The males stay as close to the female as possible 雄鲸尽可能靠近雌鲸
At the same time as bats were first moving into the air, 在蝙蝠首次上天的同时
as it has done for millions of years. 几百万年来一直如此
But just as some mammals evolved to feed on the grass, 但在一些哺乳动物 进化成以草为食的同时
something that would challenge mammals as never before. 这将对哺乳动物提出前所未有的挑战