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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When scientific research is published, the authors often confess that they wish they’d collected more data. Critical reviews of research studies often say the same thing. Indeed, if there’s anything scientists love, it’s more data.

Which is why the members of an international team of genetic anthropologists led by Sarah Tishkoff of the University of Pennsylvania are probably quite pleased with themselves. In a new study published this week in Science, the team took the concept of “more is more” to heart by collecting and analyzing the DNA of thousands of people, mostly from Africa, so that they might uncover more clues to not only the genetic make-up of modern Africans, but also the genetic history of Africans and non-Africans alike.

The scientists’ first step was to collect DNA from a diverse set of Africans. Africa is the most culturally and linguistically diverse place on Earth, so it was important to take a wide sample of individuals from all corners of the continent. In total, they collected 2,432 DNA samples from 113 diverse and distinct groups of people from across the African continent as well as 60 non-African groups. They sampled everyone from the Mozabite Berbers of Morocco to the hunter-gatherer San of the Kalahari Desert, and many in between.

But the hard work didn’t stop there. The scientists then examined 1,327 genetic markers across the human genome for each individual studied. While many studies focus on a particular part of the genome such the mitochondrial DNA or the Y chromosome, this study took a comprehensive approach. Finally, the researchers used sophisticated statistical techniques, piecing together how these populations from Africa and around the world were the same, and how they were different.

The results confirmed that Africa has the highest genetic diversity of any continent, as many scientists have proposed. In fact, the authors found genetic diversity to decrease the further one traveled away from Africa. Genetic diversity is often used as a measure of how long ago humans inhabited a region — conventional wisdom places the earliest humans in East Africa, which had exceptionally high genetic diversity according to this study, though an analysis by the researchers put the origin of the human expansion farther south near the border of Namibia and Angola.

The study also shed light on the incredible genetic diversity among African populations, said Roy King, a professor of psychiatry and anthropological geneticist from Stanford University:

Not only did farming and pastoral communities differ from hunter-gatherers, but within the broad range of agricultural populations of West and West-Central Africa — from which many African Americans derive their ancestry — the authors also found some genetic diversity. For example, the Dogon of Mali, although geographically near the Mandinka of Senegal, cluster with North African Berber populations. Thus, this study supports the notion that not only is Africa varied in culture — art, music, religion and language — but also harbors a rich genetic diversity across its multitude of ethnic groups.

The authors also found a loose connection between the genetics of a population and its language. However, there were a few exceptions, most often the result of a population adopting a new language within the last few thousand years.

The sheer size and diversity of the DNA samples collected allowed the researchers to construct a human family tree based on their analyses. Not unexpectedly, the tree they constructed fits well with current theories on the genetic relationship between Africans and non-Africans; namely that all non-Africans are descended from a particular group or groups of people who were the first humans to migrate out of Africa tens of thousands of years ago.

This study is important for a multitude of reasons. It has been able to confirm theories from the archaeological, cultural, and linguistic records on the origins and movements of Africans and non-Africans.

“It fits nicely with earlier genetic studies, while subverting the early 20th century colonialist idea of sub-Saharan Africa as constituting a homogeneous genetic an cultural unit,” King said.

It also creates a new resource that historians, linguists, archaeologists and scientists from a range of other disciplines can use in their own work. If we are lucky, this study will bring forth a flurry of activity surrounding the origins and history of the African continent, and the people who live there.

Credit: istockphoto/Erie

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I spent the better part of my undergraduate career lugging around massive biology textbooks.  General biology, genetics, embryology: It didn’t matter, they all weighed a ton. I pored over endless chapters of text, highlighting the important sentences, always wishing for more photos, more diagrams, more graphs. A single well-made diagram or image was easier to understand than the preceding 10 paragraphs about the same topic.  I always wished that my textbooks were a little more visual and a little less wordy.  An added benefit, I thought, would be that I could shave a few pounds from my backpack.

