In the Victorian era, philosophers believed that human beings were born a blank slate. That by engineering the right life experiences, we could abolish violence, greed, irrationality, and even impropriety. (They were Victorian, after all!) But like so many interesting memes, this one is dead wrong.
Human beings are born with innate fears, drives, capabilities, and even innate metaphors and archetypes. We all fear the dark. We all seek to protect our own, to rally for justice, to consume, to lust, to create and destroy. We compulsively reject the outsider, distrust the trickster, and respect the hero.
We're born knowing there are differences between the sexes, and the data proves us right. Sex differences are the largest "group" differences we can detect, impacting personality, perception, predilections, and literally hundreds of measurable physical and biochemical characteristics. All of these contribute to what the average man or woman is like. Not to mention what the average gay, lesbian, or trans person is like! They have distinct, measurable characteristics as well.
Why does it matter? Because not only does understanding humanity makes us more wise and more compassionate, but it also makes us better storytellers. Storytelling is about transmitting wisdom of the human condition, so it does no good to populate our cast with blank slates. It's a snake in the Garden of Eden, for a reason! It's Gretel that pushes the witch into the oven, for a reason! Great stories dig into the deep grooves evolution gave us. And even while great stories often subvert those grooves with some atypical characters, they do so to reveal yet deeper truths about how to live in harmony with our fundamental human nature.