Home | Category: Life and Culture in Prehistoric Europe
EVOLUTION OF MILK DRINKING
milk
Among the important developments in human evolution was the ability to digest milk after early childhood. Mutations that enabled people to drink milk throughout their life appeared independently in several parts of the world over the last 7,500 years, according to growing evidence. And those genes spread rapidly. Today, about a third of adults around the world can drink milk without stomach problems, a trait known as lactase persistence.
Ann Gibbons wrote in National Geographic: “All humans digest mother’s milk as infants, but until cattle began being domesticated 10,000 years ago, weaned children no longer needed to digest milk. As a result, they stopped making the enzyme lactase, which breaks down the lactose into simple sugars. After humans began herding cattle, it became tremendously advantageous to digest milk, and lactose tolerance evolved independently among cattle herders in Europe, the Middle East, and Africa. Groups not dependent on cattle, such as the Chinese and Thai, the Pima Indians of the American Southwest, and the Bantu of West Africa, remain lactose intolerant. Humans also vary in their ability to extract sugars from starchy foods as they chew them, depending on how many copies of a certain gene they inherit. Populations that traditionally ate more starchy foods, such as the Hadza, have more copies of the gene than the Yakut meat-eaters of Siberia, and their saliva helps break down starches before the food reaches their stomachs.” [Source: Ann Gibbons, National Geographic, September 2014 /*/]
According to leading theory, Neolithic humans adapted to digesting milk because milk provided a valuable source of vitamin D, which would’ve helped people absorb its calcium. But a study in 2014 debunked this theory. ANI reported: “Newly analyzed human skeletons from an ancient site in Spain show that the milk-drinking gene spread just as rapidly in that sun-drenched climate as it did in other places, suggesting that milk must have been beneficial there for some reason other than its vitamin D content. “Throughout the years, I have heard so many evolutionary hypotheses about lactase persistence because they are so fun to coin,” said Oddný Sverrisdóttir, an evolutionary biologist at the University of Uppsala in Sweden. “For decades now, people have hypothesized that it was because of lack of sunlight in the north of Europe that people would have had to supplement the lack of calcium and vitamin D by drinking milk. “Now, looking at this picture from Spain,” she said, “the calcium-assimilation hypothesis either didn’t affect the evolution of lactase persistence at all, or other forces were there as well.” [Source: ANI, January 22, 2014 +]
“Sverrisdóttir has long been interested in how and why Europe’s early farmers began drinking milk, so she was excited when she got her hands on well-preserved samples of skeletal remains from eight people who lived in northeastern Spain about 5,000 years ago. That was well after the milk-drinking mutation had appeared in northern Europe, and she was eager to find out if those ancient Spaniards were drinking milk, too. So the first thing she did was test their DNA for lactase persistence. “I thought at least one would have the mutation,” since so many of today’s Spanish adults can drink milk without health consequences, Sverrisdóttir said. “None did.” +\
“To figure out whether the recent and rapid spread of lactase persistence in Spain was a fluke or if natural selection was at play, Sverrisdóttir and colleagues compared the mitochondrial DNA of modern Spaniards with the ancient samples. Mitochondrial DNA changes very slowly, making it ideal for tracing family trees over time. And, the researchers report today in the journal Molecular Biology and Evolution, analyses showed that the ancient cave dwellers were indeed ancestors of people who live and frequently drink milk in Spain today.” +\
Good Websites Archaeology News Report archaeologynewsreport.blogspot.com ; Anthropology.net anthropology.net : archaeologica.org archaeologica.org ; Archaeology in Europe archeurope.com ; Archaeology magazine archaeology.org ; HeritageDaily heritagedaily.com; Livescience livescience.com/ ; Food Timeline, History of Food foodtimeline.org ; Food and History teacheroz.com/food
Milk Revolution
cheese curds
