【英语时差8,16】罕见的独角鲸-上（在线收听）

Narwhals aren’t fish, they’re mammals--a rare type of whale. They have a famous spiraled tusk. The tusk, which is commonly misconceived for a horn, is actually an elongated tooth. Only male narwhals grow tusks, which can be over six to almost ten feet long-more than half their body length. What Is The Function Of The Tusk? There is patchy evidence for several different hypotheses. Since only males grow tusks, it could have evolved in response to sexual selection. Like the tails of male peacocks, the tusk could be used to attract and impress females and intimidate rival males.