Great apes really do giggle when tickled, new research says – just like you and me.

Researchers from the University of Hannover in Germany recorded the tickle-induced vocalizations from three human infants and 21 infant and juvenile orangutans, gorillas, chimpanzees and bonobos and analyzed this acoustic data to find similarities and differences among the five species.  Their results, published online today in the journal Current Biology, show that not only are the hoots, hollers and snorts of the great apes really laughter, but the evolutionary relationships between the sounds match up with the known evolutionary relationships between the species based on genetics.

“At a minimum, one can conclude that it is appropriate to consider ‘laughter’ to be a cross-species phenomenon, and that it is therefore not anthropomorphic to use this term for tickling-induced vocalizations produced by the great apes,” the authors write.

But the researchers’ findings also indicate something more profound: rather than being a uniquely human invention, tickle-induced chuckles can be traced back 10 to 16 million years to our last common ancestor with the great apes. Analysis of the chortles of a lesser ape, the siamang, suggests that laughter may be even older.

The tree based on laughter matches the genetic tree.

Despite the all the similarities the researchers found between humans and the great apes, the fact remains that human giggles are distinct – we mostly laugh while exhaling and our vocal chords vibrate to make the “ha ha ha” sounds, while ape snickers are more of the in-and-out panting variety.  The question for future research to answer is why particularly human features emerged and what functions they may have served as laughter became a large part of human social interaction.

Insanely cute video of giggling chimps here.

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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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Almost since the 1871 publication of “The Descent of Man,” in which Charles Darwin applied his theory of natural selection to the human species, biologists have argued over whether the dramatic series of evolutionary events that led to the emergence of Homo sapiens continues to this day.

Some have argued that culture and technology have eclipsed the powerful biological forces that shaped our species in its formative years. In their view the species, no longer faced with a daily struggle for survival, is adrift in an evolutionary Sargasso Sea.

“There’s been no biological change in humans in 40,000 or 50,000 years. Everything we call culture and civilization we’ve built with the same body and brain,” the famed evolutionary biologist Stephen J. Gould once said in an interview.

In their new book “The 10,000 Year Explosion,” anthropologists Henry Harpending and Gregory Cochran argue the contrary position. They claim that in fact, far from grinding to a halt, human evolution has accelerated dramatically since the origins of agriculture about 10,000 years ago.

“We intend to make the case that human evolution has accelerated in the past 10,000 years, rather than slowing or stopping, and is now happening about 100 times faster than its long-term average over the 6 million years of our existence,” they write.

In evolutionary terms, 10,000 years is no time at all — about 400 human generations. Rabbits can go through 400 generations in not much more than a century — can you imagine rabbits being substantially different than they were 100 years ago?

Far from ending the chain of dramatic evolutionary changes that led to upright walking, advanced cognitive abilities and spoken language, Cochran and Harpending argue, the adoption of agriculture so dramatically changed the human environment that a new wave of genetic innovations flourished. These new genetic variants thrived because they helped people cope with the challenges an agricultural way of life presented, such as the shift to a low protein, high carbohydrate diet; the creation of an organized, stratified society and the rise of infectious diseases in response to increased population density.

In fact, many of the genetic variations that 23andMe provides information about are relics of those evolutionary changes. The SNP that confers lactose tolerance, for example, appears to have arisen in Europe about 8,000 years ago among the first people to herd cows and other milk-producing animals. The lactose-digesting variant quickly spread throughout the parts of Eurasia that were ecologically suited to pastoralism.

There are also a number of genetic variations covered by 23andMe that cause physiological problems when two mutated copies are present, but provide protection against infectious disease when a person has one of each version of the gene. For example, the genetic variations that cause sickle cell anemia and G6PD deficiency confer resistance to malaria. Geneticists call this situation balancing selection; over the entire population, the reproductive cost to those who end up with the genetic disease is outweighed by the benefit to others who are resistant to the infectious one.