Andrew Curry wrote in Nature: “During the most recent ice age, milk was essentially a toxin to adults because — unlike children — they could not produce the lactase enzyme required to break down lactose, the main sugar in milk. But as farming started to replace hunting and gathering in the Middle East around 11,000 years ago, cattle herders learned how to reduce lactose in dairy products to tolerable levels by fermenting milk to make cheese or yogurt. Several thousand years later, a genetic mutation spread through Europe that gave people the ability to produce lactase — and drink milk — throughout their lives. That adaptation opened up a rich new source of nutrition that could have sustained communities when harvests failed. [Source: Andrew Curry, Nature, July 31, 2013 /~/]
“This two-step milk revolution may have been a prime factor in allowing bands of farmers and herders from the south to sweep through Europe and displace the hunter-gatherer cultures that had lived there for millennia. “They spread really rapidly into northern Europe from an archaeological point of view,” says Mark Thomas, a population geneticist at University College London. That wave of emigration left an enduring imprint on Europe, where, unlike in many regions of the world, most people can now tolerate milk. “It could be that a large proportion of Europeans are descended from the first lactase-persistent dairy farmers in Europe,” says Thomas. /~/
“Young children almost universally produce lactase and can digest the lactose in their mother's milk. But as they mature, most switch off the lactase gene. Only 35% of the human population can digest lactose beyond the age of about seven or eight. “If you're lactose intolerant and you drink half a pint of milk, you're going to be really ill. Explosive diarrhoea — dysentery essentially,” says Oliver Craig, an archaeologist at the University of York, UK. “I'm not saying it's lethal, but it's quite unpleasant.” /~/
“Most people who retain the ability to digest milk can trace their ancestry to Europe, where the trait seems to be linked to a single nucleotide in which the DNA base cytosine changed to thymine in a genomic region not far from the lactase gene. There are other pockets of lactase persistence in West Africa, the Middle East and south Asia that seem to be linked to separate mutations. /~/
“The single-nucleotide switch in Europe happened relatively recently. Thomas and his colleagues estimated the timing by looking at genetic variations in modern populations and running computer simulations of how the related genetic mutation might have spread through ancient populations4. They proposed that the trait of lactase persistence, dubbed the LP allele, emerged about 7,500 years ago in the broad, fertile plains of Hungary. /~/
“Once the LP allele appeared, it offered a major selective advantage. In a 2004 study,, researchers estimated that people with the mutation would have produced up to 19% more fertile offspring than those who lacked it. The researchers called that degree of selection “among the strongest yet seen for any gene in the genome”. Compounded over several hundred generations, that advantage could help a population to take over a continent. But only if “the population has a supply of fresh milk and is dairying”, says Thomas. “It's gene–culture co-evolution. They feed off of each other.”“/~/
Studying Milk History
Andrew Curry wrote in Nature: “To investigate the history of that interaction, Thomas teamed up with Joachim Burger, a palaeogeneticist at the Johannes Gutenberg University of Mainz in Germany, and Matthew Collins, a bioarchaeologist at the University of York. They organized a multidisciplinary project called LeCHE (Lactase Persistence in the early Cultural History of Europe), which brought together a dozen early-career researchers from around Europe. [Source: Andrew Curry, Nature, July 31, 2013 /~/]
ancient milk jug from Caucasian, Albania
“By studying human molecular biology and the archaeology and chemistry of ancient pottery, LeCHE participants also hoped to address a key issue about the origins of modern Europeans. “It's been an enduring question in archaeology — whether we're descended from Middle Eastern farmers or indigenous hunter-gatherers,” says Thomas. The argument boils down to evolution versus replacement. Did native populations of hunter-gatherers in Europe take up farming and herding? Or was there an influx of agricultural colonists who outcompeted the locals, thanks to a combination of genes and technology? /~/
“One strand of evidence came from studies of animal bones found at archaeological sites. If cattle are raised primarily for dairying, calves are generally slaughtered before their first birthday so that their mothers can be milked. But cattle raised mainly for meat are killed later, when they have reached their full size. (The pattern, if not the ages, is similar for sheep and goats, which were part of the dairying revolution.) /~/
