Take a look at the second installment of 23andMe’s Human Prehistory 101 series.  23andMe’s creative team (led by chief illustrator Ariana Killoran) recently released “Out of (Eastern) Africa.”  With this new installment, we pick up where the previous video left off, when humans were starting to take their first tentative steps beyond the shores of Africa and into the unknown.

We begin this second episode around 60,000 years ago, when early human groups were exploring Africa for food and other resources. Just a few thousand years later, a few people journeyed even farther, heading east into the Arabian Peninsula, Asia, Europe and beyond. The common theme here? Things were changing for our human ancestors, who had previously stayed relatively confined to their homeland but now they were on the move. Around the time they first set foot in Asia, humans in Africa began creating sophisticated stone tools and art the likes of which had never been seen before.

As humans ventured into uncharted territory, they may have encountered other species who bore some resemblance to themselves.  In Asia, they may have run into Homo erectus, a distant relative that had journeyed into Asia from Africa almost 2 million years earlier.  In Europe humans likely came across the Neanderthals, another related species that had been braving the cold northern latitudes of Europe and western Asia for hundreds of thousands of years.

Our story continues as we see where various human populations settled over the next several thousand years, and gives us a peek at the difficulties that awaited them as the harsh Ice Age approached. Subsequent episodes will document how our human ancestors survived the harsh Ice Age conditions and how the innovation of agriculture and development of language laid the groundwork for the genetic diversity we see today.  Enjoy this latest installment and stay tuned for future episodes of Human Prehistory 101!

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About 10,000 years ago, the prehistoric hunter-gatherers of Europe began meeting some new neighbors.

These farmers spread gradually at first, expanding from the Near East through Anatolia and the Balkans. Then agriculture exploded, reaching present-day Britain within a few thousand years. The farmers settled into houses, which soon evolved into villages, towns and eventually cities.

The archaeological record tells us that much. But what it doesn’t reveal is how agriculture spread. Did it spread like a fad, as hunter-gatherer groups saw what their neighbors were doing and imitated their ways? Or was it more of an invasion, with subsequent generations of farmers advancing across the continent and overwhelming indigenous hunter-gatherer populations as they went?

Some genetic studies suggest the former. But in the September 3 issue of Science, the first study to directly compare ancient DNA (aDNA) from prehistoric burials of hunter-gatherers to that their agricultural neighbors suggests migrants spread farming through Europe.

The research team, led by Barbara Bramanti of Mainz University, sequenced the mitochondrial DNA (mtDNA) of just under 50 individuals unearthed from various prehistoric burial sites across central and eastern Europe. Half the individuals came from hunter-gatherer societies, and the other half from communities based around farming. As a comparison, they also sequenced the mtDNA of nearly 500 modern Europeans from the same parts of Europe.

The authors’ first task was to compare the hunter-gatherer mtDNA to that of the farmers. Upon doing so, they found both groups to be so different from each other that there is no way the two could be closely related. There was absolutely no overlap in the kinds of mtDNA lineages – known as haplogroups – between the hunter-gatherers and the farmers. This stark difference suggests the earliest farmers were not related to the hunter-gatherers, and most likely came to the region by migration.

And how do these two groups compare to the modern-day Europeans? The hunter-gatherers had little in common with modern people. Haplogroup U, the most common lineage among the hunter-gatherers, is one of the least common haplogroups among modern Europeans.

But the authors also found little to connect the farmers to modern Europeans. Other studies have pointed to a substantial genetic component from the Near East among Europeans, but the authors found many genetic differences between the two groups.

Based on these results, the authors have proposed an alternative theory. The unexplained component to the genetic make-up of modern Europeans may be explained by later migrations that post-date the skeletal remains examined here. It could have been a later expansion of farmers from the Near East, or perhaps an influx of hunter-gatherers from the west. The exact details remain unclear, but the authors are confident that, with additional DNA analysis, they can hope to unravel the increasingly complex story of the peopling of Europe.

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The importance of ABO blood types in transfusions is unquestioned. And the associations between blood type and certain diseases are pretty convincing. But some “scientists” have linked blood type to some pretty wacky stuff.

