sitting here too long to worn the tail off .
from the joke , the lecture should be over.

First time, I did not notice the meaning......then I rereaded it ...I got it...

haha

我们的尾巴
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（狒狒）, where are they?"
题为“人类进化过程”的演讲持续了近两个小时，可是演讲者还是没有丝毫的倦意，你听，他又开始提问了：“请问你们谁能回答一个有关进化的问题吗？”－－如果我们也像狒狒一样有一条尾巴，那这尾巴在哪里呢？
"I'll venture an answer, " said an old lady. "We have worn them off sitting here so long."
“我想来猜猜这个答案。一位年老的女士答道。我想是因为我们坐在这里太久了，所以就磨损了吧。”

我们的尾巴
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（狒狒）, where are they?"
一位演讲者就“人类进化”的演讲持续了近两个小时，这时，他又开始提问了：“让我问一个有关进化的问题吧－－如果我们也像狒狒一样有一条尾巴，那么尾巴现在在哪里呢？
"I'll venture an answer, " said an old lady. "We have worn them off sitting here so long."
“我想来试着回答。”一位年老的女士答道。“我想是因为我们坐在这里太久了，所以就磨掉了吧。”