Biological Counters

How do we know how to keep a beat with no metronome anyways? I was thinking about this a lot today. Humans can keep rhythm really well. It's like we all have clock crystal oscillators and digital counters in our brains. I wonder what that circuit looks like in biological form. Wouldn't it need some kind of oscillator?

That got me thinking why we need to keep accurate time anyways. Why can we keep a beat so well? My theory from an evolutionary standpoint is that we developed the ability at the same time we developed the ability to move. Around the time frame one of our amoeba ancestors made some neural connections enabling the ability to send out correctly timed nerve pulses which rhythmically moved part of its blob body, we developed the ability to keep a beat and make music.