structural:reformatting, information:classification, stylistic:tone
Longevity

The influence on a zoological environment on animal's longevity is not straightforward. A study of 50 mammal species found that 84% of them lived longer in zoos than they would in the wild on average. On the other hand, some research claims that elephants in Japanese zoos would live shorter than their wild counterparts at just 17 years. This has been refuted by other studies however. Such studies might not yet fully represent recent improvements in husbandry. For example, studies show that captive-bred elephants already have a lower mortality risk then wild-caught ones.