当鸭嘴兽被首次发现时，人们只能用造物主的胡闹或是上帝的幽默来形容这种外形古怪的生物。最近，鸭嘴兽基因序列的解读最终揭开了这种神秘生物的秘密：它比我们想象的还要古怪神奇。

这种地球上迄今为止发现的最古老神秘的哺乳动物的身世之谜终于随着其基因代码的解读而公之于众。基因显示，鸭嘴兽的血统里混合了鸟类，爬行动物以及哺乳动物的诸多代码。其性别代码更是诡异。众所周知人类的性别基因代码中含有X、Y两条染色体，而鸭嘴兽的性别染色体则多达10条，不同性别的鸭嘴兽各占有其中的5条染色体。

一组来自世界各地的科学家研究小组共同解读了一只名为Glennie的雌性鸭嘴兽的220万条基因信息。鸭嘴兽的源头可以追溯到1.7亿年前，爬行动物与哺乳动物过渡过程中的一条意外分支。拥有厚实的毛皮并用乳汁养育后代的同时，雌性鸭嘴兽采用下蛋之后由雄性鸭嘴兽受精的方式产生新生命 – 这也是迄今为止生物界的唯一特例。

当1798年在澳大利亚首次发现鸭嘴兽的时候，这种长相奇怪的动物甚至被动物学家George Shaw判定为由海狸变异而成的一场骗局。

最近发表于《自然》上的研究则指出，鸭嘴兽是遗传以及生物演变过程中现存的活化石。来自牛津大学药物研究协会功能染色体小组的专家Chris Ponting则表示科学家首次试图通过DNA序列来发现鸭嘴兽奇特外表下的基因之谜：“通过对鸭嘴兽基因组的解读发现，和许多其他哺乳动物一样，其中很多成分与鸟类、蜥蜴的排列类似。与大多数哺乳动物不同的是，鸭嘴兽的基因中保留了更多爬行动物时期的基因组合。”

At first dismissed as a prank, and later cited as proof that God has a sense of humour, the duck-billed platypus has finally given up its evolutionary secrets.

The creature, considered one of the strangest mammals in the world, has become the latest to have its genetic code sequenced, revealing it to be a bizarre mix of mammal, bird and reptile, with very complex sexuality. While humans have two sex chromosomes, the X and Y, the platypus has 10, with five of each kind.

An international team of scientists extracted DNA from a female platypus, named Glennie, reading all 2.2bn pairs of her genetic "letters". Thought to have begun to diverge from other mammals 170m years ago, the platypus has been regarded as the nearest thing biologists have to a missing link between the earliest reptiles and mammals. It has thick fur and produces milk for its young, yet the females lay eggs and the males produce venom - the only mammals to do so.

When first discovered in Australia in 1798, the beaver-tailed animal caused such bemusement that the zoologist George Shaw declared it could well be a hoax.

The new study, published in Nature, shows the platypus as both evolutionary relic and pioneer. Chris Ponting, at the Medical Research Council's functional genomics unit at Oxford University, said scientists had had the first chance to see if the platypus's weird appearance was reflected in its DNA: "Lo and behold, we saw genes like those in lizards and birds, as well as some like those in other mammals. It has retained many genes other mammals lost from a time when all mammals looked much like lizards."

Many of the animal's stranger characteristics are now thought to have evolved independently. The venom, which is released from the male's hind leg spurs, is thought to have developed late in the animal's history. And the remarkable electrosensitive bill, which helps the platypus hunt underwater while its eyes and ears are covered, appeared long after the platypus split from its reptilian ancestors.

The fact that the animal has five X and five Y chromosomes is "the weirdest thing about a very weird animal," said Ewan Birney, a co-author on the paper, based at the European Bioinformatics Institute, near Cambridge. "In theory it means there are 25 possible sexes, though in practice that doesn't happen."