Contribution of hybridization between polar bears and grizzly bears to polar bear extinction

This review explores whether recent hybridization events between polar bears ( Ursus maritimus ) and grizzly bears ( Ursus arctos horribilis ) will eventually contribute to the extinction of the modern polar bear. In April 2006, genetic analysis of an odd‐looking bear killed in the Northwest Territories, Canada, revealed this specimen to be a polar bear–grizzly bear hybrid, and additional hybrid bears were harvested beginning in April 2010. These events have been sensationalized by some in the media, who have speculated that the modern polar bear may become extinct due to crossbreeding with grizzly bears. Although studies support the introgression of brown bear genes into the polar bear genome during the Pleistocene, no evidence supports the occurrence of a similar event today. Even if such an introgression event occurred, hybrids evolving rapidly enough to adapt to ongoing sea ice depletion is not scientifically plausible. The loss of genetic integrity and modified morphology due to inbreeding between polar bears and grizzly bears are not considered threats to polar bear survival. As many scientists have stressed for decades, the greatest threat to the survival of the modern polar bear is sea ice depletion due to climate change. 综述探讨了最近北极熊（ Ursus maritimus ）和灰熊（ Ursus arctos horribilis ）之间的杂交事件是否会最终导致现代北极熊的灭绝。2006年4月，一只长相奇特的熊在加拿大西北部被杀，对其进行基因分析发现该个体是北极熊和灰熊的杂交后代。随后，从2010年4月开始收集到更多属于该谱系的杂交个体。这些事件被某些媒体夸大，断言现代北极熊可能会因为与灰熊的杂交而灭绝。尽管以往的研究表明在更新世时期曾发生过棕熊基因渗入北极熊基因组事件，但没有证据支持类似事件在当代也有发生。而即使发生了渗入事件，杂交后代可快速进化以适应持续的海冰融化在科学上也是不合理的。但北极熊和灰熊杂交导致遗传完整性的丢失和形态的改变并不是北极熊生存的主要威胁。正如许多科学家几十年来一直强调的那样，现代北极熊生存的最大威胁是气候变化导致的海冰融化。 In response to the hybridization events between polar bears and grizzly bears since 2006, the media's promulgation of impending polar bear extinction due to genetic maladaptation was unwarranted. Only one‐directional gene flow from polar bears to grizzly bears has been detected in modern times, and even if it occurred in the opposite direction, there is not enough time to allow for significant adaptation to a rapidly changing Arctic environment. The projected depletion of polar bear populations will be the result of insufficient sea ice rather than any contribution from genetic influences. If the preservation of the polar bear as a species is to occur, society must focus immediately on reducing the causes of global warming.