among animals with greater certainty the nearer they stand to us,
occupy a domain by themselves, and such a vast and complex one that
there can be no question of bringing it within the scope of our present
studies, and the same is true of the phyletic development of Man. But
we must at least take up a position in regard to these problems, and
there can be no question that Man has evolved from animal ancestors,
whose nearest relatives were the Anthropoid Apes. Not many years ago
bony remains of a human skeleton, or at least of some form very near
to modern Man, were found in the Diluvial deposits of Java, and this
has been designated _Pithecanthropus erectus_, and perhaps rightly
regarded as a transition form between Apes and Man. It is possible that
more may yet be discovered; but even if that is not so, the conclusion
that Man had his origin from animal forefathers must be regarded as
inevitable and fully established. We do not draw conclusions with our
eyes, but with our reasoning powers, and if the whole of the rest of
living nature proclaims with one accord from all sides the evolution
of the world of organisms, we cannot assume that the process stopped
short of Man. But it follows also that the _factors_ which brought
about the development of Man from his Simian ancestry must be the same
as those which have brought about the whole of evolution: change of
external influences in its direct and indirect effects, and, besides
this, germinal variational tendencies and their selection. And in
this connexion I should like to draw attention to a point which has,
perhaps, as yet received too little attention.
Selection only gives rise to what is suited to its end; _beyond
that it can call forth nothing_, as we have already emphasized on
several occasions. I need only recall the protective leaf-marking of
butterflies, which is never a botanically exact copy of a leaf, with
all its lateral veins, but is comparable rather to an impressionist
painting, in which it is not the reproduction of every detail that is
of importance, but the total impression which it makes at a certain
distance. If we apply this to the organs and capacities of Man, we
shall only expect to find these developed as far as their development
is of value for the preservation of his existence and no further. But
this may perhaps seem a contradiction of what observation teaches us,
that, for instance, our eyes can see to the infinite distance of the
fixed stars, although this can be of no importance in relation to
the struggle for existence. But this intensity of the power of vision
has obviously not been acquired for the investigation of the starry
heavens, but was of the greatest value in securing the existence of
many of our animal ancestors, and was not less important for our own.
In the same way our finely evolved musical ear might be regarded as a
perfecting of the hearing apparatus far beyond the degree necessary to
existence, but this is not really the case: our musical ear, too, has
been inherited from our animal ancestors, and to them, as to primitive
Man, it was a necessity of existence. It was quite necessary for the
animals to distinguish the higher and lower notes of a long scale,
sharply and certainly, in order to be able to evade an approaching
enemy, or to recognize prey from afar. That we are able to make music
is, so to speak, only an unintentional accessory power of the hearing
organs, which were originally developed only for the preservation of
existence, just as the human hand did not become what it is _in order
to play the piano_, but to touch and seize, to make tools, and so on.
_Must this, then, be true also of the human mind?_ Can it, too, only
be developed as far as its development is of advantage to Man's
power of survival? I believe that this is certainly the case in a
general way; the intellectual powers which are the common property
of the human race will never rise beyond these limits, but this is
not to say that certain individuals may not be more highly endowed.
The possibility of a higher development of certain mental powers or
of their combinations--whether it be intelligence, will, feeling,
inventive power, or a talent for mathematics, music or painting--may
be inferred with certainty from our own principles; for not only may
the variational tendencies of individual groups of determinants in the
germ-plasm be continued for a series of generations without becoming
injurious, that is to say, without being put a stop to by personal
selection, but sexual intermingling always opens up the possibility
that some predominantly developed intellectual tendencies (_Anlagen_)
may combine in one way or another, and so give rise to individuals of
great mental superiority, in whatever direction. In this way, it seems
to me, the geniuses of humanity have arisen--a Plato, a Shakespeare, a
Goethe, a Beethoven. But they do not last; they do not transmit their
greatness; if they leave descendants at all, these never inherit the
_whole_ greatness of their father, and we can easily understand this,
since the greatness does not depend upon a single character, but upon
a particular combination of many high mental qualities (_Anlagen_).
