Evolution and the origin of life

Front matter

LOWEST FORMS OF LIFE.

Fic. I.

KlG. 2.

Preface

Since the publication of my larger work, "The Beg-innings of Life," in 1S72, some long-overhanging clouds have been dispersed. Well-informed men of science no longer doubt that swarms of Bacteria can be made to appear within sealed glass vessels containing suitable fluids, after the vessels and their contents have been exposed to the temperature of boiling water. The thorough establishment of this fact has been of the greatest importance.

Statements as to the reality of so unexpected an appearance of Bacteria were previously received with actual disbelief or the profoundest scepticism. It was much easier to imagine that I had been mistaken or deceived than to suppose that living Bacteria could really appear within closed flasks which had been subjected to the conditions menvl

PREFACE.

tloued. This time-serving and popular verdict once announced, was received with all the more readiness, because others, not having exercised the necessary care, had for a time failed to confirm my results. Now, however, that the facts have been substantiated and are generally acknow- ^ ledged, the subsequent course of events has made it useful to ask, Why the majority of persons competent to judge, previously received the statements referred to with so much incredulity ?

To this question only one answer can be given. The results were discredited because it was a generally accepted belief amongst men of science that exposure to the temperature of boiling water would have killed all pre-existing Living Matter within the flasks. And this being the case, the appearance of swarms of Bacteria in the experimental fluids in the course of a few days could only be explained by the supposition that what has been called ' Spontaneous Generation ' had occuired. To ' acknov/ledge this, however, was rank heresy, and was in opposition to some of the most cherished and sacred beliefs of many men of science. , In such an emergency what were scientific in-

PREFACE.

vestijators to do ? Should they equivocate and, without definite trial as to the truth or untruth of their old belief in the destructive influence of boiling water, at once cast it aside ? This would certainly seem a strange course to pursue, seeing that a strong belief in the lethal effects of boiling water had been the measure of their previous profound unbelief of facts now demonstrated to them ! Yet this course was in some respects the easiest — it would expose those who followed it to less external friction, and it allowed them still to hold fast to a long-cherished conviction as to the truth of the dogma omne viviim cx vivo, which they perhaps found it impossible to throw aside. But whatever extenuating circumstances might be pleaded, it cannot be concealed that the course actually adopted was not the method by which men of science usually pursue their investigations.

The question of ' Spontaneous Generation,' therefore, at present stands in this position. If it be really true that all known forms of Living Matter are killed by a brief exposure in the moist state viii

PREFACE.

to the temperature of 212° F., there is no longer room for doubt. The occurrence of ' Spontaneous Generation ' must in this case be admitted as an estabHshed fact, or ' Law of Nature.'

But the evidence now in our possession concerning the death-point of heated Living Matter all tends to show that it is killed at a temperature below that of boiling water, as will be seen by the facts recorded in the last essay of this volume. The two previous papers, moreover, contain the records of experiments proving that Bacteria and the'r germs are killed at 140° F. — these being the very organisms that most frequently make their appearance in the fluids within closed experimental vessels v/hich have been previously heated to 212° F.

In the present aspect of the question, therefore, these three papers contain all the evidence needed for the establishment of the occurrence of ' Spontaneous Generation.' In the two parts of the first essay, however, I have endeavoured to show that the acknowledgment of this natural origin of Living Matter carries with it no contradictions, and is indeed in accordance with the present state of scientific knowledge. I have further striven to give.

PREFACE.

ix in brief compass, a synopsis of other evidence in favour of Archebiosis and Heterogenesis (the two processes now inchaded under the phrase * Spontaneous Generation ') ; to indicate some of the modifications in biological doctrine which a behef in the present occurrence of these pro>;esses will necessitate ; and generally to show, to the best of my ability, the weakness and untenability of the old view.

In the execution of a task so complicated and difficult, there must necessarily be many imperfections. I am anxious, however, to promote what I consider to be the cause of truth, and have therefore collected the papers included in the present volume, in the hope that they may be of some little use and interest to those desirous of obtaining information on the present aspect of the great questions to which they relate.

Contents

I.— The Evolution Hypothesis and the Origin of L:ff.

Part I

{From the Contemp >rary Review of March, 1874, with slight AlteracioMi and Additions.)

