Naked Science Forum
General Science => Question of the Week => Topic started by: thedoc on 11/01/2011 16:11:50
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Are humans the only animal to drink milk from other species?
Asked by Budi Prasetya
Find out more on our podcast page (http://www.thenakedscientists.com/HTML/podcasts/show/2011.01.09/)
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Diana - Most of us will have seen our pets and various garden wildlife taking advantage of a source of cow’s milk on occasion. But are we the only ones to drink it habitually?
Oliver - I'm Oliver Craig and I work at University of York in the Department of Archaeology.
In fact, we are – well at least, we are when we’re adults. All juvenile animals can drink milk and that's because they have the enzyme lactase to digest the milk sugars. But the genome that makes the enzyme gets switched off when they get to a certain age, so as adults, they can't drink it. Most humans in fact can't drink milk as adults and there’s only a very small fraction of the world’s population who can. What’s really interesting of course is that those people live in a very geographically restricted area, i.e., Northwest Europe and some parts of Africa. So it’s a really interesting question as to why only a certain part of the population can drink milk.
If you're lactose intolerant, you don't possess this enzyme lactase. So basically, the lactose that's in the milk doesn’t get digested. It’s a disaccharide and it passes straight through the gut and goes into the colon, and it can cause all sorts of unpleasantness, including what's generally quoted as some kind of explosive diarrhoea, and is a really, really nasty condition if you can't actually break these sugars down. But it also causes problems with water retention and all sorts of other problems as well. So really very ill, bad stomach and not actually been able to digest the sugar itself. So at some point in our history, it was a selective advantage for people in Northwest Europe at least to be able to drink milk.
Diana - But does being lactose intolerant really put you to selective disadvantage?
Oliver - Well, you wouldn’t have thought it would really, would you? It’s not going to impact on your daily life massively. It’s only going to be selective disadvantage if there’s a real advantage in being able to drink milk, fresh milk. It comes back to the question then, why is being able to drink milk such a selective advantage? The answer is that we really don't know and that's what we’re trying to research and find out. The first thing that we need to do is find out when or at what point in our history did that need to drink milk actually occur?
Diana - As far as we know, humans are the only animals to drink another species milk regularly, but only a small proportion of humans have the lactase enzyme. Cats and dogs are often seen taking delight in a serving of milk, though I’d rather not consider the consequences. An excellent find on our forum came from Jackass Penguin who cited the Red Billed Oxpecker, a bird that can perch on the udders of an Impala and drink its milk. Elsewhere, in Isla de Guadalupe, feral cats, seagulls, and sheathbills have been observed stealing the milk directly from the teats of elephant seals. So perhaps milk stealing does happen a little more than we currently know.
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I'd be interested to hear if there are any significant "in the wild" cross-species nursing, with no human intervention, and neither animal being domesticated.
There are some reports of it happening some in domestic animals, but perhaps only with human intervention.
Perhaps some opportunistic snakes or racoons, especially around domestic animals. But, I'd have to think it is rare, and may only happen with farm animals.
Most mothers are very protective of their milk, and will even have troubles adopting young of the same species.
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There are ants which "milk" aphids ... http://en.wikipedia.org/wiki/Aphid#Ant_mutualism, (but it's not really milk)
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Oxpeckers in Africa have been seen drinking milk off large mammals, such as impala ( http://img74.imageshack.us/img74/6184/img46041wt.jpg (http://img74.imageshack.us/img74/6184/img46041wt.jpg) )
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Gosh, that's amazing - though that looks like some kind of corvid (crow), which are notoriously cunning and clever, so if any animal was going to learn to exploit a ready resource, it had to be them!
I'm gobsmacked at this; a milk-thieving bird...
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I wonder if it should be named lacto-parasitism... I wouldn't be surprised either if some corvids found a way to exploit mammals in the same way but the bird in the photo is meant to be a red-billed oxpecker ( http://en.wikipedia.org/wiki/Red-billed_Oxpecker )
One wildlife film on tv once featured a footage of an oxpecker stealing milk from a giraffe or an eland but I can't remember the name of that film.
EDIT: seals have been victims of gulls and other sea birds according to this paper which actually focuses on ferals cats stealing milk from elephant seals http://www.mastozoologiamexicana.org/therya/num3/14_Gallo.pdf
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Interesting bird!
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Hedgehogs have been seen to take milk from domestic cows
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Actually it is now known that generally all human populations will produce lactase if milk products are introduced again into their diets. The previous understanding was based on population testing of areas where dairy was not normally part of the diet post infancy (North and SE Asia for example) however China is an excellent case in point where the population was previously thought to be genetically lactose intolerant but has now embraced the consumption of dairy products without any more lactose intolerance problems than any Northern European population...
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Lactase persistence is also typical in India.
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I was interested in the reasoning behind the same, but as soon as I read the author's range of knowledge regarding the geographical spread of humans drinking milk, got put off.
Seems the author has no clue about the same. I stay in India and it's a regular thing to drink milk across the subcontinent!
Safe to say, am not too trustworthy of the author's knowledge behind it all.
Sorry.
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He also mixes up gene and genome which is a fairly basic mistake to make...