This is a well researched book by Colin Spencer. For starters, I learned that primates came rather recently to meat eating. Of the 62 known genera of living primates, almost all eat fruits, vegetables, and nuts; most eat insects; but only a modest number eat birds, dead animals, or hunt small animals. Only humans hunt or breed large animals to eat. Our physiology, and especially our jaws, have evolved to accommodate cooked meat but not raw meat.
In the ancient and classical world, cruelty to animals seems to have peaked in Rome although cruelty to people (slaves and gladiators) might not have been far behind. It is interesting that among the very people who enjoyed watching man, as gladiator, combat wild beast, were some vegetarians. Perhaps future generations will say the same about contemporary pet-owners, some of whom are vegans. (See the questions in my previous post)
I was especially interested in the relationship between the biblical laws of clean and unclean animals (Kashruth) and vegetarianism. The most interesting thing is that carnivorous animals (tigers, lions, etc) were forbidden to eat. It is possible to unlink this from vegetarianism with the idea that if one animal eats an unclean animal, then one should not eat the first animal because it is derivatively unclean. In theory, there might have been a talmudic exception - though I am told there is no such thing - for a carnivorous animal observed over a long period of time only to have eaten clean animals. This seems unrealistic. Otherwise, I cannot see a connection between these religious dietary laws and vegetarianism, though I wish the author had devoted more space to this.
An interesting historical and geographical idea is that the available fuel seems to determine food consumption In Northern Europe there was plenty of wood in the middle ages, and this may have encouraged the roasting of meat. Near the Mediterranean there was more cooking of vegetables and fish (for obvious reasons) but also more cooking of doughs (think pizza) and there is a theory that this was encouraged by the ability to cook ousdoors, and year round. In the long run the vegetarian movement is associated with the rise of urban life. Animals must have been more costly to eat and, contrary to the sentiments of modern pet owners but in accord with how most farmers seem to feel, humans who live in close proximity to animals seem most comfortable in eating them.
Factory farming seems to have flourish in England as early as the 1680s. Slow killing and lots of blood seems to have been common.
Some believe that the term vegetarian was derived from the latin Vegetus meaning vigorous and lively. Spencer finds this implausible and writes that a "vegetarian seemed to signify someone passive and serene" from the earliest times. This seems to fit with the conventional claim that early vegetarians were Christian fundamentalists -- though not in India of course.
Vegetarianism became associated with animal welfare by the 1870s and did so because of objections to doctors in general and vivisection (where pain might have been apparent) in particular.
Why did vegetarianism flourish in England in the 19th century. Spencer thinks that it was a combination of fast growing cities, the yearning of urbanites for rural life, and the desire to protect what was left of it. Vegetarians became more numerous at the same time that schools began taking nature trips and cycling became a weekend hobby.