On the other hand, systematic teaching in Biology cannot be attempted with success until the student has attained to a certain knowledge of physics and chemistry: for though the phaenomena of life are dependent neither on physical nor on chemical, but on vital forces, yet they result in all sorts of physical and chemical changes, which can only be judged by their own laws.
And now to sum up in a few words the conclusions to which I hope you see reason to follow me.
Biology needs no apologist when she demands a place--and a prominent place--in any scheme of education worthy of the name. Leave out the Physiological sciences from your curriculum, and you launch the student into the world, undisciplined in that science whose subject-matter would best develope his powers of observation; ignorant of facts of the deepest importance for his own and others" welfare; blind to the richest sources of beauty in G.o.d"s creation; and unprovided with that belief in a living law, and an order manifesting itself in and through endless change and variety, which might serve to check and moderate that phase of despair through which, if he take an earnest interest in social problems, he will a.s.suredly sooner or later pa.s.s.
Finally, one word for myself. I have not hesitated to speak strongly where I have felt strongly; and I am but too conscious that the indicative and imperative moods have too often taken the place of the more becoming subjunctive and conditional. I feel, therefore, how necessary it is to beg you to forget the personality of him who has thus ventured to address you, and to consider only the truth or error in what has been said.
FOOTNOTES:
[56] "In the third place, we have to review the method of Comparison, which is so specially adapted to the study of living bodies, and by which, above all others, that study must be advanced. In Astronomy, this method is necessarily inapplicable; and it is not till we arrive at Chemistry that this third means of investigation can be used, and then only in subordination to the two others. It is in the study, both statical and dynamical, of living bodies that it first acquires its full development; and its use elsewhere can be only through its application here."--_Comte"s Positive Philosophy_, translated by Miss Martineau.
Vol. i. p. 372.
By what method does M. Comte suppose that the equality or inequality of forces and quant.i.ties and the dissimilarity or similarity of forms--points of some slight importance not only in Astronomy and Physics, but even in Mathematics,--are ascertained, if not by Comparison?
[57] "Proceeding to the second cla.s.s of means,--Experiment cannot but be less and less decisive, in proportion to the complexity of the phaenomena to be explored; and therefore we saw this resource to be less effectual in chemistry than in physics: and we now find that it is eminently useful in chemistry in comparison with physiology. _In fact, the nature of the phaenomena seems to offer almost insurmountable impediments to any extensive and prolific application of such a procedure in biology._"--COMTE, vol. i. p. 367.
M. Comte, as his manner is, contradicts himself two pages further on, but that will hardly relieve him from the responsibility of such a paragraph as the above.
[58] Nouvelle Fonction du Foie considere comme organe producteur de matiere sucree chez l"Homme et les Animaux, par M. Claude Bernard.
[59] "_Natural Groups given by Type, not by Definition...._ The cla.s.s is steadily fixed, though not precisely limited; it is given, though not circ.u.mscribed; it is determined, not by a boundary-line without, but by a central point within; not by what it strictly excludes, but what it eminently includes; by an example, not by a precept; in short, instead of Definition we have a _Type_ for our director. A type is an example of any cla.s.s, for instance, a species of a genus, which is considered as eminently possessing the characters of the cla.s.s. All the species which have a greater affinity with this type-species than with any others, form the genus, and are ranged about it, deviating from it in various directions and different degrees."--_Whewell, The Philosophy of the Inductive Sciences_, vol. i. pp. 476-7.
[60] Save for the pleasure of doing so, I need hardly point out my obligations to Mr. J. S. Mill"s "System of Logic," in this view of scientific method.
XI
ON THE PERSISTENT TYPES OF ANIMAL LIFE.
The successive modifications which the views of physical geologists have undergone since the infancy of their science, with regard to the amount and the nature of the changes which the crust of the globe has suffered, have all tended in one direction, viz. towards the establishment of the belief, that throughout that vast series of ages which was occupied by the deposition of the stratified rocks, and which may be called "geological time," (to distinguish it from the "historical time" which followed, and the "pre-geological time," which preceded it) the intensity and the character of the physical forces which have been in operation, have varied within but narrow limits; so that, even in Silurian or Cambrian times, the aspect of physical nature must have been much what it is now.
This uniformitarian view of telluric conditions, so far as geological time is concerned, is, however, perfectly consistent with the notion of a totally different state of things in antecedent epochs, and the strongest advocate of such "physical uniformity" during the time of which we have a record might, with perfect consistency, hold the so-called "nebular hypothesis," or any other view involving the conception of a long series of states very different from that which we now know, and whose succession occupied pre-geological time.
The doctrine of physical uniformity and that of physical progression are therefore perfectly consistent, if we regard geological time as having the same relation to pre-geological time as historical time has to it.
The accepted doctrines of palaeontology are by no means in harmony with these tendencies of physical geology. It is generally believed that there is a vast contrast between the ancient and the modern organic worlds--it is incessantly a.s.sumed that we are acquainted with the beginning of life, and with the primal manifestation of each of its typical forms: nor does the fact that the discoveries of every year oblige the holders of these views to change their ground, appear sensibly to affect the tenacity of their adhesion.