Geniuses, therefore, probably never raise the average of the race
through their descendants; they raise the intellectual average only
through their own performances, by increasing the knowledge and power
handed on by tradition from generation to generation. But the raising
of the average of mental capacity, which has undoubtedly taken place
to a considerable degree from the Australasian aborigines to the
civilized peoples of antiquity and of our own day, can only depend on
the struggle for existence between individuals and races.
But if the human mind has been raised to its present level through
the same slow process of selection by means of which all evolution
has been directed and raised to the height necessary for the 'desired
end,' we must see in this a definite indication that even the greatest
mind among us can never see beyond the conditions which limit our
capacity for existence, and that now and for all time we cannot hope
to understand what is supernatural. We can recognize the stars in the
heavens, it is true, and after thousands of years of work we have
succeeded in determining their distance, their size, and gravity, as
well as their movements and the materials of which they are composed,
but we have been able to do all this with a thinking power created
for the conditions of human existence upon the earth, that is to say,
developed by them, just as we do not only grasp with our hands, but
may also play the piano with them. But all that involves a higher
thinking power that would enable us to recognize the pseudo-ideas of
everlastingness and infinity, the limits of causality, in short, all
that we do not know but regard as at best a riddle, will always remain
sealed to us, because our intelligence did not, and does not, require
this power to maintain our capacity for existence.
I say this in particular to those who imagine they have summed up the
whole situation when they admit that much is still lacking to complete
knowledge, say, to a true understanding of the powers of Nature or
of the Psyche, but who do not feel that in spite of all our very
considerably increased knowledge we stand before the world as a whole
as before a great riddle. But I say it also to those who fear that the
doctrine of evolution will be the overthrow of their faith. Let them
not forget that truth can only be harmful, and may even be destructive,
when we have only half grasped it, or when we try to evade it. If
we follow it unafraid, we shall come now and in the future to the
conclusion that a limit is set to our knowledge by our own minds, and
that beyond this limit begins the region of faith, and this each must
fashion for himself as suits his nature. In regard to ultimate things
Goethe has given us the true formula, when the 'Nature-spirit' calls
to Faust, 'Du gleichst dem Geist, den Du begreifst, nicht mir!' For all
time Man must repeat this to himself, but the need for an ethical view
of the world, a religion, will remain, though even this must change in
its expression according to the advance of our knowledge of the world.
But we must not conclude these lectures in a spirit of mere
resignation. Although we must content ourselves without being able to
penetrate the arcana of this wonderful world, we must remain conscious,
at the same time, that these unfathomable depths exist, and that we
may 'still verehren was unerforschlich ist' (Goethe). But the other
half of the world, I mean the part which is accessible to us, discloses
to us such an inexhaustible wealth of phenomena, and such a deep and
unfailing enjoyment in its beauty and the harmonious interaction of the
innumerable wheels of its marvellous mechanism, that the investigation
of it is quite worthy to fill our lives. And we need have no fear
that there will ever be any lack of new questions and new problems to
solve. Even if Mankind could continue for centuries quietly working
on in the manifold and restless manner that has, for the first time
in the history of human thought, characterized the century just gone,
each new solution would raise new questions above and below, in the
immeasurable space of the firmament, as in the world of microscopical
or ultramicroscopical minuteness, new insight would be gained,
new satisfaction won, and our enthusiasm over the marvel of this
world-mechanism, so extraordinarily complex yet so beautifully simple
in its operation, will never be extinguished, but will always flame up
anew to warm and illumine our lives.
INDEX
[References to vol. ii have the volume prefixed.]
Accessory idioplasm, 383.
Acræides, immunity of, 100.
Adaptation, in leaf butterflies, ii. 346;
of the sperm-cells to fertilization, 278, 279;
facultative, ii. 278;
functional, 244;
harmonious, ii. 80, 197;
not chance but necessity, ii. 346;
all evolution depends upon, ii. 347.
Affinities, vital, within the 'person,' ii. 36;
within the id, 374.
Agassiz, L., immutability of the species, 16.
Alcoholism, ii. 68.
Aldrovandi, 13.