“On the basis of studies of growth patterns in bones, LeCHE participant Jean-Denis Vigne, an archaeozoologist at the French National Museum of Natural History in Paris, suggests that dairying in the Middle East may go all the way back to when humans first started domesticating animals there, about 10,500 years ago. That would place it just after the Middle Eastern Neolithic transition — when an economy based on hunter-gathering gave way to one devoted to agriculture. Dairying, says Roz Gillis, also an archaeozoologist at the Paris museum, “may have been one of the reasons why human populations began trapping and keeping ruminants such as cattle, sheep and goats. /~/ Dairying then expanded in concert with the Neolithic transition, says Gillis, who has looked at bone growth at 150 sites in Europe and Anatolia (modern Turkey). As agriculture spread from Anatolia to northern Europe over roughly two millennia, dairying followed a similar pattern. /~/
“On their own, the growth patterns do not say whether the Neolithic transition in Europe happened through evolution or replacement, but cattle bones offer important clues. In a precursor study, Burger and several other LeCHE participants found that domesticated cattle at Neolithic sites in Europe were most closely related to cows from the Middle East, rather than indigenous wild aurochs. This is a strong indication that incoming herders brought their cattle with them, rather than domesticating locally, says Burger. A similar story is emerging from studies of ancient human DNA recovered at a few sites in central Europe, which suggest that Neolithic farmers were not descended from the hunter-gatherers who lived there before. Taken together, the data help to resolve the origins of the first European farmers. “For a long time, the mainstream of continental European archaeology said Mesolithic hunter-gatherers developed into Neolithic farmers,” says Burger. “We basically showed they were completely different.”“/~/
Dairy Farming Began 9000 Years Ago in Anatolia?
milking a cow
The earliest date for dairy farming is about 9,000 years ago, in Anatolia (present-day Turkey). The abstract of a paper on the topic — “Earliest date for milk use in the Near East and southeastern Europe linked to cattle herding” by Richard P. Evershed et. al., published: August 6 2008 in Nature — reads: “The domestication of cattle, sheep and goats had already taken place in the Near East by the eighth millennium B.C. Although there would have been considerable economic and nutritional gains from using these animals for their milk and other products from living animals—that is, traction and wool—the first clear evidence for these appears much later, from the late fifth and fourth millennia B.C. Hence, the timing and region in which milking was first practised remain unknown.
Organic residues preserved in archaeological pottery have provided direct evidence for the use of milk in the fourth millennium in Britain, and in the sixth millennium in eastern Europe, based on the δC values of the major fatty acids of milk fat. Here we apply this approach to more than 2,200 pottery vessels from sites in the Near East and southeastern Europe dating from the fifth to the seventh millennia bc. We show that milk was in use by the seventh millennium; this is the earliest direct evidence to date. Milking was particularly important in northwestern Anatolia, pointing to regional differences linked with conditions more favourable to cattle compared to other regions, where sheep and goats were relatively common and milk use less important. The latter is supported by correlations between the fat type and animal bone evidence.
According to the paper: “The use of milk, wool and traction, so-called ‘secondary’ products,obtained from domestic animals without killing them, marks an important step in the history of domestication. But evidence for when and how this first happened is inconclusive. Some researchers have argued that once animals were domesticated the potential benefits of these products would have been exploited rapidly. Others have pointed to the late appearance of unequivocal evidence—that is, representations of milking scenes, carts and ploughs—and to barriers, such as lactose intolerance in humans, suggesting that early domestication was predominantly for meat and hides, postulating a ‘secondary products revolution’ during the fifth or fourth millennium BC, 2,000–4,000 years after the first domestication of cattle, sheep and goats in the Near East and Europe. Evidence provided by figurines and pictures of animals before 4000 BC , and from arte- facts (for example, ceramic strainers), has been variously interpreted, as has evidence from animal bone assemblages, especially the ages at which animals were killed, taken as reflecting what they were kept for and how they were managed.
