Humans have selectively bred dogs to have facial expressions like ours.

Pain empathy reduced by paracetamol

One reason we don't enjoy witnessing, hearing, or even thinking about pain in others is that it activates pain regions in our own brain.

Why mindful attention helps remould your body

Pain is reduced when holding hands with someone who cares.

The biological basis of sex shows our species to be naturally diverse and for nature to be very flexible on this issue.