The Descent of Man

The Descent of Man
and Selection in Relation to Sex
----------------------------------
PART I. THE DESCENT OR ORIGIN OF MAN
CHAPTER I. THE EVIDENCE OF THE DESCENT OF MAN FROM SOME LOWER FORM
Nature of the evidence bearing on the origin of man--Homologous
structures in man and the lower animals--Miscellaneous points of
correspondence--Development--Rudimentary structures, muscles,
sense-organs, hair, bones, reproductive organs, &c.--The bearing of
these three great classes of facts on the origin of man.
HE who wishes to decide whether man is the modified descendant of some
pre-existing form, would probably first enquire whether man varies, however
slightly, in bodily structure and in mental faculties; and if so,
whether the variations are transmitted to his offspring in accordance with
the laws which prevail with the lower animals. Again, are the variations
the result, as far as our ignorance permits us to judge, of the same general
causes, and are they governed by the same general laws, as in the case of
other organisms; for instance, by correlation, the inherited effects of use
and disuse, &c.? Is man subject to similar malconformations, the result of
arrested development, of reduplication of parts, &c., and does he display
in any of his anomalies reversion to some former and ancient type of
structure? It might also naturally be enquired whether man, like so many
other animals, has given rise to varieties and sub-races, differing but
slightly from each other, or to races differing so much that they must be
classed as doubtful species? How are such races distributed over the
world; and how, when crossed, do they react on each other in the first and
succeeding generations? And so with many other points.
The enquirer would next come to the important point, whether man
tends to increase at so rapid a rate, as to lead to occasional severe struggles
for existence; and consequently to beneficial variations, whether in
body or mind, being preserved, and injurious ones eliminated. Do the
races or species of men, whichever term may be applied, encroach on and
replace one another, so that some finally become extinct? We shall see
that all these questions, as indeed is obvious in respect to most of them,
must be answered in the affirmative, in the same manner as with the lower
animals. But the several considerations just referred to may be conveniently
deferred for a time: and we will first see how far the bodily structure
of man shows traces, more or less plain, of his descent from some
lower form. In succeeding chapters the mental powers of man, in comparison
with those of the lower animals, will be considered.........
The Bodily Structure of Man.--It is notorious that man is
constructed on the same general type or model as other mammals. All the bones
in his skeleton can be compared with corresponding bones in a monkey, bat,
or seal. So it is with his muscles, nerves, blood-vessels and internal
viscera. The brain, the most important of all the organs, follows the same
law, as shewn by Huxley and other anatomists. Bischoff, [1] who is a hostile
witness, admits that every chief fissure and fold in the brain of man has
its analogy in that of the orang; but he adds that at no period of development
do their brains perfectly agree; nor could perfect agreement be
expected, for otherwise their mental powers would have been the same.
Vulpian [2] remarks: "Les differences reelles qui existent entre l'encephale
de l'homme et celui des singes superieurs, sont bien minimes. Il ne faut
pas se faire d'illusions a cet egard. L'homme est bien plus pres des singes
anthropomorphes par les caracteres anatomiques de son cerveau que
ceux-ci ne le sont non seulement des autres mammiferes, mais meme de
certains quadrumanes, des guenons et des macaques." But it would be
superfluous here to give further details on the correspondence between man
and the higher mammals in the structure of the brain and all other parts
of the body.
It may, however, be worth while to specify a few points, not directly or
obviously connected with structure, by which this correspondence or
relationship is well shewn.