“The analysis of lipid residues from pottery, particularly our discovery that ruminant milk fatty acids can be distinguished from those of carcass fats, provided a new tool for detecting early milk use. The approach rests upon measuring the differences is the number of carbon atoms and double bonds in milk fatty acids and carcass fats.
cheese
“Our results provide new insights into the emergence of dairying as a component of the domestication of animals. The appearance of dairy products at early sites in the region is the earliest evidence so far, by,1–2 millennia, dating back to the start of ceramics in the region; this indicates an earlier date for the milking of domesticated animals than predicted by reconstructions based on other lines of evidence. Significantly, the high incidence of dairy products in pottery from sites in northwestern Anatolia points to intensification of the milking of ruminant animals, at locations remote from the original region of domestication, namely the Fertile Crescent. Importantly, the results suggest a pattern of regional variation in the importance of milk use rather than of general change with time. Milk appears to have been particularly important in the sites from northwestern Anatolia, ranging in date from the end of the seventh millennium to the fifth millennium BC , contrasting markedly with results from southeastern and central Anatolia at the same time. In neither area is there any strong suggestion of chronological change. In northern Greece, sites dating from the sixth to the fourth millennia BC gave low proportions of sherds with ruminant milk fats; the one site with intermediate results was the sixth millennium Romanian site of Ma ̆gura-Buduiasca, which concurs with an earlier study of two sites from this region.
Our earlier experiments showed that raw milk lipids absorbed by reproduction ceramics are rapidly destroyed by burial, suggesting that the high frequency of ruminant milk lipids from the northwestern Anatolian sites is indicative of milk being processed. Processing milk would have had two important advantages, providing a means of storing surplus milk as products, that is cheese, ghee, and so on, making them available throughout the year, and providing a solution for any problems of lactose intolerance; most lactose intolerant people have fewer problems with consuming processed milk products. In summary, our findings take the early history of milk use back to the seventh millennium BC, early in the evolution of animal domestication and pottery production and use. The results are significant also for two other reasons: first, they suggest that even at this date (before 6500 BC) milk was processed, making possible the storage of milk products and providing an explanation why, in spite of lactose intolerance, milk use could be adopted quickly, and second, they add to increasing indications of regional differences during the early Neolithic and into the Chalcolithic. Thus, early farming appears not to have been a fixed package; instead, it developed in different ways in different areas, probably in response partly to different environmental conditions and partly to different cultural choices of early farmers.”
Neolithic Dairy Activities Varied in the Mediterranean
Dairy-related activity differed across the Mediterranean region in the Neolithic era and may have impacted the spread of culture and animal domestication. Popular Archaeology reported: “Previous research suggests that the production of dairy products such as milk in Neolithic Mediterranean communities could have been an impetus for animal domestication. To study the rise of dairy production in the Mediterranean region, Mélanie Roffet-Salque and colleagues analyzed lipid residues on more than 550 ceramic sherds and osteo-archeological data on age-at-death for domesticated animals from 82 sites in the northern Mediterranean and Near East that dated between the seventh and fifth millennia B.C. [Source: popular-archaeology.com, November 14, 2016 ||||]
“In combination with previously published data, the ceramic and osteo-archaeological analyses revealed regional differences in the level of dairy-related activity in Early Neolithic farming communities across the Mediterranean region. Moreover, milk residues in ceramic artifacts from both the east and west of the region contrasted with data from sites in northern Greece, where high frequencies of pig bones indicated a reliance on meat production. According to the authors, except for parts of mainland Greece, dairy production was likely practiced across the Mediterranean region from the onset of agriculture and might have contributed to the spread of culture and animal domestication in the region.” ||||
Milk-Drinking Mutations Emerged after Dairy Herding?