PAGE

Evo'ution -Its Scope and Meaning — Uniformity of Nature — Modifications of Doctrine often Incomplete at First — The Nebular Hypothesis— Original Advent of Living Things on the Earth — Views of Eminent Evolutionists — Mr. Darwin — Mr. Herbert Spencer — Mr. G. H. Lewes — Professor Huxley — Apparent Inconsistencies - Origination and Giowth Compared —These Processes in Crystalline and in Living .Matter respectively —No Reason why Origina ion of Living Matter sliould have Ceased — Professor Clarice Maxwell on the Persistence of Molecular Properties — Mr. Spencer's Assumption — Professor Huxley's Views — Their Inconsi.itencies — .^ir \Vm. Thomson's Hypothesis — Misconceptions concerning Spontaneoxis Generation — The.se not to be Entertained by Evolutionists — Professor Huxley's Suppositions concerning the Past — Their Untenability when Judged by his own line of Criticism- Conditions Favouring Growth mostly Favour Origination — Present Continuance of Archebiosis — Shown by ICxislence of the Lowest Organisms— Mr. Spencer's Mode of dealing with this Question — His Views on this subject not Reconcilable with his Principles of Evolution — Has the Amoeba a Longer Line of Ancestry than Man ? Yes, unless the Continuance of Archebiosis or Heterogenesis be Conceded. 1-39 xii CONTENTS.

Part II

{From the Contemporary Revieiv of April, 1874, uith Rearrangements and Additions.)

PAGE

Inconsistency of Limiting Archebiosis to the Past— Professor Huxley's Inaugural Address — Its Partial Consideration of the Facts — Refutation of its Principal Positions — Air does not Swarm with Bacteria Germs — Bacteria will Appear in Fluids Previously Heated to 212° F. — Yet Bacteria and other low Organisms are Killed in Fluids Heated to 140° F. — Professor Huxley's Action in Face of New Facts — Behaviour of Other Opponents of Spontaneous Generation — Sir John Herschel's Precepts . . . 43-50

Necessity of Examining the New and the Old Doctrine as mere H)'potheses — Each Plypothesis Supported by an Analogical Argument — That in favour of Archebiosis — Foundations of the Counter Hypothesis — Insufficient Warrant for the Formula ' Omne Vivum ex Vivo' — It affords a Notable Instance of Faulty Induction — Weighty Considerations in Support of Archebiosis — Heterogenesis a Necessary Consequence of Archebiosis — Its Occurrence harmonious with Physical Doctrines of Life — Evidence of its Occurrence more Varied than for that of Archebiosis — Detailed Enumeration of Evidence — Panspermism Weak even as an Hypothesis — Mr. Justice Grove's Dictum — Panspermism can be Overthrown by a ' Crucial Instance ' — Vacillations and Evasions of some Evolutionists in Connection with this Part of the Subject— Concurrence of Testimony as to the Temperature at which Living Matter is Killed — Establishment of Arclieliiosis as a Law of Nature 50-69

New Views — Characteristics of Living Matter — Its Tendency to Organization— Conditions which Favour it — Cause of Reproduction — Meaning of Heterogenesis— Ephemeromorphs — ' Alternate Generation ' — Origin of Species — Limitation of Sphere of ' Natural Selection ' —

CONTENTS.

xiii

Its Real Influence — Other Causes of Modification — Organic Polarity — Speculative Deductions Concerning ' Trees of Life ' in the Past ; Concerning the Resemblance of their Products in Different Ages ; Concerning the greater Extent of this Resemblance amongst the Lowest Types ; and Concerning the possibility of the Vertebrate Type having been more than once Attained

ir. — On the Temperature at which Bacteria, Vibri-

ONES, AND THEIR SUPPOSED GeRMS ARE KILLED WHEN

Immersed in Fluids ok Exposed to Heat in a Moist State.

{From the Proceedings of the Royal Society, No. 143, 1873 )

Controversy between the Abbe Spallanzani and Needliam— Spillanzani's Conclusions — Overthrow of the Aerial-Contamination Doctrines — Professor Huxley's Criticisms — Writers' Previous Investigations on Vital Resistance of Bacteria— Method of Experimentation — Applicable for Invisible Germs and for Parent Organisms — Means for Lowering Productivity of Organic Fluids — New Inoculation Experin.ents— Tabular Results — Conclusions as to Degree of Htat which Destroys Bacteria and their Germs — Decisive Nature of these Results — Taken in Conjunction with other Experiments they Establish the Occurrence of ' Spontaneous Generation.' 79-97

III. — Further Observations on the Temperature at WHICH Bacteria, Vibkiones, and their SuiPosiiD Germs ark Killed when Exposed to Heat in a Moist State ; and on the Causes of Putrefaction and Fermentation.

