How do men's bodies know when to change during pregnancy?

Hey all!

First-time pre-dad here, my wife is in her 9th week, and I've noticed changes in myself in that time, such as nausea, a change in psyche (for example, I went away with friend for three nights, pre planned before the pregnancy, and I have never missed my wife so much as that, even though it was a short time and I was only 100km away), mood swings, more anxiety. I've done some late night research and found out that this is not uncommon, and can be triggered by hormone fluctuations

But the one question I still have unanswered is, how does my body knows that my wife is pregnant? What triggers these changes in hormones? I can only find research into what happens but not into how. Does anyone know about this?