This I did not know: the modern high five is only a few decades old:
Most scholars agree that the modern high five wasn’t popularized until about 35 years ago, in the cloudy twilight hours of October 2, 1977. It was the last game of the Major League Baseball season, and the Los Angeles Dodgers hosted the Houston Astros before a crowd of 42,501. Late in the sixth inning, Dodger Dusty Baker demolished a three-run home-run to tie the score — a significant moment that also made Los Angeles the first team in history to have four players with 30 home runs. Then, as journalist Jon Mooallem recounts, Baker’s teammate instigated something much greater:
“It was a wild, triumphant moment and a good omen as the Dodgers headed to the playoffs. Glenn Burke, waiting on deck, thrust his hand enthusiastically over his head to greet his friend at the plate. Baker, not knowing what to do, smacked it.”
“His hand was up in the air, and he was arching way back,” Baker later recalled. “So I reached up and hit his hand. It seemed like the thing to do.” The high five’s legend was sealed when Burke stepped to the plate next, hit a home run of his own, and returned to the dugout to return Baker’s high five.