My college days are long over. But my wish may have finally come true, in the form of a new graphic guide to genetics entitled The Stuff of Life: A Graphic Guide to Genetics and DNA, by Mark Schultz.  Published in December, it takes a more visual approach to presenting the most current knowledge on a particular branch of the biological sciences close to my heart: genetics.

The Stuff of Life is centered around a group of aliens who are trying to understand the genetics of all life on earth. These aliens are both rather ugly (the illustrator has drawn them to resemble sea cucumbers) and rather arrogant. They can’t seem to understand why a lowly, hairy primate has come to dominate the planet and make such amazing advances in science and technology. In the style of a comic book, with various windows and balloons leading us from the origins of the earth 4.6 billion years ago to modern day applications of genetics and DNA, it falls flat in oddly juxtaposing complex information and somewhat juvenile humor.

For anyone who hasn’t taken a college (or advanced high school level) biology class, the information presented will seem overwhelming at best, and confusing at worst. For those who are well versed in the biological sciences, the information may be understandable but the humor will seem trite and silly.  After the first few chapters of the cucumberesque aliens repeatedly exclaiming that they can’t believe humans have managed to understand how genes are passed down from parents to children, that they can’t believe humans have been able to sequence DNA, understand the genetics of cancer, and create genetically modified organisms, I began to dread their appearances. I stopped reading the sections focused on them, instead skipping to the parts that contained actual information. Once I did I began to enjoy the book much more.

The organization of the book is similar to a standard introductory genetics textbook.  It begins with a description of the structure of the cell, DNA, and how the genes housed within our DNA can determine thousands of physical traits.  Schultz then moves quickly forward, presenting important genetics concepts such as inheritance, dominant vs. recessive alleles, and why my cat has two different colors of fur.  Finally, he spends the last one-third of the book examining modern-day applications to the study of genetics.

The strategy works well by allowing the reader to understand the practical value of understanding the basic genetics concepts that were brought up in earlier chapters.  Indeed, having more applications-centric lectures during college might have silenced the students who never understood why this field is so important.  Undoubtedly, this section was written with the more general reader in mind.  It is easily the best section of the entire book.

Though the constant banter from the sea cucumber-like aliens should not interest anyone over the age of 10, this book would be of use to those currently taking an introductory course in biology, as it might help solidify more difficult concepts that might prove difficult to students.  For educators, this book could prove useful in providing fresh ideas on how to present some of the most important genetics concepts.

The uneven feeling I got from reading The Stuff of Life is something that must constantly be a fear for anyone who is trying to make science fun and accessible to the general populace.  Presenting such important topics as genetics and DNA that are easy for anyone to understand, scientifically accurate, AND enjoyable, is no easy feat.  And, while The Stuff of Life may have stumbled in some aspects, it is most certainly a noble effort, and may lighten the load in biology majors’ backpacks in the coming months.  I sincerely hope that Schultz continues with more volumes, though I could do without those sea cucumbers next time.

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Over the past decade, there has been no shortage of studies focused on the relationship between Neanderthals and our own species, Homo sapiens. Researchers have dug deep into the fossil record and our genomes to uncover how closely related we are to the Neanderthals, whether we interacted with them, and even whether our two species shared offspring.

But what about the Neanderthals themselves? We know that beginning around 400,000 years ago, they occupied over 3 million square miles of Europe and Western Asia, from Spain to Iraq.  We know that they developed a unique tool technology and that they buried their dead.  But what we really don’t know is how they compared to each other:  were there in fact distinct Neanderthal sub-groups, shaped by the vastly different environments in which they lived?  Or can they all be considered a single, genetically similar population? These questions are addressed in the most recent issue of PLoS One by anthropologists from the Université de la Méditerranée in France, using a method that is both unique and comprehensive.