Man is liable to receive from the lower animals, and to communicate
to them, certain diseases, as hydrophobia, variola, the glanders, syphilis,
cholera, herpes, &c.; [3] and this fact proves the close similarity [4] of
their tissues and blood, both in minute structure and composition, far more
plainly than does their comparison under the best microscope, or by the
aid of the best chemical analysis. Monkeys are liable to many of the
same non-contagious diseases as we are; thus Rengger, [5] who carefully
observed for a long time the Cebus Azarae in its native land, found it liable
to catarrh, with the usual symptoms, and which, when often recurrent,
led to consumption. These monkeys suffered also from apoplexy, inflammation
of the bowels, and cataract in the eye. The younger ones when
shedding their milk-teeth often died from fever. Medicines produced the
same effect on them as on us. Many kinds of monkeys have a strong taste
for tea, coffee, and spirituous liquors: they will also, as I have myself
seen, smoke tobacco with pleasure. [6] Brehm asserts that the natives of
north-eastern Africa catch the wild baboons by exposing vessels with
strong beer, by which they are made drunk. He has seen some of these
animals, which he kept in confinement, in this state; and he gives a
laughable account of their behaviour and strange grimaces. On the following
morning they were very cross and dismal; they held their aching
heads with both hands, and wore a most pitiable expression: when beer or
wine was offered them, they turned away with disgust, but relished the
juice of lemons. [7] An American monkey, an Ateles, after getting drunk on
brandy, would never touch it again, and thus was wiser than many men.
These trifling facts prove how similar the nerves of taste must be in monkeys
and man, and how similarly their whole nervous system is affected.
Man is infested with internal parasites, sometimes causing fatal effects;
and is plagued by external parasites, all of which belong to the
same genera or families as those infesting other mammals, and in the case
of scabies to the same species. [8] Man is subject, like other mammals,
birds, and even insects, [9] to that mysterious law, which causes certain
normal processes, such as gestation, as well as the maturation and duration
of various diseases, to follow lunar periods. His wounds are repaired
by the same process of healing; and the stumps left after the amputation
of his limbs, especially during an early embryonic period, occasionally
possess some power of regeneration, as in the lowest animals. [10]
The whole process of that most important function, the reproduction
of the species, is strikingly the same in all mammals, from the first act of
courtship by the male, [11] to the birth and nurturing of the young. Monkeys
are born in almost as helpless a condition as our own infants; and in
certain genera the young differ fully as much in appearance from the
adults, as do our children from their full-grown parents. [12] It has been
urged by some writers, as an important distinction, that with man the
young arrive at maturity at a much later age than with any other animal:
but if we look to the races of mankind which inhabit tropical countries
the difference is not great, for the orang is believed not to be adult till
the age of from ten to fifteen years. [13] Man differs from woman in size,
bodily strength, hairiness, &c., as well as in mind, in the same manner as
do the two sexes of many mammals. So that the correspondence in general
structure, in the minute structure of the tissues, in chemical composition
and in constitution, between man and the higher animals, especially
the anthropomorphous apes, is extremely close.
Embryonic Development.--Man is developed from an ovule, about the
125th of an inch in diameter, which differs in no respect from the ovules
of other animals. The embryo itself at a very early period can hardly be
distinguished from that of other members of the vertebrate kingdom. At
this period the arteries run in arch-like branches, as if to carry the blood
to branchiae which are not present in the higher vertebrata, though the
slits on the sides of the neck still remain (f, g, fig. I), marking their
former position. At a somewhat later period, when the extremities are
developed, "the feet of lizards and mammals," as the illustrious Von Baer
remarks, "the wings and feet of birds, no less than the hands and feet of
man, all arise from the same fundamental form." It is, says Prof. Huxley, [14]
"quite in the later stages of development that the young human being
presents marked differences from the young ape, while the latter departs
as much from the dog in its developments, as the man does. Startling
as this last assertion may appear to be, it is demonstrably true."
