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Ursid hybrid
An ursid hybrid is an animal with parents from two different species or subspecies of the Ursidae (bear) family. Species and subspecies of bear known to have produced offspring with another bear species or subspecies include brown bears, black bears, grizzly bears and polar bears, all of which are members of the ''Ursus'' genus. Bears not included in ''Ursus'', such as the giant panda, are probably unable to produce hybrids. Note all of the confirmed hybrids listed here have been in captivity (except grizzly/polar bear), but there are unconfirmed reports of hybrids in the wild.
A recent study by Kutschera and colleagues 〔Verena E Kutschera, Tobias Bidon, Frank Hailer, Julia L. Rodi, Steven R. Fain, Axel Janke (2014) Bears in a Forest of Gene Trees: Phylogenetic Inference Is Complicated by Incomplete Lineage Sorting and Gene Flow. Molecular Biology and Evolution 31(8): 2004–2017. 〕 found genetic evidence of multiple instances and species combinations where genetic material has passed the species boundary in bears (a process called introgression by geneticists). Specifically, species with evidence of past intermingling were (1) brown bear & American black bear, (2) brown bear and polar bear,〔Frank Hailer, Verena E. Kutschera, Björn M. Hallström, Denise Klassert, Steven R. Fain, Jennifer A. Leonard, Ulfur Arnason, Axel Janke (2012): Nuclear Genomic Sequences Reveal that Polar Bears Are an Old and Distinct Bear Lineage. Science Vol. 336 no. 6079: 344-347. 〕 (3) American black bear and Asian black bear, (4) bears currently distributed in Asia (sloth bear, sun bear and Asian black bear). Overall, this study shows that evolution in the bear family (Ursidae) has not been strictly bifurcating, but instead showed complex evolutionary relationships.
==Brown bear/American black bear hybrids==
In 1859, a black bear and a European brown bear were bred together in the London Zoological Gardens, but the three cubs did not reach maturity. In ''The Variation of Animals and Plants under Domestication'' Charles Darwin noted:
In the nine-year Report it is stated that the bears had been seen in the Zoological Gardens to couple freely, but previously to 1848 most had rarely conceived. In the Reports published since this date three species have produced young (hybrids in one case),...
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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