In the first part of the 20th century it seems that there was nothing some researchers didn’t think was connected to blood type. Type A people were said to have the worst hangovers.  People with type B blood were supposed to defecate more than other types.  Some thought type Os had the best teeth.  Among military personnel, people with type O supposedly had weaker characters and type Bs were more impulsive.

Even in more modern times the less-than solid science surrounding blood types continues.  Case in point: Eat Right 4 Your Type.  This diet advice book suggests that certain ailments are caused by negative reactions between blood cells and sugar-binding proteins found in food.  The book recommends specific foods for each blood type to counteract these effects.  Critics argue, however, that there is no evidence supporting these ideas (although they admit the diet advice itself is not too bad.)

In Japan, asking “What’s your blood type?” is like asking someone “What’s your sign?” Popular books, magazines and TV programs discuss how blood type contributes to a person’s personality. Write-ups of celebrities, video game characters and even political candidates include blood type so as to help people form their impressions. Matchmaking services and employers even use blood type to help determine compatibility with mates and job assignments.

People with type A blood are supposed to be sensitive perfectionists who can veer towards anxiousness. Type Bs are happy folks who can have eccentric and selfish streaks.  Type O people are said to be curious and generous on the positive side, but also sometimes stubborn. People with type AB are thought to be artsy and mysterious, ideas that probably reflect the rareness of this blood type.

The problem is, just as there’s no plausible link between the motions of the stars and a person’s fate, the idea that blood type is linked to a person’s personality, dietary needs or dental fitness is pure fantasy.  Our blood types may be different, but there’s no reason to think that explains all of our differences.

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Not long after Karl Landsteiner first described the different ABO blood types, scientists started looking for associations between blood type and other human traits.  Some of their theories were truly weird (more on these tomorrow!), but some have held up to scientific scrutiny.

Venous Thromboembolism (VTE)
People with non-type O blood (A, B and AB) have been shown to be at increased risk for VTE.  The reason is thought to be that these people have higher levels of the clot-inducing proteins factor VIII and von Willebrand factor in their blood.  Having non-type O blood further raises the already increased risk for VTE in people who carry the Factor V Leiden and prothrombin G20210A mutations.

Cancer
Since the 1950s, scientists have found that people with type O blood have decreased risk for stomach cancer compared to people with type A.  Other cancers (pancreatic, breast, ovarian, cervical) also occur at lower rates in people with type O blood.  No one is quite sure why this is.  It could be that the sugars found on type A blood cells, which are also expressed by other cells in the body, might somehow help cancers grow more aggressively.  Alternatively, some research has shown that regardless of person’s own blood type, tumors express the type A sugars. In people with type A blood, these sugars go unnoticed by the immune system because they are considered normal.  But in people with type O blood, these new sugars are recognized as foreign, spurring the immune system to destroy the tumors.

Stomach Ulcers
Although stomach cancer is less prevalent in people with type O blood, stomach ulcers are more common in people with this blood type.  The sugars that define the different blood types are also found on cells in the gastrointestinal tract.  Research has shown that these sugars influence the ability of H. pylori, a type of bacteria responsible for a large number of stomach ulcers, to attach to the lining of the stomach.  People with type A or B blood (and hence A or B sugars on their stomach cells) have fewer H. pylori receptors than people with type O.

Severe Malaria
In people infected with malaria, more severe disease is seen in those whose red blood cells are induced to form rosettes, large aggregates that block small blood vessels.  Studies have shown that people with type O blood form fewer, smaller and more easily broken up rosettes than people with type A, B or AB blood.  This is probably because the sugars found on the non-O blood cells end up helping to create larger clumps of cells.

Infectious Disease
Some studies have shown that certain bacterial and viral infections are more or less likely in certain blood types.  For example, type A blood has been linked to a predisposition to “glue ear,” which is caused by infection with Pseudomonas aeruginosa. And some studies suggest that people with type O or B blood are less susceptible to smallpox. The research supporting these and other claims of an impact of blood type on infectious diseases are not as strong as the other associations listed above, however.

