C.1     Introduction

Questions concerning how livestock were used have been complicated by the issue of lactose intolerance in adults.  Meat and blood (mainly protein and iron, with some fat content) and secondary products are all valuable uses of livestock, but today their main value to pastoralists lies in milk.  Milk products can be consumed, stored, exchanged and used to provide essential parts of the diet like iron, vitamin C and vitamin D that would have to be obtained elsewhere if not consumed in milk.  Lactose is a major component of milk.  Up until weaning, children have an enzyme called lactase, which breaks down lactose in milk, but this is biologically switched off after weaning.  After weaning humans become intolerant of milk, which can cause various unpleasant symptoms when unmodified milk is introduced into the stomach, rarely sufficiently serious to be life-threatening on their own, but potentially leading to dehydration and hunger, which may be sufficient to kill weakened or sick individuals in marginal environments.

If pastoralists were incapable of consuming milk products, there is a major question mark over why they adopted livestock at all.  If they were able to consume milk products, the spread of pastoralism throughout the eastern Sahara is easily explained by the combination of storage on the hoof and the ability to remain mobile that herds conferred upon human groups.

The question of lactose intolerance is critical to an understanding of how livestock was used in early pastoral communities.

C.2     The Value of Milk to Humans

Milk contains fat, proteins, minerals (of which calcium is the most important), vitamins (particularly vitamin C) and carbohydrates in the form of the milk sugar lactose (Mulville et al 2005, p.2).  Mulville puts particular emphasis on the value of fat, saying that “In economically marginal areas, the full exploitation of available fat resources may make the difference between the viability of that society and situation.”  Lactose promotes calcium by the production of lactase, without which there is the danger of osteoporosis and rickets.  Without milk, all of these components would have to be secured elsewhere on a regular and ongoing basis (Outram and Mulville 2005) as soon as a child is weaned.   Today more calories are obtained from milk than meat in pastoral societies (FAO 2001) and the Maasai obtain up to 64% of their dietary energy from milk (Ryan 2002, p.99).  Other benefits derived from a protein called lactoferrin, which plays a role in the absorption of iron, and also has antioxidant and anti-carcinogenic effects, whilst peptides from another protein called casein are thought to influence the behaviour of immune cells and restrict the impact of harmful bacteria (Geddes 2015, p.37).

The following table, from Degen (2007, p.10, Table 2) provides the relative values of sheep, goat and cattle milk:

Species	Fat %	Protein%	Lactose %	Solids %
Sheep	6 – 8.5	5.5 – 6.5	3.9 – 4.7	16.0 – 20.0
Goat	3.4 – 4.5	2.8 – 3.7	3.9 – 4.8	11.5 – 13.5
Cattle	3.4 – 5.5	3.3 – 4.0	4.6 – 4.9	12.3 – 14.5

Table C1 – Relative values of milk

Milk is not only of value in its untreated, soured and fermented forms.  It can also be made into dairy products including butter, yogurt, ghee and hard curd cheese. Cheese is generally only made when there is a milk surplus during the rainy season, and hard cheese can be kept for over a year (Smith, S.E. 1980, p.470).  In these forms it can be stored, shared, distributed and exchanged.  There is no need to slaughter the animal in order to obtain these benefits, meaning that the livestock are an ongoing investment, a machine that turns cellulose that is indigestible by humans into a continual and renewable supply of nutrition.

There are two mechanisms by which milk can be digested by humans.  The first is by treating the milk to make it digestible.  The second is by the spread of a genetic mutation that allows for the persistence of lactase production into adulthood.

C.3     Milk Consumption by Lactose Intolerant Humans

There are two strategies for consumption of lactose by humans who are lactose intolerant:   Consumption of small quantities or modification of the milk itself to make it more digestible, and the conversion of milk into other products.

Some lactose intolerant people report that they can consume milk without side-effects if they drink little amounts spread out over the day, and this is supported by research that demonstrates that genuinely lactose intolerant people can consume up to 240ml at a time, and perhaps twice this quantity if consumption is spread over the course of a day (Geddes 2015, p.35).