Analysis of fossilized bones suggests milk-drinking mutations emerged after dairy herding. Erika Check wrote in Nature: “When did ancient populations learn that drinking milk 'does a body good'? A team of scientists in Germany has tried to answer this question by studying ancient DNA extracted from skeletons thousands of years old. Many adult humans can drink cow's milk — a rare feat among mammals, which usually lose the ability to digest the sugar in milk after they are weaned. Scientists have found the genetic mutations that allow many Europeans and some Africans to digest milk (see 'Human evolution: How Africa learned to love the cow'). Geneticists have estimated that these mutations first spread 3,000 to 7,000 years ago in eastern Africa, and slightly earlier than that in Europe. [Source: Erika Check, Nature, February 26, 2007 \=/]
“But some researchers have posed a 'chicken-and-egg' question about milk drinking: was dairy herding adopted only by those populations who could already drink milk? Or did the invention of dairy herding favour those people who had the mutation, so that the mutation quickly spread throughout the population? \=/
“Joachim Burger of the University of Mainz, Germany, and colleagues worked with Mark Thomas of University College London, UK, to address this riddle by studying DNA from skeletons scattered throughout Europe. The team examined ten skeletons ranging in age from 3,800 to nearly 6,000 years old. The skeletons were discovered at archaeological sites in Germany, Hungary, Poland and Lithuania. \=/
“The team drilled into bone and tooth samples from the skeletons, and extracted DNA from the samples. They then checked the DNA for the most common milk-drinking mutation found in Europeans today. The team did not find any evidence of this mutation, it reports in the Proceedings of the National Academy of Sciences today. Burger and his colleagues say this supports the dominant theory on how milk drinking evolved — that milk-drinking mutations were uncommon before the practice of dairying began. Then, when humans learned to herd cattle, the milk-drinking mutations spread rapidly, because they conferred a huge advantage on those who had them — perhaps due to the extra protein and fats available in cow's milk, the team speculates. \=/
Lactase peristance in the Old World
“Burger says this is the first time that scientists have tried to use very old DNA to answer questions about milk drinking: "While the technique is common in modern-day population genetics, this is the first time that it is published for really ancient DNA," he says. Other scientists cautioned that with so few skeletons analysed, from different areas, the results are not necessarily definitive. But, they said, the method adds a new way to look at milk drinking and other traits. "The study does provide an excellent example of cross-checking the age estimates based solely on modern variations with datable ancient DNA," says Diane Gifford-Gonzalez, an anthropologist who studies the origins of dairying at the University of California, Santa Cruz. \=/
Migration of Lactase Persistence
Andrew Curry wrote in Nature: “Given that dairying in the Middle East started thousands of years before the LP allele emerged in Europe, ancient herders must have found ways to reduce lactose concentrations in milk. It seems likely that they did so by making cheese or yogurt. (Fermented cheeses such as feta and cheddar have a small fraction of the lactose found in fresh milk; aged hard cheeses similar to Parmesan have hardly any.) [Source: Andrew Curry, Nature, July 31, 2013 /~/]
“To test that theory, LeCHE researchers ran chemical tests on ancient pottery. The coarse, porous clay contains enough residues for chemists to distinguish what type of fat was absorbed during the cooking process: whether it was from meat or milk, and from ruminants such as cows, sheep and goats or from other animals. “That gave us a way into saying what types of things were being cooked,” says Richard Evershed, a chemist at the University of Bristol. /~/
“It's been an enduring question in archaeology — whether we're descended from Middle Eastern farmers or indigenous hunter-gatherers.”Evershed and his LeCHE collaborators found milk fat on pottery in the Middle Eastern Fertile Crescent going back at least 8,500 years, and Roffet-Salque's work on the Polish pottery offers clear evidence that herders in Europe were producing cheese to supplement their diets between 6,800 and 7,400 years ago. By then, dairy had become a component of the Neolithic diet, but it was not yet a dominant part of the economy. /~/
“That next step happened slowly, and it seems to have required the spread of lactase persistence. The LP allele did not become common in the population until some time after it first emerged: Burger has looked for the mutation in samples of ancient human DNA and has found it only as far back as 6,500 years ago in northern Germany. /~/
“Models created by LeCHE participant Pascale Gerbault, a population geneticist at University College London, explain how the trait might have spread. As Middle Eastern Neolithic cultures moved into Europe, their farming and herding technologies helped them to out-compete the local hunter-gatherers. And as the southerners pushed north, says Gerbault, the LP allele 'surfed' the wave of migration. /~/
“Lactase persistence had a harder time becoming established in parts of southern Europe, because Neolithic farmers had settled there before the mutation appeared. But as the agricultural society expanded northwards and westwards into new territory, the advantage provided by lactase persistence had a big impact. “As the population grows quickly at the edge of the wave, the allele can increase in frequency,” says Gerbault. The remnants of that pattern are still visible today. In southern Europe, lactase persistence is relatively rare — less than 40% in Greece and Turkey. In Britain and Scandinavia, by contrast, more than 90% of adults can digest milk. /~/
By the late Neolithic and early Bronze Age, around 5,000 years ago, the LP allele was prevalent across most of northern and central Europe, and cattle herding had become a dominant part of the culture. “They discover this way of life, and once they can really get the nutritional benefits they increase or intensify herding as well,” says Burger. Cattle bones represent more than two-thirds of the animal bones in many late Neolithic and early Bronze Age archaeological sites in central and northern Europe.