(23andMe customers can get a prediction of their ABO blood type based on their DNA data through the new ABO Lab feature.)

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When it comes to blood transfusions, what’s good for one person might be deadly for another.

This might seem obvious today, but until 1900 the idea of “blood types” wasn’t understood. A person in need of a transfusion could find himself getting a donation from just about anyone, and sometimes even an animal!

But in 1900 Austrian scientist Karl Landsteiner noticed that when the blood of different people was mixed together the cells would often clump up, a process he correctly attributed to an immune reaction between the two blood samples. By the next year he had used this clumping reaction to define three main types of blood, which he named A, B and O. (The fourth blood type, AB, was identified in 1902 by two other scientists, Decastello and Struli.)

After hundreds of years of performing blood transfusions unguided, scientists finally had what they needed to safely transfer blood between people. In 1907, the first blood transfusion utilizing the new typing techniques was successfully carried out, and by World War I transfusions were being performed safely on a large scale.

But knowing what blood to give someone and having it on hand are two different things.

Blood banks are faced with the daunting task of making sure there is enough blood of the right type for everyone who needs it at all times. Blood type O, the “universal donor,” tends to be overused. This presents a problem for the approximately 40% of Americans are type O and thus can receive only this type in a transfusion. If supplies run low, their lives could be in danger. At the same time, donated blood with the rare B and AB types can sit unused for so long that it becomes outdated and must be discarded.

One solution to managing the blood supply would be to transform all blood into type O, thus making it suitable for everyone. In the early 1980’s scientists found a way to do this using an enzyme from coffee beans that could strip certain sugars off of type B blood cells. Clinical trials showed that this method was safe and effective, but the method itself was too time consuming and costly to ever be of clinical use. New research, however, has identified bacterial enzymes that can carry out this same process more efficiently. Research with this new method is still in progress.

(23andMe customers can get a prediction of their ABO blood type based on their DNA data through the new ABO Lab feature.)

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The Neanderthals have always held a special place in the field of anthropology.  The skeletal remains of our short, stocky evolutionary relatives have been found everywhere from Spain to Iraq.

Their physical likeness to our own species, and the possibility that humans and Neanderthals may have interacted, has long fascinated experts and enthusiastic novices alike.  But simply studying their skeletal remains and artifacts seemed to leave more questions than answers.

More than 10 years ago an international team of scientists became the first to extract and analyze ancient DNA (aDNA) from a Neanderthal skeleton. By examining the mitochondrial DNA (mtDNA) — which is more abundant in our cells than our nuclear DNA and therefore more likely to preserve — they found that there were enough genetic differences between this Neanderthal and modern humans to classify the two as separate species.

Since this initial foray into Neanderthal genetics there have been attempts to improve aDNA analysis, with the goal of filling in the gaps that traditional anthropological techniques had been unable to.  Earlier this year, scientists at the Max Planck Institute for Evolutionary Anthropology became the first to sequence the entire Neanderthal mitochondrial genome – no easy feat. Now scientists have taken aDNA analysis to the next level by developing a novel technique to extract it more easily, yielding the most comprehensive and accurate results to date.  Along the way, they have uncovered some intriguing clues to the possible fate of the Neanderthals. Their results are reported in the July 17 issue of Science.

This new study, also led by Max Planck Institute scientists, centers around a novel method for finding and extracting that elusive aDNA from Neanderthal remains. The study took advantage of a new kind of aDNA extraction process, called Primer Extension Capture (PEC). This technique has many advantages over the others, primarily because it allows the aDNA to be completely isolated from all the other molecular junk  that can accumulate over time. This yields highly accurate results with much less effort. So instead of simply using this technique on one Neanderthal individual, they analyzed five.

The remains they chose had been excavated from a variety of locations, from Croatia to Germany to Spain and Russia.  Most of the remains were between 35,000 and 40,000 years old, which is very close to when Neanderthals were believed to have disappeared from most of their range.  They also examined Neanderthal remains from Russia that dated to between 60,000 and 70,000 years old.