This study is of interest not only because it attempts to understand Neanderthal diversity, but also because it utilized data from a various sources.  First, the researchers collected data from the mitochondrial DNA sequences of 12 separate Neanderthal skeletons. These skeletons ranged in age from 29,000 to 100,000 years and were uncovered in various parts of the Neanderthal homeland, from Siberia to Spain.  The researchers then took physical measurements of the skeletons themselves. Finally, they developed and ran complex computer simulations based on the genetic and skeletal data, in an attempt to discover the most likely scenario for how Neanderthals evolved and spread across much of Eurasia.

The authors concluded that the most likely scenario for how the Neanderthals populated Europe and Western Asia involves three Neanderthal sub-groups: one centered in Western Europe, another in Southern Europe, and the final group in the Levant/Western Asia.  They propose that the Neanderthals within each of these sub-groups were more genetically — and perhaps physically — similar to each other than they were to members of another sub-group.  This is contrary to the idea that the Neanderthals were a single, uniform population.

This result begs the question of cultural distinctions between the sub-groups.  After all, if they were genetically and physically different from one another, it is entirely plausible that cultural differences, such as tool technologies, between the sub-groups also existed.  The authors hope to understand cultural differences between Neanderthal sub-groups in the same way as they’ve understood genetic and physical differences.  And, as more fossils are found and more DNA extracted, we will hopefully develop — with even more confidence — a clear picture on the origins and movements of Neanderthals.

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Ever since European explorers first came upon the African Pygmies in the mid-19th century, they have fascinated anthropologists and other researchers.  Their short stature (they rarely grow to over 5 feet), unique languages, and distinct genetic signatures have led to much speculation on how such groups of humans evolved.  Now, a new study published in the April 10 issue of PLoS Genetics tackles this speculation head-on, using a novel and comprehensive approach in unraveling the origins of Pygmies.

When examining the origins of a particular group of people, many studies focus on a single part of the human genome; the Y-chromosome for example, or mitochondrial DNA.  However, the authors of this study wanted to get a complete picture of the genetic history of the Pygmies, so they looked at 24 separate regions of the human genome.  Altogether, the authors examined more than 33,000 letters of DNA for each of the 236 individuals they sampled.

After collecting and analyzing DNA samples from several different Pygmy groups, nearby Bantu-speaking farmers and other hunter-gatherer groups, the authors ran more than a million computer simulations on the data they had collected, allowing them to deduce the most likely scenario for how the Pygmies became so genetically distinct.

This is the second time in recent months that geneticists have offered an account of Pygmy population history. In February, a paper in Current Biology concluded that western Pygmies began interbreeding with their agricultural neighbors about 2,800 years ago.

The new PLoS paper concludes that Pygmies and their neighbors, non-Pygmy African farmers, had been separated for more than 50,000 years before that. They both shared a common genetic ancestor who lived nearly 56,000 years ago at a time when humans were spreading throughout the African continent, settling and thriving in the rainforests, savannahs, and coastal regions.  It is also around this time that the first human groups left Africa, journeying into Asia.

As these various groups of people began finding their own niches in the diverse African environment, they began to distinguish themselves culturally, physically and genetically.  The authors of this study believe that it is from this time onward that the unique physical form of African Pygmies began to evolve.

But the computer simulations also revealed much about the genetic diversity of the Pygmies themselves.  Pygmies today are generally divided into two ethnic groups:  eastern and western. Each has a somewhat different history, culture and genetic signature, though both are relatively similar in stature.

The authors believe that it was the environment that led to the separation of these two groups.  About 20,000 years ago, the Ice Age was at its peak.  As glaciers covered most of northern Europe, and sea levels dropped across the globe, the abundant rainforests of sub-Saharan Africa began to shrink.  A once lush and expansive tropical forest was now a series of smaller, drier forests, interspersed with savannah grassland.  The growing separation of the forests, the authors propose, led to the growing separation of peoples who had once lived side by side. Various Pygmy groups retreated to isolated pockets of the shrinking forests.  By the Ice Age’s peak, the once homogeneous Pygmies had split into two main groups.  The computer simulations confirmed the authors’ hypotheses, putting the most likely split at around 21,000 years ago.

