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1. How Human Beings Almost Vanished From Earth In 70,000 B.C. October 22, 201212:33 PM ET Commentary ROBERT KRULWICH Robert Krulwich/NPR Add all of us up, all 7 billion human beings on earth, and clumped together we weigh roughly 750 billion pounds. That, says Harvard biologist E.O. Wilson, is more than 100 times the biomass of any large animal that's ever walked the Earth. And we're still multiplying. Most demographers say we will hit 9 billion before we peak, and what happens then? Well, we've waxed. So we can wane. Let's just hope we wane gently. Because once in our history, the world-wide population of human beings skidded so sharply we were down to roughly a thousand reproductive adults. One study says we hit as low as 40. Forty? Come on, that can't be right. Well, the technical term is 40 "breeding pairs" (children not included). More likely there was a drastic dip and then 5,000 to 10,000 bedraggled Homo sapiens struggled together in pitiful little clumps hunting and gathering for thousands of years until, in the late Stone Age, we humans began to recover. But for a time there, says science writer Sam Kean, "We damn near went extinct." I'd never heard of this almost-blinking-out. That's because I'd never heard of Toba, the "supervolcano." It's not a myth. While details may vary, Toba happened. Toba, The Supervolcano Once upon a time, says Sam, around 70,000 B.C., a volcano called Toba, on Sumatra, in Indonesia went off, blowing roughly 650 miles of vaporized rock into the air. It is the largest volcanic eruption we know of, dwarfing everything else... Robert Krulwich/NPR That eruption dropped roughly six centimeters of ash — the layer can still be seen on land — over all of South Asia, the Indian Ocean, the Arabian and South China Sea. According to the Volcanic Explosivity Index, the Toba eruption scored an "8", which translates to "mega-colossal" — that's two orders of magnitude greater than the largest volcanic eruption in historic times at Mount Tambora in Indonesia, which caused the 1816 "Year Without a Summer" in the northern hemisphere. With so much ash, dust and vapor in the air, Sam Kean says it's a safe guess that Toba "dimmed the sun for six years, disrupted seasonal rains, choked off streams and scattered whole cubic miles of hot ash (imagine wading through a giant ashtray) across acres and acres of plants." Berries, fruits, trees, African game became scarce; early humans, living in East Africa just across the Indian Ocean from Mount Toba, probably starved, or at least, he says, "It's not hard to imagine the population plummeting." Then — and this is more a conjectural, based on arguable evidence — an already cool Earth got colder. The world was having an ice age 70,000 years ago, and all that dust hanging in the atmosphere may have bounced warming sunshine back into space. Sam Kean writes "There's in fact evidence that the average temperature dropped 20-plus degrees in some spots," after which the great grassy plains of Africa may have shrunk way back, keeping the small bands of humans small and hungry for hundreds, if not thousands of more years. So we almost vanished. But now we're back. It didn't happen right away. It took almost 200,000 years to reach our first billion (that was in 1804), but now we're on a fantastic growth spurt, to 3 billion by 1960, another billion almost every 13 years since then, till by October, 2011, we zipped past the 7 billion marker, says writer David Quammen, "like it was a "Welcome to Kansas" sign on the highway." In his new book Spillover, Quamman writes: We're unique in the history of mammals. We're unique in this history of vertebrates. The fossil record shows that no other species of large-bodied beast — above the size of an ant, say or an Antarctic krill — has ever achieved anything like such abundance as the abundance of humans on Earth right now. But our looming weight makes us vulnerable, vulnerable to viruses that were once isolated deep in forests and mountains, but are now bumping into humans, vulnerable to climate change, vulnerable to armies fighting over scarce resources. The lesson of Toba the Supervolcano is that there is nothing inevitable about our domination of the world. With a little bad luck, we can go too. We once almost did. Radiolab regular Sam Kean's new book on genetics, The Violinist's Thumb, tells the story of Toba, the supervolcano, to explore how human genes record a "bottleneck" or a drastic narrowing of genetic diversity 70,000 years ago. David Quammen's new book Spillover is about people pushing into forests, swamps and places where viruses have been hiding. Those viruses are now beginning to cross over into horses, pigs, bats, birds and, inevitably, they threaten to "spillover" into us. For a virus, or bacteria, 7 billion potential hosts look like a fantastic opportunity. 