After successfully extracting and analyzing the DNA of these remains, the researchers came to a few startling conclusions.  First, the level of genetic diversity among the samples was exceedingly low.  In fact, the amount of genetic diversity of the Neanderthal samples was less than one-third the diversity we see in modern humans today. For example, two of the samples — one from Croatia and the other from Germany — had identical mtDNA genomes. For two individuals living nearly 1,000 miles apart, this is quite unusual; unless there wasn’t much variation in mtDNA in the first place.

The authors of this report think this genetic homogeneity means that there were far fewer Neanderthals living in Europe and western Asia than they’d previously thought. Based on their analysis of the five individuals, the they estimated that the total population size of Neanderthals in Europe 35,000 years ago may have had as few as 3,500 females (because mtDNA is passed down maternally, it cannot be used to estimate male population size).

The authors believe there are two possible explanations for this small population size.  The first is that, over the 400,000 year history of Neanderthals, their population may have always been small.  After all, for much of their existence they survived harsh ice age conditions, so low population size may have been necessary for survival.

But the authors offer an alternate explanation as well. They think this small population size is the result of long-term population decline, perhaps beginning about 40,000 years ago and continuing until Neanderthals were wiped out. To test their hypothesis, the researchers re-analyzed the Neanderthal mtDNA genomes and found that their protein-encoding genes had evolved much more quickly than those of humans or chimpanzees since the three species split, millions of years ago.

This high rate of evolution, the authors argue, was not present in the older Russian Neanderthal sample.  This fact implies a pattern of decline in population size, not a population that had been small from the start. These results support their idea that the Neanderthal numbers were on the decline.  Without direct evidence, they can only speculate as to the cause of of their decline, but the scientists believe it may be tied to the arrival of humans in Europe and western Asia about 40,000 years ago.

Today most experts believe the Neanderthals were being out-competed by the incoming humans, who had superior technology and language skills.  Over time, the Neanderthals were forced to move to more isolated regions in the mountains of France and Spain.  By 30,000 years ago, only a few traces remained.  Soon after, they were gone.  This study reveals some compelling evidence that humans were in fact responsible – whether directly or indirectly – for the demise of the Neanderthals.

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It may be you’ve heard a rumor that males are on the brink of extinction.

Whatever you may think of that prospect, the rumor is false. But over the past decade, numerous studies have hinted that the Y chromosome, a male necessity, is going the way of the dodo.

Though other studies have suggested this idea may be a bit of an exaggeration, a new report this week suggests that the Y chromosome may indeed be endangered.

In most mammals, such as us humans, two chromosomes determine the sex of each individual organism:  the X and the Y.  If an individual’s cells contain two copies of the X chromosome, then they will be genetically female.  If they contain one copy of the X and another of the Y, they will be male.

Yet even though these aptly named sex chromosomes have a similar duty — to confer sex — the X and the Y could not be more different.  The most striking difference between the two is their size; the Y is less than half as big as the X, and contains only 78 genes, compared to the more than 2,000 found along the X chromosome.  The evolutionary history of the two sex chromosomes and the question as to why they are so different from each other has been the subject of heated debate for many years.  Now scientists at Pennsylvania State University believe they’ve found a way to uncover not only the difference between the X and Y, but how and why it arose and what this means for the future of the small, but essential, Y chromosome.  Their results are reported in the July 17 issue of PLOS Genetics.

The research team, led by biologists Kateryna Makova and Melissa Wilson, believes the key to understanding the origins and future of the Y chromosome lie in some of our most distant mammalian relatives.  There are three classes of mammals: egg-layers like the platypus, marsupials like the kangaroo, and the eutherians, which includes humans and thousands of other similar species.  While there are many differences between the three groups, one of the most striking is the difference in the organization of the sex chromosomes.  As Makova explained, “In eutherian mammals, the sex chromosomes contain an additional region of DNA whereas, in the marsupials and egg layers, this additional region of DNA [is not on a distinct chromosome, but] is [a region of] the non-sex chromosomes.”

