Science Interviews


Sun, 4th Nov 2012

Pre-Historic Dairy Cows - Planet Earth Online

Julie Dunne, University of Bristol

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Cows milk is a remarkable food – not only for drinking, but for cheese and butter, yoghurt and cream. So when did we first decide to use cows as walking larders to fulfil our nutritional needs?

Scientists from the University of Bristol have analysed pots found in, what is now, the Sahara Desert in Libya but – thousands of years ago – was verdant countryside.

By studying chemical residues found in these containers, they’ve discovered the first direct evidence that people in Africa were using cattle for milk more than 7000 years ago.

Planet Earth podcast presenter, Richard Hollingham, has been talking to archaeological scientist Julie Dunne, at the University’s farm in Somerset….

Julie -   Well, what we looked at was lipids in ceramics that were excavated from the rock shelter in the region and those lipids tell us that those people were using milk products and also animal fat products and processing them in their pots.

Richard -   And they were using this milk for what?

Julie -   Well it probably would have been making butter, cheese and yoghurt.  We could tell it was processed in the pots and the reason they would have probably processed it is because most humans are... well humans then were lactose intolerant, in other words they couldn't drink milk, they would have been quite ill, they would have had very unpleasant symptoms.  If you process milk that reduces a lot of the lactose content and they could have eaten it without becoming ill.

cow and zebraRichard -     These pots were from 7,000 years ago, so pre-history and in that time we've managed to evolve the ability to digest milk?

Julie -   Yes, it's quite remarkable. It's a very good example of selection in action. Around about 10,000 years ago when people started dairying and settled down living a farming lifestyle as opposed to being hunter gatherers nobody could tolerate milk.  But obviously the new technology comes in and there are these wonderful creatures called cows, they are walking larders and people obviously want a bit of this new technology. They're like an iPad of the ancient world and once you start processing these milk products and using them, within about a thousand years a gene evolves which allows people to tolerate milk so we've become lactose persistent.

Richard -   How do you know they were after the milk rather than milk as a by product, that milk was the key to this?

Julie -   We can identify whether they were processing either milk or the fats from the animal, the flesh of the animal in the pots.  When we did what we call lipid analysis, 50% of the pots showed evidence that milk was processed in them. So it was clearly important to these people.  Bear in mind that region, although it had been quite green and wet in the last ten thousand years it was beginning to dry up, and as cattle start to come into the area you are getting these periods of aridity.  Cattle are important because they're a source of liquid on the hoof as it were, so these people were moving around the landscape with their cattle and if there wasn't any water they would be able to get a drink from the cattle.

Richard -    So the cattle became much more valuable for producing milk than they did for meat or by products like skins or whatever?

Julie -   Yes, we think so, we think so. We think it's what we call the secondary products of the animal, the milk, the cheese, the butter, the yoghurts; those are the things that were much more important to ancient people rather than the actual flesh of the animal. Why would you kill something that is going to give you food every day?

Richard -   What sort of difference did this make to humans and human civilisation?

Julie -   The transition from becoming hunted gatherers to settling down - it enabled the development of much bigger communities and so on which eventually led to the establishment of things like city states and so on and so on and finally to where we are today.

Richard -   So this was happening in Africa - how did we end up here farming cows, drinking milk, making cheese, all this stuff?

Julie -   Yeah, we really do so a kind of different pattern emerging in Europe, so cattle were actually domesticated in Europe, we think, and they moved into Africa but they also moved with people the other way and spread out right across Europe and into Britain and Ireland finally getting here round about 4,000 BC, so six thousand years ago.  Pretty much across Europe people settled down, they became farmers and they started using milk and its products.

Richard -   So cattle turn out to be incredibly important for these prehistoric people and for the development of humans, and they're still important today?

Julie -    Absolutely, yes. These cattle were incredibly important to these ancient humans. For a start they created the most remarkable rock art which shows how much they clearly thought about and relied on their animals. They were clearly just as important then as they are today.



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I find it interesting that there could be such a widespread genetic adaptation to a single food. 

I looked up maps on lactose intolerance.  There are a few different maps on the internet.

What I would wonder is whether a large portion of the lactose intolerance is due to a lack of access to milk, and thus no reason to maintain the enzymes. 

So, a family that had access to cow's milk, or other milk products may not have the same issues.

Cheese & butter, of course, also gives us a variety of foods (which humans crave), but also a good way to preserve the milk. CliffordK, Tue, 6th Nov 2012

Lactose intolerance after weaning is normal in all mammalian species, perhaps to reduce energy consumption producing unnecessary lactase enzymes (as CliffordK suggests). It is believed that this was the normal condition in all early human populations, prior to the development of agriculture.

Lactose persistence is genetically dominant, and can be enabled by changing as little as a single DNA letter (a SNP: Single Nucleotide Polymorphism) in a promoter region for the Lactase enzyme; several independent mutations are known:

From the interview:

Re Terminology: You often hear this loosely expressed like "a gene evolves which allows people to digest milk" (or "for bacteria to digest citrate" in the case of the Lenski experiment). Both of these would involve the evolution of a large and complex enzyme (1927 amino acid units/5781 nucleotides, in the case of the lactase protein-coding region:

However, what we have here is a mutation which disables a regulatory function for an existing enzyme. This disabling can occur due to a point mutation, which is far more likely to occur in a short amount of time, compared to the evolution of a new enzyme.

I guess this confusion is propagated in the general media because when the reporter hears "a new gene", they cannot conceive (and hence cannot convey) the huge difference between "a new enzyme" and "a tweaked promoter for an existing enzyme", so the audience just assumes the former.   

It's important for science communicators to be clear about such differences. evan_au, Thu, 8th Nov 2012

I can imagine the benefits of lifelong milk and calcium consumption for the elderly (post child bearing years).

However, does milk consumption make that much of a difference for children and young adults?  How common is calcium deficiency Rickets (usually caused by Vitamin D deficiency)? 

I guess I'm having troubles imagining what could drive the selection process for a single enzyme (or enzyme regulation mechanism).  It is easy enough to avoid a "toxic" food.

Could cowpox have helped select for the persistence of the lactase enzyme?

I.E.  Those individuals with lactase persistence would have a higher likelihood to be dairy farmers, and could have naturally received resistance to smallpox.  And, thus natural selection for dairy farmers. CliffordK, Thu, 8th Nov 2012

Differences in height, weight and fractures were seen when genetics of lactase persistance were considered in a health study:

I wonder if another advantage would be in preserving the life of babies whose mothers had died or were too malnourished or thirsty to breastfeed? It's not a big conceptual jump from "I can't feed this baby milk" to "That cow has milk!".

I imagine such children would eventually stop drinking cows milk when lactase production declined, and they started to get an upset stomach.
However, a child with a lactase preservation mutation would happily continue to drink cows/goats/camel milk, even when other people in their tribe were suffering malnutrition or thirst. The fact that even one copy of the gene is very beneficial (ie it is a dominant gene) allows it to spread rapidly in a population.

I think that the biggest jump would be from "That cow has milk!" to "Ah, now I have the milk"! evan_au, Thu, 8th Nov 2012

I should have known there would be a wikipedia article.

So, this is likely more about preserving the ability of older children and adults to also drink the milk.

It is a good point that humans may have tried to milk goats, cows, camels, and other newly domesticated species to help save the lives of orphans, or children of mothers who had insufficient milk, especially as childbirth was very dangerous in the past. CliffordK, Thu, 8th Nov 2012

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