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 XII. Geographical Distribution. Present distribution cannot be accounted for by differences in physical conditions—Importance of barriers—Affinity of the productions of the same continent—Centres of creation—Means of dispersal by changes of climate and of the level of the land, and by occasional means—Dispersal during the Glacial period—Alternate Glacial periods in the north and south
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 XII.
Geographical Distribution.
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Present distribution cannot be accounted for by differences in physical conditions—Importance of barriers—Affinity of the productions of the same continent—Centres of creation—Means of dispersal by changes of climate and of the level of the land, and by occasional means—Dispersal during the Glacial period—Alternate Glacial periods in the north and south
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CHAPTER XIII.
Geographical Distribution—continued.
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Distribution of fresh-water productions—On the inhabitants of oceanic islands—Absence of Batrachians and of terrestrial Mammals—On the relation of the inhabitants of islands to those of the nearest mainland—On colonization from the nearest source with subsequent modification
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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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