Sexual competition among ducks wreaks havoc on penis size - Nature

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[tama_lion]

鳥にはふつうペニスはないが、カモの仲間には巨大ドリルちんちんをもつ種もいる。これは毎年生え変わり、雄間競争が強いと(雄が雌の2倍いる集団で飼うと)雌雄ペア飼育時より長いのが生えてくる。性淘汰すごい