[argondonor]

But animals don't synthesize B12 either, they only store the B12 that they consume. There's no benefit not to just consume it ourselves.

[bena]

Ruminates like cows produce B12 through their gut bacteria. That's synthesis.

And before you say "that's the bacteria, not them", then we technically digest anything because gut bacteria is essential for digestion. We are gestalt organisms. Always have been.