At the end of the book, Cochran and Harpending make the controversial argument that balancing selection is responsible for the increased incidence of a number of genetic diseases among people of Ashkenazi Jewish descent — and for their higher intelligence relative to other groups.

The authors do raise some interesting points about the anomalously high frequency among Ashkenazi of genetic disorders that stimulate the growth of neurons in the brain. And they cite studies that have shown increased intelligence among people with some of these diseases.

But genetic explanations for between-group differences in intelligence are best taken with a whopping dose of skepticism. Even the definition of intelligence is a matter of intense debate, not to mention the degree to which it can be inherited through genetics. in the end, their case is little more than a just-so story.

In telling it Cochran and Harpending blunt the rest of their book’s powerful message: human evolution is not over by a long sight.

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Generally when you think about what separates humans from other species, features like upright walking, large brains and language come to mind.

But diet has actually played an enormous role in human evolution. Today at the annual meeting of the American Association for the Advancement of Science, a panel of anthropologists, geneticists and paleontologists got together to discuss how who we are has been shaped by what we eat.

Perhaps the most surprising conclusion was that — despite what some diet gurus may say — there is no “natural” human diet. Not only can humans thrive on a wide variety of diets, from the highly carnivorous fare of nomadic Siberians to the virtually all-potato menu consumed by native Peruvians, but thanks to evolution our species can change its diet surprisingly readily.

“You can find humans living well and healthily from a tremendous diversity of diets,” said William Leonard, an anthropologist at Northwestern University in Evanston, Ill.

But all cultures have one dietary feature in common, said Harvard University primatologist Richard Wrangham — they cook their food. Wrangham believes the advent of cooking during human prehistory was a major evolutionary milestone, because it essentially pre-digested starches and proteins and softened food, helping increase the amount of energy that could be extracted on it. In fact, he pointed out that people in modern technological societies who take up so-called “raw food” diets usually lose substantial amounts of weight.

Many diet books advise following a high-protein, low-carbohydrate diet in order to emulate the eating habits of pre-agricultural humans. Whatever the benefits of such a diet, however, it is clear that in the 10,000 years since the development of farming our genes have responded to the increasing availability of foods such as rice, grains and milk.

“I would say most people who descend from agricultural populations are actually pretty well adapted to a starch diet, because most of the world eats a lot of rice, a lot of corn and a lot of potatoes, said Anne Stone, a geneticist at Arizona State University.

Stone and her colleagues have studied the gene AMY1, which encodes a salivary protein called amylase that breaks down starch. All people have multiple copies of the AMY1 genes. But those from traditionally agricultural populations, such as the Japanese and Europeans, have many more than those from cultures that have never practiced agriculture.

Customers of 23andMe may be able to see the evolutionary effects of an agricultural heritage in their own genetic data. Before people started herding cattle, goats and sheep, the human biological machinery for digesting milk was turned off not long after infancy — perhaps to prevent older children from getting in destructive fights over breast milk. But with herd animals on the scene, when a genetic modification that kept milk digestion functioning into adulthood arose in Europe around 8,000 years ago, it was so beneficial that it eventually spread throughout the continent.

23andMe customers have one modified version of the lactase gene for each A at the SNP rs4988235.

Similar scenarios happened in several other parts of the world as well, so that now many people of European and some of African ancestry can easily digest large amounts of milk.

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The Spittoon has pointed out several times in the last few months (here, here and here) that when researchers look for evidence of interbreeding between early humans and Neanderthals, they often fail to find any.

But there are still a number of geneticists who would like us to pay heed to the words of former defense secretary Donald Rumsfeld, who once pointed out that “the absence of evidence is not evidence of absence.”

During a briefing for science writers this morning at Stanford University, geneticist Bruce Lahn argued that interbreeding with Neanderthals may have introduced into the human gene pool a mutation that appears to confer an evolutionary advantage with regard to brain development.

“We argue that in modern humans there may actually be some Neanderthal genes,” Lahn said at the Council for the Advancement of Science Writing’s New Horizons in Science briefings.

