...and then there's always the point about it being unlikely that a human brain could have evolved without meat-eating ancestors.

Interesting point! Even if it's true, though (and sorry, I'm not intentionally doubting you - I just genuinely don't have the knowledge on this score), wouldn't that still leave the question of whether meat-eating is ethical NOW?

Also, I can well imagine that meat would have been required at earlier stages of our evolutionary development, not least because our ancestors wouldn't have had the access to the wide range of vegetables, fruits and grains that we have these days. Meat is undoubtedly a very concentrated source of all kinds of essential nutrients, so "back then" it was probably an excellent solution. But whether it would still have been essential if they'd had the array of alternatives we have today is perhaps another question.

I suspect I'm sounding more hardline on this question than I actually am - I occasionally eat meat and fish myself. But I do see vegetarianism as the preferable option, for the reasons I gave before. Even if most of us just made a point of eating less meat and avoiding buying the factory-farmed stuff, there'd be a big reduction in animal suffering and extravagant use of resources.

EDIT: OK, in the interests of scrupulous honesty, I have to acknowledge that there may be an element of post-rationalisation in what I've written: I do think vegetarianism is the more ethical option ... but that's not actually the reason I choose to eat veggie food most of the time: it's simply that I prefer it! And I also find having lumps of dead animal in my fridge rather nauseating.