Today, the western – or Mbenga – Pygmies inhabit the West Congo Basin, while the eastern – or Mbuti – Pygmies, live in the forests of the Democratic Republic of the Congo.  And, while each group is short in stature, the past 20,000 years of biological and cultural evolution has made each group unique.  This study serves as a reminder of the wealth of history that is housed in our genes, if we only know where to look.

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Before 500 years ago people rarely went far to find a mate, choosing a husband or wife from the locally available pool of men and women. But with the dawn of European colonialism people from different parts of the world were suddenly living side by side, and had a whole new set of people to choose from when picking a mate. This trend continues especially in today’s world, where education and work opportunities have flung young people across the globe, allowing them to interact – and potentially marry – people from opposite sides of the globe.

There is ample historical evidence for an increase in exogamy (that is, marrying someone outside your village or town) over the past few hundred years, but could there be evidence stored in our genes as well?  In this week’s PLoS Genetics, an international team of scientists claims to have found genetic clues that allow them to see decreases in inbreeding across the 20th century.

Every person has two copies of each gene — one from our mother and the other from our father.  The more closely related a person’s parents are, the more similar those two copies are to one another.

The authors of the PLoS Genetics study examined the DNA of more than 800 Americans of European ancestry who ranged in age from 19 to 99. Then they looked at how closely each person’s two DNA strands matched one another, a measure called autozygosity that roughly corresponds to the amount of inbreeding in an individual’s pedigree.

The results overwhelmingly confirmed the notion that levels of autozygosity have significantly decreased over time.  When the authors examined the DNA of the youngest subjects, they found significantly lower levels of autozygosity when compared to the oldest subjects.  In fact, they found a steady decrease in levels as they went from oldest to youngest.

What does this mean?  In the last several generations, there’s been a steady decrease in marrying someone from the same town, village, or region (who could potentially be a distant relative).  Instead, the percentage of people who’ve chosen to marry someone from a different town, village, region, or even continent, has been on the rise.

According to the authors there are benefits to this increase in genetic diversity, primarily a reduction in the risk of recessive genetic diseases.

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Biology has changed a lot over the past 150 years. Scientists have discovered entirely new forms of life, deciphered the molecular code of heredity and observed the machinery of life on the smallest dimensions. And through it all, one scientific theory has stood the test of time.

New discoveries in genomics, medicine, developmental biology, and countless other fields could have derailed the the theory of evolution. But the core principles of evolutionary theory, proposed by Charles Darwin 150 years ago, have remained among the strongest explanations of the natural world ever published.

In honor of Darwin Day 2009, which celebrates the 200th anniversary of Charles Darwin’s birth and the 150th anniversary of the publication of his seminal work, On the Origin of Species, we’d like to take a look at how evolution has itself ‘evolved’ over the decades — how new advances in science and technology have both reinforced Darwin’s original idea and given us insight into the inner workings of the theory that explains so much about the world in which we live.

In 1859, the phrase ‘evolution by natural selection’ was already beginning to make the rounds among the scientific elite in Europe and in America.  This was the year Darwin published On the Origin of Species, and his ideas about how species change over time were causing heated debate among the experts.  But Darwin didn’t invent the idea of ‘evolution’ (that is, the idea that species change over time).  What he brought to the table was an explanation of how species change, a process Darwin called ‘natural selection.’  On his famous journey to the Galapagos Islands 25 years earlier, Darwin had witnessed unique variation in hundreds of species.  As he pored over his notes for the next two decades, Darwin pieced together the notion that species must adapt to environmental pressures (like changes in climate or a volcanic eruption), in order to survive.  If they did not adapt to these pressures, then they may not survive.  It was natural selection, Darwin argued, that was the basis for the vast differences we see in plant and animal species across the globe.

