Planet Earth Online

Biting off more than we can chew

6 November 2008

The beginning of agriculture was one of the biggest changes in the relationship between people and the environment. Prehistoric human populations independently domesticated different animals and plants in several parts of the world, but more intensive use of plants and animals became established in the Middle East around 12,000 years ago. This led to the world's first farmers.

Before the origins of agriculture, highly mobile hunter-gatherers had migrated to almost all inhabitable regions of the planet. Their diets were based on a broad range of locally-available plants and animals, and their physiques were adapted to local conditions (see 'Skeleton key', Planet Earth 2006).

The transition to agriculture, wherever it occurred, involved the shift from diverse diets based on a variety of wild animals and plants, to relying on one or a few agricultural 'superfoods'. Among the most important of these were wheat in the Levant, rice in Eastern Asia and maize in parts of the New World.

Agricultural plants produce much more food per acre than hunting and gathering. The primary advantage of this to our ancestors was they could store surpluses. The productivity and stability of agricultural resources led to dramatic population increases. With agricultural food surpluses, mothers were able to have children more frequently, and children were more likely to survive through childhood.

Another advantage of agriculture was that not everyone needed to be involved in food production, which allowed for greater specialisation in certain tasks and runaway technological and economic development. This marked another major change in the relationship between humans and the environment.

An agricultural error?

As the basis for the primary socio-economic system in the world today, agriculture is responsible for the growth of the world's human population to more than six billion. It is also responsible for advancing and proliferating technology because it frees up people to specialise in different crafts and trades. All of this would seem to imply that agricultural development was a beneficial breakthrough for our species.

How can we tell if this is the case? One way is by examining the skeletons that our ancestors left behind. Hundreds of thousands of human skeletons have been excavated from archaeological sites and are held in museums and research institutions around the world.

Each of these skeletons contains valuable information which tells us about how people lived in the past, and the relationship between changing environments and human health and behaviour. Several researchers have used the archaeological record of human skeletons to measure how agriculture affected people in the past. In most areas where these studies have been conducted, the results show evidence for a deterioration of human health with agriculture.

The main reason for this seems to be that most agricultural crops lack certain essential nutrients, and overdependence on these resources results in nutritional deficiencies. But these negative effects on health would have also been compounded by additional factors: humans were living in closer contact with animals, exposing them to a wide variety of new diseases; and they were living in more permanent villages. The accumulation of waste nearby leads to poor hygiene.

The woes of farming

With these factors in mind, it is not surprising that researchers have commonly noted an increase in skeletal indicators of stress and disease following the beginning of agriculture in different parts of the world. The author Jared Diamond has argued that as well as harming peoples' health, agriculture ultimately led to major disparities in human technology, social stratification, and human exploitation to the extent that it could be considered 'the worst mistake in human history'.

The view that the origin of agriculture was bad for human health has been widely supported by archaeological evidence. But one of the limitations of this work is that the majority of studies focus on the dichotomy between preagricultural hunter-gatherers and early agricultural or neolithic societies. When research is driven by such a dichotomy, looking at the health of people before and after they adopted agriculture, the results are bound to be dichotomous. What then becomes impressive is the near universality of evidence for a decline in health, rather than the subtleties of changes in health over time.

While we can blame deteriorating human health as hunter-gatherers turn to agriculture on nutritional deficiencies and the conditions of the first agricultural villages, the deterioration of health is more difficult to square with the conditions we see today.

In contemporary society, economics are the biggest determinant of the health of a population: those populations rich enough to buffer themselves from environmental stress are healthier than those without. So how did we get from the poor health of early agricultural villages to the more consistently healthy populations of today?

Egyptian evidence

The populations of ancient Egypt and the Nile valley are an excellent place to look for evidence of long-term changes in human health. There is a wonderful archaeological record of human skeletons in this region spanning the last 15,000 years, from hunting and gathering groups through the dynasties of the ancient Egyptian civilisation. My recent research with Anne Starling of Duke University, North Carolina, investigated changes in health over 10,000 years in the Nile Valley.

We studied evidence of periodic disturbances in the formation of tooth enamel, called Linear Enamel Hypoplasia, or LEH, a consistent and well-understood indicator of prehistoric health. These defects of enamel development occur in times of severe illness or malnutrition during childhood and lead to horizontal bands of thinner enamel running across the teeth (see picture).

Hunter-gatherers that lived in the region around 12,000 BC had low frequencies of LEH, appearing in around six per cent of teeth. The earliest farmers in the Nile Valley, about 5000 BC, had frequencies of LEH 2.5 times higher than the hunter gatherers, reflecting how health worsened with the transition to agriculture in the region.

Most interestingly, however, the frequencies of LEH dropped in the Early and Late Dynastic periods of the Egyptian Empire, from 3100 BC to 1500 BC, when frequencies were even lower than the early hunter-gatherers. This suggests that the development of the Egyptian state, and related improvement in the distribution of resources, improved human health over the long term.

The evidence we discovered demonstrates how we can use skeletal remains to explore long term trends in the relationship between human health, behaviour and the environment. It also provides the first systematic evidence that socio-economic development, trade, and infrastructure can balance the physiological stress and disease associated with the initial transition to agriculture.

Lessons learned from the archaeological past are relevant today. In our present society, we are committed to an agricultural strategy by necessity of our population size. While agriculture has not brought health and prosperity to everyone, what matters most is how we choose to manage and distribute the natural, agricultural and economic resources that we have.

Keywords: Africa, Environmental change, Geology, Natural resources,

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