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Concept
Macroevolution
Résumé
Macroevolution usually means the evolution of large-scale structures and traits that go significantly beyond the intraspecific variation found in microevolution (including speciation). In other words, macroevolution is the evolution of taxa above the species level (genera, families, orders, etc.).
Macroevolution is often thought to require the evolution of completely new structures such as entirely new organs. However, fundamentally novel structures are not necessary for dramatic evolutionary change. For instance, the evolution of mammal diversity in the past 100 million years has not required any major innovation. All of this diversity can be explained by modification of existing organs, such as the evolution of elephant tusks from canine teeth.
Philiptschenko distinguished between microevolution and macroevolution because he rejected natural selection in the sense of Darwin as an explanation for larger evolutionary transitions that give rise to taxa above the species level in the Linnean taxonomy. Accordingly, he restricted Darwinian "microevolution" to evolutionary changes within the boundary of given species that may lead to different races or subspecies at the most. By contrast, he referred "macroevolution" to major evolutionary changes that correspond to taxonomic differences above the species level, which in his opinion would require evolutionary processes different from natural selection. An explanatory model for macroevolution in this sense was the "hopeful monster" concept of geneticist Richard Goldschmidt, who suggested saltational evolutionary changes either due to mutations that affect the rates of developmental processes or due to alterations in the chromosomal pattern. Particularly the latter idea was widely rejected by the modern synthesis, but the hopeful monster concept based on evo-devo explanations found a moderate revival in recent times. Occasionally such dramatic changes can lead to novel features that survive.
Source officielle
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