About two-thirds of the world's population is lactose intolerant. So although dairy products are a daily part of the diet for many living in Europe, Northern India and North America, drinking milk in adulthood was only possible from the Bronze Age, over the past 4500 years.
For most of human history, adults lost the ability to consume milk after infancy - and the same is true of people who are lactose-intolerant today. After weaning, people with lactose intolerance can no longer produce the enzyme lactase.
This is necessary to break down the lactose sugars in fresh milk into compounds that can be easily digested. People with lactose intolerance experience unpleasant symptoms, such as bloating, flatulence and diarrhoea, if they consume dairy products.
Ancient DNA analysis on human skeletons from prehistoric Europe places the earliest appearance of the gene lactase gene (LCT) - which keeps adults producing lactase - to 2500BC. But there is plenty of evidence from the Neolithic period (around 6000-2500BC in Europe) that milk was being consumed.
This is not totally surprising though, as the Neolithic marks the start of farming in most regions of Europe - and the first time humans lived closely alongside animals. And although they were unable to digest milk, we know Neolithic populations were processing milk into substances they could consume.
Archaeological evidence
Using a technique called "lipid analysis", sherds of ancient pottery can be analysed and the fats which have been absorbed into the clay identified. This allows archaeologists to find out what was cooked or processed inside the pots.
Although it is not yet possible to identify the species of animal, dairy fats can be distinguished.
It is also challenging to determine what techniques were being used to make dairy products safe to consume, with many potential options.
Fermenting milk, for example, breaks down the lactose sugar into lactic acid. Cheese is low in lactose because it involves separating curd (from which cheese is made) from whey, in which the majority of the lactose sugars remain.
Clay sieves from Poland, similar to modern cheese sieves, have been found to have dairy lipids preserved in the pores of clay, suggesting they were being used to separate curds from the whey.
Whether the curds were then consumed or attempts made to preserve them by pressing into a harder cheese is unknown. Fermentation of milk was also possible for our ancestors, but harder to explore with the techniques now available.
Early cheesemaking
Though bioarchaeology techniques have provided this fantastic detail on Neolithic diets, where the science stops, experimental archaeology can explore what was possible.
We have been making cheese using the utensils, plants and techniques available to Neolithic farmers. The aim of the experiments is not to faithfully recreate early cheeses, but to begin to capture some of the decisions available to early cheesemakers - and the experiments have thrown up some interesting results.
By using these ancient techniques, we have discovered that a wealth of different means of curdling the milk would have been possible, each producing different forms, tastes and amounts of cheese.
Such specialist knowledge may have been akin to the spread of bronze smelting at the end of the Neolithic.
Dairy may have had a special status among foodstuffs. For example, at the major late Neolithic feasting site of Durrington Walls, not far from and contemporary with Stonehenge, dairy residues were found in a particular kind of pottery vessel and concentrated in the area around a timber circle - a form of Late Neolithic monument.
From the Bronze Age, lactase persistence offered an advantage to some people who were able to pass this on to their offspring. It also seems that this advantage was not solely because of increased calorie and nutrient intake alone - but because of the special status dairy foods may have had.
The development of this biological adaption to fresh milk took place after humans had found ways to safely include dairy products in the diet.
This shows humans are not only able to manipulate their food to make it edible, but that what we consume can also lead to new adaptations in our biology.
• Penny Bickle, Lecturer in Archaeology, University of York
- This article was originally published on The Conversation. Read the original article.