As some of my readers may never have seen a drawing of an embryo, I
have given one of man and another of a dog, at about the same early
stage of development, carefully copied from two works of undoubted
accuracy. [15]
After the foregoing statements made by such high authorities, it would
be superfluous on my part to give a number of borrowed details, shewing
that the embryo of man closely resembles that of other mammals. It may,
however, be added, that the human embryo likewise resembles certain
low forms when adult in various points of structure. For instance, the
heart at first exists as a simple pulsating vessel; the excreta are voided
through a cloacal passage; and the os coccyx projects like a true tail,
"extending considerably beyond the rudimentary legs." [16] In the embryos of
all air-breathing vertebrates, certain glands, called the corpora Wolffiana,
correspond with, and act like the kidneys of mature fishes. [17] Even at a
later embryonic period, some striking resemblances between man and the
lower animals may be observed. Bischoff says "that the convolutions of
the brain in a human foetus at the end of the seventh month reach about
the same stage of development as in a baboon when adult." [18] The great
toe, as Professor Owen remarks, [19] "which forms the fulcrum when standing
or walking, is perhaps the most characteristic peculiarity in the human
structure;" but in an embryo, about an inch in length, Prof. Wyman [20]
found "that the great toe was shorter than the others; and, instead
of being parallel to them, projected at an angle from the side of the foot,
thus corresponding with the permanent condition of this part in the
quadrumana." I will conclude with a quotation from Huxley, [21] who after
asking, does man originate in a different way from a dog, bird, frog or fish?
says, "the reply is not doubtful for a moment; without question, the
mode of origin, and the early stages of the development of man, are identical
with those of the animals immediately below him in the scale: without
a doubt in these respects, he is far nearer to apes than the apes are to
the dog."
Rudiments.--This subject, though not intrinsically more important
than the two last, will for several reasons be treated here more fully. [22]
Not one of the higher animals can be named which does not bear some
part in a rudimentary condition; and man forms no exception to the rule.
Rudimentary organs must be distinguished from those that are nascent;
though in some cases the distinction is not easy. The former are either
absolutely useless, such as the mammae of male quadrupeds, or the incisor
teeth of ruminants which never cut through the gums; or they are of such
slight service to their present possessors, that we can hardly suppose that
they were developed under the conditions which now exist. Organs in this
latter state are not strictly rudimentary, but they are tending in this
direction. Nascent organs, on the other hand, though not fully developed,
are of high service to their possessors, and are capable of further
development. Rudimentary organs are eminently variable; and this is partly
intelligible, as they are useless, or nearly useless, and consequently are no
longer subjected to natural selection. They often become wholly suppressed.
When this occurs, they are nevertheless liable to occasional reappearance
through reversion--a circumstance well worthy of attention.
The chief agents in causing organs to become rudimentary seem to
have been disuse at that period of life when the organ is chiefly used (and
this is generally during maturity) and also inheritance at a corresponding
period of life. The terms "disuse" does not relate merely to the lessened
action of muscles, but includes a diminished flow of blood to a part
or organ, from being subjected to fewer alternations of pressure, or from
becoming in any way less habitually active. Rudiments, however, may
occur in one sex of those parts which are normally present in the other
sex; and such rudiments, as we shall hereafter see, have often originated
in a way distinct from those here referred to. In some cases, organs have
been reduced by means of natural selection, from having become injurious
to the species under changed habits of life. The process of reduction
is probably often aided through the two principles of compensation and
economy of growth; but the later stages of reduction, after disuse has
done all that can fairly be attributed to it, and when the saving to be
effected by the economy of growth would be very small, [23] are difficult to
understand. The final and complete suppression of a part, already useless
and much reduced in size, in which case neither compensation nor economy
can come into play, is perhaps intelligible by the aid of the hypothesis
of pangenesis. But as the whole subject of rudimentary organs has
been discussed and illustrated in my former works, [24] I need here say no
more on this head...........
The ears of the chimpanzee and orang are curiously like those of man,
and the proper muscles are likewise but very slightly developed. [30] I am
also assured by the keepers in the Zoological Gardens that these animals
never move or erect their ears; so that they are in an equally rudimentary
condition with those of man, as far as function is concerned. Why these
animals, as well as the progenitors of man, should have lost the power of
erecting their ears, we can not say. It may be, though I am not satisfied
with this view, that owing to their arboreal habits and great strength they
were but little exposed to danger, and so during a lengthened period moved
their ears but little, and thus gradually lost the power of moving them.