Amixia, ii. 285, 286.
Ammon, O., the variation-playground, ii. 199, 202.
Amœba 'nests,' ii. 219.
Amphigony, 267;
as a factor in maintaining species, ii. 204.
Amphimixis, general significance of, ii. 192;
antiquity of, ii. 202;
Ammon's playground of variations, ii. 206;
Amœba 'nests' as a preliminary stage, ii. 219;
beginnings of, ii. 213;
parthenogenesis as self-fertilization, ii. 233;
in Coccidium, ii. 214, 216;
chromosomes in Protozoa, ii. 216;
the 'cycle' idea, 326;
increased stability due to, ii. 200;
continued inbreeding, ii. 231;
'formative' stimulus, ii. 229;
Galton's curves of frequency, ii. 206;
in relation to rudimentary organs, ii. 226;
immediate consequences of, ii. 224;
plastogamy as a preliminary stage of, ii. 222;
alters individuality, ii. 192;
and natural death, 335;
direct advantages of, ii. 198;
origin of, ii. 211;
association of, with reproduction, ii. 210;
increases power of adaptation, ii. 223;
preliminary stages of, ii. 213;
not a rejuvenescence in the sense of preserving life, ii. 221.
Ancestral plasm, ids of, ii. 38.
Ants, several kinds of ids in the germ-plasm of, 390;
harmonious adaptation of sterile forms, ii. 89;
degeneration of wings and ovaries in the workers, ii. 90;
transition forms between females and workers, ii. 92;
Wasmann's explanation of these, ii. 93;
_Polyergus rufescens_, ii. 95;
dimorphism of workers, ii. 96;
number of queens, ii. 98.
Apes, furred, in Tibet, ii. 269.
Arctic animals, sympathetic colouring in, 62.
Aristotle, 10.
Assimilation, ii. 371.
Auerbach, spindle-figure of the dividing cell-nucleus, 289.
Autotomy, self-amputation, ii. 18.
Baer, K. E. von, development of the chick in the egg, 25.
Barfurth, on the segmentation of the egg in the sea-urchin, 408.
Bates, discovery of mimicry, 91;
on the Sauba ant, ii. 96.
Beccari, _Amblyornis inornata_, 223.
Bees, harmonious adaptation in the workers, ii. 89;
influence of nutrition on the degeneration of the ovaries, ii. 92;
importance of the fact that there is only one queen, ii. 97.
Belt, plants and ants, 171.
Beneden, E. van, fertilization of the ovum of _Ascaris_, 295;
deutoplasm, 282;
theory of mitotic cell-division, 291.
Bickford, Elizabeth, experiments on regeneration, ii. 90.
Binswanger, on artificial epilepsy in guinea-pigs, ii. 68.
Biogenetic Law, Fritz Müller's view, ii. 160;
crustacean larvæ, ii. 161;
Haeckel's views, ii. 173;
markings of the caterpillars of the Sphingidæ, ii. 177;
shunting back of the stages in the ontogeny, ii. 177.
Biophors, the smallest vital units, 369;
struggle of the, ii. 52;
spontaneous generation of, 369.
Birds, adaptation in, ii. 315.
Blochmann, on the directive corpuscles in parthenogenetic ova, 304;
on the development of the ovum of the bee, 336;
on chromosomes in unicellulars, ii. 217.
Blumenbach, 'nisus formativus,' 352;
inheritance of mutilations, ii. 66.
Bois-Reymond, doubts as to the inheritance of functional
modifications, 242.
Bonnet, preformation theory, 350, 351.
Bordage, regeneration, ii. 20.
Borgert, proof of the splitting of the chromosomes in the division of
unicellulars, ii. 216.
Boveri, fertilization of non-nucleated pieces of ovum with nucleus of
another species, 341.
Brandes, on the extinction of _Machairodus_ species and the giant
armadillos, ii. 358, 359;
on the supposed transformation of the stomach in birds as a result
of nutrition, 267.
Brown-Séquard, artificial epilepsy in guinea-pigs, ii. 67.
Brücke, Ernst, organization of the living substance, 368.
