Secondary Products Revolution: Milk, Wool and the Plough

The Secondary Products Revolution is a theory proposed by the British archaeologist Andrew Sherratt in 1981 to explain a major change in prehistoric farming. He argued that between about 4000 and 3000 BC, people in south-west Asia and Europe began to use domestic animals systematically for milk, wool and pulling power, not only for meat. The idea transformed debates about early economies, and decades of scientific research have since confirmed some parts of it and overturned others.

Background: the first farmers and their animals

Farming began in the Fertile Crescent of south-west Asia around 9500-8500 BC, during the Neolithic Revolution. Sheep and goats were domesticated by about 8500 BC, and cattle and pigs soon after. From there, farming spread into Anatolia, Europe, North Africa and beyond.

Early domestic animals were valuable mainly as “primary products”: meat, hides, bone and sinew, all of which require killing the animal. Sherratt contrasted these with “secondary products”, which can be harvested again and again from a living animal. The most important are milk, wool and hair, and traction, the use of animal strength to pull ploughs and vehicles or to carry loads.

Sherratt’s theory

Andrew Sherratt, of the Ashmolean Museum and the University of Oxford, set out his model in a chapter published in 1981 in Pattern of the Past, a volume in honour of the archaeologist David Clarke. He developed it further in later papers, especially in World Archaeology in 1983.

Sherratt argued that the systematic use of secondary products appeared together, as a “package”, in the fourth millennium BC. He linked it to several innovations that appear in the record around the same time: the ard plough pulled by oxen, wheeled wagons, woolly sheep, and new types of pottery that may have been used for milk and alcoholic drinks.

In his view the consequences were enormous. Ploughs allowed farmers to cultivate larger and heavier soils. Milk and wool made it possible to live from herds without killing them, encouraging pastoralism and the settlement of grasslands and marginal land. Wealth could now be stored in herds, which helped to create new forms of inequality, trade and mobility, including the spread of steppe herders across Eurasia.

The evidence for traction and the plough

Some of the strongest support for Sherratt’s model comes from evidence for animal traction. In northern and western Europe, archaeologists have found criss-cross scratch marks left by ards in old land surfaces preserved beneath burial mounds. Among the best known are those beneath the South Street long barrow near Avebury in England, dating to the mid-fourth millennium BC.

Wheeled vehicles appear in the same period. The Bronocice pot from southern Poland, made by the Funnelbeaker culture and dated to about 3600-3400 BC, bears one of the earliest known images of a four-wheeled wagon. Other early evidence includes wooden wheels and wheel tracks in northern Europe and pictographs from Uruk in Mesopotamia, discussed further in the article on the invention of the wheel.

Cattle bones also provide clues. Animals used for heavy pulling often develop characteristic changes in the joints of their feet. Such pathologies have been identified in fourth-millennium herds, although some researchers argue that cows were occasionally used for traction even earlier in the Neolithic.

Milk: an older story

The biggest challenge to Sherratt’s theory concerns milk. In 2008 a team led by the chemist Richard Evershed published analyses of fatty residues absorbed into ancient pottery. They found milk fats in vessels from north-western Anatolia dating to around 6500 BC, at least 2,500 years before the date Sherratt had proposed.

Later studies found dairy residues in early Neolithic pottery across Europe, from the Balkans to Britain, and in the central Sahara around 5000 BC. Ages at death of cattle, sheep and goats, worked out from their teeth and bones, also point in some cases to herds managed for milk from an early date.

Most adult humans at the time could not digest lactose, the sugar in fresh milk, because the genetic trait of lactase persistence was rare. Early farmers probably processed milk into cheese, yoghurt and butter, which contain much less lactose. Genetic research suggests that lactase persistence became common in Europe only in the Bronze Age or later.

Wool and textiles

Wild sheep have a coat of hair with a short woolly undercoat, and the first domestic sheep and goats were not woolly. Breeding sheep for long, fine wool was a gradual process. Evidence from Mesopotamian texts, animal bones and textile finds suggests that woolly sheep became important in south-west Asia during the fourth millennium BC, spreading into Europe over the following centuries.

Before wool, textiles were mostly made from plant fibres such as flax. The rise of wool production had important economic effects. In early Mesopotamian cities, wool became a major product of temple and palace economies and a key export.

How the theory looks today

Archaeologists today generally accept that Sherratt identified a real and important transformation, but not a single sudden revolution. Haskel Greenfield, in a review published in 2010, described the process as a series of changes that began at different times in different places. Milking began early, while traction, wheeled transport and wool became widespread mainly in the fourth millennium BC.

The concept remains widely used because it highlights how the relationship between people and animals changed after domestication. It also helps explain the expansion of pastoralism, long-distance movement and new forms of wealth in late prehistoric Eurasia.

Myths and facts

“Early farmers did not drink milk.” Chemical evidence shows that milk was being processed by around 6500 BC. What was rare was the ability of adults to digest fresh milk, so most milk was probably turned into cheese, yoghurt or butter.

“The plough arrived with the first farmers.” The earliest farmers in Europe and south-west Asia appear to have worked their fields mainly with digging sticks and hoes. Clear evidence for animal-drawn ards becomes common only around the fourth millennium BC.

“It was a single revolution.” Sherratt’s word “revolution” emphasised the size of the change, but the different secondary products were adopted at different times and speeds across a very large area.

By the numbers

Timeline

• c. 8500 BC: Sheep and goats domesticated in south-west Asia.
• c. 6500 BC: Milk fats in pottery from north-western Anatolia, the earliest known evidence of dairying.
• c. 5000 BC: Dairying attested in the central Sahara.
• c. 3600–3400 BC: The Bronocice pot shows an early image of a wagon.
• c. 3500 BC: Ard marks preserved under burial mounds in north-western Europe.
• 1981: Andrew Sherratt publishes “Plough and pastoralism”.
• 2008: Richard Evershed and colleagues publish evidence for milk use around 6500 BC.

Why it matters

The Secondary Products Revolution changed the way archaeologists think about early farming. It drew attention to milk, wool and animal power as drivers of social and economic change, and the debate it started has produced some of the most important scientific discoveries about prehistoric diets, herding and technology.