This would be a parallel case with that of those large and heavy birds,
which, from inhabiting oceanic islands, have not been exposed to the attacks
of beasts of prey, and have consequently lost the power of using
their wings for flight. The inability to move the ears in man and several
apes is, however, partly compensated by the freedom with which they can
move the head in a horizontal plane, so as to catch sounds from all directions.
The bearing of the three great classes of facts now given is unmistakable.
But it would be superfluous fully to recapitulate the line of argument
given in detail in my 'Origin of Species.' The homological construction
of the whole frame in the members of the same class is intelligible,
if we admit their descent from a common progenitor, together with
their subsequent adaptation to diversified conditions. On any other view,
the similarity of pattern between the hand of a man or monkey, the foot
of a horse, the flipper of a seal, the wing of a bat, &c., is utterly
inexplicable. [56] It is no scientific explanation to assert that they have
all been formed on the same ideal plan. With respect to development, we can
clearly understand, on the principle of variation supervening at a rather
late embryonic period, and being inherited at a corresponding period,
how it is that the embryos of wonderfully different forms should still retain,
more or less perfectly, the structure of their common progenitor.
No other explanation has ever been given of the marvellous fact that the
embryos of a man, dog, seal, bat, reptile, &c., can at first hardly be
distinguished from each other. In order to understand the existence of
rudimentary organs, we have only to suppose that a former progenitor possessed
the parts in question in a perfect state, and that under changed
habits of life they became greatly reduced, either from simple disuse, or
through the natural selection of those individuals which were least encumbered
with a superfluous part, aided by the other means previously
indicated.
Thus we can understand how it has come to pass that man and all
other vertebrate animals have been constructed on the same general
model, why they pass through the same early stages of development, and
why they retain certain rudiments in common. Consequently we ought
frankly to admit their community of descent; to take any other view, is
to admit that our own structure, and that of all the animals around us, is
a mere snare laid to entrap our judgment. This conclusion is greatly
strengthened, if we look to the members of the whole animal series, and
consider the evidence derived from their affinities or classification, their
geographical distribution and geological succession. It is only our natural
prejudice, and that arrogance which made our forefathers declare that
they were descended from demi-gods, which leads us to demur to this
conclusion. But the time will before long come, when it will be thought
wonderful that naturalists, who were well acquainted with the comparative
structure and development of man, and other mammals, should have
believed that each was the work of a separate act of creation.
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[1] 'Grosshirnwindungen des Menschen,' 1868, s. 96. The conclusions of
this author, as well as those of Gratiolet and Aeby, concerning the brain, will
be discussed by Prof. Huxley in the Appendix alluded to in the Preface to this
edition.
[2] 'Lec. sur la Phys.' 1866, p. 890, as quoted by M. Dally, 'L'Ordre des
Primates et le Transformisme,' 1868, p. 29.
[3] Dr. W. Lauder Lindsay has treated this subject at some length in the
'Journal of Mental Science,' July 1871; and in the 'Edinburgh Veterinary
Review,' July 1858.
[4] A Reviewer has criticised ('British Quarterly Review,' Oct. 1st, 1871,
p. 472) what I have here said with much severity and contempt; but as I do not
use the term identity, I cannot see that I am greatly in error. There appears
to me a strong analogy between the same infection or contagion producing the
same result, or one closely similar, in two distinct animals, and the testing
of two distinct fluids by the same chemical reagent.
[5] 'Naturgeschichte der Saugethiere von Paraguay,' 1830, s. 50.
[6] The same tastes are common to some animals much lower in the scale.
Mr. A. Nicols informs me that he kept in Queensland, in Australia, three
individuals of the Phaseolarctus cinereus; and that, without having been taught
in any way, they acquired a strong taste for rum, and for smoking tobacco.