(Fiotn the Proceedings of the Royal Sociity, No. 145, 1873.)

Different Behaviour of Saline Fluids and Organic Infusions when Inoculated — Cause of this Difference — Two-fold Composition of Inoculating Malerial— Its Living and its Me'e Organic Elements — The Temperature of 140° F.

PAGE

69-76

€OA'TENTS.

may De-energize the Former but not the La'ter — Experiments with Infusions of Different Strengths tend to Prove this — Reasons for Believing the Delayed Putrefaction in Inoculated Organic Fluids Heated to 140° F. to be due to the Mere Organic Matter of the Inoculating Medium — Proof of this— And proof by New Experiments that Bacteria and their Germs are Killed in Organic Fluids Heated to 140° F 101-112

Uniformity of Evidence as to Death-point of Living Ferments — Important Difference between Living and Not- Living Ferments as regards their Power of Resisting He^t — This Point of View Steadfastly Ignored by M. Pasteur and his Followers — Absence of all Evidence to Show that Heat is Less Destructive to Living Matter in Some Fluids than in Others— M. Pasteur's Experiments never Distinctly capable of Supporting such a Conclusion — He Ignored an Equally Possible though Opposite Interpretation whose Truth has been now Established . 112-116

Inadequacy of M. Pasteur's ' Vital Theory ' of Fermentation— What New Experiments Teach — Three Degrees of Fermentability — Self-Fermentable Fluids — Tabular Statement Concerning — Second Degree of Fermentability — Explanation of M. Pasteur's Celebrated Experiments in which he Sowed mere Organic Fragments and called ihem ' Germs ' — Explanation of Other Experiments — Origin of Torulse — Meaning of their Appearance — Fermentation may gradually Merge into Putrefaction — T bird < r Lowest Degree of Fermentability — Fluids which only Change under Inlluence of Most Potent Ferments (Living Organisms)— Uniformity of Results in Inoculation Experiments This Adverse to Explanation of Cases of Delayed

or Smouldering Fermentation by M. Pasteur's Theory — Living Ferments Act Promptly and with Regularity

Not-living Ferments often Act Slowly and with Great

Irregularity — Results of Several Series of Different Experiments point to Archebiosis as the only Means of Reconciliation— Conclusions • • 1 16-129

CONTENTS.

XV

J" AGE

IV. The Destructive Influence of Heat upon

Living Matter.

{^From the Contemporary Rev'nv of September, 1874, with many Additions and slignl Altei-ation . )

Effects of Boiling Water on Human Tissues— lis Action upon

Eggs — Importance of Definite Information upon th's

Subject — Peliictance of the Modern Panspermatists to

Seek it — Original Investigations by Spallanzani — Reasons

for Referring io them — His Frank Announcement of the

Points in Dispute — Method and Results of his New

Experiments — His Conclusions and Reasoning thereon —

His attempt at Reconciliation of Different Experimental

Results — The Assumptions by which alone he could Stave

off a Belief in ' Sj ontaneous Generation' 133^155

His Assumptions regarded by the Light of Modem Science — Bacteria and their Germs not able to Survive Desiccation — Untenability of Another Assumption on which he Relidl — Reasons for Belief in the Ascertained Death-Point of Bacteria (140° K.) —Harmonious Results ai rived at by Max Schultze, Kiihne, and others — Evidence Concerning Organisms in Hot Springs — Unanimity of Different Observers as to Death-point of Living Matter — • This in Accordance with known Unity of Protoplasm — Curious Attitude assumed by Opponents of ' Spontaneous Generation' — Considerations under which ihey seek Refuge— The ' Lump ' Theory and its Explosion — New Difficulties for Consideration of Opponents — Two Most Important Experiments — Impossibility of Explaining their Results except by Archebiosis 155-1S0

Some Misapprehensions Discussed — Ileterogenesis and what it Means — The Evolutionist Must Distinguish it from Archebiosis — The Vitalist could not believe in Archebiosis — The Evolutionist must distinguish between Living and Dead Organic Matter — Archebiosis may occur amongst Dead Organic Materials — The Term therefore Applicable to the Process occurring in C)rdinary Flask Experiments and also to the Primordial Origin of Life — The Actual Process of Giowtli ii as inexplicable as the Process of Ori£,ination l8o-l86

I

I. The Evolution Hypothesis, And The Origin Of Life

PART I.