Budding and division, ii. 1.
Bütschli, theories of amphimixis, 330;
discovery of the spindle-figure in nuclear division, 289.
Burdach, inheritance of mutilations, ii. 65.
Buttel-Reepen, Hugo von, on fertilization in the bee ovum, 306.
Butterflies, their enemies, 98;
aggressive colourings, 68, 70;
aberrations due to cold, ii. 274;
transmissibility of these, 275;
endemic species, 285;
polar and Alpine species, 285;
species of the Malay region, 291.
Butterflies, protective coloration in, 74.
Cænogenesis, ii. 173.
Calkins, conjugation of infusorians, 329.
Caterpillars, protective coloration in, 67.
_Catocala_, adaptive coloration in the various species, ii. 310.
Cell-division, integral and differential, 374;
differential in Ctenophores, 408;
proofs of differential, 377.
Centrospheres, 289, 309.
Ceratium, ii. 326.
Chance, elimination sometimes due to, 44, 47.
Characters, purely morphological, ii. 133.
Child, determination of, at fertilization, ii. 46.
Chromatin, the hereditary substance, 287;
grounds for the belief, 337-43.
Chromosomes, their occurrence in unicellulars, ii. 217;
simple and plurivalent (-idants), 349, 350;
individuality of, 349;
number of, in different species, 291;
indications of complexity of their structure, 292;
reasons for their existence, 303.
Chun, segmentation of the ovum in Ctenophores, 408;
Kerguelen cabbage and rabbits, ii. 362;
deep-sea investigation, ii. 322.
Cirrhipeds, ii. 241.
Climate, influence of, in causing variation, ii. 269.
Climatic varieties, ii. 269, 272.
Coadaptation, ii. 80;
in crustaceans, ii. 81;
in the markings of butterflies, ii. 87;
in the forelegs of the mole-cricket, ii. 86.
Cold aberrations in butterflies, transmissibility of, ii. 275.
Coloration, animal, its biological import, 58;
sympathetic in butterflies, 74;
in moths, 76;
of animals in green surrounding, 64;
of eggs, 60;
of nocturnal animals, of polar animals, 64;
water animals, 63.
Coloration, shunting backwards of, in the ontogeny, 73.
Colour-adaptation, double, 64, 73;
colour change in fishes, amphibians, reptiles and
Cephalopoda, ii. 278.
Combinations of determinants, ii. 40.
Conjugation, in Protozoa, 317;
in _Paramæcium_, 319.
Conklin, on the behaviour of the centrosphere in the ovum
of _Crepidula_, 309, ii. 41.
Connective tissue of vertebrates, 386.
Constancy and variability, periods of, ii. 294, 295;
degree of constancy of a character increases with its age, ii. 200.
Convergence, ii. 323.
Cope, supposed palæontological proofs for the Lamarckian
principle, ii. 77.
Copernicus, 13.
Copulation of _Coccidium proprium_, ii. 217.
Correlation of the parts of the body, 41;
of determinants of the germ-plasm, ii. 153.
Correns on Xenia, ii. 59.
Corsica, endemic butterflies of, ii. 285.
Crampton, segmentation in a marine snail, _Ilyanassa_, 409.
Crystal animals, sympathetic colouring, 63.
Cultivated plants, asexual reproduction in, ii. 261.
Cuvier, 16;
his dispute with St.-Hilaire, 24.
Dahl, the ants of the Bismarck Archipelago, ii. 101.
Danaides, immune butterflies, 94.
_Danais erippus_ and _Limenitis archippus_ (mimicry), 113, 114.
Darwin, Charles, first appearance of _The Origin of Species_, 28;
story of his life, 29.
Darwin, Erasmus, theory of evolution, 17.
Darwin and Nägeli, ii. 322.
Darwinian theory, dependence of the frequency of species on
enemies, 47;
on external circumstances, 45;
correlation of parts, 41;
races of pigeons, 34;
of domesticated animals, 31;
geometrical ratio of increase, 46;
struggle for existence, 47;
struggle between individuals of the same species, 52;
artificial selection, 39;
natural selection, 42;
affects all parts and stages, 54;
variation, 43;
summary, 55;
origin of flowers, 182;
pangenesis, ii. 62.
