existence of which in all living forms 
may be proved by observation ; the: other, the influence of sur- 
rounding conditions, both upon the parent form and upon the 
variations which are evolved from it. Now, as often as the first 
factor makes itself felt, and modified forms take their origin out 
of a common parent form, it will depend entirely on the condi- 
tions which give rise to the struggle for existence, whether the 
variations which are produced shall survive and supplant the 
parent, or whether the parent form shall survive and supplant 
the variations. If the surrounding conditions are such that the 
parent-form is more competent to deal with them and flourish in 
them, than the derived forms, then, in the struggle for existence, 
the parent-form wii] maintain itself, and the derived forms will be 
exterminated. But if, on the contrary, the conditions are such as 
to be more favourable to a derived than to a parent-form, the 
parent-form will be extirpated, and the derived form will take 
its place. In the first place there will be no progression, no 
change of structure through any imaginable series of ages; in 
the second place there will be modification and change of form. 
So far Huxley. Ne doubt but he has made us acquainted 
with a very reliable explanation of how the variation of any 
form of animals or plants may be retarded. The hypothesis of 
degeneration first formulated by Anton Dohrn, and afterwards 
warmly advocated by Ray Lankester, is no doubt of considerable 
importance for our comprehension of numerous lower stages of 
organisation in the animal and vegetable world, which may no 
longer be looked upon as parent-forms of more highly ifferen- 
tiated groups, but which, on the contrary, have in their lineage | 
much more complicated ancestors than their own stage of orga- 
nisation would appear to show. At first sight these degenerated 
animals show different points of similarity with animal forms, 
lower than those to which they are genetically allied. 
So, for example, the Tunicata have for a long time been 
arranged amongst or close to the Mollusca, but lately-continued 
researches have evermore tended towards the conclusion that we 
have here before us the degenerate descendant of animals which 
had already attained the level of the lowest Vertebrates, but 
whose descendants, thanks to degeneration, have at present all 
the appearance of Invertebrates. In this way the number of 
lower avimal types which may be looked upon as_ primi- 
tive, and whose persistence throuzh geological periods gives rise 
to the questions as formulated above, is deceptively increased 
by forms, which we must remove from ainongst them, and 
place in the vicinity of their more direct allies. 
The process of degeneration is, however, confined within 
certain limits ; it cannot do the same service tewards the refuta- 
tion of the objection here dealt with as can Huxley’s argumenta- 
tion above referred to, which is fully directed against the cardinal 
point, and the value of which I cannot estimate highly enough. 
Still it appears to me that his explanation of the lengthened 
persistence of so many of the lower organised animals and plants 
can yet be supplemented by a new hypothesis. 
To this I give the name of the hypothesis of accelerated de- 
velopment hy primogeniture. If I have the advantage to lay it 
before you to-day, you will bear in mind that it has as yet only 
a preliminary shape, and that for its ultimate confirmation 
extensive researches will yet be required. 
The fact is daily confirmed by continuous observation, that not 
only numerous vertebrates, but also very many invertebrates, can 
attain a very old age without the capacity for reproduction being 
essentially diminished. This is confirmed by the recently pub- 
lished researches of Weissmann 2 on the connection between the 
length of the reprcductive period and the duration of life. We 
may fairly assume that all those animals attaining an old age 
leave issue which has been born at different periods—issue from a 
youthful age, which itself has again brought forth children and 
* American Addresses, p. 
2 A. Weissmann, “ Ueber die Dauer des Lebens,”’ 1881. 
NATURE 
[ Fan. 25, 1883 
grandchildren, and issue from old age, which is on a level with 
the fcurth or fifth generation of the first-born descendants. An 
example of old age combined with successful attempts towards 
reproduction is furnished by the well known sea-anemone, 
““Granny,” which was captured in 1828 by Dalyell on the 
Scotch coast, and being still alive, last year gave birth to a 
certain number of young Actiniz. 