Lahn based his argument on a gene known as microcephalin. Because certain mutations in the gene can cause underdevelopment of the brain, microcephalin is assumed to be involved in that organ’s development.

Lahn described research that he and several colleagues first described two years ago in the Proceedings of the National Academy of Sciences. The researchers sequenced microcephalin in 89 people from populations around the world. They found that the sequences fell into two very different groups — so different, in fact, that they apparently traced back to a common ancestor older than the human species itself.

Moreover, each of the two groups appeared to have a very distinct history of its own. One appeared to have arisen about a million years ago, and diversified at a steady pace since then. The other group, however, appeared to have arisen just 37,000 years ago and spread rapidly throughout 70% of the human population. That kind of pattern suggests what evolutionary biologists call a “selective sweep,” the introduction of an advantageous genetic variant that quickly wipes out older versions of the gene.

Usually when geneticists see a selective sweep in action, the new variant appears to arise out of the pre-existing one. But in this case, Lahn argues, the new genetic variation traces back to a common ancestor that precedes both populations. He believes Neanderthals could have been that population, and that they could have transferred the “new” variation to the into the human gene pool through interbreeding about 40,000 years ago.

It’s just a hypothesis at this point — and one that many geneticists consider difficult to confirm. But if ongoing efforts to sequence the Neanderthal genome find a version of the microcephalin gene identical to the one that is currently sweeping through the human population, Lahn will have strong evidence for his claim.

Photo: K. Mowbray

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Before efforts to sequence the human genome began, scientists thought they’d find about 100,000 protein coding genes in the three billion bases pairs of DNA that are found in almost every cell. But much to everyone’s surprise, the true number turned out to be much lower. It’s now thought that the human genome contains only about 20,000 protein-coding genes, representing less than 2% of the contents of the genome.

Much of the remaining 98% of the genome remains a mystery. Some chunks of this DNA are referred to as “ultraconserved elements” because they have remained practically unchanged through hundreds of millions of years of evolution in many species.

It is a basic principle of biology that if something goes unchanged for that long, it ought to be good for something. Yet the function of ultraconserved elements is completely unknown. In fact, laboratory studies in mice have shown that the animals do just fine when some of the ultraconserved elements are deleted.

To find out if ultraconserved elements really are dispensable, Cory McLean and Gill Bejerano of Stanford University analyzed ultraconserved elements and non-conserved DNA sequences in five mammalian genomes.

Their results, published online today in Genome Research, show that regions of DNA that are identical or very similar between humans, macaques, and dogs are about 300 times less likely to be missing in rats and mice than regions that are not as closely conserved between the primate and dog species.

It’s not that ultraconserved regions are somehow protected from change. The researchers suggest that in the wild, mutations in these elements put affected animals at a disadvantage, causing the changes to be swept away over time by natural selection. But in the lab there isn’t a whole lot of natural selection — in an environment where mice are treated to filtered air, an absence of predators, and all the food and water they could ever want, any loss of fitness due to lost ultraconserved elements doesn’t seem to have any observable consequences.

McLean and Bejerano also found that DNA sequences that can be traced farther back in evolutionary time are more likely to be conserved in diverse species today.

“The longer the sequence has been in us, the less likely it is to be lost. It’s almost like the bricks in the foundation of a building, which hold up the rest of the structure,” said Bejerano in a statement.

Detailed new genome sequences from a variety of mammals will allow Bejerano’s research team to further analyze ultraconserved elements and perhaps ultimately understand what it is they are doing in the genome.

“Evolution is a lot of fun,” said Bejerano. “You answer one question, and five others pop up. But one of the most rewarding things to me is the fact that we’re developing a growing appreciation for how much these regions actually matter.”

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An animal’s ability to survive often depends on how well it can avoid predators.  Many species of fish, birds, and mammals have evolved ingenious methods of staying hidden from predators by blending into the background in one form or another.  

