For those of us interested in moral development and a good theory (or map) on how humans develop in moral thought and behavior, along with implications for animal rights, Lawrence Kohlberg’s Stages of Moral Development is excellent. Below is a link to learn more. There are criticisms noted at the bottom of the page, but the criticisms are pretty minor, leaving Kohlberg’s theory strong and intact. To my knowledge, nothing of much significance has been levied against Kohlberg’s theory since these criticisms were made by the mid-1980s, and Kohlberg’s theory is still an excellent way of thinking about moral development.
Unfortunately, most people in society remain in Kohlberg’s “Conventional Stages”, which at least partially explains why it is so difficult to get people to think for themselves when it comes to animals and society’s horrific treatment of them.