Lactose tolerance in the Old World
Why Was Milk-Drinking So Advantageous to Our Ancestors?
Andrew Curry wrote in Nature: “The LeCHE researchers are still puzzling out exactly why the ability to consume milk offered such an advantage in these regions. Thomas suggests that, as people moved north, milk would have been a hedge against famine. Dairy products — which could be stored for longer in colder climes — provided rich sources of calories that were independent of growing seasons or bad harvests. [Source: Andrew Curry, Nature, July 31, 2013 /~/]
“Others think that milk may have helped, particularly in the north, because of its relatively high concentration of vitamin D, a nutrient that can help to ward off diseases such as rickets. Humans synthesize vitamin D naturally only when exposed to the sun, which makes it difficult for northerners to make enough during winter months. But lactase persistence also took root in sunny Spain, casting vitamin D's role into doubt. /~/
“The LeCHE project may offer a model for how archaeological questions can be answered using a variety of disciplines and tools. “They have got a lot of different tentacles — archaeology, palaeoanthropology, ancient DNA and modern DNA, chemical analysis — all focused on one single question,” says Ian Barnes, a palaeogeneticist at Royal Holloway, University of London, who is not involved in the project. “There are lots of other dietary changes which could be studied in this way.” /~/
“The approach could, for example, help to tease apart the origins of amylase, an enzyme that helps to break down starch. Researchers have suggested that the development of the enzyme may have followed — or made possible — the increasing appetite for grain that accompanied the growth of agriculture. Scientists also want to trace the evolution of alcohol dehydrogenase, which is crucial to the breakdown of alcohol and could reveal the origins of humanity's thirst for drink. /~/
“Some of the LeCHE participants are now probing further back in time, as part of a project named BEAN (Bridging the European and Anatolian Neolithic), which is looking at how the first farmers and herders made their way into Europe. Burger, Thomas and their BEAN collaborators will be in Turkey this summer, tracing the origins of the Neolithic using computer models and ancient-DNA analysis in the hope of better understanding who the early farmers were, and when they arrived in Europe. /~/
“Along the way, they will encounter beyaz peynir, a salty sheep's-milk cheese eaten with nearly every Turkish breakfast. It is probably much like the cheese that Neolithic farmers in the region would have eaten some 8,000 years ago — long before the march of lactase persistence allowed people to drink fresh milk.” /~/
cheese and asparagus in Pompeii
Scandinavians Unable to Digest Milk 4000 Years Ago
Uppsala University reported: “The hunter-gatherers who inhabited the southern coast of Scandinavia 4,000 years ago were lactose intolerant. This has been shown by a new study carried out by researchers at Uppsala University and Stockholm University. The study, which has been published in the journal BMC Evolutionary Biology, supports the researchers’ earlier conclusion that today’s Scandinavians are not descended from the Stone Age people in question but from a group that arrived later. “This group of hunter-gatherers differed significantly from modern Swedes in terms of the DNA sequence that we generally associate with a capacity to digest lactose into adulthood,” says Anna Linderholm, formerly of the Archaeological Research Laboratory, Stockholm University, presently at University College Cork, Ireland. [Source: Uppsala University, April 1, 2010]
According to the researchers, two possible explanations exist for the DNA differences. “One possibility is that these differences are evidence of a powerful selection process, through which the Stone Age hunter-gatherers’ genes were lost due to some significant advantage associated with the capacity to digest milk,” says Anna Linderholm. “The other possibility is that we simply are not descended from this group of Stone Age people.”