The large Tridacnas and the gigantic Cephalopods which have 
now and then been observed, must also have attained a consider- 
able age ; nothing authorises us to maintain that these have been 
infertile in all the later years of their lives. We need not stop 
to consider the higher groups: fishes, birds, and mammalia. 
They all contribute during a shorter or longer time towards the 
procreation of the species, and the considerable age which both 
fishes and birds are known to attain is the cause of a very 
considerable difference in age of the oldest and the youngest 
individuals of their own breeding. And so all of them will 
leave both first-born and last-born posterity. With the first-born 
this will in their tarn be the case, so with ¢he?v posterity, and so 
forth. Similarly the Jast-born, when they have attained matu- 
rity, will bring forth a series of descendants of very different ages ; 
the last-born of the last-born being the final term of this series. 
After centuries the effect will be this: From one pair of 
parents a large number of descendants will have sprung, a small 
number of these being the descendants in a direct line of the 
first-born of every successive generation ; another small number 
being the descendants in a direct Jine of the last-born of every 
successive generalion, whereas the remainder belong to interme- 
diate stages. The first-born are separated from the primitive 
parent f rm by a number of generations, x, which is necessarily 
a considerable multiple of the number of generations y, which 
lies between the same parent form and their last-born descen- 
dants. Evidently the difference in age between the first-born 
descendant and his parents is a minimum, for the sole reason of 
his being the firs -born, that between the last-born descendant 
and these same parents being on :imilar grourds a maximum. 
Thus, if we follow up in the direct line of descent the series of 
first-born of the first born, &c., we find that the distance between 
two terms of that series corresponds to a much smaller number of 
years tha. the distance between two terms of the series of the 
continually last-born, which have always descended from last-born. 
Cempart ig these two series simultaneously after the lapse of 
centuries, the series of the fir-t-born will count numerous terms, 
many generations, at short distances from each other, whereas 
the series of the last-born will,.on the contrary, consist of a much 
smaller number of terms, each of which is separated from its pre- 
decess r by a much more considerable distance. It is the num- 
ber of these terms which in the one case I wished to express by 
x, in the other by y.? 
From this fact we are led to propose the following question : 
Is there any reason to expect, that in the struggle for existence, 
the representatives of each of the two divergent series are collec- 
tively provided with different weapons? Or are both these 
groups quite equal to each other in the struggle? 
Eoth observation and theoretical deduction force the conclu- 
sion upon us that a difference is indeed present. A difference, 
(1) in the external circum: tances under which the first-born and 
the Jast-born come into existence ; (2) in the internal properties 
and acquirements with which both series are provided ; a differ- 
ence which does not appear sporadically between certain repre- 
sentatives of both groups, but which may indeed be collectively 
observed between all of them. 
As to the first point, the external circumstances, I call your 
attention to the following example, which shows how nature 
indeed makes a difference on a large scaie in the conditions— 
under which she awaits the first-born and the last-born pro- 
geniture. 
* I am doubtful whether there are indeed first-born descendants in the 
pure signification of the word, z#.e. such which, both from the paternal and 
frc m the maternal side, count only first-born in the whole of their ancestry. 
However, this does net materially influence our argument. We bring toge- 
ther in the series of first-born all those descendants in which mixture and 
intercrossing with second and third births was always reduced to a minimum, 
whereas on the other hand, in the group of the last-born, not only those 
cases which are theoretically pure are brought tcgether, but those in wh'ch the 
number of ancestors on both sides most closely approaches to the number of 
generations y, which lies between the last born 7x aé-tracto and the common 
parent form. Inthe majority of cases, however, intercrossing and blending 
will have occurred on a large scale, and the average number of generations 
which leads from them to this parent form nay be expressed by * +7. The 
calculus of probabidites wculd be able to furnish us in any given case, sup- 
posing enough data are available, with the exact grouping of these numbers. 
