Selections from Darwin's The Origin of Species.
The Shape of the Argument.
Preface
The Origin
of Species argues that all living beings has descended from common ancestors
through natural selection.
General Introduction
The world
of living things is historical; it came into being through time and by means of
causes that act in time.
W. Whewell: The world was divinely creates but can only be understood by the scientist, not the theologian.
Bacon: both natural science and biblical study deserve the most intense attention.
Darwin represented his theory through the image of the tree of life; groups were compared to branches originating from a common stem, a common ancestor.
W. Whewell: The world was divinely creates but can only be understood by the scientist, not the theologian.
Bacon: both natural science and biblical study deserve the most intense attention.
Darwin represented his theory through the image of the tree of life; groups were compared to branches originating from a common stem, a common ancestor.
Introduction
Purpose:
gain an insight of the means of modification and coadaptation.
“Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which I formerly entertained – namely, that each species has been independently created – is erroneous.”
“I am convinced that natural selection has been the main but not exclusive means of modification.”
“Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which I formerly entertained – namely, that each species has been independently created – is erroneous.”
“I am convinced that natural selection has been the main but not exclusive means of modification.”
Editor's Introduction to Chapter 1
The Idea of Selection
Selection: analogy between domestication and the works of nature.
Activities of domestic breeding:
Varieties, Subvarieties and Breeds
Breeds: various kinds of cultivated animals and plants that are human production, systematic cultivation.
Species: cultivated plants and animals.
Variation
Issues on variation:
PigeonsAll existing pigeon varieties arose from a single wild progenitor, the rock dove.
Supports for claim:
Selection: analogy between domestication and the works of nature.
Activities of domestic breeding:
- Particular organisms are notices and specially attended to.
- Only these ‘selected’ specimens are allowed to reproduce.
Varieties, Subvarieties and Breeds
Breeds: various kinds of cultivated animals and plants that are human production, systematic cultivation.
Species: cultivated plants and animals.
Variation
Issues on variation:
- What is the origin or cause of variation?
- What causes the incidence of variation within a living population to increase or decrease?
- What distinguishes between heritable and nonheritable variations?
PigeonsAll existing pigeon varieties arose from a single wild progenitor, the rock dove.
Supports for claim:
- All domesticated pigeons share characteristics with C. Liva
- Domesticated breeds when crossed have young that resemble the rock pigeon more than their parents.
- No other wild pigeons are like the rock dove to be alternative candidates for ancestry.
Chapter 1
Variation Under Domestication
Under domestication, the plants differ more from one another than the ones from nature. There is more variability under domestication than in the wild.
At what stage of life does variability happen?
Darwin seems to believe that the cause of variability is in the male and female reproductive elements prior to conception.
Reasons:
Any variation that has not been uninherited in unimportant for the argument.
“If strange, rare deviations of structure are truly inherited, less strange and commoner deviations may be freely admitted to be inheritable.”
“Perhaps the correct way of viewing the whole subject, would be, to look at the inheritance of every character whatever as the rule, and non-inheritance as the anomaly.”
“Believing it is always best to study some special group, I have taken up domestic pigeons.”
There is a great diversity of pigeons.
Even though there are great differences in breeds of pigeons, it is believed that they all descended from the rock-pigeon, Culumba Liva.
Selection:
Steps by which domestic races have been reproduced
“One of the most remarkable features in our domesticates races is that we see in them adaptation, not indeed to the animal’s or plant’s own good, but to man’s use of fancy.”
“The key is man’s power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him.”
“I believe that the conditions of life, from their action on the reproductive system, are so far of higher importance in causing variability.”
Under domestication, the plants differ more from one another than the ones from nature. There is more variability under domestication than in the wild.
At what stage of life does variability happen?
Darwin seems to believe that the cause of variability is in the male and female reproductive elements prior to conception.
Reasons:
- Results of breeding under confinement
- Habit; depending on habit they change.
Any variation that has not been uninherited in unimportant for the argument.
“If strange, rare deviations of structure are truly inherited, less strange and commoner deviations may be freely admitted to be inheritable.”
“Perhaps the correct way of viewing the whole subject, would be, to look at the inheritance of every character whatever as the rule, and non-inheritance as the anomaly.”
“Believing it is always best to study some special group, I have taken up domestic pigeons.”
There is a great diversity of pigeons.
Even though there are great differences in breeds of pigeons, it is believed that they all descended from the rock-pigeon, Culumba Liva.
Selection:
Steps by which domestic races have been reproduced
- Habit
- Adaptation
- Suddenly
- Man modifies breeds
- Direct action of external conditions of life
“One of the most remarkable features in our domesticates races is that we see in them adaptation, not indeed to the animal’s or plant’s own good, but to man’s use of fancy.”
