Laws of Variation | Textpedia

Effects of Changed Conditions

I have hitherto sometimes spoken as if the variations — so common and multiform with organic bein...

Effects of the increased use and disuse of parts, as controlled by natural selection.

From the facts alluded to in the first chapter, I think there can be no doubt that use in our dom...

Acclimatisation.

Habit is hereditary with plants, as in the period of flowering, in the time of sleep, in the amou...

Correlated variation.

I mean by this expression that the whole organisation is so tied together, during its growth and ...

Compensation and Economy of Growth.

The elder Geoffroy and Goethe propounded, at about the same time, their law of compensation or ba...

Multiple, Rudimentary, and Lowly-organised Structures are Variable.

It seems to be a rule, as remarked by Is. Geoffroy St. Hilaire, both with varieties and species, ...

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.

Several years ago I was much struck by a remark to the above effect made by Mr. Waterhouse. Profe...

Specific characters more variable than generic characters.

The principle discussed under the last heading may be applied to our present subject. It is notor...

Summary.

Our ignorance of the laws of variation is profound. Not in one case out of a hundred can we prete...

Causes of Variability

Effects of Habit and the Use or Disuse of Parts; Correlated Variation; Inheritance.

Character of Domestic Varieties; difficulty of distinguishing between Varieties and Species; origin of Domestic Varieties from one or more Species.

Breeds of the Domestic Pigeon, their Differences and Origin.

Principles of Selection anciently followed, and their Effects.

Unconscious Selection.

Circumstances favourable to Man's power of Selection.

Individual Differences

Doubtful Species

Wide-ranging, much-diffused, and common Species vary most.

Species of the Larger Genera in each Country vary more frequently than the Species of the Smaller Genera.

Many of the Species included within the Larger Genera resemble Varieties in being very closely, but unequally, related to each other, and in having restricted ranges.

Summary.

The Bearing of Struggle for Existence on Natural Selection

The Term, Struggle for Existence, Used in a Large Sense

Geometrical Ratio of Increase.

Nature of the Checks to Increase.

Complex Relations of all Animals and Plants to Each Other in the Struggle for Existence.

Struggle for Life most severe between Individuals and Varieties of the same Species.

Natural Selection: Its Power Compared with Man’s Selection

Sexual Selection.

Illustrations of the Action of Natural Selection, or the Survival of the Fittest.

On the Intercrossing of Individuals.

Circumstances favourable for the production of new forms through Natural Selection.

Extinction caused by Natural Selection.

Divergence of Character.

The Probable Effects of the Action of Natural Selection through Divergence of Character and Extinction, on the Descendants of a Common Ancestor.

On the degree to which organisation tends to advance.

Convergence of Character.

Summary of Chapter.

Effects of Changed Conditions

Effects of the increased use and disuse of parts, as controlled by natural selection.

Acclimatisation.

Correlated variation.

Compensation and Economy of Growth.

Multiple, Rudimentary, and Lowly-organised Structures are Variable.

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.

Specific characters more variable than generic characters.

Summary.

Difficulties of the Theory of Descent with Modification

On the absence or rarity of transitional varieties.

On the Origin and Transition of Organic Beings with peculiar Habits and Structure.

Organs of extreme Perfection and Complication.

Modes of transition.

Special difficulties of the theory of natural selection.

Organs of little apparent Importance, as affected by Natural Selection.

Utilitarian Doctrine, how far true: Beauty, how acquired.

Summary: The Law of Unity of Type and of the Conditions of Existence embraced by the Theory of Natural Selection.

Instincts Comparable with Habits, but Different in Their Origin

Inherited Changes of Habit or Instinct in Domesticated Animals.

Special Instincts.

Objections to the Theory of Natural Selection as applied to Instincts: Neuter and Sterile Insects.

Summary.

Distinction between the Sterility of First Crosses and of Hybrids

Laws governing the Sterility of first Crosses and of Hybrids.

Origin and Causes of the Sterility of first Crosses and of Hybrids.

Reciprocal Dimorphism and Trimorphism.

Fertility of Varieties when Crossed, and of their Mongrel Offspring, not universal.

Hybrids and Mongrels compared, independently of their fertility.

Summary of Chapter.

On the Absence of Intermediate Varieties at the Present Day.

On the Lapse of Time, as inferred from the rate of Deposition and extent of Denudatym.

On the Poorness of our Palæontological Collections.

On the Absence of Numerous Intermediate Varieties in any Single Formation.

On the sudden Appearance of whole Groups of allied Species.

On the sudden Appearance of Groups of allied Species in the lowest known Fossiliferous Strata.

On the Slow and Successive Appearance of New Species

On Extinction.

On the Farms of Life changing almost simultaneously throughout the World.

On the Affinities of Extinct Species to each other, and to Living Forms.

On the State of Development of Ancient compared with Living Forms.

On the Succession of the same Types within the same Areas, during the later Tertiary periods.

Summary of the preceding and present Chapters.

Present Distribution Cannot Be Accounted for by Differences in Physical Conditions

Means of Dispersal.

Dispersal during the Glacial Period.

Alternate Glacial Periods in the North and South.

Fresh-water Productions

On the Inhabitants of Oceanic Islands.

Absence of Batrachians and Terrestrial Mammals on Oceanic Islands.