An African elephant in her home range, Krueger National Park, S.A., [J. Siry. 2002] and a yearling in the Etosha Pan of the Namibian desert. [J. Siry. 2013].
|Table of Contents|
|1||Variation under Domestication|
|2||Variation under Nature|
|3||Struggle for Existence|
|5||Laws of Variation|
|6||Difficulties on Theory|
|9||On the Imperfection of the Geological Record|
|10||On the Geological succession of organic beings|
|11||Geographical Distribution (A)|
|12||Geographical Distribution (B)|
|13||Mutual Affinities of Organic Beings|
|14||Recapitulation and Conclusion|
|Charles Darwin in 1855 just before receiving Wallace's letter and manuscript.|
"When we no longer look at an organic being as a savage looks at a ship, as something wholly beyond his comprehension; when we regard every production of nature as one which has had a history; when we contemplate every complex structure as and instinct as the summing up of many contrivances, each useful to the possessor, nearly in the same way as when we look at any great mechanical invention as the summing of labor, the experience, the reason and even the blunders of numerous workmen; when we thus view each organic being, how far more interesting,...will the study of natural history become."
When on board H.M.S. 'Beagle,' as a naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seem to me to throw some light on the origin of species -- that mystery of mysteries, as it has been called by one of our greatest philosophers."
1 Variation under Domestication
"When we look to the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us, is, that they generally differ much more from each other than do the individuals of any one species or variety in the state of nature."
"It seems pretty clear that organic beings must be exposed during several generations to the new conditions of life to cause any appreciable amount of variation; and that when the organism has once begun to vary, it generally continues to vary for many generations."
2 Variation under Nature
"I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms."
"Finally, then, varieties have the same general characteristics of species, for they can not be distinguished from species,-- except, firstly, by the discovery of intermediate linking forms, and the occurrence of such links cannot affect the actual characters of the forms which they connect;...but the amount of difference considered necessary to give to two forms the rank of species is quite indefinite."
"we can clearly understand these analogies [varieties to species], if species have once existed as varieties, and have thus originated: whereas, these analogies are utterly inexplicable if each species has been independently created."
"And thus, the forms of life throughout the universe become divided into groups subordinate to groups."
3 Struggle for Existence
"I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection, in order to mark its relation to man"s power of selection."
"But natural selection, as we shall see, is a power incessantly ready for action, and is immeasurably superior to man"s feeble efforts,..." (61)
"all organic beings are exposed to severe competition." (62)
"I use the term Struggle for Existence in the large and metaphorical sense, including the dependence of one being on another, and including not only the life of the individual, but success in leaving progeny." (62)
"A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase." (63)
"There is no exception to the rule that every organic being naturally increases at so high a rate, that if not destroyed, the earth would soon be covered by the progeny of a single pair." (64)
I am tempted to give one more instance showing how plants and animals, most remote in the scale of nature, are bound together by a web of complex relations. I shall hereafter have occasion to show that the exotic Lobelia fulgens, in this part of England, is never visited by insects, and consequently, from its peculiar structure, never can set a seed. Many of our orchidaceous plants absolutely require the visits of moths to remove their pollen-masses and thus to fertilise them. I have, also, reason to believe that humble-bees are indispensable to the fertilisation of the heartsease (Viola tricolor), for other bees do not visit this flower. From experiments which I have tried, I have found that the visits of bees, if not indispensable, are at least highly beneficial to the fertilisation of our clovers; but humble-bees alone visit the common red clover (Trifolium pratense), as other bees cannot reach the nectar. Hence I have very little doubt, that if the whole genus of humble-bees became
[page] 74, MUTUAL CHECKS TO INCREASE. CHAP. III.
extinct or very rare in England, the heartsease and red clover would become very rare, or wholly disappear. The number of humble-bees in any district depends in a great degree on the number of field-mice, which destroy their combs and nests; and Mr. H. Newman, who has long attended to the habits of humble-bees, believes that "more than two thirds of them are thus destroyed all over England." Now the number of mice is largely dependent, as every one knows, on the number of cats; and Mr. Newman says, "Near villages and small towns I have found the nests of humble-bees more numerous than elsewhere, which I attribute to the number of cats that destroy the mice." Hence it is quite credible that the presence of a feline animal in large numbers in a district might determine, through the intervention first of mice and then of bees, the frequency of certain flowers in that district!
"Even slow-breeding man has doubled in twenty-five years, and at this rate, in a few thousand years, there would literally not be standing room for his progeny."
