Man is not the only animal to drink other species’ milk. It is however the only one to discuss whether this is healthy or appropriate.
Before I start – I am not trying to argue in this post whether or not milk is good for you. My personal view is that it is good for you unless you are lactose intolerant, but I respect that other people have other views on this topic, and I am not trying to convince them otherwise.
What I want to achieve in this post though is to address three arguments that are commonly brought forward by the opponents of milk, and that, I will argue here, are – even though (partially) true – not relevant in this context. Those arguments are the following
- Humans have only herded for x-thousands of years which, in evolutionary terms, is not enough time to adapt
- We are the only species that drinks other animals’ milk
- We are the only species that drinks milk after childhood
Humans have only herded for x-thousands of years
Adapting to drink milk is not like growing a third leg. All children can tolerate milk and afaik most of them can even tolerate the milk of other species. Not losing a certain capability that every child has in adulthood seems to me to be a rather small step.
Add to this to the fact that in a herding community with limited supply of food the ability to be able to efficiently digest milk is a big advantage: When times are tough those that can rely on milk will prosper, grow big, become kings, and have 10 wives and 100 children – you get the picture.
Ultimately, the proof is in the pudding: descendants of herders have adapted to drinking milk, ie they remain lactose tolerant throughout their lives.
We are the only species that drinks other animals’ milk
That’s true (well, it isn’t quite, more of this below) but we are also the only species that eats with knife and fork, and who get their water from the tap rather than from the watering hole amongst other things. My non-flippant underlying point is that this argument confuses skill with metabolic ability. Of course no other species drinks other animals’ milk – how would a wolf ever get to the milk of a cow for example? And given that they can’t get it in the first place, the fact that they don’t drink it does not allow any conclusion as to whether they are metabolically able to digest it or not.
In fact there are species that – when given access to it – love other species milk. Just check any children’s book with cats (I got lots of those at home…): most of them will feature a saucer of milk, as milk is what cats eat – every child knows that :-).
We are the only species that drinks milk after childhood
This is again probably true (apart from the aforementioned cats of course). But there are good reasons for it other than the metabolic ability and health of the consumer of the milk.
As every mother will tell you, producing milk is incredibly hard on the body, so there is a trade-off between the hardship for the mother (and the risk that due to this hardship she will be less able to care for the child) and the nutritional benefit for the child. Also, it is very inefficient from a caloric point of view, so with limited food resources available it makes sense to not waste them by feeding the children via the mother. Finally, children are designed to outlive their parents so at one point they will obviously have to live without their mothers milk in any case.
Putting all of this together this means that there is some optimal point (from a systemic point of view, not necessarily from a metabolic point of view of the individual) where the child should go off milk, and at this point the body might lose the capability to digest milk as it is no longer needed.
This changes however with the ascent of herding: it does not really matter if it is hard on the cows – you simply replace them. Therefore herders can have access to milk throughout their lives, and many of them have indeed adapted to do so.