Why Do We Shake Hands?

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Why Do We Shake Hands?
Why do we shake hands in the first place?

At the beginning of the pandemic, some thought COVID would mean the end of the handshake. And for a while that was true.  

We stayed apart and waved in place of shaking hands.  

But now many are back to shaking hands. 

To shake hands or not may still be a personal preference. But why do we shake hands in the first place?