A herd of buffalo can only move as fast as the slowest buffalo, and when the herd is hunted, it is the slowest and weakest ones at the back that are killed first. This natural selection is good for the herd as a whole, because the general speed and health of the whole keeps improving by the regular culling of the weakest members.

In much the same way…

A man was crossing a road one day when a frog called out to him and said: “If you kiss me, I’ll turn into a beautiful princess”. He bent over, picked up the frog and put it in his pocket. …

Five surgeons were taking a coffee break and discussing their work.

The first said…

A mathematician and an engineer are sitting next to each other on a long flight. The mathematician leans over to the engineer and asks if he would like to play a fun game. The engineer just wants to take a nap, so he politely declines and rolls over to the window to catch a few winks.