Interbreeding organisms {species, ecology}| are basic biological units. Similar organisms share gene sets. Related species share similar structures, functions, and genes.
New species can arise from existing species {speciation}|.
hybridization
Hybrids between two different species sum chromosome-pair numbers. If eggs are fertile, self-fertilization starts new species intermediate between parent species. Chromosome doubling created many plant species and some animal species.
chromosome change
New species can arise through chromosome-number or gene-order change. Human chromosomes differ from chimpanzee chromosomes by inversions in nine chromosomes and by fusion of two chromosomes.
New species can appear if species diverge {principle of divergence} {divergence principle}. Typically, species gradually diverge into varieties, then subspecies, and then species. Behavior traits can diverge in ten generations. Major changes, such as brain development, diverge in 100 generations. New species diverge in 2000 generations. Species formation by divergence typically requires subspecies geographic isolation, to prevent gene dilution by other subspecies. Species diverge if organisms have different niches in same geographic area. Species converge if organisms live in separate areas with similar niches.
Species have original varieties {holotype}.
Organisms can perform similar functions using different structures {homoplasy}.
Organisms can have similar internal structures {homogeny} {homology, organism}|. Homology can result from keeping fundamental internal structure during evolution {parallelism, evolution} or having same external pressures during evolution and evolving to similar structures {convergence, evolution}.
Early eukaryotes incorporated primitive bacteria {endosymbiont hypothesis}, which evolved to mitochondria and chloroplasts.
Larval stages can become sexually mature {heterochrony}, to make new species.
Larval stages can become sexually mature, to make new species {paedomorphosis}.
Adult stages can add features, to make new species {peramorphosis}.
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Date Modified: 2022.0225