But what about animals that do the opposite?  How and why would such attention-grabbing features as a lion’s mane, a male deer’s antlers, or a peacock’s tail evolve?  

As it turns out, these traits can be explained by something called sexual selection.  Sexual selection is an aspect of evolutionary theory developed by Charles Darwin in the 19th century after he began to notice many traits that were exaggerated, especially among the male members of the species.  Darwin reasoned that within a species, there must be a “struggle between the individuals of one sex, generally the males, for the possession of the other sex.”  So in the same way that women may prefer men with broad shoulders, female peacocks prefer their male counterparts to have ornate feathers – the larger the better.

Evolutionary biologists have understood the concept of sexual selection for years, but there has been much debate over how this process occurs at the genetic level.  For example, male and female lions have basically the same set of genes. So how are these genes modified such that male lions develop a mane while females do not?  The answer, as it turns out, is surprisingly simple.

In this week’s issue of Cell, molecular biologists tackled the question of how sexual selection works by examining the genetics of fruit flies. Male fruit flies have evolved a unique coloring pattern on their abdomens that apparently attracts females in the same way that a peacock’s feathers do.  Females lack the markings, yet they have basically the same genome males do. So how is it that the same basic genome (aside from sex chromosomes) can lead males and females to develop different physical traits?

According to University of Wisonsin-Madison biologist Sean Carroll, “The flies did not need new genes … they just changed how males and females use a common set of genes.”

Carroll and his team discovered that while both male and female fruit flies have the genes necessary to create the abdominal coloring pattern, it is only the males who have that gene switched on.  In female fruit flies, this gene lies dormant.

“With this particular trait, it evolved by exploiting (genetic) information that was already there to make male bodies different from female bodies,’ explains Carroll.

So how does the genetics of a coloring pattern on fruit fly abdomens apply to sexual selection in other species?  According to Carroll and his colleagues, the same genetic mechanisms that are at play in the fruit fly also operate in a multitude of other animals – including lions, deer, peacocks, and even humans.  

This study, in showing the genetic means for how sexual selection may operate, illustrates the ingenuity of evolution – how a seemingly simple genetic switch can create such beautiful and elaborate features in the male members of thousands of the world’s species.

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Despite mounting genetic evidence that modern humans are not descended from Neanderthals, there are still some who argue that our two species interbred when both roamed Europe about 35,000 years ago.

A report appearing tomorrow in the journal Cell puts another nail in that theory’s coffin. Svante Paabo’s group at the Max Planck Institute for Anthropology in Germany has produced the first-ever complete sequence of a Neanderthal’s mitochondrial genome. Their analysis shows that the last common ancestor of humans and Neanderthals walked the Earth on the order of 660,000 years ago – hundreds of millennia earlier than the most recent common ancestor of all humans living today.

Mitochondrial DNA is passed down intact from mother to child. All people living today can use mitochondrial DNA to trace their maternal line back to the Mother of all Mothers (MoM), who probably lived about 175,000 years ago in eastern Africa.

When working with ancient DNA, researchers have to contend with several technical problems. Contamination by DNA from laboratory workers must be carefully avoided. And even if contamination is controlled, the inevitable chemical breakdown of DNA that has been buried for thousands of years can skew results. Lead author Richard Green and his colleagues avoided both of these pitfalls by sequencing the mitochondrial DNA nearly 35 times over.

“For the first time, we’ve built a sequence from ancient DNA that is essentially without error,” Green said in a statement.

The authors say that their success at sequencing the mitochondrial genome of a Neanderthal will help in their ultimate goal of sequencing the species’ much larger and more complicated nuclear genome, which could then be compared with a modern human genome to identify genes that were important in the emergence of Homo sapiens.

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Art Nouveau architecture at the Codorníu winery outside of Barcelona.

