Neo-Darwinism
Revisions of
Darwin’s Theory
Neo-Darwinism
The most serious weakness in Darwin’s theory was his failure to identify correctly the mechanism of inheritance. Darwin saw heredity as a blending phenomenon in which the characteristics of the parents melded together in the offspring. Darwin also invoked the Lamarckian hypothesis that an organism could alter its heredity through use and disuse of body parts and through the direct influence of the environment. August Weismann rejected Lamarckian inheritance by showing experimentally that modifications of an organism during its lifetime do not change its heredity (see Principles of Genetics:A Review), and he revised Darwin’s theory accordingly. We now use the term neo-Darwinism to denote Darwin’s theory as revised by Weismann.
Mendelian genetics eventually clarified the particulate inheritance that Darwin’s theory of natural selection required. Ironically, when Mendel’s work was rediscovered in 1900, it was viewed as antagonistic to Darwin’s theory of natural selection. When mutations were discovered in the early 1900s, most geneticists thought that they produced new species in single large steps. These geneticists relegated natural selection to the role of executioner, a negative force that merely eliminated the obviously unfit.
Emergence of Modern Darwinism: the Synthetic Theory
In the 1930s a new generation of geneticists began to reevaluate Darwin’s theory from a different perspective. These were population geneticists, scientists who studied variation in natural populations of animals and plants and who had a sound knowledge of statistics and mathematics. Gradually, a new comprehensive theory emerged that brought together population genetics, paleontology, biogeography, embryology, systematics, and animal behavior in a Darwinian framework.
Population geneticists study evolution as a change in the genetic composition of populations. With the establishment of population genetics, evolutionary biology became divided into two different subfields. Microevolution pertains to evolutionary changes in frequencies of different allelic forms of genes within populations. Macroevolution refers to evolution on a grand scale, encompassing the origins of new organismal structures and designs, evolutionary trends, adaptive radiation, phylogenetic relationships of species, and mass extinction. Macroevolutionary research is based in systematics and the comparative method. Following the evolutionary synthesis, both macroevolution and microevolution have operated firmly within the tradition of neo- Darwinism, and both have expanded Darwinian theory in important ways.
Neo-Darwinism
The most serious weakness in Darwin’s theory was his failure to identify correctly the mechanism of inheritance. Darwin saw heredity as a blending phenomenon in which the characteristics of the parents melded together in the offspring. Darwin also invoked the Lamarckian hypothesis that an organism could alter its heredity through use and disuse of body parts and through the direct influence of the environment. August Weismann rejected Lamarckian inheritance by showing experimentally that modifications of an organism during its lifetime do not change its heredity (see Principles of Genetics:A Review), and he revised Darwin’s theory accordingly. We now use the term neo-Darwinism to denote Darwin’s theory as revised by Weismann.
Mendelian genetics eventually clarified the particulate inheritance that Darwin’s theory of natural selection required. Ironically, when Mendel’s work was rediscovered in 1900, it was viewed as antagonistic to Darwin’s theory of natural selection. When mutations were discovered in the early 1900s, most geneticists thought that they produced new species in single large steps. These geneticists relegated natural selection to the role of executioner, a negative force that merely eliminated the obviously unfit.
Emergence of Modern Darwinism: the Synthetic Theory
In the 1930s a new generation of geneticists began to reevaluate Darwin’s theory from a different perspective. These were population geneticists, scientists who studied variation in natural populations of animals and plants and who had a sound knowledge of statistics and mathematics. Gradually, a new comprehensive theory emerged that brought together population genetics, paleontology, biogeography, embryology, systematics, and animal behavior in a Darwinian framework.
Population geneticists study evolution as a change in the genetic composition of populations. With the establishment of population genetics, evolutionary biology became divided into two different subfields. Microevolution pertains to evolutionary changes in frequencies of different allelic forms of genes within populations. Macroevolution refers to evolution on a grand scale, encompassing the origins of new organismal structures and designs, evolutionary trends, adaptive radiation, phylogenetic relationships of species, and mass extinction. Macroevolutionary research is based in systematics and the comparative method. Following the evolutionary synthesis, both macroevolution and microevolution have operated firmly within the tradition of neo- Darwinism, and both have expanded Darwinian theory in important ways.
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