Much of these ideas and facts are touched on in the Neurobiology and the Development of Human Morality. I highly recommend it if you are interested in a more thorough textbook explanation of our current understanding of morality and development. The most important thing to realize is that the “continuum of caring” mentioned in the video is a biological fact of our world. Many people will simply find it almost impossible to develop caring to high levels due to their development as a person, whether it be genetic, epigenetic, intrauterine, or cultural pressures that form their worldview and perspectives.
As Marsh states in the video, some research seems to suggest that the mean is shifting toward the right (i.e. the world is getting more moral) on that continuum of caring and that is largely because we are getting wealthier, better educated, and developing more understanding of the aspects that influence the development of altruism, or a concern for the well-being of others. Wealth, education, and greater understanding all work together to allow us to lower stress levels throughout the development process and thereby give us the psychological slack to “turn outward” from a self-interested position of simply surviving to a position of wanting to explore and influence our surroundings in positive ways.