"It will convince us of our ignorance on the mutual relations of all organic beings; a conviction as necessary, as it seems to be difficult to acquire." (78)
All that we can do, is to keep steadily in mind that each organic being is striving to increase at a geometrical ratio; that each at some period of its life, during some season of the year, during each generation or at intervals, has to struggle for life and to suffer great destruction."
When we reflect on this struggle, we may console ourselves with the full belief, that war of nature is not incessant, that no fear is felt, that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply."
4 Natural Selection
"Let it be borne in mind how infinitely complex and close fitting are the mutual relations of all organic beings to each other and to the physical conditions of life." (80)
"This preservation of favorable variations and the rejection of injurious variations, I call Natural Selection." (81)
"We shall best understand the probable course of natural selection by taking the case of a country undergoing some physical change, for instance, of climate." (81)
"In such a case, every slight modification, which in the course of the ages chanced to arise, and which in any way favored the individuals of any species, by better adapting them to their altered conditions, would tend to be preserved; an natural selection would thus have free scope for the work of improvement." (82)
"nature cares nothing for appearances, except in so far as they may be useful to any being. She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life." (83)
"Under nature, the slightest difference of structure or constitution may well turn the nicely-balanced scale in the struggle for life, and so be preserved." (83-84)
"It may be said that natural selection is daily and hourly scrutinizing, throughout the world, every variation, even the slightest,... silently and incessantly working, whenever and wherever opportunity offers, at the improvement of each organic being relation to its organic and inorganic conditions of life." (84)
"This principle of preservation, I have called, for the sake of brevity, Natural Selection. Natural selection, on the principle of qualities being inherited at corresponding ages, can modify the egg, seed, or young, as easily as the adult."
Natural selection, also, leads to divergence of character; for more living beings can be supported on the same area the more they diverge in structure, habits and constitution, of which see proof by looking at the inhabitants of any small spot or at naturalized productions."
"Therefore..., the more diversified these descendants become, the better will be their chance of succeeding in the battle for life." (128)
"The affinities of all the beings of the same class have sometimes been represented by a giant tree."
"As buds give rise by growth by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications."
5 Laws of Variation
"Nevertheless, we can here and there dimly catch a faint ray of light, and we may feel sure that there must be some cause for each deviation of structure, however slight." (132)
How much direct effect difference of climate, food, & c., produces on any being is extremely doubtful."
"complex co-adaptations of structure between one organic being and another, which we see everywhere throughout nature."
"When a variation is of the slightest use to a being, we cannot tell how much of it to attribute to the accumulative action of natural selection, and how much to the conditions of life."
the effects of use & disuse (134)
Acclimatization -" Habit is hereditary with plants, as in the period of flowering, in the amount of rain requisite for seeds to germinate, in the time of sleep,..." (139)
"as Goethe expressed it, "in order to spend on one side, nature is forced to economize on the other side." I think this holds true to a certain extent with our domestic productions..."
"A part developed in any species in an extraordinary degree or manner, in comparison with the same part in allied species, tends to be highly variable."
["with respect to the length of the arms of the ourang-outang"] (150)
"Distinct species present analogous variations; and a variety of one species often assumes some of the characters of an allied species, or reverts to some of the characters of an allied species, or reverts to some of the characters of an early progenitor."
"Habit in producing constitutional differences, and use in strengthening, and disuse in weakening and diminishing organs, seem to have been more potent in their effects."
"Although new and important modifications may not arise from reversion and analogous variation, such modifications will add to the beautiful and harmonious diversity of nature."
"Whatever the cause may be of each slight difference in the offspring from their parents -- and a cause for each must exist -- it is the steady accumulation; through natural selection, of such differences, when beneficial to the individual, that gives rise to all the more important modifications of structure, by which the innumerable beings on the face of this earth are enabled to struggle with each other, and the best adapted to survive."
6 Difficulties on Theory
Like produces like (wolves do not come from bears or whales from manatees)Darwin means the capacity to "survive" is that offspring live to produce progeny.
"LONG before having arrived at this part of my work, a crowd of difficulties will have occurred to the reader. Some of them are so grave that to this day, I can never reflect on them without being staggered; but to the best of my judgment, the greater number are only apparent, and those that are real are not ...fatal to my theory."
"Firstly, why,...do we not everywhere see innumerable transition forms." [of species, or "missing links"]
"Secondly, is it possible that an animal having, for instance the structure and habits of a bat, could have been formed by the modification of some animal with wholly different habits?"