The authors argue that the key to the origins of the X and the Y chromosomes may lie in this fundamental difference.  By analyzing the X and Y of humans compared to the sex-determining regions of marsupials and egg-laying mammals, Makova and Wilson found that the X and Y split from the other chromosomes about 80 to 130 million years ago.

But that is not all they found.  The authors also examined how fast the X and Y mutated over time, and noticed a startling change that occurred at about the same time as the split.  “Our research revealed that the Y-specific DNA began to evolve rapidly at the same time that the DNA region split into two entities, while the X-specific DNA maintained the same evolutionary rate as it had previously,” Makova explained.

In other words, as soon as the X and the Y split their own distinct chromosomes, the Y began to evolve much more quickly than its counterpart, mutating at a much higher rate with each new generation.  The faster the Y evolved, the faster its genes disappeared.  Whereas at one point the Y may have contained thousands of genes, that number has dwindled to the mere 78.

The disappearance of these genes over time and the small number of those remaining on the Y begs the question:  will the Y chromosome ever disappear entirely?  The authors believed this was an important question to answer as well, and began additional analysis to determine the fate of the Y.

Makova and Wilson reasoned that there must be some utility to the Y, or else it surely would have disappeared by now.  As Wilson states, “we know that a few of the genes on the Y chromosome are important, such as the ones involved in the formation of sperm … .  Although there is evidence that the Y chromosome is still degrading, some of the surviving genes on the Y chromosome may be essential.”  By performing additional tests, they found that there were indeed some genes on the Y that will probably never disappear entirely.  But they also found several genes that were already disappearing, and were likely to be gone many generations from now.

Some recent studies have produced evidence that the genes on the Y may not be disappearing as fast as was initially thought. But, according to Makova, the Y chromosome may not be out of the woods just yet. “We still think there is a chance that the Y chromosome eventually could disappear,” she says.  “[But] if this happens, it won’t be the end of males.”  Instead, she believes that a new pair of sex chromosomes will arise from the genome, latching on to those few remaining genes, keeping alive the genes necessary for male survival.

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Most experts agree that the earliest examples of farming and animal domestication lie in the aptly named Fertile Crescent, in present day Iraq.  But still many questions have lingered over the years, especially with regard to remnants of farming or animal domestication that have not survived to the present day.  What kind of tools did they use to farm the earliest crops? How did they transport these crops to neighboring communities? Now a new archaeological discovery in the mountains of Turkmenistan has finally given us more answers than questions, and has shed light on some of earliest farming communities in western Asia.

The finds center around the discovery of several model-sized carts at the archaeological site of Altyndepe, a Bronze Age settlement near the city of Ashgabat in southern Turkmenistan. These tiny carts may have been used in ritual ceremonies, or may have simply been the toys of young children.  But the most interesting aspect of these carts is that they depict camels as the main beasts of burden. Archaeologists are always interested in artifacts that reveal clues about daily life from ancient civilizations, and these camel-pulled carts are a comparative jack-pot.

An article about the carts recently appeared on the Discovery News website. They were documented by Lyubov Kircho of the Institute for the History of Material Culture at the Russian Academy of Sciences and are described (in Russian) in the journal Archaeology, Ethnology and Anthropology of Eurasia. An English version will be published in the Proceedings of the 19th International Conference of the European Association of South Asian Archaeologists.

Archaeologists have discovered cattle-pulled carts from the region, dating to about 6,000 years ago. These carts were originally used for transporting necessities like grain, but later carried other items like alabaster and the prized stone lapis lazuli from hundreds of miles away. Trade networks with neighboring communities began to spring up, and by 3,500 BC one of the first dedicated ‘highways’ for vehicles ran between Altyndepe and nearby towns in present-day Iran and Afghanistan.

But by 3,000 BC, the climate was becoming more arid and the people of Altyndepe could not longer trust their cattle-pulled carts to make the long journeys. Archaeologists already suspected that the communities must have switched to camels, which were better able to handle the drier climate. Now these model carts show that their suspicions were correct; camel-pulled carts were the standard for this region, and were such an integral part of daily life that miniature versions were created as children’s toys.

