Humans fancy we are conscious of everything important, but don't understand that evolution has armed us with many subconscious tools that help us survive. We are both genetically and culturally programmed to avoid certain foods and certain conditions often with physical expressions of disgust overlaying strong emotion.
The author tells us that disgust is the newest of 6 basic emotions and is an extension of fear. She is not sure if other animals share this emotion with us, but suggests perhaps elephants might. That idea is based on the fact that elephants have an awareness of their own mortality. Fear of mortality is a basic requirement of disgust.
Disgust helps protect us against rotting food at its simplest. Smells, mold and appearances of scabs can set off a disgust reaction. We avoid signs of spoiled food or ill living creatures. Many humans would react to someone vomiting by vomiting themselves. This could help purge some infection that got into some communal food.
Disgust has gone beyond what we eat and can include more of our environment. We detest strange things as we often fear them. This can be people of a lower class or of a different culture/race. This disgust has taught us to be wary of strangers. The author claims that disgust is the most egotistical emotion, by which I think she means we see ourselves as the standard for everything and the further someone is from our standard the more inferior and fearful they are.
Disgust is partly genetic, but a lot of it is cultural. The author gives many examples of what one culture loves that another is disgusted with. Cheeses that are considered delicacies in some cultures are repulsive in others. Disgust with some food can be counter productive and the author cites insects. With an overpopulated world insects could provide more nutrition more cost effectively than typical farm animals. Some cultures accept this idea, but most of us do not.
She makes some political observations. Liberals are primarily concerned with not hurting others and being fair. Conservatives give higher weight to purity, loyalty and respect. These traits are related to how disgust is felt and expressed.
Rachel contrasts disgust with empathy. Being empathetic means we identify with the other person. Studies show that women are more empathetic than men, but they are also more disgust oriented. In general familiarity deepens our understanding and acceptance of strange things.
Rachel has written another book inspired by our sense of smell, "The Scent of Desire" which I am putting on my list of books to read. We humans value sight, sound and touch more than smell, but in fact smell influences us and our animal cousins a great deal.
It is always worthwhile to better understand how our emotions affect us. Without a better understanding our emotions can take over our decisions. To learn more about Rachel's studies visit her website at http://www.rachelherz.com/