[7] Brehm, 'Thierleben,' B. i. 1864, s. 75, 86. On the Ateles, s. 105.
For other analogous statements, see s. 25, 107.
[8] Dr. W. Lauder Lindsay, 'Edinburgh Vet. Review,' July 1858, p. 13.
[9] With respect to insects see Dr. Laycock, "On a General Law of Vital
Periodicity," 'British Association,' 1842. Dr. Macculloch, 'Silliman's North
American Journal of Science,' vol. xvii. p. 305, has seen a dog suffering from
tertian ague. Hereafter I shall return to this subject.
[10] I have given the evidence on this head in my 'Variation of Animals
and Plants under Domestication,' vol. ii. p. 15, and more could be added.
[11] Mares e diversis generibus Quadrumanorum sine dubio dignoscunt
feminas humanas a maribus. Primum, credo, odoratu, postea aspectu. Mr.
Youatt, qui diu in Hortis Zoologicis (Bestiariis) medicus animalium erat, vir
in rebus observandis cautus et sagax, hoc mihi certissime probavit, et
curatores ejusdem loci et alii e ministris confirmaverunt. Sir Andrew Smith et
Brehm notabant idem in Cynocephalo. Illustrissimus Cuvier etiam narrat multa
de hac re, qua ut opinor, nihil turpius potest indicari inter omnia hominibus
et Quadrumanis communia. Narrat enim Cynocephalum quendam in furorem incidere
aspectu feminarum aliquarem, sed nequaquam accendi tanto furore ab omnibus.
Semper eligebat juniores, et dignoscebat in turba, et advocabat voce gestuque.
[12] This remark is made with respect to Cynocephalus and the
anthropomorphous apes by Geoffroy Saint-Hilaire and F. Cuvier, 'Hist. Nat. des
Mammiferes,' tom. i 1824.
[13] Huxley, 'Man's Place in Nature,' 1863, p. 34.
[14] 'Man's Place in Nature,' 1863, p. 67.
[15] The human embryo (upper fig.) is from Ecker, 'Icones Phys.,'
1851-1859, tab. xxx. fig. 2. This embryo was ten lines in length, so that the
drawing is much magnified. The embryo of the dog is from Bischoff,
'Entwicklungsgeschichte des Hunde-Eies,' 1845, tab. xi. fig. 42 B. This
drawing is five times magnified, the embryo being twenty-five days old. The
internal viscera have been omitted, and the uterine appendages in both drawings
removed. I was directed to these figures by Prof. Huxley, from whose work,
'Man's Place in Nature,' the idea of giving them was taken. Hacket has also
given analogous drawings in his 'Schopfungsgeschichte.'
[16] Prof. Wyman in 'Proc. of American Acad. of Sciences,' vol. iv. 1860,
p. 17.
[17] Owen, 'Anatomy of Vertebrates,' vol. i. p. 533.
[18] 'Die Grosshirnwindungen des Menschen,' 1868, s. 95.
[19] 'Anatomy of Vertebrates,' vol. ii. p. 553.
[20] 'Proc. Soc. Nat. Hist.' Boston, 1863, vol. ix. p. 185.
[21] 'Man's Place in Nature,' p. 65.
[22] I had written a rough copy of this chapter before reading a valuable
paper, "Caratteri rudimentali in ordine all' origine dell' uomo" ('Annuario
della Soc. d. Nat.,' Modena, 1867, p. 81), by G. Canestrini, to which paper I
am considerably indebted. Hackel has given admirable discussions on this whole
subject, under the title of Dys teleology, in his 'Generelle Morphologie' and
'Schopfungsgeschichte'
[23] Some good criticisms on this subject have been given by Messrs. Murie
and Mivart, in 'Transact. Zoolog. Soc.' 1869, vol. vii. p. 92.
[24] 'Variation of Animals and Plants under Domestication,' vol. ii. pp.