“The key is man’s power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him.”
“I believe that the conditions of life, from their action on the reproductive system, are so far of higher importance in causing variability.”
Editor's Introduction to Chapter 3
“Is there enough
variation in nature to support his doctrine that continual modification of a
geographical race of one species can result in a new species?”
In the chapter before Darwin argues that there is enough variation in nature to support his claim.
Variation in Nature
Nature has enough variation to generate all the races, varieties and sub varieties.
Struggle for Existence
In order for natural selection to operate, the world must have a certain competitive character.
In the chapter before Darwin argues that there is enough variation in nature to support his claim.
Variation in Nature
Nature has enough variation to generate all the races, varieties and sub varieties.
Struggle for Existence
In order for natural selection to operate, the world must have a certain competitive character.
Chapter 3
Struggle for Existence
"How is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species, which in most cases obviously differ from each other far more than do the varieties of the same species."
"How do those groups of species, which constitute what are called distinct genera, and which differ from each other more than do the species of the same genus arise?"
Natural selection:
In the struggle for life, any variation, however slight and from whatever causes preceding, if it is in any degree profitable to an individual species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. Then the offspring will also have a better chance of survival.
Struggle for existence:
"As more individuals are produces that can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life."
Plants and animals tend to increase at a geometrical ratio.
But this would cause over population.
"The obvious explanation is that their conditions of life have been very favorable, and that there has consequently been less destruction of the old and young, and that nearly all young have been enabled to breed."
Considerations to keep in mind while looking at nature:
Survival from:
"As climate chiefly acts in reducing food, it brings on the most severe struggle between individuals, whether of the same or of distinct species, which subsist on the same kind of food."
Plants and animals are bound together by a web of complex relations:
they are all related to one another as in a sort of chain. You affect one and all end up being affected.
Corollary:
"The structure of every organic being is related in the most essential yet often hidden manner, to that of all other organic beings, with which it comes into competition for food or residence, or from which it has no escape, or on which it preys."
"We may console ourselves with the full belief that the 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."
"How is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species, which in most cases obviously differ from each other far more than do the varieties of the same species."
"How do those groups of species, which constitute what are called distinct genera, and which differ from each other more than do the species of the same genus arise?"
Natural selection:
In the struggle for life, any variation, however slight and from whatever causes preceding, if it is in any degree profitable to an individual species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. Then the offspring will also have a better chance of survival.
Struggle for existence:
- Between various species
- Between the same species
"As more individuals are produces that can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life."
Plants and animals tend to increase at a geometrical ratio.
But this would cause over population.
"The obvious explanation is that their conditions of life have been very favorable, and that there has consequently been less destruction of the old and young, and that nearly all young have been enabled to breed."
Considerations to keep in mind while looking at nature:
- Every being is striving to increase its numbers.
- Each life struggles at some period of its life.
- Heavy destruction falls inevitable on young or old, during each generation or at intervals.
Survival from:
- Space
- Climate
"As climate chiefly acts in reducing food, it brings on the most severe struggle between individuals, whether of the same or of distinct species, which subsist on the same kind of food."
Plants and animals are bound together by a web of complex relations:
they are all related to one another as in a sort of chain. You affect one and all end up being affected.
Corollary:
"The structure of every organic being is related in the most essential yet often hidden manner, to that of all other organic beings, with which it comes into competition for food or residence, or from which it has no escape, or on which it preys."
"We may console ourselves with the full belief that the 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."
Editor's Introduction to Chapter 4
"It has been said that Darwin's chief strength as a scientist was his allegiance to the facts rather than to unsustained speculation."
The examples in this chapter are imaginary ones.
Illustrations of the theory of natural selection
His imagined cases are:
"The branching of the tree of life represents the living world as continually coming into existence; it is not a static image but a highly dynamic one."
The examples in this chapter are imaginary ones.
Illustrations of the theory of natural selection
His imagined cases are:
- Wolves (survival between wolves)
- Flowers and insects (cooperation)
- Intercrossing
- Individuals in closely populations breeding with one another on the border of their range
- Individuals of different species breeding with one another
- Hermaphroditic flowers on the same plant eschewing self-fertilization instead of crossing with other flowers.
- Isolation
- by geographical barriers
- without geographical barriers
"The branching of the tree of life represents the living world as continually coming into existence; it is not a static image but a highly dynamic one."
- Divergence of character
Chapter 4
Natural Selction
“Let it be borne in mind in what an endless number of strange peculiarities our domestic productions, and in a lesser degree, those under nature, vary; and how strong the hereditary tendency is.”