2. European Roots for Native Americans? An analysis of ancient DNA from a 24,000-year-old Siberian skeleton generates a new model for the original peopling of the Western Hemisphere. By 237Bob Grant | October 29, 2013 Models of gene flow from Aisa to the Americas, like this one from a 2007 PLOS ONE paper, may need to be reconsidered.WIKIMEDIA, ERIKA TAMM ET AL.Native Americans may not have descended from East Asians who crossed the Bering Land Bridge more than 15,000 years ago, according to a new genomic analysis of a millennia-old Siberian skeleton. A portion of the nuclear DNA recovered from the upper arm bone of a 4-year-old boy that was buried near the Siberian village of Mal’ta about 24,000 years ago is shared by modern Native Americans and no other group. But the boy appears to have been descended from people of European or western Asian origin. Eske Willerslev, a University of Copenhagen ancient DNA expert, announced the findings last week at the Paleoamerican Odyssey conference in Santa Fe, New Mexico, and the resulting manuscript is in press at Nature. In addition to finding genome regions shared by modern Native Americans, he and collaborator Kelly Graf of Texas A&M University found that the boy’s Y chromosome and mitochondrial DNA belonged to haplogroups that are found almost exclusively in Europeans and people living in Asia west of the Altai Mountains. Conspicuously absent from the child’s DNA, however, was any connection to modern East Asians, a genetic relationship present in the genomes of virtually all Native Americans. This means that the population from which the boy came must have included ancestors of modern Native Americans, upsetting the popular belief that the original inhabitants of North, Central, and South America descended directly from East Asians. According to Science, Willerslev and Graf suggest that at some point before 24,000 years ago, the ancestors of modern Native Americans and those of East Asians split into two genetically distinct groups. The Mal’ta boy belonged to a population that migrated to Siberia from Eurasia and mixed with the second before the newly formed population moved into the New World, eventually populating the Americas. Previously, the presence of European DNA in the modern Native American genome was attributed to interbreeding after Europeans made contact. This new finding may turn that supposition on its head. “The west Eurasian [genetic] signatures that we very often find in today's Native Americans don't all come from postcolonial admixture,” Willerslev said during his presentation. “Some of them are ancient.” Though reconstructing humanity’s westward expansion into the New World involves some speculation, recovering the intact DNA of the Mal’ta boy represents a technological feat: his is oldest complete genome of a modern human sequenced to date. 3. Caribbean lizards settle 'founder effect' controversy February 2, 2012 University of California - Davis In the first experimental study of the founder effect in a natural setting, researchers found that natural selection does not overwhelm the founder effect. This is a founder pair of Caribbean brown anole lizards, one of the actual colonist couples, shortly after release. They were involved in the first experimental study of the founder effect -- a long-simmering controversy in evolutionary biology -- in a natural setting. The study by UC Davis researchers and others is published in the Feb. 3 edition of the journal Science Express, the online publication of the journal Science. Credit: Manuel Leal/Duke University When a devastating 2004 hurricane wiped out a Caribbean lizard population, University of California, Davis, researchers had an unprecedented opportunity to address a long-simmering controversy in evolutionary biology. Their findings -- from the first experimental study of the so-called "founder effect" in a natural setting -- are published in the Feb. 3 edition of Science Express, the online publication of the journal Science, which will publish the study in print on Feb. 17. The founder effect describes the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. But the extent to which this effect contributes to evolution has been up for debate since the early 1940s, when German evolutionary biologist Ernst Mayr first outlined it. Some scientists argue that the founder effect is pivotally important in how a species evolves. Others argue that it is a bit player on the evolutionary stage, quickly overwhelmed by the forces of natural selection. In their new paper, UC Davis scientists, together with researchers from Harvard and Duke, suggest that both sides are right. Complicating the debate has been the dearth of data from nature: Founder events are rarely observed. "Founder effects are very hard to study," said Thomas Schoener, a professor of evolution and ecology at UC Davis and a coauthor of the study. "One must be in exactly the right place at the right time to observe the founder event -- and then fortunate enough to be able to follow a population through time." That opportunity presented itself in September 2004, when Hurricane Frances submerged several small, low-lying islands near Great Abaco, Bahamas. Before the hurricane, these islands supported populations of a Caribbean lizard, the brown anole, Anolis sagrei. After the hurricane, seven of the islands were thoroughly searched. No lizards were found. In May 2005, the researchers randomly selected one male and one female brown anole from lizards collected on a nearby larger island to found new anole populations on seven small islands. During the next four years, the researchers repeatedly sampled lizards from the source island, from the seven experimental founder islands, and from 12 nearby islands that served as a control. The team found that all lizard populations adapted to their environment, yet retained characteristics from their founders. For instance, lizard limb length correlates with the average diameter of vegetation on an island. Because