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It proposes instead that evolution is guided differently, by physical forces which shape the development of an animal's body, and sometimes implies that these forces supersede selection altogether. Structuralists have proposed different mechanisms that might have guided the formation of body plans .
The current theory of evolution, the modern evolutionary synthesis (or neo-darwinism), explains that evolution of species occurs through a combination of Darwin's mechanism of natural selection and Gregor Mendel's theory of genetics as the basis for biological inheritance and mathematical population genetics. [80]
The theory of evolution explains these homologous structures: all four animals shared a common ancestor, and each has undergone change over many generations. These changes in structure have produced forelimbs adapted for different tasks. [49] The bird and the bat wing are examples of convergent evolution.
The following approaches can all be seen as exemplifying a generalization of Darwinian ideas outside of their original domain of biology. These "Darwinian extensions" can be grouped in two categories, depending on whether they discuss implications of biological (genetic) evolution in other disciplines (e.g. medicine or psychology), or discuss processes of variation and selection of entities ...
Megaevolution has been extensively debated because it has been seen as a possible objection to Charles Darwin's theory of gradual evolution by natural selection. [1] A list was prepared by John Maynard Smith and Eörs Szathmáry which they called The Major Transitions in Evolution. [2] [3] On the 1999 edition of the list they included:
Some who came to accept evolution, but disliked natural selection, raised religious objections. Others felt that evolution was an inherently progressive process that natural selection alone was insufficient to explain. Still others felt that nature, including the development of life, followed orderly patterns that natural selection could not ...
The evolution of biological complexity is one important outcome of the process of evolution. [1] Evolution has produced some remarkably complex organisms – although the actual level of complexity is very hard to define or measure accurately in biology, with properties such as gene content, the number of cell types or morphology all proposed as possible metrics.
They can shape the structure of whole genomes and thus explain genome evolution to a large extent. Examples include the Homeobox genes in animals. These genes not only underwent gene duplications within chromosomes but also whole genome duplications. As a result, Hox genes in most vertebrates are spread across multiple chromosomes: the HoxA–D ...