As a fellow environmentalist, animal-protection advocate and longtime vegetarian, I could properly be in the same camp as Emma Marris on the issue of zoos.

Environmental vegetarians call for a reduction of First World consumption of meat, but not the elimination of it, while at the same time campaigning for greener agricultural practices.

What if we decided on a vegetarian, rather than vegan diet? After all, milk and eggs are very efficient ways of producing animal calories, second only to factory-reared broiler chickens.