The presence of these carts – combined with previous ideas on the sharing of ideas and culture throughout this part of western Asia – also have implications for the genetic history of the region. It is well documented that about 10% of modern Europeans contain a genetic signature of the early agriculturalists who arrived from the Near East beginning about 9,000 years ago, bringing their farming techniques and DNA with them. Scientists now believe that while some of these Near Eastern farmers did travel west into the heart of Europe, others headed into the plateaus and foothills east of the Caspian Sea. Like their western counterparts, these farmers brought their farming tools and techniques to the indigenous people of southern Turkmenistan. And like their western counterparts, they probably brought their genes. In fact, some genetic studies have examined the genetic make-up of modern day residents of Turkmenistan, and have found that many of these people also bear the genetic signatures of the early farmers of the Fertile Crescent.

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Not many people could survive the harsh conditions of the Sahara Desert.  Yet the Tuareg have lived in the the region for millennia.

The Tuareg call themselves the Imazghan, meaning “free people.” Today they are known for a distinctive dark blue turban worn by the men, and for their long history as gatekeepers of the Sahara Desert. They are a semi-nomadic people who inhabit the West-Central Sahara, which encompasses parts of western Libya, Algeria, Mali, Niger, and some neighboring countries.

The Tuaregs were first mentioned by the ancient Greek historian Herodotus, who spoke of a group known as the Garamantes living in the Fezzan region of southwest Libya that operated trans-Saharan trade routes, connecting the heart of Africa to the North African coast. It is now believed that he was speaking of the Tuareg.

Though known to scholars since Herodotus’ depiction thousands of years ago, the Tuaregs remain shrouded in mystery. Their extreme isolation in one of the earth’s harshest environments has made them difficult for cultural anthropologists to study.  There have been only a handful of studies published on the Tuaregs’ genetic history, and even these examined only the genetics of western Tuaregs from Mali, Niger and Nigeria. The eastern Tuaregs who inhabit the Fezzan of Libya remain far less studied.  So a team of scientists decided to rectify this lack of genetic data, analyzing the mitochondrial DNA (mtDNA) of more than 100 Tuaregs from the Fezzan region of Libya. Their results are reported in the July issue of Annals of Human Genetics.

The authors chose to analyze the mtDNA for a variety of reasons, but mostly as a way of comparing their results to the previous genetic studies that had also used mtDNA. After extracting the DNA of the Tuaregs and assigning each individual to a specific maternal ancestry branch, or haplogroup, they found that the majority of Tuaregs fell into the same haplogroup: H1. In fact, over 61% of the individuals bore haplogroup H1.  This piqued the researchers’ interest, mainly because H1 is often thought to have spread with people from the Iberian peninsula across Europe after the end of the Last Ice Age about 12,000 years ago. The results of this study indicate that somehow H1 must have traveled into North Africa as well.

Not only did the researchers find that so many Tuaregs bear the same maternal haplogroup, but there was low genetic diversity among the population overall. This low genetic diversity can be tied to the fact that the Tuaregs are a very isolated people, and it is uncommon for them to venture too far outside their community when looking for a spouse. Indeed it seems that these Libyan Tuaregs are even genetically isolated from their West African counterparts, who showed far less European ancestry and far more ancestry tracing back to sub-Saharan Africa, despite the fact that both eastern and western Tuaregs share a common language and culture.

The authors have used these bits of information to piece together a scenario for the origins of the Libyan Tuaregs.  Environmental data reveal that, about 5,000 years ago, the Sahara was quickly shifting from its post-Ice Age period of relative stability and good living conditions to a less stable and more arid environment. This shift, the authors propose, was responsible for a series of human migrations throughout the Sahara that led different Tuareg groups living in the region to separate.  It caused other Tuareg groups to intermingle with neighboring groups.  Some Tuaregs, like those in Mali, Niger, and Nigeria, probably had more contact with sub-Saharan West Africans, which accounts for the higher percentage of sub-Saharan maternal haplogroups found by previous genetic studies.  Others, like the Libyan Tuaregs analyzed here, may have met and mingled with groups such as the Berbers of the Mediterranean coast of North Africa.  Apparently migrations from Spain after the Last Ice Age, across the Strait of Gibraltar into Morocco, brought H1 into the African continent. It then made its way into the North African Berber populations, eventually finding its way into the Libayan Tuaregs.

