Penguins and other birds, certain animals, seahorses… share the burden. Human females carry the baby for nine months giving birth to a helpless baby, who remain that way til, well, 30 sometimes. I think women are more nurturing instinctively. They do not even require a man to reproduce. That is nature. Genes. DNA. Then there is your upbringing, environment, parenting, schooling, character etcetera. No two people are alike. There are amazing dads, single parent or not, and horrible moms. But instinctively, I’d say girls and women are usually the more caring, reliable and nurturing of our fucked-up species.