The making of modern humans

What is it exactly that makes modern humans modern? We are subject to jet lag? We can walk and text at the same time (some of us, kind of?) Our minds and bodies bear the brunt of all the junk we’ve been spewing into the earth’s air, water, and soil since the Industrial Revolution?

Chris Stringer, a research leader in human origins at the Natural History Museum London, recently wrote a Comment in Nature speculating on what the precise features might be that define us as modern. Recent DNA evidence has shown that after modern humans left Africa around 60,000 years ago, they interbred with different groups of archaic humans—Neanderthals and Denisovans. As a result, different populations walking around today have varying amounts of this archaic DNA in their genomes.

Stringer is aware that this information could lead to the very dangerous assertion that all humans are modern, but some are more modern than others. So he writes, “All living humans are members of the extant species H. sapiens and, by definition, all must equally be modern humans.”

The making of modern humans

SUNY Orange

Bugs pick up pesticide resistance from pesticide-eating bacteria

The indiscriminate spraying of pesticides has probably caused as many problems as it has solved, but here's one that was not expected: some bacteria have decided that one insecticide is a very tasty meal. Unfortunately for us, one of the strains of bacteria that has evolved the ability to digest the toxin happens to be able to find a home in an insect's gut. When it does so, it provides the insect with resistance.

Several factors had to come together for this to take place, but one was the heavy use of fenitrothion, which is described as "one of the most popular organophosphorus insecticides used worldwide" by the authors of a study of these insects. It has apparently been so widely deployed that a variety of bacteria have evolved the ability to use it as a food source. Most of these simply inhabit the soil in the fields where it is used and, at worst, cut down on the level of insecticide present and thereby make life a bit easier for the insects.

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Missing rocks may explain why life started playing shell games

The familiar Cambrian explosion, which started around 540 million years ago, was a game-changer for life on Earth. Bacteria (and archaea) had ruled the planet for over 3 billion years before multi-cellular animals came on the scene. When they did, they diversified rapidly (at least in terms of the span of geologic time). Though we’re right to be impressed by the sudden explosion of life, it’s not the only remarkable thing in that portion of Earth’s history.

There’s a widespread gap in the rock record immediately preceding the Cambrian explosion called the Great Unconformity. The boundary is so prominent—often separating very old igneous and metamorphic rocks from the much younger sedimentary rocks above, as is the case at the base of the Grand Canyon—that all rocks older than this are often lumped together as simply "Precambrian."

Having such a block of time missing just before the rapid Cambrian explosion has made some people suspicious that it might not have been as much of an explosion as it appears. It would be a bit like feeling confused at the climax of a story because you had skipped the setup. A new paper in Nature suggests that far from concealing the story of the Cambrian explosion, the events that created the Great Unconformity may actually explain it.

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Nest-making orangutans build for comfort and strength

Great apes are our closest relatives, and they are constantly surprising us with their human-like abilities and tendencies; here at Ars, we've seen studies showing that they plan ahead, they engage in wars over territory, and they respond to being tickled, just to name a few. Now, a new study in PNAS adds to the growing list of ways in which great apes are similar to us: they value a good night’s sleep, and they have the technological know-how to build pretty impressive beds from some very basic materials.

Many species of great ape, including chimpanzees, gorillas, bonobos, and orangutans, build nests in the forest canopy. Generally, these nests are slept in for just one night, then abandoned. The nests are thought to benefit the apes in several ways: sleeping above the ground reduces disturbances, protects them from predators, leaves them less vulnerable to mosquitoes and other pests, and generally increases the quality of their sleep. However, we know very little about how these nests are actually constructed. To figure out how much skill goes into nest-building, a group of scientists studied nests made by Sumatran orangutans in Indonesia.

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Evolution in motion: organisms once stuck to rocks can now evade predators

Not to belittle sharks—they have their own week, after all—but the most voracious eaters in the oceans may not even have a spine. Sea urchins are omnivores and, when they dine on kelp, they can completely wipe out a kelp forest, leaving urchin-filled barrens on the ocean floor. But they don't limit themselves to plants. Sea urchins will happily eat any animals that don't get out of the way. Now, researchers have examined the fossils of a marine invertebrate, and find that it actually evolved the ability to get out of the way. Any of these creatures, called crinoids, that share a habitat with sea urchins can now go mobile.