Natural selection:
The preservation of favorable variations and the rejection of injurious variations.
Understanding Natural Selection:
If climate changes in a country, the inhabitants would undergo a change and some might become extinct. And if climate affects some species, then the extinction of such species would affect other species. Then it would be better if some of the inhabitants were modified, these would tend to be preserved.
But climate changes and isolation are not necessary for natural selection.
“Man can act only on external and visible characters: nature cares nothing for appearances, except insofar as they may be useful to any being.”
“Man selects only for his own good; nature only for that of the being which she tends.”
Natural selection can:
Natural selection cant:
Illustrations of the action of natural selection
Imaginary illustrations:
The plants might then turn attractive to insects to help them with this process.
“Thus I can understand how a flower and a bee might slowly become, either simultaneously or one after the other, modifies and adapted in the most perfect manner to each other, by the continued preservation of individuals presenting mutual and slightly favorable deviations or structure.”
“Natural selection can act only by the preservation and accumulation of infinitesimally small inherited modifications, each profitable to the preserved being.”
Circumstances favorable to natural selection
“A large number of individuals, by giving a better chance for the appearance within any given period of variations will compensate for a lesser amount of variability in each individual.”
Natural selection does not happen in an indefinite period.
Circumstances:
Divergence of Character
How is it that species become so different?
Early differences continued by natural selection and time become greater. This forms sub-breeds. And after centuries these sub-breeds become different breeds.
“Principle of divergence, causing differences, at fist barely appreciable, steadily to increase, and the breeds to diverge in character both from each other and from their common parent.”
“But as a general rule, the more diversified in structure the descendants from any one species can be rendered, the more places they will be enabled to seize on, and the more modifies progeny will be increased.”
Summary of the chapter
Principle of preservation:
If useful variation occurs to individuals, these will have the best chance of being preserved in their struggle for life, and their offspring will tend to be similarly characterized.
Principle of preservation = natural selection
Natural selection leads to divergence of character: more living beings can be supported in the same are the more they diverge in structure, habits and constitution.
“Let it be borne in mind in what an endless number of strange peculiarities our domestic productions, and in a lesser degree, those under nature, vary; and how strong the hereditary tendency is.”
Natural selection:
The preservation of favorable variations and the rejection of injurious variations.
Understanding Natural Selection:
If climate changes in a country, the inhabitants would undergo a change and some might become extinct. And if climate affects some species, then the extinction of such species would affect other species. Then it would be better if some of the inhabitants were modified, these would tend to be preserved.
But climate changes and isolation are not necessary for natural selection.
“Man can act only on external and visible characters: nature cares nothing for appearances, except insofar as they may be useful to any being.”
“Man selects only for his own good; nature only for that of the being which she tends.”
Natural selection can:
- Modify the structure of the young in relation to the parent.
- Modify the parent in relation to the young.
- Adapt the structures of each individual for the benefit of the community.
Natural selection cant:
- Modify the structures of one species without giving it advantage, for the good of another species
Illustrations of the action of natural selection
Imaginary illustrations:
- Wolf
- Juice in plants sought by insects
The plants might then turn attractive to insects to help them with this process.
“Thus I can understand how a flower and a bee might slowly become, either simultaneously or one after the other, modifies and adapted in the most perfect manner to each other, by the continued preservation of individuals presenting mutual and slightly favorable deviations or structure.”
“Natural selection can act only by the preservation and accumulation of infinitesimally small inherited modifications, each profitable to the preserved being.”
Circumstances favorable to natural selection
“A large number of individuals, by giving a better chance for the appearance within any given period of variations will compensate for a lesser amount of variability in each individual.”
Natural selection does not happen in an indefinite period.
Circumstances:
- Intercrossing: helps nature by keeping the individuals of the same species of variety true and uniform. Good genes pass on.
- Isolation: the organic and inorganic conditions of life will be greatly uniform. So all of the species of the same area will modify in the same manner in relation to the same conditions.
Divergence of Character
How is it that species become so different?
Early differences continued by natural selection and time become greater. This forms sub-breeds. And after centuries these sub-breeds become different breeds.
“Principle of divergence, causing differences, at fist barely appreciable, steadily to increase, and the breeds to diverge in character both from each other and from their common parent.”
“But as a general rule, the more diversified in structure the descendants from any one species can be rendered, the more places they will be enabled to seize on, and the more modifies progeny will be increased.”
Summary of the chapter
Principle of preservation:
If useful variation occurs to individuals, these will have the best chance of being preserved in their struggle for life, and their offspring will tend to be similarly characterized.