The capacity to consume unprocessed milk into adulthood is regarded as having been of great significance for human prehistory. This capacity is closely associated with the transition from hunter-gatherer to agricultural societies,” says Anders Götherström of the Department of Evolutionary Biology at Uppsala University. He serves as coordinator of LeCHE (Lactase persistence and the early Cultural History of Europe), an EU-funded research project focusing on the significance of milk for European prehistory. “In the present case, we are inclined to believe that the findings are indicative of what we call “gene flow,” in other words, migration to the region at some later time of some new group of people, with whom we are genetically similar,” he says. “This accords with the results of previous studies.”The researchers’ current work involves investigating the genetic makeup of the earliest agriculturalists in Scandinavia, with an eye to potential answers to questions about our ancestors.
Development of Milk-Drinking in Africa
Erika Check wrote in Nature: “The development of lactose tolerance in sub-Saharan Africa is a fascinating tale of genetic convergence, The Dinka people of southern Sudan, it is said, have 400 different words to refer to the cattle that they prize above all other things. The Maasai, who live in Kenya and northern Tanzania, have traditionally believed that all cattle on Earth were given to them by the gods, and value those in their possession accordingly. The Zulu, Xhosa and Swazi in South Africa devote themselves to their strikingly patterned Nguni cattle, whose hides are now prized by high-end interior designers. [Source: Erika Check, December 21, 2006 \=/]
“And in all these pastoralist or semi-pastoralist groups, which rely on herding for survival, people drink milk — which is something of a puzzle. Most adult humans (those of European stock are largely an exception) find the sugar in milk, called lactose, indigestible. The gene for lactase, the enzyme that breaks lactose down into the more digestible forms of glucose and galactose, is normally switched off as children are weaned. Without lactase, lactose is of little use to a milk drinker; but it is still a valid food for some stomach bacteria, which can have unsettling and unpleasant results. Thus, most adults tend not to drink much milk. \=/
Churning of the Ocean of Milk in Hindu mythology
“Now, genetic detective work is showing how, in parts of Africa, evolution found a way round this problem — just as it did a few thousand years earlier in northern Europe. The results should help clarify the origins and spread of cattle rearing in Africa, and provide a textbook illustration of the ways in which the same social innovation can write its consequences into the human genome in different times and places. \=/
Sarah Tishkoff of the University of Maryland, College Park designed a project to collect DNA samples from 43 ethnic groups in three East African countries and to correlate the data with various physiological characteristics relevant to taste perception, disease susceptibility and other things — including lactose metabolism. It was an ambitious plan at best — a foolhardy undertaking at worst. Few researchers, if any, had ever collected such a large, diverse set of genetic samples from Africa... Tishkoff set out with a 30-year-old Land Rover full of cases of energy bars and camping gear. Over the next three years, on and off, she and her students roamed around Tanzania, Kenya and Sudan, collecting data in some dangerous as well as out of the way places.
“At most stops, Tishkoff's group hired a translator to explain the purpose of her research, get permission from local leaders, and recruit people for their research. In all, they took samples from 470 people. To test for lactase, the team members stirred powdered lactose into cups of water, gave it to each person, and took a series of timed blood samples. That told the researchers how well each person could digest lactose, as well as providing samples of the individual's DNA. \=/
Findings from Research of Milk-Drinking DNA in Africa
Erika Check wrote in Nature: “In 2002, while the work was under way, a team of Finnish researchers reported that it had found a genetic mutation that seemed to cause lactase persistence in North Europeans. A small change in an 'enhancer' region upstream of the lactase gene seemed to keep the gene from being switched off after infancy. All of the 137 lactase-persistent Finns studied had the mutation in question, and studies of other populations showed that the frequency of the mutation matched that of the lactase persistence. But two years later, another team reported that the Finns' genetic variant was not found in East Africans, even though some are lactase persistent. [Source: Erika Check, December 21, 2006 \=/]