Crinoids like the sea lilly have a simple body plan, consisting of a body with multiple arms and a mouth, attached to a long stalk. They've been around for hundreds of millions of years, having survived two mass extinctions. Early on in their history, they were generally sessile, meaning they attached themselves to a solid surface and remained stationary for the rest of their lives. Over time, however, that changed. The species that lived in shallow waters started evolving the ability to detach from their stalks, or even move their base of operations to new locations on the ocean floor. Now, the only sessile species exist in very deep waters.

What drove this change? The authors of a new paper make a compelling case that sea urchins did. They've actually gone through and matched bite marks on fossil crinoids to the damage on crinoid stalks that have been partly digested by sea urchins. They've also gone through the fossil record and compared the diversity of crinoid species to that of sea urchins. As sea urchin diversity goes up, the number of sessile crinoids drops, and the number of species that can either detach or move to new locations rises.

It probably doesn't take much to outrun a sea urchin, but it still represents a pretty radical change in lifestyle for the crinoids. And, if the sea urchin's pursuit of its prey is a bit slow motion, it's got nothing on the millions of years it took this evolutionary shift to play out.

PNAS, 2012. DOI: 10.1073/pnas.1201573109 (About DOIs).

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Recalibrated DNA clock suggests we can stop looking for early primate fossils

The earliest primate fossils unearthed thus far are only 56 million years old, but molecular estimates of the rate of primate evolution predict that there should be some dating back to the Late Cretaceous, closer to 82 million years ago. This is embarrassing for scientists, akin to the time in 1929 when Edwin Hubble measured the age of the Universe as less than half the age of the Earth.

One possible explanation is that earlier fossils are out there, but that no one has found them yet. But Michael Steiper and Erik Seiffert have proposed an alternate reconciliation in a new study of the molecular rate of evolution. Their work was published in the Proceedings of the National Academy of Sciences.

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Researchers pin down genes responsible for drug-resistant malaria

Over the last few decades, malarial parasites have evolved resistance to most of the drugs that we've thrown at them. This development leaves us with just one effective treatment: artemisinin. Artemisinin is currently delivered as part of artemisinin-combination therapy (ACT) with other drugs that are intended to take out any resistant parasites. But recent developments in Southeast Asia have suggested that time may be running out for ACTs, as they're taking much longer to clear parasites.

Understanding artemisinin resistance is complicated by the fact that we're not entirely sure how the drug works. We also lack any understanding of the biochemical basis for resistance. All of that makes devising a test for resistant malaria a big challenge. Now, researchers have taken the first step toward nailing things down by identifying a chunk of the parasite's genome that accounts for a significant percentage of the resistance.

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Feathers may have helped T. rex’s relatives ride out a cold climate

Feathers are the defining feature of birds, but that wasn't always the case. For millions of years, various species of dinosaurs sported feathers, some of which have left behind fossilized impressions. But for the most part, the feathers we've found have been attached to smaller dinosaurs, many of them along the lineage that gave rise to birds.

That situation was changed dramatically by a species that is described in today's issue of Nature. Three nearly complete skeletons have revealed a feathered dinosaur that its finders term "gigantic." At nearly 1,500kg and over forty times the weight of any previous feathered dinosaur, Yutyrannus huali was a beast—almost certainly an apex predator, and related to the ancestors of Tyrannosaurus Rex.

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"Teach the controversy" science education bills advance in Tennessee, Oklahoma

Earlier this week, legislators in Tennessee approved a bill that singles out public school science education for special attention. Now, the Oklahoma House has passed a very similar bill that attacks an identical range of subjects that the legislation deems controversial: biological evolution, the chemical origins of life, global warming, and human cloning.

Both bills contain identical language, saying they "shall not be construed to promote any religious or nonreligious doctrine." There's also identical language about how they're intended to "help students develop critical thinking skills they need in order to become intelligent, productive, and scientifically informed citizens." However, the subjects they target are not areas where there are significant scientific controversies; either the bills' sponsors are poorly informed (and thus shouldn't be injecting themselves into science education), or they have non-educational goals in mind.

In any case, the legislators want to do what they can to enable science teachers to teach the controversy. To that end, they're basically attempting to block any educational authority—school board, principal, the state board of education—from punishing a teacher for covering the "scientific strengths and scientific weaknesses of existing scientific theories." The Oklahoma bill goes a bit further, adding protections for students who choose voice their disagreements with the science in any medium.

Given the staggering amount of scientific-sounding misinformation available on topics like evolution and climate change, these bills are a recipe for chaos in the science classrooms. It's a chaos that state legislators are inviting local school districts to sort out at great expense via lawsuits.

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