Without at all denying the considerable positive differences which really exist between the ancient and the modern forms of life, and leaving the negative ones to be met by the other lines of argument, an impartial examination of the facts revealed by palaeontology seems to show that these differences and contrasts have been greatly exaggerated.
Thus, of some two hundred known orders of plants, not one is exclusively fossil. Among animals, there is not a single totally extinct cla.s.s; and of the orders, at the outside not more than seven per cent. are unrepresented in the existing creation.
Again, certain well marked forms of living beings have existed through enormous epochs, surviving not only the changes of physical conditions, but persisting comparatively unaltered, while other forms of life have appeared and disappeared. Some forms may be termed "persistent types" of life; and examples of them are abundant enough in both the animal and the vegetable worlds.
Among plants, for instance, ferns, club mosses, and _Coniferae_, some of them apparently generically identical with those now living, are met with as far back as the carboniferous epoch; the cone of the oolitic _Araucaria_ is hardly distinguishable from that of existing species; a species of _Pinus_ has been discovered in the Purbecks, and a walnut (_Juglans_) in the cretaceous rocks.[61] All these are types of vegetable structure, abounding at the present day; and surely it is a most remarkable fact to find them persisting with so little change through such vast epochs.
Every sub-kingdom of animals yields instances of the same kind. The _Globigerina_ of the Atlantic soundings is identical with the cretaceous species of the same genus; and the casts of lower Silurian _Foraminifera_, recently described by Ehrenberg, a.s.sure us of the very close resemblance between the oldest and the newest forms of many of the _Protozoa_.
Among the _Coelenterata_, the tabulate corals of the Silurian epoch are wonderfully like the millepores of our own seas, as every one may convince himself who compares _Heliolites_ with _Heliopora_.
Turning to the _Mollusca_, the genera _Crania_, _Discina_, _Lingula_, have persisted from the Silurian epoch to the present day, with so little change, that very competent malacologists are sometimes puzzled to distinguish the ancient from the modern species. _Nautili_ have a like range, and the sh.e.l.l of the lia.s.sic _Loligo_ is similar to that of the "squid" of our own seas. Among the _Annulosa_, the carboniferous insects are in several cases referable to existing genera, as are the _Arachnida_, the highest group of which, the scorpions, is represented in the coal by a genus differing from its living congeners only in the disposition of its eyes.
The vertebrate sub-kingdom furnishes many examples of the same kind. The _Ganoidei_ and _Elasmobranchii_ are known to have persisted from at least the middle of the Palaeozoic epoch to our own times, without exhibiting a greater amount of deviation from the typical characters of these orders, than may be found within their limits at the present day.
Among the _Reptilia_, the highest group, that of the _Crocodilia_, was represented at the beginning of the Mesozoic epoch, if not earlier, by species identical in the essential character of their organization with those now living, and presenting differences only in such points as the form of the articular faces of their vertebrae, in the extent to which the nasal pa.s.sages are separated from the mouth by bone, and in the proportions of the limbs. Even such imperfect knowledge as we possess of the ancient mammalian fauna leads to the belief that certain of its types, such as that of the _Marsupialia_, have persisted with no greater change through as vast a lapse of time.
It is difficult to comprehend the meaning of such facts as these, if we suppose that each species of animal and plant, or each great type of organization, was formed and placed upon the surface of the globe at long intervals by a distinct act of creative power; and it is well to recollect that such an a.s.sumption is as unsupported by tradition or revelation as it is opposed to the general a.n.a.logy of Nature.
If, on the other hand, we view "Persistent Types," in relation to that hypothesis which supposes the species of living beings living at any time to be the result of the gradual modification of pre-existing species--a hypothesis which though unproven, and sadly damaged by some of its supporters, is yet the only one to which physiology lends any countenance--their existence would seem to show, that the amount of modification which living beings have undergone during geological time is but very small in relation to the whole series of changes which they have suffered. In fact, palaeontology and physical geology are in perfect harmony, and coincide in indicating that all we know of the conditions in our world during geological time, is but the last term of a vast and, so far as our present knowledge reaches, unrecorded progression.
FOOTNOTES:
[61] I state these facts on the authority of my friend Dr. Hooker.--T.
H. H.
XII
TIME AND LIFE.
MR. DARWIN"S "ORIGIN OF SPECIES"
Everyone knows that that superficial film of the earth"s substance, hardly ten miles thick, which is accessible to human investigation, is composed for the most part of beds or strata of stone, the consolidated muds and sands of former seas and lakes, which have been deposited one upon the other, and hence are the older the deeper they lie. These mult.i.tudinous strata present such resemblances and differences among themselves that they are capable of cla.s.sification into groups or formations, and these formations again are brigaded together into still larger a.s.semblages, called by the older geologists, primary, secondary, and tertiary; by the moderns, palaeozoic, mesozoic, and cainozoic: the basis of the former nomenclature being the relative age of the groups of strata; that of the latter, the kinds of living forms contained in them.
