What are the main ideas in the book Peoplewatching: The Desmond Morris Guide to Body Language?

In the nonfiction book Peoplewatching: The Desmond Morris Guide to Body Language, the author promotes the concept of interpreting body language. A renowned zoologist, ethologist, and TV program host in England, Desmond Morris spent many years observing the behavior of people and animals.
One of the main ideas in the book is that people say just as much, if not more, with their body language as they do verbally. Morris posited that our body language is an essential component of our communication.
Another idea that Morris detailed in the book is the dependency of body language (e.g., gestures) to a specific culture. Meaning, body language is not an inherent trait or a part of our biological design, but is learned just like verbal and written language. For instance, eye contact is a sign of respect in Western culture, but it could mean the opposite in another culture. Likewise, a handshake is a formal greeting to an American, but bowing is the traditional way of greeting to a Japanese person.