“Tishkoff's team showed why this was. Ranciaro sequenced DNA from her subjects and noticed several mutations close to the lactase gene. A collaborator at the Wellcome Trust Sanger Institute in Cambridge, UK, Panos Deloukas, checked for the mutations in the full set of 470 people, and Tishkoff and a postdoctoral fellow working with her, Floyd Reed, noticed that one of these mutations was tightly linked to lactase persistence in Tanzanians and Kenyans. The team also found that two other mutations were associated with lactase persistence in people in northern Kenya and Sudan, though not as strongly. It was immediately clear that these mutations had arisen independently from the one found in Finland. \=/
The DNA also showed evidence that the mutation seen in the Tanzanians had spread very quickly. DNA accumulates small, random imperfections over the generations, and yet the stretches of DNA surrounding the lactase persistence mutation were identical in most of those who had it. This uniformity shows that the gene evolved recently and spread rapidly — which in turn means that it must have conferred an advantage strongly selected for by evolution. Statistical models of Tishkoff's data suggest that the mutation arose between 3,000 and 7,000 years ago — a blink of an eye in evolutionary time. \=/
“Tishkoff and Reed conclude that lactase persistence bears one of the strongest signatures of positive selection ever observed in the human genome. Mutations that favour malaria resistance, such as the sickle-cell gene and an inability to make the enzyme glucose-6-phosphate dehydrogenase, or G6PD, are also strongly favoured and spread rapidly. (They seem to have got going at about the same time, too, and are also related to domestication — malaria is thought to have first become a major problem for Africans when they started to live in settlements.) But the positive selection for lactase persistence seems even stronger, perhaps because the costs of the mutation are less severe than those for malaria. Tishkoff and Reed suspect that the advantage might go beyond the extra calories that could be gained from the lactose. Lactase persistence might also have allowed people to stay alive during times of drought, when those benefiting from the mutation would have been able to drink milk without the risk of diarrhoea, which exacerbates dehydration. \=/
herding cattle and goats in Africa
“Tishkoff's work also highlights the incredible genetic diversity in African people, a diversity that as yet has been studied very little. For example, the African DNA samples in the Haplotype Map6— the catalogue of genetic diversity published last year — come from only one ethnic group: the Yoruba of West Africa. But, traditionally, the Yoruba don't herd cattle, and Tishkoff didn't discover any mutations for lactase persistence in them (although in some populations of West African pastoralists, fewer people have the 'European' lactase persistence mutation). Such blindspots could be a problem, because scientists hunting for the genetic causes of diseases often rely on HapMap data. "There's such a huge amount of genetic diversity in Africa that we're clearly going to have to look at all the ethnic groups in different regions to find all the variants," Tishkoff says. "Otherwise, we could be completely missing things that are important in disease." She worries that the fragmentation and disappearance of traditional cultures will make it harder to access and understand that diversity in the future. \=/
“There's also a significant achievement. Scientists have to date found little genetic evidence for convergent evolution in people: "This is the best example of convergent evolution in humans that I've ever seen," says Joel Hirschhorn, a geneticist and paediatrician at Children's Hospital Boston, Massachusetts. "Lactase persistence has always been a textbook example of selection, and now it'll be a textbook example in a totally different way.
“Convergent evolution is not unknown in humans; lighter skin colour seems to have evolved independently in Europe and Asia, and a range of different malaria adaptations are known. But lactase persistence offers a particularly simple and tractable example: there's a single gene involved, with different mutations in different parts of the world having similar effects. The challenge now is to learn from this textbook example how to spot more subtle convergences that have been forced on human biology by shared experiences and cultural innovations — or that are still under way today.” \=/
Image Sources: Wikimedia Commons
Text Sources: National Geographic, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Nature, Scientific American. Live Science, Discover magazine, Discovery News, Ancient Foods ancientfoods.wordpress.com ; Times of London, Natural History magazine, Archaeology magazine, The New Yorker, Time, Newsweek, BBC, The Guardian, Reuters, AP, AFP, Lonely Planet Guides, “World Religions” edited by Geoffrey Parrinder (Facts on File Publications, New York); “History of Warfare” by John Keegan (Vintage Books); “History of Art” by H.W. Janson (Prentice Hall, Englewood Cliffs, N.J.), Compton’s Encyclopedia and various books and other publications.
Last updated May 2024