9 Nov 2015
Sara Pedersen
Job Title
The development of agriculture was a turning point in human history, and at the centre of this was the domestication of cattle.
The “secondary products revolution” realised the use of cattle not only for meat, hide and bones, but for other resources that could be harvested or used while cattle were still alive and included milk, power and manure. Whether harvesting milk was a consequence or casual factor in the domestication of cattle is still hotly debated among zooarchaeologists, but either way, evidence points to milk playing a pivotal role in ancient diets.
Unlike the modern dairy cow, primitive cattle breeds only produced milk in the presence of the calf, so once the calf was removed from the dam, she ceased production (Balasse, 2003). Therefore, it is unlikely milk was harvested in the early periods post-domestication, since breeds would not have produced sufficient milk to provide for more than the calf alone.
The study of mortality patterns (assessing cattle remains to determine age at slaughter) provided evidence as to the apparent shift in the use of cattle purely for meat to one where they were kept as part of a dairy enterprise. Assessment of the ratios of collagen and nitrogen isotopes in the dentine of molars also gave an indication as to whether animals were pre or post-weaned at the time of death, since these altered dependent on diet (Vigne and Helmer, 2007).
Weaning occurred at around six to nine months during the neolithic period (around 4,000 BC to 3,000 BC in Europe) and a spike in mortality at this age was consistent with the concept of “post-lactational slaughter”. Calves were slaughtered at the end of the summer season when they were no longer useful for milk exploitation so they didn’t have to be fed through the winter season.
This was a change from slaughter patterns previously seen, which had only shown a spike in mortality at two to four years that was associated with exploitation for meat (Vigne and Helmer, 2007).
The earliest evidence of milk forming part of ancient diets stems from evidence in the Fertile Crescent from 8,500 years ago (Evershed et al, 2008) and central Poland around 7,000 years ago (Salque et al, 2012). Sherds of pottery, which were dotted with tiny holes, were found in settlements that had been inhabited by some of Europe’s first farmers (Figure 1). Analysis of the fatty acid residues that had been preserved in the clay identified high levels of milk fat.
Thus, it was concluded the clay had been baked while pierced with pieces of straw to create vessels that acted as sieves to separate fatty milk solids from liquid whey during the cheesemaking process. This was the first step of the revolution; however, although dairy had become a component of neolithic diets, dairying was yet to play a prominent role in the economy.
Fermentation of milk to cheese or yoghurt was necessary during early civilisation to reduce the lactose content of the milk. At this time, unlike children, adults were unable to produce the lactase enzyme required to digest the lactose in milk – that is, they became lactose-intolerant or “lactase nonpersistent” around the age of six to eight due to the lactase enzyme “switching off”.
The second stage of the revolution came when a gene mutation occurred that meant adults were able to retain the ability to digest lactose – that is, the lactase enzyme persisted into adulthood. This trait has been linked to a single nucleotide in which the DNA base cytosine changed to thymine in a genomic region that was in close position to that of the lactase gene (Curry, 2013).
It is proposed this genetic mutation first occurred around 7,500 years ago in what is now Hungary. Residues on the lining of pottery vessels from this period were analysed; however, critically they differed from those found previously in the perforated vessels. Unlike the milk fat residues, these residues were mid-chain ketones, which are the product of lipid pyrolysis, suggesting dairy products had been heated instead of simply strained.
Neolithic people had therefore heated milk, either to drink alone or mix with other foods such as cereals. Since lactose sugar isn’t hydrolysed during the cooking or heating process, this means people at this time must have had the ability to digest milk and it provides evidence the mutation had reached those geographical areas at this point in time.
Once the now named lactase-persistent (LP) allele appeared, it created a major selective advantage in terms of survival (Itan et al, 2009). Studies estimate people who had the LP allele would have produced up to 19% more fertile offspring than those without it, leading to the conclusion this degree of selection was among the strongest of any gene in the genome (Bersaglieri et al, 2004).
The second stage of the revolution evolved slowly as the mutation spread slowly throughout the population. The Lactase Persistence and the Early Cultural History of Europe, or LeCHE, project run by University College London has been mapping the spread of the mutation and thus the movement of neolithic farmers from the Middle East across Europe. It is thought as Middle Eastern neolithic cultures migrated into Europe and moved north, they were able to displace the existing hunter-gatherer populations due to their advanced farming and herding technologies, thus the LP allele spread.
There is less evidence of the allele in southern parts of Europe since the mutation occurred after the formation of farming settlements in these areas. This could explain the pattern of lactose intolerance seen across the world today. In northern Europe more than 90% of adults are lactose tolerant, yet in southern Europe less than 40% of the population are able to digest milk (Figure 2).
By 5,000 years ago lactose tolerance was prevalent across the majority of northern and central Europe and dairy enterprises were common and, more importantly, playing a dominant role in the culture of these societies.
The reason why lactose tolerance provided settlers in northern Europe with an advantage over existing populations remains to be concluded. However, it is speculated milk would have provided a buffer against the risk of famine since dairy products lasted longer in colder climates and would have provided a rich source of energy throughout the year.
It is likely farmers brought crops native to their original regions in the Fertile Crescent with them as they migrated, such as wheat and barley. The shorter growing seasons in northern Europe would have made these crops more likely to fail, resulting in famine. Thus, during these times milk drinking would have increased and those able to digest milk would have been more likely to survive and pass on the LP allele.
It is also possible it may have provided an essential source of vitamin D in areas where sun exposure was limited during the winter months (Curry, 2003) and it is also speculated milk gave humans the advantage against malaria in Africa and southern Europe, and rickets in northern Europe.
Although as humans we haven’t always been able to drink milk and a large proportion of the world’s population is still unable to do so, it is clear milk played an important part in the shaping of early civilisation. While there still remain many gaps to fill in terms of why this mutation suddenly occurred and exactly what drove the first person to milk a cow, it is clear milk was the first superfood of its time and gave those able to drink it the edge in evolutionary terms.