Principle of preservation = natural selection
Natural selection leads to divergence of character: more living beings can be supported in the same are the more they diverge in structure, habits and constitution.
Introduction to Chapter 6
This
chapter faces the principal difficulties faced by natural selection.
“Natural selection takes advantage of and transforms structures that are already present and which may originally have had a very different function.”
But natural selection doesn’t have intention, it doesn’t aim at anything.
“Darwin is to be appreciated… for having initiated a certain way of thinking about nature – a way that is constantly being refined and even revolutionized. This is a more modest, and a more realistic way of thinking about the founding of any science.”
- Sterility of
hybrids between species
- Gaps in the
fossil record
- Complex structures
- Elaborate instincts
“Natural selection takes advantage of and transforms structures that are already present and which may originally have had a very different function.”
But natural selection doesn’t have intention, it doesn’t aim at anything.
“Darwin is to be appreciated… for having initiated a certain way of thinking about nature – a way that is constantly being refined and even revolutionized. This is a more modest, and a more realistic way of thinking about the founding of any science.”
Haz clic aquĆ para modificar.
Chapter 6
Difficulties on Theory
On the absence or rarity of transitional varieties.
Natural selection making profitable modifications for preservation, the organism will take the place of or exterminate less-favorable forms.
Extinction and natural selection go hand in hand.
If we find a species that descended from an unknown form, probably it is because its parents and transitional varieties have already been exterminated.
But then why don’t we find these fossils? Because the record is less perfect than supposed.
“The crust of the earth is a vast museum; but the natural collections have been made only at intervals of time immensely remote.”
Organs of extreme perfection and complication
These organs seem absurd to have been formed by natural selection. (for example the eye)
But they are. There have been transitional grades.
Variations = slight alterations.
If Darwin finds a complex organ that existed without any modifications, his theory would break down, but no case has been found.
Sometimes organs that function for one purpose are converted into another one for another purpose.
“The same way as two men have sometimes independently hit on the very same invention, so natural selection, working for the good of each being and taking advantage of analogous variations, has sometimes modifies in very nearly the same manner two parts in two organic beings.”
- Why don’t we see everywhere innumerable transitions?
- Could an animal be formed, with habits resembling other animals by a transformation of another?
- Can instincts be modified?
- Why, when a species being crossed they are sterile, and when varieties are crossed they have good fertility?
On the absence or rarity of transitional varieties.
Natural selection making profitable modifications for preservation, the organism will take the place of or exterminate less-favorable forms.
Extinction and natural selection go hand in hand.
If we find a species that descended from an unknown form, probably it is because its parents and transitional varieties have already been exterminated.
But then why don’t we find these fossils? Because the record is less perfect than supposed.
“The crust of the earth is a vast museum; but the natural collections have been made only at intervals of time immensely remote.”
Organs of extreme perfection and complication
These organs seem absurd to have been formed by natural selection. (for example the eye)
But they are. There have been transitional grades.
Variations = slight alterations.
If Darwin finds a complex organ that existed without any modifications, his theory would break down, but no case has been found.
Sometimes organs that function for one purpose are converted into another one for another purpose.
“The same way as two men have sometimes independently hit on the very same invention, so natural selection, working for the good of each being and taking advantage of analogous variations, has sometimes modifies in very nearly the same manner two parts in two organic beings.”
Editor's Introduction to Chapter 11
“Darwin
thought that the distribution of animals and plants around the globe was one of
the most powerful pieces of evidence in favor of his historical approach to the
origin of the variety of earth and life.”
The Distribution of Land Masses
Single Centers of Creation
“Whenever one species evolves into another, a very large number of circumstances – including variations in the organism and changing environmental conditions – must come together in the right order.”
“A species is thus a unique production of nature happening in a localized region of space and time and which, if it vanishes, will never occur again.”
Geological Ages
Mesozoic era: Dinosaurs 248-65 million years ago
Cenozoic: 65 million years ago – now
Epochs: Pliocene and Pleistocene
Ice Ages
Northern Europe and North America were covered with a sheet of ice a mile or more thick.
The Argument
It’s like a story of the distribution of plants and animals in Europe.
The Distribution of Land Masses
- Land masses are mostly concentrated in the northern hemisphere.
- Masses turn to points towards the south.
- Antarctica was not taken into account by Darwin.
- Only large independent land masses in southern hemisphere: Australia.
Single Centers of Creation
“Whenever one species evolves into another, a very large number of circumstances – including variations in the organism and changing environmental conditions – must come together in the right order.”
“A species is thus a unique production of nature happening in a localized region of space and time and which, if it vanishes, will never occur again.”