Death, natural, 260.
Degeneration of a typical organ not an ontogenetic but a phylogenetic
process, ii. 91;
of disused parts, ii. 116.
Delage, the germ-substance, 401;
'a portmanteau theory,' ii. 3;
experiments with sea-urchins, 342.
Desert animals, sympathetic colouring in, 62.
Determinants, active and passive state, 380;
controlling the cells, 381;
proofs of their existence, 361, 371, 408;
in limbs of Arthropods, 361;
liberation of, 382;
size and number, 369.
Determinates, 355.
Deutoplasm, 280.
Dewitz, degeneration of wings in the ontogeny of worker-ants, ii. 90.
Diatoms, ii. 324.
Dimorphism, sexual, its idioplasmatic cause, 388.
Disappearance of disused parts, ii. 135;
unequal rate of, ii. 129.
Dividing apparatus of the ovum, 288, 308.
Division, proof of differential nuclear division (_Phylloxera_), 377;
multiplication by division, ii. 1.
Dixon, isolation as a condition of species formation, ii. 284.
Döderlein, increase of characters in diluvial forms, ii. 139.
Dog, breeds of, 31;
attachment to man, ii. 73.
Driesch, 'prospective' importance of a cell, 378, 408.
Dzierzon, discovery of parthenogenesis in bees, 303.
Echinoderms, mesoderm cells of, 386, 387.
Ectocarpus, 334.
Egg-cell, form and structure, 280;
its migrations, 281.
Ehrlich, experiments with ricin and abrin, ii. 106.
Eigenmann, on blind cave-salamanders, ii. 347;
on species of Leptocephalus, ii. 133.
Eisig, on symbiosis, 162.
Elimination, ratio of, 47.
_Elymnias_, a genus of mimetic butterflies, 103.
Emery, on extinction of species, ii. 357;
on _Colobopsis truncata_, ii. 96;
on germinal selection, ii. 139;
'mixed' forms in ants, ii. 93;
variation of homologous parts, ii. 189.
Empedocles, 9;
ii. 370, 378.
Endemic species, ii. 283.
Endres, 'prospective' significance of the blastomeres of the ovum of
the frog, 407.
Epigenesis and evolution, 350.
Epilepsy, artificial, in guinea-pigs, ii. 67.
Equilibrium between species of a region, 49.
Evolution, phyletic, ii. 332;
paths of, ii. 381;
forces of, ii. 381;
mechanism of, 353;
facts of, 406.
Evolution, progressive, attempt of species to extend its
range, ii. 383;
unlimited diversity of forms of life, ii. 391;
parable of the traveller, ii. 386.
Evolution theory, general meaning of, 6;
'prospective' import of the cell, 378.
Exner, electric adaptation of the fur of mammals and feathers of
birds, ii. 316;
vision of insects, 216.
Eye-spots, 69;
ii. 179.
Falkland Islands, influence of climate on cattle and horses, ii. 268.
Feathers, regarded as an adaptation, ii. 316.
Fertilization, process of, 286;
in lichens, 313;
in _Ascaris_, 296;
in the sea-urchin ovum, 293;
in Phanerogams, 313;
in higher plants, ii. 251;
importance of the chromatin, 290;
conjugation, 317;
the centrosphere the dividing apparatus of the cell, 289;
chromatin the hereditary substance, 287;
differentiation of individuals among the Protozoa, 322;
number of chromosomes reduced to half, 297;
rôle of the centrosphere, 308;
summary of process of fertilization, 343.
Fischel, segmentation, of the Ctenophore ovum, 408;
regeneration of the lens in Triton, ii. 20.
Fischer, E., experiments with butterfly pupæ in low
temperature, ii. 275.
