For example, we can will ourselves breathe/blink faster, or choose to hold our breath. But at the same time, we can’t will a faster or slower heart rate or digestion when it might be advantageous to do so. What is the difference in the muscles involved or brain regions associated with these automated functions?
Disclaimer: not a doctor or biologist, just someone who reads a lot.
Lots of these posts are talking about why some things are more important than others, which is why they are reflexes and not actively processed (using the heart as an example). Another point about the heart which isn’t being mentioned, is that your heart develops to pump blood before you have a fully formed brain stem. So regardless of the relative importance between these body parts in a fully grown human – we couldn’t have evolved if the heart couldn’t beat on its own