Let’s try something right now.

Please place your hand flat on a table.

Next, bend your middle finger under your hand, so that the knuckle rests on the table like this. Perfect.

I bet that you can’t lift your third finger up and down, and tap it on the table.

Sounds simple? No matter how hard you try, you won’t be able to do it!

Congratulations, you have just carried out your very first bet, and now you can use it to amuse and amaze others.

But hold on. I can hear the more curious among you thinking, ‘That’s great, but why does it work?’ It’s an excellent question and I am glad you asked.

Your forearm muscles are connected to the bones in your fingers via tough cords of tissue called tendons. When you contract your forearm muscles the tendons tighten and your fingers move.

Your thumb, first finger and little finger each have their own tendon, but your middle and third fingers share a tendon. When you tuck your middle finger under your hand this tendon is stretched, and so can’t move your third finger.

And why do these two fingers share a tendon? Because you use them to grasp large objects, and they are more effective if they work together. In fact, scientists think that this mechanism evolved to allow our primate ancestors to hold heavy stone tools.

So now you know. A moment ago it was a fun bet. Now it illustrates a vital stage in human evolution and has changed the entire course of history.

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Oh, and you can take your hand off the table now.