I absolutely believe it has to do with birth.

My gf and I were talking about this yesterday and she's certainly not in any way associated with any birthing communities iykwim? Just a mum who had 2 kids. And she feels the trauma of her sons birth in a lot of ways lead to a similar feeling that animals go through when the birthing process is traumatic or tampered with. Like a state of emotional rejection. Not a physical rejection of the child but a feeling of "who is this?" iykwim?