So much new research was discussed in Barcelona it’s hard to decide which were the most notable presentations. But here are a few of the ones I found most interesting:
Were humans shaped more by history or local environment?
A major debate in the human evolutionary genetics talks and posters considered the origin of the genetic differences seen in humanity today: Were they shaped more by populations splitting apart and coming together, or evolutionary adaptation to local environments? Interestingly, people from the lab of our SAB member Jonathan Pritchard presented arguments on both sides. Both talks presented strong evidence using similar data sets. Perhaps one phenomenon has more impact locally and the other more regionally. Certainly the debate continues.

James Cai and coauthors from Stanford (including our very own R&D scientist Mike Macpherson) and The Hebrew University of Jerusalem showed that the history of the human genome cannot be explained simply by neutral variants – variants that do not cause a functional change. All across the genome there is evidence of “selective sweeps” where an advantageous version of a gene quickly increased in frequency in a population or species. For example, the gene FOXP2 has undergone a selective sweep in all humans within the past several hundred thousand years and may have contributed to our ability to use advanced language. More recent selective sweeps in the Duffy and Lactase genes (both have variants that 23andMe customers or demo account holders can read more about in My Gene Journal (now called Health and Traits)) happened after human populations diverged and thus didn’t sweep across the entire globe but are confined to specific regions: primarily western Africa for the Duffy-0 variant and Europe, the Near East, eastern Africa, and southern Asia for Lactose Tolerance.

Selective sweeps tend leave evidence in the form of nearby DNA that gets dragged along with the variant as it sweeps across a population. Similarly, new variants that are disadvantageous (or become disadvantageous when, say, moving into a new environment) can leave these similar signals as they are dragged out of the population. However, it is often difficult to separate out effects of population history from these selective forces. By using a novel statistic that controls for population history, Cai and colleagues show that many locations on the human genome have been affected by these selective sweeps. While previous scans for positive selection required these selective sweeps to be incomplete (see here and here, for example), the authors use a metric which can go back even further to look at the timing and strength of selective sweeps which have affected the entire human population, even going back as far as one million years. This work is an extension of previous research on Drosophila.

Interestingly, one of the data sets used for this work was the complete genome of Jim Watson, who co-discovered the structure of DNA.

Population Structure, History, and Migrations
Sarah Tishkoff of U. Penn gave a talk on her incredible data set of sub-Saharan African populations. So much of the world’s genetic diversity is located in this region, yet its inhabitants have been relatively under-sampled so far. Tishkoff’s data, in the context of global variation, makes it apparent just how important it is to understand the history of sub-Saharan populations in order to understand the history of our species. In one example, Tishkoff used a technique known as Principal Components Analysis (PCA) to collapse all their genetic data into three dimensions. Individuals near each other in PCA are more similar. In her plot, a hunter-gatherer population from Tanzania known as the Hadza can be found in their own dimension on the plot, which suggests that the Hadza, while having a small population size, have been isolated for a long, long time and are quite divergent from other populations, even including the 52 in the CEPH-HGDP data.
Tishkoff also showed how difficult it is to extrapolate from one African population to the next, even if they neighbor each other. One example of this is in parts of western Africa where the Fulani have increased malaria resistance compared to other groups such as the Mossi and Rimaibe – even within the same town.
Several talks and posters looked at the new lactase persistence variants discovered last year in sub-Saharan Africa and the Near East. These variants are functionally the same as their much more common counterparts, which allows Europeans and South Asians to drink milk into adulthood without experiencing lactose intolerance (23andMe customers can look up their genotype for this variant in My Gene Journal (now called Health and Traits)). But because they differ genetically, these newly discovered variants illustrate the importance of milk digestion for populations that relied on herding in their past. Multiple research groups showed that the eastern African persistence variants made their way down to the San Bushmen and neighboring populations of southern Africa.
When normal inheritance breaks down

Genomic imprinting in action. Here, the color of the offspring comes from the father, regardless of which genotype he has.