But there was a lot that Darwin did not know when he published his ideas of evolution.  He did not know, for instance, how changes in a species’ appearance (a longer beak, a bigger shell, or a thicker coat of fur) are passed down from generation to generation.  The idea of discrete units — ‘genes’ that are passed down from parents to children — had not even occurred to Darwin, nor to most of the other scientists of the time.  Even when, in 1866, an Austrian monk named Gregor Mendel reported his ideas on patterns of inheritance in pea plants in the obscure Proceedings of the Natural History Society of Brünn, few took notice.

In fact, the word ‘genetics’ wasn’t coined until 1905, by biologist William Bateson. Bateson, who is sometimes credited with ‘rediscovering’ the lost works of Mendel, helped to usher in a new wave of research and discovery — this time looking at how species differ from each other at the molecular, or genetic, level.  Bateson’s push for the use of genetics in evolutionary research reached fruition in 1952, when Cambridge scientists James Watson and Francis Crick decoded the structure of DNA. Soon others discovered how specific genes are passed down from generation to generation, and how changes in our genetic code are connected to changes in species.  As each new genetic discovery allowed us to better understand the natural world at a microsopic level, Darwin’s theory of evolution by natural selection was continually reinforced.

The evolution of our species, Homo sapiens, forms the basis for virtually everything we can learn from 23andMe’s Personal Genome Service^TM.  The signature of millions of years of evolution is present in every person’s genome, and often in our physiology, rendering some of us resistant to malaria, others unable to digest milk, and even causing some to have lower risks of cancer or other diseases.  As advances in science and technology continue to bring us more information hidden within our genes, we can be thankful that 150 years ago, an amateur naturalist from Shrewsbury, England, boarded a ship bound for South America and began piecing together the evolutionary story of not just our species but of all life on earth.

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What is it about humans that distinguishes us from the rest of the animal kingdom?  Is it our upright walking?  Our language?  Our love of Reality TV?  Even though we are said to be 99% genetically identical to our closest evolutionary relative, the chimpanzee, we clearly differ vastly from them physically and behaviorally.

For many years, scientists have attempted to understand how our species came to be so different from any other on the planet.  In the October issue of Nature Reviews Genetics, scientists at the UCLA and the Howard Hughes Medical Institute examine recent research to understand how genetic mutations have set us apart from our nearest relatives. In addition, they discuss how these genetic changes relate to the vast array of physical and behavioral differences that also have to be considered to fully understand what makes our species so unique.

The 1% Difference

The authors begin their examination of human uniqueness by focusing on the overall genetic differences between our species and chimpanzees.  Many years ago, research revealed that humans and chimpanzees are remarkably similar in terms of both genetic and biochemical structure.  Scientists hypothesized that because the two species are so structurally similar, the differences between humans and chimps would turn out to be primarily in the way that genes – and therefore proteins – are expressed.  Further analysis confirmed that there is only a 1% difference in overall genetic and biochemical structure between the two species — a number many people still cite today.

However, the authors argue that more recent analysis has actually shown that deletions and duplications of DNA in both species bring the genetic difference between the two to about 4% across the entire genome.  These and other findings have, according to the authors, “dashed the hope that it would be simple to determine the key genetic differences between humans and closest evolutionary relatives, that is, the genomic aspects of ‘what makes us human’ ”.

Yet many recent breakthroughs in comparative genomics have identified human genetic features that may be unique.  Below are two examples:

MYH16

One key difference between humans and chimpanzees is the difference in brain size.  Humans have an average brain volume of about 1500 cm³, which is roughly three times the size of a chimp’s.  While having a comparatively large brain was one of the most important factors in the evolution of our species, it has also resulted in an organ that is very expensive to maintain.  In fact, many anthropologists have argued that in order for our large brains to have evolved, there must have been a simultaneous reduction in the size of other organ systems and muscle mass.