Flowers, origin of, 179;
adaptation to insects, 189;
in _Aristolochia_, _Pinguicula_, and _Daphne_, 186;
colour as an attraction to insects, 195;
collecting apparatus of bee, 193;
cross-fertilization, means for securing, 182;
in _Salvia_, 183;
lousewort, 184;
flowers adapted to fly-visits, 185;
orchids, 187;
deceptive flowers, _Cypripedium_, 200;
fertilization of Yucca, 202;
imperfection of adaptation a proof of origin through selection, 204;
mouth-parts of insects, 189;
bee, 172;
butterfly, 193;
cockroach, 191;
wind-pollination, 182.
Forel, Auguste, alarm-signals in ants, ii. 83.
Fraisse, on regeneration, ii. 30.
Function, passively functioning parts in relation to the Lamarckian
principle, ii. 77;
harmonious adaptation in these, ii. 81.
Fungi, reproduction of, ii. 267.
Fur of mammals, adaptation to the conditions of life, ii. 269.
Galapagos Islands, fauna of, ii. 283, 292.
Galileo, Galilei, 13.
Galls, plant, 385;
ii. 271.
Gall-wasps, reproduction of, ii. 245.
Galton, Francis, on continuity of the germ-plasm, 411;
on inheritance of talents, ii. 150;
curves of frequency, ii. 206;
doubt of the Lamarckian principle, 242.
Genius, human, ii. 394.
Germ-cells, and somatic cells, 411;
development of, 410;
their mutual attraction, ii. 230.
Germinal infection, ii. 69.
Germinal Selection, ii. 113;
influenced by personal selection, ii. 155;
relation of determinants to determinates, ii. 153;
combination of mental gifts, ii. 150;
influence of amphimixis, ii. 125;
influence of the multiplicity of ids, ii. 124;
objections on the score of smallness of the substance of the
germ-plasm, ii. 156;
degeneration of a species through cultivation, ii. 144;
there are only plus and minus variations, ii. 151;
excessive increase of variations, ii. 139;
basis of sexual characters, ii. 135;
its sphere of operation, ii. 127;
small hands and feet in the higher classes, ii. 147;
climatic forms, ii. 134;
bud-variations, ii. 141;
play of forces in the determinant system, ii. 154;
artificial selection, ii. 123;
short-sight, ii. 146;
milk-glands, ii. 147;
deformities, ii. 137;
muscular weakness in the higher classes of men, ii. 147;
positive variation, ii. 122;
regulated by personal selection, ii. 131;
source of purely morphological characters, ii. 132;
disappearance of disused parts, ii. 119, 129;
self-regulation of the germ-plasm, ii. 128;
specific talents, ii. 149;
sport-variations, ii. 140;
spontaneous and induced, ii. 137;
excessive increase of a variation tendency, ii. 130;
preponderance of panmixia, ii. 120;
origin of secondary sexual characters, ii. 143.
Germinal vesicle, 295.
Germ-plasm, conception of, 410;
continuity of, 411;
at once variable and persistent, ii. 220;
disintegration of, in ontogeny, 379;
nutritive variations within the, 379;
structure of the, 373;
variation of, due to environment, ii. 267;
to nutrition, ii. 268.
Germ-plasm theory, 345;
accessory idioplasm, 383;
active and passive state of determinants, 379;
connective tissue-cells, 386;
determinants and determinates, 355;
lithium-larvæ, 383;
ids, conception of, 349;
idants, 349;
male end female ids, 389;
mesoderm cells of sea-urchin, 387;
plant-galls, 385;
polymorphism, 390;
proofs of existence of determinants (_Lycæna agestis_, insect
metamorphosis, &c.), 356;
sexual dimorphism, 388.
Germ-tracks, 411.
Gesner's _Book of Animals_, 13.
Godelmann, regeneration of Phasmids, ii. 28 _n._
Goebel, 269.
Goethe, archetypal animal and plant, 18.
Green animals, 64.
Gruber, A., regeneration experiments on the Protozoa, 340.
Guignard, fertilization of Phanerogams, 315.
Gulick, snails in the Sandwich Islands. ii. 329.
Haase, Erich, on Pharmacopagæ, 101;
on mimicry, 104.
Haberlandt, protection of leaves, ii. 133;
Auxo-spores, ii. 221.