Natural Selection

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Charles Robert Darwin, 2/ 12/ 1809 – 4/ 19/ 1882.

On the Origin of Species: or The Preservation of Favoured Races in the Struggle for Life, (1859).

14 chapters

Mayr on species| variation | struggle | selection | species | instinct | hybrids | Darwin - on - line


Table of Contents
 Chapters  Charles Darwin's words  Alfred Russel Wallace (1859) Wallaces' words
 1 Variation under Domestication
 2 Variation under Nature
 3 Struggle for Existence
 4 Natural Selection
 5 Laws of Variation
 6 Difficulties on Theory
 7 Instinct
 8 Hybridization Reversion of Domesticated varieties
 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


Chapter 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." (52)

"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." (58-59)

"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." (59)

finches drawing of finch beaks

"And thus, the forms of life throughout the universe become divided into groups subordinate to groups."

variation | struggle | selection | species | instinct | hybrids

Chapter 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)

"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)

ynx and hare predation

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." (79)

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." (79)

[Malthus' influence]

variation | struggle | selection | species | instinct | hybrids

Chapter 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."


"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." (127)

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." (127-28)

"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." (129)

"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."


variation | struggle | selection | species | instinct | hybrids

Chapter 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." (132)

"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." (133)

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..." (147)

"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)

variabiloty of fisnch species

"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." (159)

"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." (170)

variation | struggle | selection | species | instinct | hybrids

Chapter 7,

instinct is the drive of the cuckoo to lay her eggs in the other birds' ( species ) nests

instinct "Any 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,…."
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.

Experimental evidence
Darwins' 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 218
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." 239

different castes of neuters in the same species 240

" 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." 242

"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." 242

"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."

variation | struggle | selection | species | instinct | hybrids

Chapter 8,


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


Chapter 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." 279



Chapter 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. 314

variation | struggle | selection | species | instinct | hybrids

The Origin of Species: or the Preservation of Favoured races in the Struggle for Life. by Charles Darwin

Table of Contents
 Chapters  Charles Darwin's words  Alfred Russel Wallace (1858) Wallaces' words
 1 Variation under Domestication "varieties in a state of domesticity"
 2 Variation under Nature  2. The Law of Population of Species
 3 Struggle for Existence  1. "Struggle for existence"
 4 Natural Selection  
 5 Laws of Variation  Useful variation
 6 Difficulties on Theory  3. perfect adaptation to the conditions of existence
 7 Instinct  
 8 Hybridization Reversion of Domesticated varieties  
 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  

Mayr defines species.

Complete works of Darwin available

variation | struggle | selection | species | instinct | hybrids


Notes by Joseph Siry based on the facsimile edition of the Origin edited by Ernst Mayr and with numerous conversations with the late Ernst Mayr.

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