Colin Spencer does an excellent job of covering the last couple million years of vegetarianism. This book is not an easy read, especially in the sections about the diet of early man, and the analysis of some of the early Christian sects. You'll learn why mainstream society traditionally looks at vegetarians as "cranks" Puritanical, or just plain heretical. This is slowly beginning to change, but I think that in some areas of the world, (esp. where I live) vegetarians are still those weird outsiders who are thumbing their nose at the hallowed institution of eating meat. You'll also learn that early vegetarians weren't vegetarians for animal welfare reasons. For the Greeks like Plutarch or Pythagoras it was all about reincarnation (metempsychosis or transmigration of souls) For the early Christian sects eating meat was a symbol of man's Fall from grace. Some early Christian hermits also abstained from meat & alcohol because they thought consuming these didn't jive with the ascetic lifestyle; you had to deprive yourself of luxuries to become spiritually closer with your God.
My only quibble is that Spencer could've covered the last 100 years in more depth. The last 50 pages is surprisingly lacking in the same kind of detail that Spencer devoted to, (for instance) the Early Christian era. Maybe the last 100 years has been covered better in other books? I don't know, since this is the first book of its type that I've read.
OK, actually I have one other quibble.....In the last 20 pages, Spencer goes off on a rant about corporate farming, the effects of livestock farming on the environment, the dangers of eating meat (salmonella, heart disease, cancer). I thought this was a "history" of vegetarianism??? I mean, I agree with all the things he says about the above topics. I'm an ardent vegetarian myself, but I wish he had devoted more space to the last 100 years of vegetarianism, instead of the polemic.
Another thing to consider is tha Spencer goes go more in detail about vegetarianism in Europe and the UK. If you want a lengthier discussion on vegetarianism in the U.S try somewhere else. This is still an excellent book for a history of vegetarianism. I hope that other authors will take up this topic.