And what of the 35% of Libyan Tuaregs with sub-Saharan African genetic ancestry?  The authors of this study believe this to be a genetic signature of the trans-Saharan slave trade, which the Libyan Tuaregs famously operated during the 1st century BC, and which brought them to the attention of Herodotus so many years ago.

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Type 1 diabetes is on the rise in European children, says a new report.

Researchers studied type 1 diabetes data collected between 1989 and 2003 at 20 centers in 17 European countries. Their results, published online yesterday in the Lancet, show that more children, especially younger children, are being diagnosed with the disease each year.  Based on the trends they saw, the scientists calculate that there were 94,000 kids under the age of 15 with type 1 diabetes in Europe in 2005, and that by 2020 that number will soar to 160,000.

While researchers aren’t exactly sure why this is, they do know that it’s not due to changes in the prevalence of susceptibility genes.  Genes just don’t change that quickly.

An almost 70% increase in disease prevalence in one generation must be due to changes in non-genetic factors. Most random genetic changes in a population come and go pretty quickly, especially mutations that reduce fitness.  And if a new mutation does manage to stick, it would take millions of years, not tens of years, to see its effects.  Even for mutations that provide a benefit, like the one that led to the lactose tolerance seen in many people with European ancestry today, it takes a few hundred years to build-up to high enough levels in the population to cause an observable change in a trait.

An increase in disease incidence due to changes in non-genetic factors, whether they are environmental or cultural, has been seen for many diseases.  It’s especially apparent when groups migrate from low- to high-risk countries for a particular condition.  Just this month a study showed that Asian Americans who are more “westernized” have adopted the sunbathing ways of their families’ new homes, which the authors suggest may be the cause of increasing rates of skin cancer in this group.

But the effects of lifestyle changes can also be seen in shifts in disease rates within a population. The prevalence of obesity in United States adults, for example, jumped from 15% in the late 1970’s to nearly 35% today thanks to the trend toward eating more and exercising less.  And because of the increase in obesity, rates of type 2 diabetes are also up.

Many scientists attribute the increase in incidence of several immune system-related disease to what on the surface seems like a good thing about modern lifestyles: fewer infections.  The so-called “hygiene hypothesis” suggests that without the types of infections our species evolved to deal with (many of which are still prevalent in developing nations), our immune systems don’t get the right training.  The lack of challenges to the immune system has been linked to increased rates of allergic diseases like asthma and eczema and autoimmune diseases like Crohn’s and multiple sclerosis.

For some diseases, the reason behind their apparent increases has more to do with increased detection than changes in environment. Up until a few years ago, for example, it was thought that only about one in every 3,000 people in the United States had celiac disease.  But now, thanks to better guidelines on how to diagnose the disease, physicians are finding that about one in every 133 is affected.

On the other hand, some conditions may appear to be increasing because disease awareness is a hammer that makes a lot of people feel like nails.  It has been put forward that restless legs syndrome, for example, is far less prevalent than some estimates suggest and that increases in diagnoses can be traced to “disease mongering” by pharmaceutical companies.

The authors of the Lancet study suggest that the changes in type 1 diabetes rates they are seeing are due to something about modernization.  They point to the fact that the biggest increases were seen in eastern European countries, which have seen the most rapid changes in lifestyle in the last few decades.  But whatever the culprit is, it is obviously not affecting all children.  And that’s where genetic susceptibility comes in.  DNA variations that increase risk may not be changing in prevalence, but type 1 diabetes, like almost every other common disease, is the result of a complex interplay of genes and environment.

(23andMe customers can see how their genes influence their risk of type 1 diabetes in Clinical Reports.)

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