317 and 397 See also 'Origin of Species,' this edit. p. 346.
[25] For instance, M. Richard ('Annales des Sciences Nat.,' 3d series,
Zoolog. 1852, tom. xviii. p. 13) describes and figures rudiments of what he
calls the "muscle pedieux de la main," which he says is sometimes "infiniment
petit." Another muscle, called "le tibial posterieur," is generally quite
absent in the hand, but appears from time to time in a more or less rudimentary
condition.
[26] Prof. W. Turner, 'Proc. Royal Soc. Edinburgh,' 1866-67, p. 65.
[27] See my 'Expression of the Emotions in Man and Animals,' 1872, p. 144.
[28] Canestrini quotes Hyrtl. ('Annuario della Soc. dei Naturalisti,'
Modena, 1897, p. 97) to the same effect.
[29] 'The Diseases of the Ear,' by J. Toynbee, F. R. S., 1860, p. 12. A
distinguished physiologist, Prof. Preyer, informs me that he had lately been
experimenting on the function of the shell of the ear, and has come to nearly
the same conclusion as that given here.
[30] Prof. A. Macalister, 'Annals and Mag. of Nat. History,' vol. vii.,
1871, p. 342.
[31] Mr. St. George Mivart, 'Elementary Anatomy,' 1873, p. 396.
[32] See also some remarks, and the drawings of the ears of the
Lemuroidea, in Messrs. Murie and Mivart's excellent paper in 'Transact.
Zoolog. Soc.' vol. vii. 1869, pp. 6 and 90.
[33] Ueber das Darwin'sche Spitzohr, Archiv fur Path. Anat. und Phys.
1871, p. 485
[34] 'The Expression of the Emotions' @@
[35] Muller's 'Elements of Physiology,' Eng. translat., 1842, vol. ii. p.
1117. Owen, 'Anatomy of Vertebrates,' vol. iii. p. 260; ibid. on the Walrus,
'Proc. Zoolog. Soc.' November 8th, 1854. See also R. Knox, 'Great Artists and
Anatomists,' p. 106. This rudiment apparently is somewhat larger in Negroes
and Australians than in Europeans, see Carl Vogt, 'Lectures on Man,' Eng.
translat. p. 129.
[36] The account given by Humboldt of the power of smell possessed by the
natives of South America is well known, and has been confirmed by others. M.
Houzeau ('Etudes sur les Facultes Mentales,' &c., tom. i. 1872, p. 91) asserts
that he repeatedly made experiments, and proved that Negroes and Indians could
recognise persons in the dark by their odour. Dr. W. Ogle has made some
curious observations on the connection between the power of smell and the
colouring matter of the mucous membrane of the olfactory region as well as of
the skin of the body. I have, therefore, spoken in the text of the
dark-coloured races having a finer sense of smell than the white races. See
his paper, 'Medico-Chirurgical Transactions,' London, vol. liii., 1870, p. 276
[37] 'The Physiology and Pathology of Mind,' 2nd edit. 1868, p. 134.
[38] Eschricht, Ueber die Richtung der Haare am menschlichen Korper,
'Muller's Archiv fur Anat. und Phys.' 1837, s. 47. I shall often have to refer
to this very curious paper.
[39] Paget, 'Lectures on Surgical Pathology,' 1853, vol. i. p. 71.
[40] Eschricht, ibid. s. 40, 47.
[41] See my 'Variation of Animals and Plants under Domestication,' vol.
ii. p. 327. Prof. Alex. Brandt has recently sent me an additional case of a
father and son, born in Russia, with these peculiarities. I have received
drawings of both from Paris
[42] Dr. Webb, 'Teeth in Man and the Anthropoid Apes,' as quoted by Dr. C.
Carter Blake in 'Anthropological Review,' July 1867, p. 299
[43] Owen, 'Anatomy of Vertebrates,' vol. iii. pp. 320, 321, and 325.
