The Definitive Book of Body Language by Allan Pease, Barbara Pease (2006, Hardcover)

First off, when reading this book, one should be aware that just because the title says it's "the definitive book" doesn't make it so.
I could write a book called "Upton Sinclair's The Jungle", and it would not make me Upton Sinclare.
Pease is above all, a salesman, and the things he says regarding sales and the body language involved therin is very sound. This is probably why he spends an inordinate amount of time discussing things such as the psychology of the hand shake. That is not to say the rest of it is rubbish. In fact, much of the rest of the book is pretty accurate as far as how to interpret what you see.
Unfortunately, Pease also thinks he should for some reason explain why these gestures and postures came to be. Here, he mixes a bunch of pop paychology (mid 70's versions, such as expoused by Desmond Morris to better effect) and wild guesses.
This leads to some pretty hilarious results.
Pease is well aware of his critics, and that competing explanations are out there, which is most likely why he tried to sieze the high ground by calling his own work "definitive"
He attempts to answer many of his critics in absentia, by putting forth their arguements in his own words, and then answering them.
An example used throuout the book is whenever someone suggests that they feel more comfortable in one position or another,(for example, arms folded) he dismisses it with the arguement "of course you feel more comfortable with your arms folded when you are defensive." and then throuout the book, extends this logic to every argument he imagines.
Pease wants to describe every behavior as attributable to some facet of human evolution, again with ludichris results. For example, he cites security guards rocking up on their toes to "try to look taller" when in fact, as he evidently did not notice, they most often bend their knees slightly when rocking, which actually makes them shorter. More likely? their feet hurt.
Also, straight from the beginning, Pease has difficulty distinguishing body language from sign language. The difference, of course, is that body language is a universal, unconcious language, where as sign language, is well, a language. He then uses supposed American ignorance of other countries local use of sign langusge to belittle Americans. This in itself is a popular cause among the elitist movements in this countries, and Pease seems to enjoy putting Americans down at every chance, whether deserved or not. ( I am not saying that many Americans are not jerks, but believe me, the rest of the world has just as many, or more.) As an example, Pease likes to point out that many hand signs Americans use are taken quite differently in different parts of the world. If there is a misunderstanding, well, then, its the uncultured, untravelled American that is at fault.
Throuout the first half of the book, he argues the point that every nuance of body language has resulted from years of evolution, and tries to tie it in with specific reasons, however tenuous and convoluted. However, this becomes downright risible as he tries to explain how the size of a briefcase equates to the status of the carrier.
However, he fails, in my opinion, to prove that mankind evolved with their briefcases, and if they did, what survival benefits they imparted upon their bearers.
I could go on and on, but I have wasted too much time already on this subject.
Suffice to say, its not a bad guide, but it's not definitive, either.