The theory of evolution by Darwin is a composite theory, i.e. it has five component theories: 1. Evolution as such is the simple proposition that the characteristics of lineages of organisms change over time 2. Common descent is a radically different view of evolution than the scheme Lamarck proposed. Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. 3. Gradualism – Darwin’s proposition that the differences between even radically different organisms have evolved incrementally, by small steps through intermediate forms. The alternative to this theory, as discussed in later sections, is saltation with great reference to large differences that are believed to have evolved by leaps without intermediates. 4. Populational change – Darwin’s thesis that evolution occurs by changes in the proportions of individuals within a population that have different inherited characteristics. 5. Natural selection – Darwin’s brilliant hypothesis, independently conceived by Wallace. Natural selection is the process through which populations of living organisms adapt and change. Individuals in a population are naturally variable, meaning that they are all different in some ways.
The theory of evolution by Darwin is a composite theory, i.e. it has five component theories:
1. Evolution as such is the simple proposition that the characteristics of lineages of organisms change over time
2. Common descent is a radically different view of evolution than the scheme Lamarck proposed. Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time.
3. Gradualism – Darwin’s proposition that the differences between even radically different organisms have evolved incrementally, by small steps through intermediate forms. The alternative to this theory, as discussed in later sections, is saltation with great reference to large differences that are believed to have evolved by leaps without intermediates.
4. Populational change – Darwin’s thesis that evolution occurs by changes in the proportions of individuals within a population that have different inherited characteristics.
5. Natural selection – Darwin’s brilliant hypothesis, independently conceived by Wallace. Natural selection is the process through which populations of living organisms adapt and change. Individuals in a population are naturally variable, meaning that they are all different in some ways.
Given the titles of the three chapters of the theory of Evolution with their descriptions:
CHAPTER VII.
Miscellaneous Objections to the Theory of Natural Selection.
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Longevity—Modifications not necessarily simultaneous—Modifications apparently of no direct service—Progressive development—Characters of small functional importance, the most constant—Supposed incompetence of natural selection to account for the incipient stages of useful structures—Causes which interfere with the acquisition through natural selection of useful structures—Gradations of structure with changed functions—Widely different organs in members of the same class, developed from one and the same source—Reasons for disbelieving in great and abrupt modifications
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CHAPTER VIII.
Instinct.
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Instincts comparable with habits, but different in their origin—Instincts graduated—Aphides and ants—Instincts variable—Domestic instincts, their origin—Natural instincts of the cuckoo, molothrus, ostrich, and
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CHAPTER IX.
Hybridism.
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Distinction between the sterility of first crosses and of hybrids—Sterility various in degree, not universal, affected by close interbreeding, removed by domestication—Laws governing the sterility of hybrids—Sterility not a special endowment, but incidental on other differences, not accumulated by natural selection—Causes of the sterility of first crosses and of hybrids—Parallelism between the effects of changed conditions of life and of crossing—Dimorphism and Trimorphism—Fertility of varieties when crossed and of their mongrel offspring not universal—Hybrids and mongrels compared independently of their fertility
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The question is, based on the given description of each chapter, identify what component theory (Evolution as such, Common descent, Gradualism, Populational change, or Natural selection) does each chapter fall into?
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