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[17] [18] They argued further that there was a "pre-Mendelian" phase of the evolution of animals, involving physical forces, before genes took over. [ 17 ] [ 19 ] Darwinian biologists freely admit that physical factors such as surface tension can cause self-assembly , but insist that genes play a crucial role.
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.
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:
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 ...
As the most celebrated argument in evolutionary biology, (Edwards, 1998, pp. 564–569) Fisher's principle is a staple of popular science books on evolution. For example, see: Gould, Stephen Jay (2002). The Structure of Evolutionary Theory. pp. 648– 649, 678, 692. Dawkins, Richard; Wong, Yan (2004). "The Seal's Tale".
Evolutionary progress as a tree of life. Ernst Haeckel, 1866 Lamarck's two-factor theory involves 1) a complexifying force that drives animal body plans towards higher levels (orthogenesis) creating a ladder of phyla, and 2) an adaptive force that causes animals with a given body plan to adapt to circumstances (use and disuse, inheritance of acquired characteristics), creating a diversity of ...
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.