However, the most common solution is to process the milk into other forms.  This depends on bacterial action.  The bacteria feed on the lactose, which helps to reduce its content in the milk (Outram and Mulville 2005).  Three principal mechanisms are employed: separation, souring and fermentation.

Cattle dairy products created to reduce lactose may include hard whey cheese, butter, ghee, which contains no lactose, sour milk, yogurt and fermented milk, which tastes a little like yogurt.  It should be noted, however, that the lactose in goat and sheep milk contains similar levels in cheese and yogurt as it does in milk (Geddes 2015, p.35).  Finally, goat milk has lower concentrations of lactose than cow milk and may have been used to supplement cow milk.

Today, the most usual form of milk consumption is sour milk.  The milk is placed into smoked pot and left in a warm place to sour.  Butter is made by various churning techniques, but a common form is to place the milk into an inverted goat skin, which is suspended and rocked until butter granules are produced, which are drained or scooped out.  This leaves buttermilk which can be consumed or turned into white cheese curds by being placed in a pot and heated gently for 10 minutes until it separates into curds and whey.  Over a period of up to 30 days the liquid is poured off and the curds are kneaded with salt before being formed into balls and dried.  Ghee is of particular value as it has no lactose content and can be stored without refrigeration.  In the Middle East butter is heated gently and stirred continually in a pot to which salt is added first, then water is added and then crushed barley.  Over 20 minutes later the butter separates out as a clear yellow liquid.  It is filtered into a container and the liquid solidifies out as storable ghee.  The barley, swollen with water, is then usually eaten. (Degen 2007, p.10-11).

C.4     Lactase Persistence

The enzyme that breaks down lactose is called lactase, which works by breaking down the sugars in lactose into glucose and galactose.  But following weaning, the genetic programme of the human body decides that the enzyme is now longer required and switches it off (Check 2006, p.994).  However, amongst some geographical areas, groups and individuals there is a condition called “lactase persistence” where the lactase function is not switched off, and lactase continues to be produced in adults, enabling them to digest milk.

In two papers the team of Sarah Tishkoff has identified several different genetic mutations that have allowed for lactase persistence in African populations (Tishkoff et al 2007 and Ranciaro et al 2014).  In the first sample DNA was collected from 43 ethnic groups in three African countries, and in the second, 819 samples were collected from 63 populations, whilst 54 samples were obtained from outside Africa for comparative purposes.  The combined results of the studies demonstrated that the mutations spread very quickly. In the Tanzanian sample it had spread between 3000 and 7000 years ago (Tishkoff et al 2007).  From the second study, the team were able to chart the spread of the mutation across Africa, and found that the history of the mutations corresponds to the beginning of livestock domestication and, in particular, to the spread of the mutation from the Middle East at c.12,300-5000 years ago into northern Africa, which in turn corresponds to the spread of domesticated livestock in the same direction.  Intermingling of populations allowed the mutation to be spread, and a second wave of its evolution corresponds to the spread of pastoralism to eastern Africa between 6800 and 2700 years ago (Ranciaro et al 2014).

Some individuals may be able to consume lactose without ill-effect even without the genetic mutation. Ranciaro et al 2014 give the example of some members of the hunting and gathering Hadza of Tanzania.

C.5     The Ecology of Pastoral Milk Production

Milk is produced following the production of offspring so that the mother can feed her child, so the availability of milk depends on regular production of calves, lambs and kids.  Humans are therefore in a position where they share the milk production with the offspring of their livestock.  In the Middle East the Assawi fat-tailed sheep usually lactates for around 250 days, during which lamb is fed for 100 days and the ewe is milked for 150.

Sheep and goat tend to be more tolerant of arid conditions and diseases, with goat better adapted to aridity than sheep.  However, whereas goats generally produce more milk and have a longer lactation period than sheep, sheep milk has a higher fat and total solids content than goat milk (Linseele 2010).  In the present day Negev desert of Israel, eastern Sinai and in the Jejaz of Saudi, the Bedouin goat is adapted to requiring water only every 2-4 days, and although efforts are made to ensure daily watering during lactation this is not always necessary (Degen 2007, p.9).  Goat is probably the most viable of the three species for arid conditions (Degen 2007, p.9) although a diversified livestock holding will have ensured greater insurance against loss in the form of disease.