In 2004, scientists discovered a gene, MYH16 that may have been involved in that trade-off between increased brain size and decreased muscle mass.  Believed to be related to the growth of muscles in the jaw of chimpanzees and other apes, MYH16 has been mutated in humans so it remains switched off.  Scientists hypothesize that the gene’s lack of expression in humans causes an eight-fold reduction in the size of muscle fibers in the human jaw.  Interestingly, the timing of this mutation appears to have happened about 2 million years ago, when Homo erectus – the first of our fossil ancestors to exhibit a significant increase in brain size, evolved in Africa.

FOXP2

Sometimes referred to as “the language gene,” FOXP2 made a splash in the popular media when it was first described in 2002, because a very slight mutation in the human version is believed by some to have led to the evolution of language in humans.

FOXP2 is not unique to humans.  In fact, many species – including songbirds and alligators – have the gene, which is required for proper brain development.  Though the human FOXP2 gene is slightly different, it has been found to be related to vocal learning in birds, and may even be tied to the evolution of echolocation in bats.

In addition, new research has suggested that it may not be the FOXP2 gene itself, but rather a related genetic pathway, and it is that related gene that may be involved in the evolution of speech and language development in humans.  At the moment the exact relationship between FOXP2 and human language remains unresolved — an illustration of the genome’s complexity.

Genotype vs. Phenotype

The authors conclude their review by proposing a method of examining human uniqueness from a genomic perspective in light of the fact that “traditional evolutionary biology approaches have yet to explain most of the unique features of humans.”  They argue that in order to move the field of evolutionary genomics forward, and to truly understand what it means to be ‘human,’ there must be more of an effort to connect changes at the genetic level (our genotype) to changes at the physical level (our phenotype).  Interestingly, questions of the relationship between genotype and phenotype form the cornerstone of 23andMe’s research arm, 23andWe.

Finally, the authors argue that it will take scientists from a variety of disciplines – developmental biology, genetics, anthropology, anatomy, sociology, and many others – to fully examine the myriad of ways in which humans are set apart from our closest relatives.  It is at this point, the authors conclude, that we will fully understand what it means to be ‘human.’

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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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There has been plenty of research in both genetics and archaeology recently trying to figure out how the New World was colonized. Was it by boat or via the frozen wasteland of the Bering Strait? Was it a fast trip down to South America, or did these first inhabitants take a more leisurely stroll? And when did all this happen anyway?

As each new study is published we are learning vital information on the peopling of the Americas. Ideas and theories continue to be retooled as new evidence comes to light.

This will certainly be the case with regards to a paper in the May 2008 issue of PLoS Genetics. In this article, researchers from Oxford and Cornell Universities report on a new computer model they have developed to trace prehistoric human migrations across the globe.

Using genetic information from various populations alive today, the authors estimated how those groups may be related to one another. Then they used those relationships to piece together the prehistoric movements of early humans.

As expected, their analysis showed a single migration out of Africa that eventually populated Eurasia and the Americas. However, the results for the Peopling of the Americas were more surprising.

The conventional wisdom states that the first inhabitants of the Americas came from Asia in a single wave more than 10,000 years ago. But when the authors compared the genetic data of two Native American groups (one in Colombia and one in the American Southwest) to groups in East Asia, what they found supported a two-wave migration.

The Colombian sample of Native Americans was actually more closely related to the East Asian sample than it was to the American Southwest sample. That suggests the two populations come from independent sources – and that there were at least two separate migrations of humans into the New World. Clearly, one of these migrations would have come from East Asia and made its way into South America. However, the data suggest a separate migration, probably from a different part of Asia or Siberia, came at a different time, and this time only made it to North America. This conclusion is significant, as it contradicts current theories on the topic, which argue a more constant flow of migrants from an original source somewhere in Asia.

There are still plenty of questions regarding this research, especially with regard to how it compares to the archaeological record and to previous genetic studies. The answers to these questions can only come with additional research, which, thankfully, is always forthcoming on the peopling of the Americas.

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