[44] 'On the Primitive Form of the Skull,' Eng. translat. in
'Anthropological Review Oct. 1868, p. 426.
[45] Prof. Montegazza writes to me from Florence, that he has lately been
studying the last molar teeth in the different races of man, and has come to
the same conclusion as that given in my text, viz., that in the higher or
civilized races they are on the road towards atrophy or elimination.
[46] Owen, 'Anatomy of Vertebrates,' vol. iii. pp. 416, 434, 441.
[47] 'Annuario della Soc. d. Nat.' Modena, 1867, p. 94.
[48] M. C. Martins ("De l'Unite Organique," in 'Revue des Deux Mondes,'
June 15, 1862, p. 16), and Hackel ('Generelle Morphologie,' B. ii. s. 278),
have both remarked on the singular fact of this rudiment sometimes causing
death.
[49] With respect to inheritance, see Dr. Struthers in the 'Lancet,' Feb.
15, 1873, and another important paper, ibid., Jan. 24, 1863, p. 83. Dr. Knox,
as I am informed, was the first anatomist who drew attention to this peculiar
structure in man; see his 'Great Artists and Anatomists,' p. 63. See also an
important memoir on this process by Dr. Gruber, in the 'Bulletin de l'Acad.
Imp. de St. Petersbourg,' tom xii. 1867, p. 448.
[50] Mr. St. George Mivart, 'Transact. Phil. Soc.' 1867, p. 310.
[51] "On the Caves of Gibraltar," 'Transact. Internat. Congress of
Prehist. Arch.' Third Session, 1869, p. 159. Prof. Wyman has lately shewn
(Fourth Annual Report, Peabody Museum, 1871, p. 20), that this perforation is
present in thirty-one per cent. of some human remains from ancient mounds in
the Western United States, and in Florida. It frequently occurs in the negro.
[52] Quatrefages has lately collected the evidence on this subject.
'Revue des Cours Scientifiques,' 1867-1868, p. 625. In 1840 Fleischmann
exhibited a human foetus bearing a free tail, which, as is not always the case,
included vertebral bodies; and this tail was critically examined by the many
anatomists present at the meeting of naturalists at Erlangen (see Marshall in
Niederlandischen Archiv Fur Zoologie, December 1871).
[53] Owen, 'On the Nature of Limbs,' 1849, p. 114.
[54] Leuckart, in Todd's 'Cyclop. of Anat.' 1849-52, vol. iv. p. 1415. In
man this organ is only from three to six lines in length, but, like so many
other rudimentary parts, it is variable in development as well as in other
characters.
[55] See, on this subject, Owen, 'Anatomy of Vertebrates,' vol. iii. p.
675, 676, 706.
[56] Prof. Bianconi, in a recently published work, illustrated by
admirable engravings ('La Theorie Darwinienne et la creation dite
independante,' 1874), endeavours to show that homological structures, in the
above and other cases, can be fully explained on mechanical principles, in
accordance with their uses. No one has shewn so well, how admirably such
structures are adapted for their final purpose; and this adaptation can, as I
believe, be explained through natural selection. In considering the wing
of a bat, he brings forward (p. 218) what appears to me (to use Auguste Comte's
words) a mere metaphysical principle, namely, the preservation "in its
integrity of the mammalian nature of the animal." In only a few cases does he
discuss rudiments, and then only those parts which are partially rudimentary,
such as the little hoofs of the pig and ox, which do not touch the ground;
these he shows clearly to be of service to the animal. It is unfortunate that
he did not consider such cases as the minute teeth, which never cut through the
jaw in the ox, or the mammae of male quadrupeds, or the wings of certain
beetles, existing under the soldered wing-covers, or the
vestiges of the pistil and stamens in various flowers, and many other such
cases. Although I greatly admire Prof. Bianconi's work, yet the belief now
held by most naturalists seems to me left unshaken, that homological structures
are inexplicable on the principle of mere adaptation.
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