"Thirdly, can instincts be acquired and modified through natural selection?"
"Fourthly, how can we account for species when crossed, being sterile...?
"To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberrations, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree."
"but, I may remark that several facts make me suspect that any sensitive nerve may be rendered sensitive to light, and likewise to those coarser vibrations of the air which produce sound."
"I can indeed hardly doubt that all vertebrate animals having true lungs have descended by ordinary generation from an ancient prototype, of which we know nothing, furnished with a floating apparatus or swim bladder."
"It is generally acknowledged that all organic being have been formed on two great laws--Unity of Type and the Conditions of Existence."
"On my theory, Unity of type is explained by unity of descent. The expression of the conditions of existence,...is fully embraced by the principle of natural selection."
"Hence, in fact, the Law of the Conditions of existence is the higher law; as it includes through the inheritance of former adaptations, that Unity of Type."
" it is said that instinct impels the cuckoo to migrate and lay her eggs in the other birds' ( species ) nests."
"An action" "when performed by an animal, more especially by a very young one, without any experience, and when performed by many individuals in the same way, without their knowing for what purpose it is performed, is usually said to be instinctive."
readily performed, yet unconscious actions displayed by large numbers of similar animals
"none of these characters of instinct is universal." 208
caterpillar"s hammock and its seven stages of producing the cocoon
"It can clearly be shown that the most wonderful instincts with which we are acquainted, namely, those of the hive-bee and of many ants, could not possibly have been thus acquired."
"instincts are as important as corporeal structure for the welfare of each species."
"As modifications of corporeal structure arise from, and are increased by, use or habit, and are diminished by loss or disuse, so I do not doubt it has been with instincts."
"No complex instinct can possibly be produced through natural selection, except by the slow and gradual accumulation of numerous, slight, yet profitable, variations."
"The canon of 'Natura non facit saltum.' applies with almost equal force to instincts as to bodily organs".
instinct functions to "adapt the creature more accurately with the vicissitudes of life."
Darwin's Curly dock, aphids and the ants as instinctually altruistic behavior (cows & humans) --
"it then began to play with its antennae on the abdomen first f one aphis and then another; and each aphis, as soon as it felt (smelt) the antennae, immediately lifted up it abdomen and excreted a limpid drop of sweet juice, which was eagerly devoured by the ants."
"instincts certainly do vary -- for instance, the migratory instinct"
So it is with the nests of birds "Audubon has given several remarkable cases of differences in nests of the same species in the northern and southern United States."
fear of man is slowly acquired" "the magpie so wary in England, is tame in Norway, as is the hooded crow in Egypt."
breeds of dogs
"These domestic instincts, which are in a like manner become curiously blended together, and for a long period exhibit traces of the instincts of either parent."
"Natural instincts are lost under domestication." 215
Three cases: the cuckoo nest parasitism, slave maker insects, & comb making hive bees
cuckoos and nesting
parasitic bees & wasps
slave making insects
witnessed a "migration from one nest to another, and it was a most interesting spectacle to behold the masters carefully carrying, "their slaves in their jaws."
reconnoiters after ant nests
sterile worker ants
ant raiding another species nest for "pupa"
Cell-making instinct of the bee-hive
"Let us look to the great principle of gradation, and see whether Nature does not reveal to us her method of work."
"It is obvious that the Melipona save wax by this manner of building; for the flat wall between the adjoining cells are not double, but are of the same thickness as the outer spherical portions, and yet each flat portion forms a part of two cells."
"I believe the hive -bee has acquired , through natural selection, her inimitable architectural powers.
"It seems at first to add to the difficulty of understanding how the cells (wax comb) are made, that a multitude of bees all work together ;"
"it is known that bees are hard pressed to get sufficient nectar; and I am informed "that it has been experimentally found that no less than from 12-15 pounds of dry sugar are consumed by a hive of bees for the secretion of each pound of wax.... Hence the saving of wax by largely saving honey must be a most important element of success in any family of bees....altogether independent of the quantity of honey that the bees could collect."
"The motive power of the process of natural selection having been the economy of wax."
"they have been acquired by independent acts of natural selection."
the neuters of sterile females in insect communities.."
"the difficulty lies in understanding how such correlated modifications of structure could have been slowly accumulated by natural selection."
