Where are the tails? 尾巴哪去了？

The lecturer on evolution had been going on for nearly two hours, then he started again, and said he: "Let me ask the evolutionist a question -- if we had tails like a baboon, where are they?" 

"I'll venture an answer," said an old lady, "We have worn them off sitting here so long.". 

教进化论的老师已经滔滔不绝地讲了快两个小时，他的话题又来了：“让我向进化论者提个问题——如果我们曾经像狒狒那样长着尾巴，那么现在尾巴到哪里去了？” 

“我来试试看，”一位老太太说， “该是我们在这里坐这么久把它们磨掉了吧。”