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Milk may have been a key ingredient to the rise of civilizations. New research by a team of archaeologists and biologists from the University College Dublin has discovered that the ability to digest milk into adulthood developed much later in human populations than previously thought. People had mastered the domestication of animals and even the processing of cheese and yogurt by 7,500 years ago. However, lactose tolerance was not a regular part of the human genome until 3,000 years ago. The timing indicates that rather than exposure to dairy creating lactose tolerance, a change in genes brought about the growth of cities and civilizations.
A new breakthrough in paleo-genetics has allowed scientists to study the DNA of 13 individuals found on the Great Hungarian Plain of central Europe. The human remains span 5,000 years and date from between 5,700 BCE and 800 BCE. The Great Hungarian Plain was a crossroads between the east and the west with many cultures and peoples passing through. The individuals range from the stone age through the copper age, bronze age and early iron age so researchers can examine human DNA from a variety of times, ethnicities and technologies. Extracting and isolating human DNA from ancient skeletons is a new procedure. Just a decade ago mapping the human genome took years and millions of dollars. Now, with a good DNA specimen, it takes just days and a fraction of that cost. However, most ancient DNA is degraded or corrupted, especially if the remains were exposed to water. At times scientists find as little as zero to 20 percent of the DNA sampled is actually human. Then scientists began looking at the petrous bone. It is an extremely dense bone near the base of the skull with the purpose of protecting the delicate inner ear. In fact, the word petrous comes from the latin word for stone because the bone is so hard. Scientists were surprised to find that the human DNA found in the petrous bone exceeded that of the more traditionally used teeth, finger and rib bones by 183 times. As much as 90 percent of the DNA extracted from some of the remains was human. This allowed the researchers at University College Dublin to map the complete genomes of the individuals, including which genes were being expressed and when.
In recent years, archaeologists have been discovering that many theories about when and why genes changed were wrong. The human genome is more strongly linked to technology and diet than to place. For example, it was assumed that humans developed lighter skin as they migrated out of Africa and needed to absorb more vitamin D from the weaker sunlight in the north. A study published in January states that humans expressed the gene for dark skin for most of their history. Only when their diet changed to incorporate more grains did they develop a need for more Vitamin D and their skin lighten in response. The neolithic revolution not only changed the human lifestyle, it influenced the human genome.
Well-known anthropologist Jared Diamond posits that the development of agriculture was a huge nutritional mistake for humans. Hunting and gathering was difficult, but the Paleolithic diet was well-balanced; people ate a little bit of everything. Farming provided a steady food source, but people relied on a few basic grains and no longer sought a variety of nutritional foods. Early Neolithic farmers were less healthy than their nomadic predecessors. Height decreased five inches, infant mortality rose; they showed signs of tooth decay, anemia and low bone density. Humans developed diseases such as scurvy, rickets, beriberi, heart disease and diabetes. Rather than a time of plenty, early farming seems to have been a critical period for humans and surviving the technological advance was uncertain.
Along with growing grain, the Neolithic revolution brought the domestication of animals, especially milk producing mammals such as cows and goats. Like other mammals, human babies express a gene to produce the enzyme lactase which breaks down the milk-sugar lactose into easily digestible glucose and galactose. Without the enzyme, lactose causes milk to rot in the digestive system effecting symptoms from stomach cramps to fatal diarrhea. As mammals grow and stop drinking their mothers’ milk, they stop producing the enzyme. Lactose intolerance is the natural state of adult mammals, including humans. As a result, humans did not drink animal milk but processed it into yogurt and cheese. The fermentation process breaks down the lactose. For 4,000 years humans were eating dairy products in the form of cheese and yogurt and reaping the nutritional benefits, so why did some populations suddenly develop life-long lactose tolerance?
The mutation of lactase persistence seems to have sprung up near Turkey and spread quickly west throughout Europe to Scandinavia and the British Isles, and east as far as the Himalaya Mountains. Lactose tolerance also arose and spread rapidly in Africa and the Middle East, but nearly the entire populations of the Americas, Oceania and the Far East remained lactose intolerant.
Biological archaeologists are confounded by two aspects of the ascension of lactose tolerance. The first is that it developed in human populations long after people began domesticating animals and processing dairy products. The second is how rapidly the mutation moved through human populations to become dominant. Based on the DNA evidence, the team from the University College Dublin estimates that lactose tolerance became the dominant allele about 3,000 years ago. Within 1,000 years the human population of Europe had selected for lactose tolerance to such an extent that it became the norm. In Ireland, for example, lactose tolerance is nearly universal. Termed a high selection differential, the ability to drink milk seems to have become a matter of life and death during this time. Supplementing a poor, carb-heavy diet with nutrient-rich milk allowed those expressing the gene for lactase to survive and reproduce – passing on their genome.
The rise of lactose tolerance coincides not with the rise of agriculture, but with the rise of civilizations. The nutrients provided by milk may have supplemented the diet of a settled people enough to allow them to organize, build cities and begin job specialization. The early neolithic years were a time of struggle. Civilizations grew not simply because humans had more food, but because farmers were finally meeting their nutritional needs with greater variety and more stability. Got Milk? It is fortunate that early humans did have milk because it may have been key to the rise of civilizations.
By: Rebecca Savastio