Thus, the category of “parent” and/or “child” has been around for 200 million years. That’s longer than birds have existed. That’s longer than flowers have grown. It’s not a billion years, but it’s still a very long time. It’s plenty long enough for male and female and parent and child to serve as vital and fundamental parts of the environment to which we have adapted. This means that male and female and parent and child are categories, for us—natural categories, deeply embedded in our perceptual, emotional and motivational structures.