Andrew Clark of Cornell has been looking at versions of genes in mice that change the traits of offspring depending on whether they are inherited from the mother or father. This phenomenon, called Genomic Imprinting, has been detected in many mammals before, including humans, although interestingly it isn’t found in marsupials or the egg-laying monotremes like the Platypus. However, the traits affected by genomic imprinting have not been surveyed using a genome-wide approach.
Clark and colleagues used the Solexa sequencing platform to look for differences in the mouse brain between mice crossed from two different strains. By switching the strains of the mother and father researchers can detect traits that derive exclusively, or “imprint on”, one parent.
It turns out a good number of genes exhibit genomic imprinting Genes imprinted on the father tend to show only the trait of the father. Genes imprinted on the mother tend to let some of the father’s trait come through, albeit at much lower numbers. In addition, the researchers found differences in the organs affected by imprinting: genes imprinted on the mother were more likely to be expressed in the reproductive organs and those imprinted on the father were found more in the brain.
It appears that imprinting has no immediate benefit for offspring and may have originated in mammals completely by accident, a quirk of our histories. But learning about how imprinting evolved will help us understand how they came to be.

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The Stormtroopers in Star Wars were modeled after these air vents at La Pedrera in Barcelona.

Part One: Benvinguts a Barcelona!

The pace of genetics research has increased dramatically over the past few years. What was possible only in a large, well-funded lab a few years ago can now be done by a solitary grad student on a laptop.
Many people at the conference were studying large publicly available sets of genetic data, such as the 23andMe-sponsored data set of 650,000 SNPs from 1,000 individuals in 52 populations (data available here, for those interested). Others were taking advantage of next-generation sequencing platforms (such as 454 and Solexa) to investigate everything from differences in protein expression in different strains of mice to the genetic makeup of extinct organisms – even Neanderthals.
Over the next few posts in this series I’ll discuss some of the most interesting talks and topics; but I’ll start with why we went to Barcelona.

Maternal history of populations

We were happy to present research we’ve done that puts a date on every major branch point in the human mitochondrial DNA tree. Because mitochondrial DNA is passed directly from mothers to their offspring, it can be used to trace the maternal ancestry of every person on the planet (for customers and demo account holders, that’s the maternal line feature). We used more than 4,000 publicly available complete mitochondrial genomes from Genbank, assigned to maternal haplogroups using their full sequence, to accomplish this goal.
Why would we want to do this? Well, calculating the dates of common ancestors allows us to tell someone how long ago he or she shared a maternal relative with a friend, coworker, or even a celebrity. Our study is the first time all the haplogroups on the tree (or at least over 550 of them) have been dated all at once. For example, thanks to our research 23andMe can state confidently that Jesse James and Jimmy Buffett can both trace their female lineages back to a single woman who lived 60,000 years ago, probably somewhere in the Near East.

In addition, by looking at dates of common ancestors across the entire maternal tree we can fill in some details relating to the history of our species. We know that everyone living on Earth today descends from a woman who lived in Africa around 175,000 years ago. But each lineage that connects back to that woman has had a different history of mutations. Looking at this mutation history can tell us about the different groups of humans that expanded from eastern Africa to settle across the planet. For instance, we might be able to tell if certain groups were large or small when they split off from the tree, or whether they faced different environmental challenges that led to their rise or fall.
Interestingly, we see an increase in mutation rates along certain mitochondrial DNA lineages that arose after the out-of-Africa expansion around 50-60,000 years ago, but before the glaciers retreated in the last Ice Age (around 18,000 years ago). This contradicts previous work – maybe because we used much more data than previous studies and it was gathered from a much more diverse set of people. Whether the increased mutation rates were due to natural selection as humans moved into different environments or other events in the history of our ancestors remains to be seen – we’re working towards resolving the importance of various evolutionary processes in the history of the human maternal lineage.
In the next installment, I’ll blog some more about other interesting topics and presentations at the SMBE conference.

Adéu for now!

Click here for a PDF of our poster entitled: “How do you date all humans at once? The use of complete genomes to date nodes on the human mitochondrial tree.”

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