Though but a film if compared with the total diameter of our planet, the total series of formations is vast indeed when measured by any human standard, and, as all action implies time, so are we compelled to regard these mineral ma.s.ses as a measure of the time which has elapsed during their acc.u.mulation. The amount of the time which they represent is, of course, in the inverse proportion of the intensity of the forces which have been in operation. If, in the ancient world, mud and sand acc.u.mulated on sea-bottoms at tenfold their present rate, it is clear that a bed of mud or sand ten feet thick would have been formed then in the same time as a stratum of similar materials one foot thick would be formed now, and _vice versa_.
At the outset of his studies, therefore, the physical geologist had to choose between two hypotheses; either, throughout the ages which are represented by the acc.u.mulated strata, and which we may call _geologic time_, the forces of nature have operated with much the same average intensity as at present, and hence the lapse of time which they represent must be something prodigious and inconceivable, or, in the primeval epochs, the natural powers were infinitely more intense than now, and hence the time through which they acted to produce the effects we see was comparatively short.
The earlier geologists adopted the latter view almost with one consent.
For they had little knowledge of the present workings of nature, and they read the records of geologic time as a child reads the history of Rome or Greece, and fancies that antiquity was grand, heroic, and unlike the present because it is unlike his little experience of the present.
Even so the earlier observers were moved with wonder at the seeming contrast between the ancient and the present order of nature. The elemental forces seemed to have been grander and more energetic in primeval times. Upheaved and contorted, rifted and fissured, pierced by d.y.k.es of molten matter or worn away over vast areas by aqueous action, the older rocks appeared to bear witness to a state of things far different from that exhibited by the peaceful epoch on which the lot of man has fallen.
But by degrees thoughtful students of geology have been led to perceive that the earliest efforts of nature have been by no means the grandest.
Alps and Andes are children of yesterday when compared with Snowdon and the c.u.mberland hills; and the so-called glacial epoch--that in which perhaps the most extensive physical changes of which any record remains occurred--is the last and the newest of the revolutions of the globe.
And in proportion as physical geography--which is the geology of our own epoch--has grown into a science, and the present order of nature has been ransacked to find what, _hibernice_, we may call precedents for the phenomena of the past, so the apparent necessity of supposing the past to be widely different from the present has diminished.
The transporting power of the greatest deluge which can be imagined sinks into insignificance beside that of the slowly floating, slowly melting iceberg, or the glacier creeping along at its snail"s pace of a yard a day. The study of the deltas of the Nile, the Ganges, and the Mississippi has taught us how slow is the wearing action of water, how vast its effects when time is allowed for its operation. The reefs of the Pacific, the deep-sea soundings of the Atlantic, show that it is to the slow-growing coral and to the imperceptible animalcule, which lives its brief s.p.a.ce and then adds its tiny sh.e.l.l to the muddy cairn left by its brethren and ancestors, that we must look as the agents in the formation of limestone and chalk, and not to hypothetical oceans saturated with calcareous salts and suddenly depositing them.
And while the inquirer has thus learnt that existing forces--_give them time_--are competent to produce all the physical phenomena we meet with in the rocks, so, on the other side, the study of the marks left in the ancient strata by past physical actions shows that these were similar to those which now obtain. Ancient beaches are met with whose pebbles are like those found on modern sh.o.r.es; the hardened sea-sands of the oldest epochs show ripple-marks, such as may now be found on every sandy coast; nay, more, the pits left by ancient rain-drops prove that even in the very earliest ages, the "bow in the clouds" must have adorned the palaeozoic firmament. So that if we could reverse the legend of the Seven Sleepers,--if we could sleep back through the past, and awake a million ages before our own epoch, in the midst of the earliest geologic times,--there is no reason to believe that sea, or sky, or the aspect of the land would warn us of the marvellous retrospection.
Such are the beliefs which modern physical geologists hold, or, at any rate, tend towards holding. But, in so doing, it is obvious that they by no means prejudge the question, as to what the physical condition of the globe may have been before our chapters of its history begin, in what may be called (with that licence which is implied in the often-used term "prehistoric epoch") "pregeologic time." The views indicated, in fact, are not only quite consistent with the hypothesis, that, in the still earlier period referred to, the condition of our world was very different; but they may be held by some to necessitate that hypothesis.
The physical philosopher who is accurately acquainted with the velocity of a cannon-ball, and the precise character of the line which it traverses for a yard of its course, is necessitated by what he knows of the laws of nature to conclude that it came from a certain spot, whence it was impelled by a certain force, and that it has followed a certain trajectory. In like manner, the student of physical geology, who fully believes in the uniformity of the general condition of the earth through geologic time, may feel compelled by what he knows of causation, and by the general a.n.a.logy of nature, to suppose that our solar system was once a nebulous ma.s.s, that it gradually condensed, that it broke up into that wonderful group of harmoniously rolling b.a.l.l.s we call planets and satellites, and that then each of these underwent its appointed metamorphosis, until at last our own share of the cosmic vapour pa.s.sed into that condition in which we first meet with definite records of its state, and in which it has since, with comparatively little change, remained.