Conception and birth usually take place in rainy seasons (Dahl and Hjort 1976, p.142-146). In marginal dryland environments cattle can only breed during one part of the year and may lactate for up to 8 months in very favourable conditions but only 3-4 when conditions are unfavourable (Dahl and Hjort 1976, p.142).   The rate and volume of lactation are influenced by the nutrition and water available (Ryan 2002) so the fat and protein value of milk is lower in the dry season, when pasture and water are low, than in the wet season when they are readily available (Degen 2007; Linseele 2010).

Guletat’s research into the Himba, Herero and Demara groups of northwest Namibia, in an area of 100-200mm average rainfall per annum, found that individual cows produced an average of 1.3 litres of milk per day during the dry season and an average of 4.8 litres a day during the wet season.  Goat, by contrast, produce an average only 0.24 litres per day during the dry season and 0.68 per day during the wet season (Guletat 2002, p.44).  Goats are milked during droughts and when no cows are owned, but cows are seen as the principal source of dairy (Degen 2007, p.12).  Degen noted that each household consisted of c.7.9 individuals and that each household had, on average 213 heads of livestock, of which 73% were goat, 18% cattle and 6% sheep.

C.6     Archaeological indicators of milk consumption

The earliest clear evidence for milking in Egypt is the tomb of Hor-Aha, the second king of the First Dynasty (c.3050 – 2890BC), where funerary vessels were subjected to chemical analysis and suggested that the contents was cheese, which was confirmed by the hieroglyphic inscriptions (Simoons 1971).  There is  earlier evidence from residues in pottery sherds in Libya that at least half of the fats in 29 of the 81 residue samples were from dairy, dating to 6000-3000BC (Dunne et al 2012).  Rock art shows cows being milked (Le Quellec 2001), although the dating remains controversial.

Evershed et al 2008 have demonstrated that milk-based dairy products, as opposed to other animal fat products, were in use by the seventh millennium BC, albeit with marked regional differences in the onset of milk consumption at this time (Evershed et al 2008, p.530).  In Egypt the earliest evidence for milking is at Saqqara, where residues were found in vessels dating to around 3000BC, but there are earlier examples elsewhere in the eastern Sahara.  Although there are images of milking captured in Saharan rock art, dating these is difficult (di Lernia, and Gallinario 2010).  Animal bone remains preserve few indications of how cattle were used (Dunne et al 2012, p.390) however there are positive identifications of dairy residues in prehistoric pottery vessels in the Sahara, (Dunne et al 2012) and low numbers of cattle bones at eastern Saharan sites suggests that cattle were kept either in very low numbers or primarily for purposes other than meat consumption.  Goat and/or sheep tend to be found in higher numbers and could therefore have been used for both purposes.  Most telling is that potsherds from the Takarkori rock shelter in southwest Libya, produces evidence for “extensive processing of dairy products” during the Middle Pastoral Period (5200-3800 BC), (Dunne et al 2012, p.394).

C.7     Conclusions

Although Linseele considered it doubtful that the earliest pastoralists considered milk to be an important staple and that the milk yield of early domesticates did not exceed that of wild herbivores (Linseele 2010, p.59) it has been shown that milk had a high potential value to early food producers.  The presence of milk in prehistoric contexts in the Near East from the 7^th Millennium BC and from the southwest Libyan Sahara from the 4^th Millennium BC supports the proposal that milk was a significant source of nutrition for pastoralists.  It seems plausible that a) they made use of milk products even if they were lactose intolerant by means of modifying milk into lactose-reduced products and that b) over time individuals, groups and communities may have been recipients of the mutated gene by which they acquired lactase persistence from the time of the introduction of the first domesticates that were brought from the Near East.  In the long term, lactase persistence would have made dairy farming viable and sustainable throughout later prehistory and into historic times.