How far back does your handshake go?

The biologist Stephen J Gould's pHd advisor had shaken Charles Darwin's hand, so Gould had 2 degrees of separation from Darwin by handshake.

When my grandfather was a child his father held him in the air during Theodore Roosevelt's 1900 whistlestop campaign so they could shake hands.

Correction- the timeline is impossible, and apparently Gould shook his advisor's hand, who had shaken someone else's hand who had shaken Darwin's hand.