I

B

Year by year the word ' Evolution ' becomes dififused more widely through our literature, and the central idea which it implies grows familiar to an ever-increasing^ multitude of readers. We have witnessed within the last few years a marvellous awakening of interest in the minds of the public generally to questions of science, and it so happens that a discussion of the Doctrine of Evolution has been more or less directly involved in those departments of Science and Philosophy which have during this period received the largest share of popular attention.

Perhaps the greatest impetus was given to the spread of the doctrine about fourteen years ago, by the publication of Mr. Darwin's now celebrated " Origin of Species." This volume has been followed by quite a library of works and memoirs on the same subject — partly scientific and partly popular. From about the same date also, Mr. Herbert Spencer has been engaged in systematically elaborating the

B 2 principles of an all- comprehensive Evolution Philosophy, and the results of his genius and labour are now undoubtedly influencing the thoughts of a rapidly widening circle of readers. Both in this country and abroad the doctrine of Evolution is gradually but surely gaining ground amongst the most reflective, and although many other writers have been more or less influential in determining this result, it has been in the main brought about by the two above mentioned.

Evolution implies continuity and uniformity. It teaches us to look upon events of all kinds as the products of continuously operating causes — it recognises no sudden breaks or causeless stoppages in the sequence of natural phenomena. It equally implies that natural events do not vary spontaneously. It is a philosophy which deals with natural phenomena in their widest sense : it emj braces both the present and the far-distant past. It seeks to assure us that the properties and tendencies now manifest in our surrounding world of things, are in all respects similar to those which have existed in the past. Without a basis of this kind, the Evolution Hypothesis would be a mere idle dream. Uniformity is for it an all-pervading necessity. Starting from facts of daily observation and from scientific experiments, the properties and

ORIGIN OF LIFE.

tendencies of things are noted and grouped ; whilst philosophers, using the knowledge thus gained, seek to trace back the progress of events and show how this complex world has gradually been derived from a world of more and more simple composition. We are taken back in imagination even much further. We are referred to a primal haze or nebula — as the gigantic germ of a future Universe. This was the | | conception of Kant and of Laplace.

But whether we follow the philosopher in his bold speculations concerning the past, or listen to the biologist making his predictions as to the future stages which the germ of a given animal will pass through in the progress of its evolution — in each case the ' uniformity of nature ' is tacitly assumed. This assumption underlies almost all our thoughts and actions, even in every-day life. And without such a belief regarding the succession of events science would be impossible — the verj^idea of it, in fact, could never have arisen. In its absence we could neither fathom the past nor illumine the future. As Mr. Mill said,* — " Were we to suppose (what it is perfectly possible to imagine) that the present order of the universe were brought to an end, and that a chaos succeeded in which there was no fixed succession of events, and the past gave no assurance of the future, if a human

* Syst. of Logic, 6th edit. vol. ii. p. 98.

EVOLUTION A ND TllE being were miraculously kept alive to witness this change, he surely;jwould soon cease to believe in any I ^ uniformity, the uniformity itself jio longer existing." It is true that in earlier times no absolute belief in the uniformity of nature existed, even amongst the select few. The Greek philosophers, including Aris- ^ totle, recognised 'chance' and 'spontaneity' as find- ^^.,^.ing a definite place in Nature, and to this extent they were not sure that the future would reseinble the past. But as we have become more familiar with a wider range of natural phenomena and with their mutual relations or order of appearance, so has the conception of chance or spontaneity disappeared from the scientific horizon — driven out of the field by the steady advance of Law_and Or^er. Those who embrace the Evolution Philosophy are foremost in this opinion — they believe that no effects of whatsoever kind can occur without adequate causes, and, (the conditions being similar^that the same results will alway follow the action of any given cause. Their whole creed is, in fact, pre-eminently based upon an assumed Uniformity of Nature, v^*^}''

The present is essentially a time of transition in matters of opinion. Men who have been educated in one system of scientific beliefs are gradually being converted to another, because the new system is

ORIGIN OF LIFE.

