Lactose intolerance is the inability to digest milk and dairy products from cows, goats and other non-human animals. Lactose intolerance definitely exists (duh), but I have 2 specific problems with conventional wisdom about it.
1) Humans are the only animal that drink another animal's milk
Wrong. Cats do too.
Okay, cats are not setting up industrial farming to obtain dairy products for their own black market. But they will drink it if you give them some, and cats have been drinking cow's milk - via humans - for centuries (or possibly millennia, given the Egyptians' love of cats).
I did a quick search for "should cats drink milk", and the internet overwhelmingly says NO, you shouldn't give cats milk, because they are lactose intolerant. But this argument seems incomplete and/or circular. Cats will drink milk because they like it, often very happily. I haven't heard of cats complaining about being given milk because they know it'll give them catty diarrhoea.
Dairy has never been available to cats in the wild (apart from maybe the odd feline-fetishist cow). Meanwhile, cats have a very careful sense of smell and taste, and human breeding hasn't managed to get rid of what evolution has given them. Perhaps humans breeding domestic cats encouraged a taste and/or tolerance in cats for cow's milk? I'm not so sure about that.
So - if milk gives cats mild or strong indigestion, they may be physically lactose intolerant. But if they like drinking it, and keep coming back even after having bad catty poos, is it right to classify them as lactose intolerant?
Of course dogs will drink milk too, but dogs will eat anything that's put in front of them and have no class whatsoever.
2) Asian people are lactose intolerant
No they're not, or at least no-one told Asian people (i.e. China/Far East/Oriental Asia - not British "Asia", the Indian subcontinent).
In Bangkok last month I was struck by the existence of dairy products in supermarkets and 7-11s, such as flavoured milk drinks and cheese.
Yet a figure that I keep hearing in conversation is that "95% of Asian people are lactose intolerant". It's one of many loose statistics people throw around, and people often make assumptions which don't reflect a more complicated picture, even if the statistic or "fact" is true.
The rough historical view is that during the development of agriculture, some European communities "broke" our programming on digesting cow's milk, and this gene played a key role in survival. I'm sure this is correct, although I do wonder why all the myriad Asian peoples failed to develop it when they also developed agriculture and had herd animals.
I asked a guy working at my Bangkok guest house if he drank milk, and what he thought about dairy products in Asia. His reply struck me as pretty wise: "It's a treat for the rich". Certainly this would fit with industry reports on the web which complain about the slow growth of dairy sales in Asia, yet also confirm its established presence there.
I can't confirm this myself but I'm quite confident there's a similar range and quantity of dairy products in the fancy supermarkets and 7-11s of other Asian countries too. I'd also happily assume there are more dairy products in urban parts of more developed Asian countries, e.g. Japan, China, Korea, than countries like Laos, Vietnam, Cambodia etc.
So the picture is confused. Yes, most Asian people probably do have problems digesting cow's milk/cheese/etc., and diary products are still seen as an expensive treat out of reach - and foreign in culture - to most poor and rural Asian people.
But that would mean that only a majority of a majority of Asian people can't and don't eat dairy products. Does that account for "95%"? What about foreign genes? Are these dairy-eating Asian people all mixed-race descendants, getting their lactose-friendly genes from white parents and grandparents? It's surely a factor, but I'd find it hard to account for all of that last "5%".
I also wonder about the specifics of lactose-intolerant genes and if they are fixed or flexible. In China's rapid development over the last 20 years, I bet dairy consumption has rocketed, reflecting an equally huge increase in lactose tolerance. But is it possible for 2 lactose intolerant parents to give birth to a lactose tolerant child? Can an individual "break" their lactose intolerance, either as a young person or gradually over their life? Or are they all just newly-middle-class Chinese people eating cheese, having stomach issues, and just not caring?
It's only the last 10-15 years that even the idea of lactose intolerance has become mainstream, certainly in the UK, and it's still not fully accepted as an actual condition. This probably explains a possible fuzzy logic around it.
The history of animals eating other animals' milk is a fascinating picture, and full of complex stories both small and big. It's always tempting to use broad strokes and colours to describe what you don't know, such as "humans are the only animal to drink another animal's milk" - but all you need to do is say "cats", and the entire point changes fundamentally, even if the original statement is almost entirely true. "Almost" is not "actually".
Sorry for the unscientific, unsourced nature of this blog post - I'm lazy and can't be bothered to find and make links. Mostly this blog is me asking questions, because I don't have the answers. But it's also about asking you, dear reader, to ask questions too. I think you can easily question simplistic conversational "facts", which are often taken for granted, with just a little logic and objective thinking. (And perhaps Snopes and Hoaxslayer.) Of course, for answers, there's no substitute for science and evidence.