"The sterile condition of certain members of the community, has been advantageous to the community:"
neuter ant castes
and "aphids, or the domestic cattle as they may be called, which our European ants guard or imprison."
different castes of neuters in the same species
" As ants work by inherited instincts and by inherited tools or weapons, and not by acquired knowledge and manufactured instruments, a perfect division of labor could be affected with them only by the workers being sterile; for had they been fertile, they would have intercrossed, and their instincts and structure would have been blended."
"the power of natural selection ....The case...proves that with animals, as with plants, any amount of modification in structure can be effected by the accumulation of numerous, slight and we must call them accidental, variations which are in any manner profitable, without exercise or habit having come into play."
"I have endeavored"to show that the mental qualities of our domestic animals vary, and that the variations are inherited."
"instincts vary slightly in the state of nature."
"natura non facit saltum"
"instincts" corroborate the theory of natural selection"
British & the S. American thrushes line their nest with mud!
North American & British wrens isolation , yet same type of odd nest
"a habit wholly unlike that of any other known bird." 243
In summary he looked at such instincts as:
young cuckoo dumping out rival eggs from the nest
ants making slaves,
the larvae of ichumonidae feeding within the live bodies of caterpillars
"not as specially endowed or created instincts, but as small consequences of one general law, leading to the advancement of all organic beings, namely multiply, vary, let the strongest live and the weakest die."
The view generally entertained by naturalists is that species, when intercrossed, have been specially endowed with the quality of sterility, in order to prevent the confusion of all organic forms."
The importance of the sterility in hybrids
9 On the Imperfections in the Geological record
"I have endeavored to show, that the life of each species depends in a more important manner on the presence of other already defined organic forms, than on climate; and, therefore, that the really governing conditions of life do not graduate away quite insensibly like heat or moisture."
10 The Geological succession of Organic Beings
"I believe in no fixed law of development, causing all the inhabitants of a country to change abruptly, or simultaneously, or to an equal degree. The process of modification must be extremely slow."
11 Geographical distribution
(cannot be accounted for by differences in physical conditions)
"Notwithstanding this parallelism (of climates and features in the continents) in the conditions of the Old and New Worlds, how widely different are their living productions!"
"In the southern hemisphere, if we compare large tracts of land in Australia, South Africa, and western South America,...we shall find parts extremely similar in all their conditions, yet it would not be possible to point out three faunas and floras more utterly dissimilar."
12 Geographical distribution
(dispersal of freshwater forms)
"As exemplifying the effects of climatic changes on distribution, I have attempted to show how important has been the influence of the modern Glacial period, which I am fully convince simultaneously affected the whole world, or at least great meridional belts."
"remember that some forms of life change most slowly, enormous periods of time being thus granted for their migration, I do not think that the difficulties are insuperable."
13 Mutual Affinities of Organic Beings, or Embryology
"I have attempted to show, that the subordination of group to group in all organisms throughout all time; that the nature of the relationship, by which all living and extinct beings are united by complex, radiating, and circuitous lines of affinities into one grand system,....all naturally follow on the view of common parentage of those forms which are considered by naturalists as allied, together with their modification through natural selection, with its contingencies of extinction and divergence of character"
Ernst Haeckel's page on comparative embryos, a proponent of Darwin from Germany.
14 Recapitulation and Conclusion
"As this whole volume is one long argument, it may be convenient to the reader to have the leading facts and inferences briefly recapitulated." restated
"the following propositions – that gradations in the perfection of any organ or instinct, which we may consider. . . – that all organs and instincts are, in ever so slight a degree, variable,– and lastly, that there is a struggle for existence leading to the preservation of each profitable deviation of structure or instinct."
"All the individuals of the same species, and all the species of the same genus, or even higher group [family, order, etc.], must have descended from common parents; and therefore, in however distant and isolated parts of the world they are now found, they must in the course of successive generations have passed from some one part to the others."
"It is interesting to contemplate an entangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner, have all been produced by laws acting around us.
These laws, taken in the largest sense, being Growth with Reproduction; Inheritance which is almost implied by reproduction; Variability from the indirect and direct action of the external conditions of life, and from use and disuse; a Ration of Increase so high as to lead to a Struggle for Life, and as a consequence to Natural Selection, entailing divergence of character and the extinction of less-improved forms.
Thus from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows."
"There is a grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved."
"Conditions of Existence is the higher law;"
"The process of modification must be extremely slow."
The absolute necessity of comparing differences and similarities in variation around a norm in natural and artificial selection.
Fossil and biogeographical records combine too many anomalous populations that demand a more parsimonious and accurate portrait.
Alfred Russel Wallace, Contributions to the Theory of Natural Selection, 1871.