thoueht to be more harmonious with the observed order of natural phenomena. This has been the case even with our chief exponents of Evolution. They have themselves had to unlearn much which they had previously learned. The doctrine of Evolution has thus been developed only by the sacrifice of many previous early beliefs and modes of thought. But it often happens that an old belief will — unknown perhaps to the person himself — leave decided traces of its previous influence, and thus prevent for a time the full realization or adoption of all the logical consequences of new views. This vestige of the old state of opinion or habit of thought is more especially apt to remain in directions where unexplained facts still exist and strong prepossessions or prejudices bar the way. Some modes of this half-unconscious inconsistency may become obvious to one worker or thinker, and some to another, according to the particular direction which his investigations or thoughts may have taken; and if they are of an important nature such inconsistencies .should be pointed out from time to time. With the view, therefore, of strengthening an hypothesis which I, in common with so many other workers in science, believe to be true, I now venture to allude to certain apparent anomalies in the declared opinions of the most prominent upholders of the doctrine of Evolution in this country. It seems all the more desirable that this should be done, since the inconsistencies may be easily shown to be wholly uncalled for, and to involve sundry unscientific conceptions. Yet the modifications of opinion which appear to be demanded — on the ground of fact as well as on the ground of reason— will necessitate very considerable and almost revolutionary changes in the accepted code of biological doctrines.

An examination of the facts of science generally and of various every-day phenomena, teaches us, according to the Evolutionist, that Matter of different kinds, situated as it is and has been, gradually tends within certain limits to become rngre and more complex in its internal and external constitution. Coupling this conclusion with various astronomical data, with geological data, and with facts derived from the study of the past forms of Life upon our globe, the Evolutionist essays to penetrate through the long vista of bygone ages, till he may rest his speculative gaze upon a vast rotating nebular mass of gaseous matter of comparatively simple though i unknown constitution, from which he supposes our 'Universe to have been slowly evolved. Without futile questionings as to the explanation or cause of the existence of the Nebula — without speculation as to what simpler or more complex matter may have immediately preceded it — it is obvious that we may

ORIGTK OF LIFE.

for our own convenience direct our attention especially to any particular stage of its hypothetical existence. At the same time we must be equally free to admit that, in concentrating our attention upon the nebular stage, or upon any other, we arbitrarily break into a mysterious cycle of existence whose Cause is to us unfathomable. It is needless for my purpose, however, to attempt to concentrate the reader's attention upon a period so remote in the history of our Universe. We are led to believe that the primordial nebula as it cooled and condensed acquired a more rapid axial rotation ; that masses were gradually thrown off from its circumference ; and that these in their turn condensed into rotating spheroids, which continued to circulate round the parent mass in elliptical orbits. Assuming, then, with the Evolutionist, that our own planet had a past history of this kind, we mu.-st also assume that it gradually changed from a__gaseous_to_a fluid state before beginning to solidify by the formation of a .superficial crust — a crust which gradually thickened as the fervent heat of it and of the fluid nucleus abated by heat radiations into space. Until this stage of the Earth's history had been far advanced, z^-'^*^" no Ljving Things could have existed upon its surface. 'J^"^**^ "Hence," as Sir William Thomson said,* "when'^'^'"

Inaugural Address at Meeting of Britisli Association, Nature, ^--^"^^ ■^"g- 3. 1871, p. 269. , * J '

the Earth was first fit forjife there were no living things_pn it. There were rocks, sohd and disintegrated, water, air all round, warmed and illuminated by a brilliant sun, ready to become a garden." Living things must, however, have appeared upon its surface at some very remote epoch, since their remains are to be found far down in the rocks which, at present constitute its crust. How, therefore, it may be asked, is the first appearance of ' Living matter ' upon the earth to be accounted for

We should not needlessly invoke an unknown act of Creative Power — we must not, even with Sir William Thomson, resort to the strange notion of an importation of living germs upon a " moss-grown fragment from the ruins of another world," unless more ordinary natural causes fail and it be found really necessary to invent some such hypothesis — and the necessity here could never be shown since Sir W. Thomson's hypothesis shirks the question of the Origin of Life so far as our earth is concerned, and merely hands it over as an unsolved problem to the denizens of another sphere. Now, the thoroughgoing Evolutionist repudiates the notion of Creadon^in^ its ordinary sense ; he believes that the operation of natural causes, working in their accustomed manner, were alone quite adequate to bring into existence a kind of matter presenting a new order of complexity, and

ORIGIN OF LIFE.

