I heard various rumours/myths dont know how true these are but cowboys popularlised shake hands to check neither was holding a gun. It was mostly born out of mistrust and my parents would tell me its damn unhygenic.

Instead they promoted Namaste, where you don't touch someone elses hand and get their germs, but both saying Namaste articulated that you both respect each others divinity.

- its as old as civilization (examples from babylon)

- the quakers popularized it in america (supplanting the bow)