the founder islands had smaller vegetation than the source island, the length of lizard limbs decreased, as expected, due to natural selection. But islands containing lizards with the largest limbs at the beginning of the study still had the lizards with the longest limbs at the end of the study. "Natural selection drives them all down, while the founder effect keeps the order the same," said Schoener. "So they're both right, in a sense." If natural selection had overpowered the founder effect, lizards' limbs would have converged at the same length, regardless of how long-legged the founders were. Instead, limb length decreased roughly in parallel, signifying the persistence of the founder effect. "Our study is an entirely unique approach to a question of longstanding importance for evolutionary biology regarding the founder effect: Will it persist in the face of the strong selection that would often exist in the colonized environment?" said Schoener. "The answer we found is that founder effects can leave a persistent signal as generations replace one another over time, even as populations adapt to new conditions. Our study of these fundamental evolutionary principles affects our general understanding of how the biological world works." Journal Reference: J. J. Kolbe, M. Leal, T. W. Schoener, D. A. Spiller, J. B. Losos. Founder Effects Persist Despite Adaptive Differentiation: A Field Experiment with Lizards. Science, 2012; DOI: 10.1126/science.1209566 4. Evolution myths: Mutations can only destroy information By Michael Le Page, New Scientist, 2008 Biologists are uncovering thousands of examples of how mutations lead to new traits and even new species. This claim not only flies in the face of the evidence, it is also a logical impossibility Most people lose the ability to digest milk by their teens. A few thousand years ago, however, after the domestication of cattle, several groups of people in Europe and Africa independently acquired mutations that allow them to continue digesting milk into adulthood. Genetic studies show there has been very strong selection for these mutations, so they were clearly very beneficial. Most biologists would see this as a gain in information: a change in environment (the availability of cow’s milk as food) is reflected by a genetic mutation that lets people exploit that change (gaining the ability to digest milk as an adult). Creationists, however, dismiss this as a malfunction, as the loss of the ability to switch off the production of the milk-digesting enzyme after childhood. Rather than get bogged down trying to define what information is, let’s just look at a few other discoveries made by biologists in recent years. For instance, it has been shown a simple change in gene activity in sea squirts can turn their one-chambered heart into a working two-chambered one. Surely this counts as increasing information? TRIMming the genome Some monkeys have a mutation in a protein called TRIM5 that results in a piece of another, defunct protein being tacked onto TRIM5. The result is a hybrid protein called TRIM5-CypA, which can protect cells from infection with retroviruses such as HIV. Here, a single mutation has resulted in a new protein with a new and potentially vital function. New protein, new function, new information. Although such an event might seem highly unlikely, it turns out that the TRIM5-CypA protein has evolved independently in two separate groups of monkeys. In general, though, the evolution of a new gene usually involves far more than one mutation. The most common way for a new gene to evolve is for an existing gene to be duplicated. Once there are two or more copies, each can evolve in separate directions. The duplication of genes or even entire genomes is turning out to be ubiquitous. Without a duplication of the entire genome in the ancestor of modern-day brewer’s yeast, for instance, there would be no wine or beer. It is becoming clear that every one of us has extra copies of some genes, a phenomenon called copy number variation. The evolution of more complex body plans appears to have been at least partly a result of repeated duplications of the Hox genes that play a fundamental role in embryonic development. Biologists are slowly working out how successive mutations turned a pair of protoHox genes in the simple ancestors of jellyfish and anemones into the 39 Hox genes of more complex mammals. Newly minted Can mutation really lead to the evolution of new species? Yes. Several species of abalone shellfish have evolved due to mutations in the protein “key” on the surface of sperm that binds to a “lock” on the surface of eggs. This might appear impossible, but it turns out that some eggs are prepared to be penetrated by deviant sperm. The same thing can happen in fruit flies, and likely in many other groups too. In yeasts, the mutations that led to some new species forming have not only been identified, they have even been reversed. The list of examples could go on and on, but consider this. Most mutations can be reversed by subsequent mutations – a DNA base can be turned from an A to a G and then back to an A again, for instance. In fact, reverse mutation or “reversion” is common. For any mutation that results in a loss of information, logically, the reverse mutation must result in its gain. So the claim that mutations destroy information but cannot create it not only defies the evidence, it also defies logic.