[Someone]

> While a robot can keep beat at 123, most humans can’t keep 123.45.

Isn’t it also true that while a robot can keep beat at 123.45, most humans can’t keep 123?

Apart from training, there isn’t anything that links human biology and psychology with the length of a second, is there?

[scrumper]

Kinda ish. Healthy resting heartbeat is around 60bpm and comfortable exertion heart rate - like doing an indefinitely sustainable run, the kind of thing we evolved to do to run down prey - around double that. The most broadly popular styles of dance music tend to float around 120bpm. It just feels natural to humans. At a guess, some combination of biomechanics (muscle twitch speed, pendulum effect of limb sizes against their articulating joints), heart beat, what most people can manage in terms of sustained exercise (as mentioned above), and attention span linked to multiples of musical phrases.

Specifically about keeping tempo, human drummers don't really. They will move around a central tempo, slowing in verses and increasing tempo in choruses and as the song progresses. If you're hearing a fixed tempo in a song, it's because it was recorded with a click track in the drummer's ear. Super common these days because popular tastes for recorded music currently skew towards perfection.