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The basic number of chromosomes in the somatic cells of an individual or a species is called the somatic number and is designated 2n. In the germ-line (the sex cells) the chromosome number is n (humans: n = 23). [4] [5] p28 Thus, in humans 2n = 46. So, in normal diploid organisms, autosomal chromosomes are present in two copies.
Evolution is the change in the heritable characteristics of biological populations over successive generations. [1] [2] It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certain characteristics becoming more or less common within a population over successive generations. [3]
The idea of evolution by natural selection was proposed by Charles Darwin in 1859, but evolutionary biology, as an academic discipline in its own right, emerged during the period of the modern synthesis in the 1930s and 1940s. [8] It was not until the 1980s that many universities had departments of evolutionary biology.
Inversion (evolutionary biology) – Hypothesis in developmental biology; Mosaic evolution – Evolution of characters at various rates both within and between species; Parallel evolution – Similar evolution in distinct species; Quantum evolution – Evolution where transitional forms are particularly unstable and do not last long
The discipline of biology that studies the evolution of biological organisms and the processes by which it operates, including natural selection, adaptation, common descent, and speciation. A core element of the modern synthesis , evolutionary biology integrates concepts from genetics , systematics , ecology , paleontology , developmental ...
The idea of a tree of life arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being).Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in the book Elementary Geology, by Edward Hitchcock (first edition: 1840).
Therefore the evolution of the lineages of such species has likely been substantially influenced by sexual interactions. In the fossil record, lineages with the capability for sexual reproduction first appeared about 2.0 billion years ago in the Proterozoic Eon, [5] [6] although a later date, 1.2 billion years ago has also been proposed.
In biology, evolution is the process of change in all forms of life over generations, and evolutionary biology is the study of how evolution occurs. Biological populations evolve through genetic changes that correspond to changes in the organisms ' observable traits .