Geological Ages
Mesozoic era: Dinosaurs 248-65 million years ago
Cenozoic: 65 million years ago – now
Epochs: Pliocene and Pleistocene
Ice Ages
Northern Europe and North America were covered with a sheet of ice a mile or more thick.
The Argument
It’s like a story of the distribution of plants and animals in Europe.
Chapter 11
Geographical Distribution
The bond = inheritance.
This produces organisms that are alike or varieties.
The reason why they differ in different regions = modification through natural selection, modified because of the physical conditions.
“On this principle of inheritance with modification we can understand how it is that sections of genera, whole genera, and even families are confined to the same areas.”
The degree of modification in each species will not be uniform.
The view that each species what produced in a certain region captivates the mind. This is when we find that the same animal (mammal) inhabits distant points (too far to swim).
Darwin’s explanation: they weren’t created at different points. They were produced in one area and then migrated as far as they possibly could.
Dispersal During the Glacial Period
Plants and animals living on distant mountain summits.
This was by influence of the glacial climate.
In the glacial period there was uniform artic fauna and flora, which means that the animals living in the mountains could go down into the valleys. When the glacial period retreated these artic animals remained isolated at the tops of the mountains.
This is why alpine plants and animals are similar to artic ones.
Also some are different because while up in the mountains their physical environment will have produced changes.
“Thus many of these wanderers, though still plainly related by inheritance to their brethren of the northern or southern hemispheres, now exist in their new homes as well-marked varieties or as distinct species.”
- Similarity or dissimilarity of the inhabitants can be accounted for by climatical or physical conditions.
- Barriers or obstacles to free migration are important to the differences of production of various regions.
- Affinity of productions of the same continent, though species in them are at different points and stations (in different continents there seems to be versions of a specific animal)
The bond = inheritance.
This produces organisms that are alike or varieties.
The reason why they differ in different regions = modification through natural selection, modified because of the physical conditions.
“On this principle of inheritance with modification we can understand how it is that sections of genera, whole genera, and even families are confined to the same areas.”
The degree of modification in each species will not be uniform.
The view that each species what produced in a certain region captivates the mind. This is when we find that the same animal (mammal) inhabits distant points (too far to swim).
Darwin’s explanation: they weren’t created at different points. They were produced in one area and then migrated as far as they possibly could.
Dispersal During the Glacial Period
Plants and animals living on distant mountain summits.
This was by influence of the glacial climate.
In the glacial period there was uniform artic fauna and flora, which means that the animals living in the mountains could go down into the valleys. When the glacial period retreated these artic animals remained isolated at the tops of the mountains.
This is why alpine plants and animals are similar to artic ones.
Also some are different because while up in the mountains their physical environment will have produced changes.
“Thus many of these wanderers, though still plainly related by inheritance to their brethren of the northern or southern hemispheres, now exist in their new homes as well-marked varieties or as distinct species.”
Editor's Introduction to Chapter 14
“Darwin
looks ahead to outline how he believes the study of living things will be
transformed by his vision of the radical historicity of life.”
Geographical race:
A population of living things that share a life in all its aspects, including coming together to produce the next generation.
Darwin regards this as the fundamental entity.
“Although he is quite sure that the fundamental similarities among living forms imply that life on earth had but a single beginning, he is not sure how that beginning happened.”
He leaves a possibility open that for large classes (vertebrae, arthropods) could have emerged by something other than natural selection.
Geographical race:
A population of living things that share a life in all its aspects, including coming together to produce the next generation.
Darwin regards this as the fundamental entity.
“Although he is quite sure that the fundamental similarities among living forms imply that life on earth had but a single beginning, he is not sure how that beginning happened.”
He leaves a possibility open that for large classes (vertebrae, arthropods) could have emerged by something other than natural selection.
Chapter 14
Recapitulation and Conclusion
“But the chief cause of our natural unwillingness to admit that one species have given birth to other and distinct species, is that we are always slow in admitting any great change of which we do not see the intermediate steps.”
All members of whole classes can be connected by chains of affinity. And all can possibly be classified on the same principle. Animals have descended at most from four or five progenitors.
“Therefore I should infer from this analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.”
Darwin is foreseeing a revolution in natural history with his ideas.
- It can’t be asserted that beings are not subject to variation.
- There is no clear distinction between species and varieties.
“But the chief cause of our natural unwillingness to admit that one species have given birth to other and distinct species, is that we are always slow in admitting any great change of which we do not see the intermediate steps.”
All members of whole classes can be connected by chains of affinity. And all can possibly be classified on the same principle. Animals have descended at most from four or five progenitors.
“Therefore I should infer from this analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.”
Darwin is foreseeing a revolution in natural history with his ideas.