II displaying the phenomena which we have generalised under the word * Life.' Living matter is thus supposed to have come into being by the further operation under new conditions of the same agencies as had previously led to the formation of the various inorganic constituents of the Earth's crust — such mineral and saline substances as we see around us at the present day. What we call ' Life,' then, is regarded as one of the natural results under actual conditions of the growing complexity of our primal nebula. So that, in accordance with this view, we have no more reason to postulate a miraculous iaterference or exercise of Creative Power to account for the evolution of ' living matter ' in any suitable portion of the Universe (whether it be on this Earth or elsewhere), than to explain the appearance of any other kind of matter — the magnetic oxide of iron, for instance. So far, all through Evolutionists are quite agreed. This is the view of Spencer, Le^s, Huxley, and others — possibly of Darwin. I say possibly of Darwin, because on this subject it so happens that the language of this most distinguished exponent of Evolution is quite unusually tinctured with a previous point of view. Speaking of the probable commencement of Life upon our globe, Mr. Darwin says * : — " I believe that animals have * Origin of Species, 6th edit, 1872, pp. 424 and 429.

descended from at most only four or five progenitors, and plants from an equal or lesser number. Analogy would lead me one step further, namely, to the .belief that all animals and plants have descended from some one prototype. . . . There is grandeur in this view of life, with its several powers, having been originally breathed by the Creator into a few forms, or into one ; and that whilst this planet has gone cycling on according to the fixed lav/ of gravity, from so simple a beginning endless forms, most beautiful and most wonderful, have been and are being evolved." Taking into account the phraseology made use of in the above quotation, we have little difficulty in recognising the views of an Evolutionist, dwarfed and modified though they are by an ultimate appeal to a Creative act only a little less miraculous and singular than the mythical origin of our reputed ancestors — Adam and Eve. Some existing naturalists may perhaps contend that Mr. Darwin ought to have kept more closely to the Mosaic record —replacing his one primordial form by a dual birth of male and female, without whose mutual influence no " biological individuals " can in their opinion come into existence. Such a supposition, it is true, would be as antiquated and unnecessary from the Evolutionist's point of view as is the whole notion of^life having been originally "breathed" into one

ORIGIN OF LIFE.

or more organic forms. Mr. Spencer's language is happily free from both these defects : he neither uses the phraseology of the Creative Hypothesis, nor does he adopt a definition of biological "individuality" at variance with the Evolution Philosophy. He distinctly teaches that living matter must have been at first formless, and that multiplication would have taken place, as amongst the lowest living units of the present day, exclusively by agamic methods — nay, more, he teaches that living matter must have been the gradual product or outcome of antecedent material combinations. " Construed in terms of evolution," he says,* " every kind of being is conceived as a product of modifications wrought by insensible gradations on a pre-existing kind of being, and this holds fully of the supposed 'commencements of organic life,' as of all subsequent developments of organic life."

But on the question whether the process of Archebiosis (life-evolution) is likely to have occurred once only, as Mr. Darwin seems to hint, or in multitudinous centres scattered over the earth's surface, Mr. Spencer makes no definite statement. The latter belief would, however, be entirely in accordance with his general doctrine ; and we seem all the more entitled to infer that Mr. Spencer inclines to the notion of a multiple

* Principles of Biology, vol. ii. Appendix, p. 482.

occurrence of Archebiosis, both in space and in time, since he does not reject the possibility of its occurrence in our own day. Granting " that the formation of organic matter and the evolution of life in its lowest forms may go on under existing cosmical conditions," he believes it "more likely that the formation of such matter and of such forms took place at a time when the heat of the earth's surface was falling through those ranges of temperature at which the higher organic compounds are unstable." But conclusions which we are only able to infer from the writings of Mr, Spencer have been distinctly enunciated by Mnjj\ H. Lewes. In a criticism of the " Darwinian Hypotheses," he very forcibly pointed out that it is quite compatible with the hypothesis of evolution to admit a variety of starting points for the formation of living matter, and he consequently laid down in principle a very important extension of the Darwinian doctrine, in its application to higher organisms. He said:* ''Although observation reveals that the bond of kinship does really unite many divergent forms, and the principle of Descent with Natural Selection will account for many of the resemblances and differences, there is at present no warrant for assuming that aU resemblances and