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Ever Wonder What a Neanderthal Considered a Delicacy?

I suppose “Neanderthal delicacy” may sound like an oxymoron. Most people think of Neanderthals and other ancient people as cave men, brutes capable of little more than smashing and grunting. To the extent you’ve ever thought about what they ate, you probably assumed it was, well, whatever they could get their dirty hands on.

Or maybe you remember The Clan of the Cave Bear, the 1980 bestseller that helped shape Neanderthals in the popular imagination. In the book, a Homo sapiens girl named Ayla is adopted by Neanderthals who communicate mainly through hand signals and seem incapable of learning.

Yet the more we learn about our ancient cousins, the more sophisticated we find them to be. Amazing work on Neanderthal genetics by Svante Pääbo has found that they possessed a gene called FOXP2 that is key to speech in modern humans, raising the question of whether Neanderthals had language. They may even have been capable of abstract thinking and art.

Now, a new study suggests that the Paleolithic crowd had its own version of fine dining, unsettling as the choice of fare may be. It appears that baby elephants may have been a particular delicacy—basically, pachyderm veal.

Most studies of ancient diets have focused on simply figuring out what people ate, not what they liked. But Ran Barkai of Tel Aviv University and his graduate student Hagar Reshef wondered if there was any way to make a reasonable guess about the tastes of early hominins. They report their findings in an upcoming issue of Quaternary International.

“The direct investigation of taste preference in Paleolithic times is impossible,” says Reshef, but there’s “plenty of circumstantial evidence.”

First, the scientists point to recent evidence that Neanderthals did have a sense of taste. Work by Carles Lalueza-Fox found taste-related genes in Neanderthals, specifically for bitter tastes, that could have shaped their food preferences. The gene varied, as it does in modern humans. “What seems clear is that keeping a wide range of taste perception was key in hominin groups,” Lalueaza-Fox says.

As for what they ate, the butchered bones of mammoths and ancient elephant species, and particularly young elephants, are fairly common in Paleolithic archaeological sites around the world. In some cases, such as the Middle Pleistocene sites Gesher Benot Ya’akov in Israel and Notarchirico in Italy, the skulls of young elephants appear to have been dismantled, perhaps to eat the brain.

Young elephants would presumably be easier to kill than large ones, which could explain why more young ones were eaten. But even young elephants aren’t exactly easy to capture and kill, leaving Reshef wondering whether they were also hunted as a preferred food—because they’re tasty.

That raises one obvious question: Are baby elephants tasty? Here, Reshef and Barkai looked at the historical record and modern-day hunter-gatherers. A 1967 study of the Liangula hunters in East Kenya reported that they preferred young elephants because they tasted better, and reports from other groups followed suit, with the general consensus being that elephants, and especially the young, taste sweet and fatty.

The team also checked out the nutritional value and quality of elephant meat. Studies of the biochemical composition of fat tissue reveals a high nutritional value for young elephants compared with adults.

We can’t wind back time to ask a Neanderthal what he liked, but it seems plausible that they put some effort into finding food they liked, and that baby elephant was on the list. “I would say that both the vulnerability and taste are relevant,” Reshef says.

Why would we care what Neanderthals or other hominins liked to nosh on? They sharpened their flints while dreaming of slicing into baby elephant; I wait in line for two hours to eat fancy ramen noodle soup. To each his own, right?

Perhaps. But it’s also part of understanding what makes us human.

“I believe that taste preference in ancient times was a motivating power in human evolution by pushing creative and technological abilities,” says Reshef.

Just think about that for a second. The quest for deliciousness: a motivating power in human evolution.

I could buy it. Given how much human time, creativity, and effort go into food today (Exhibit A: any Whole Foods store), it’s easy to believe that we are who we are, at least just a little bit, because we have been working for so long on new ways to perfect the snack. Thank you, sense of taste.

(A special thank you to my keen-eyed colleague Mark Strauss for pointing out the elephant study.)

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World’s Oldest Murder Mystery Was 430,000 Years in the Making

The first known murder was just as brutal as any other. The attacker smashed the victim twice in the head, leaving matching holes above the victim’s left eyebrow. The dead body was then dropped down a 43-foot shaft into a cave—where it lay for nearly half a million years.

Talk about your cold case.

Paleontologists pieced together the 430,000-year-old skull and reported their forensic analysis Wednesday in the journal PLOS ONE. Injuries to the skull represent the oldest direct evidence of homicide, the scientists say.

As for whether this was the first murder ever to occur, “for sure that’s not the case,” says Nohemi Sala, lead author of the study. The scientists can describe this victim as a young adult, but the age and even gender are unknown.

“In the fossil record, there are many cases of traumatic injury, but not a lot of evidence of killing,” says Sala, a paleontologist at the Instituto de Salud Carlos III in Madrid.

That doesn’t mean killing was uncommon before modern times, of course, but fossilized remains of any kind are relatively rare so far back.

The last several tens of thousands of years, on the other hand, are littered with grisly scenes. Take the case of Shanidar-3, a Neanderthal who lived about than 50,000 years ago. A cut on one of his left ribs shows that Shanidar-3 was probably killed by a spear, making him perhaps the oldest known murder victim prior to the new find.

The latest skull comes from the Sima de los Huesos, or “Pit of Bones,” site in Spain, where paleontologists have found the remains of at least 28 individuals. Who were these people? Well, they weren’t modern humans, and they weren’t really Neanderthals either.

Exactly what to call the Sima de los Huesos people has been debated, but Sala and her colleagues identify them as members of the species Homo heidelbergensis, an early human ancestor that gave rise to the Neanderthals.

Cause of death

To figure out whether the skull fractures resulted from blows or from the fall down the cave shaft, the team compared the injuries to those from modern cases of violence and falls. A face-to-face attack with a blunt instrument best fits the pattern of injury, the scientists say. The bones showed no evidence of healing, so the victim probably died immediately or soon after the attack.

© Javier Trueba/Madrid Scientific Films, from Arsuaga et al/Science 2014
The “Pit of Bones” cave in Spain. © Javier Trueba/Madrid Scientific Films, from Arsuaga et al/Science 2014
The remains of 28 individuals who lived over 400,000 years ago were found in this cave, the "Pit of Bones" in Spain.

What’s more, the two holes in the skull are the same shape and appear to have been made by the same weapon. It’s very unlikely that an accidental fall onto a rock would produce two nearly identical skull fractures, the team says.

The weapon

Sala says the weapon was probably “something very hard,” but we’ll never know if it was made of wood or rock, or something else.

The scientists scoured the site, she says, but didn’t turn up any potential murder weapons. There was only stone tool found at the site, and it wasn’t the right shape.

The motive

Another unsolved mystery: what drove an ancient person to kill. “Life was hard in the past,” Sala says, so there could have conflicts over resources or any number of reasons for a fight.

Even with difficult lives, though, Sala describes the Sima de los Huesos people as caring for one another. “There were 28 individuals at the site of different ages,” she says. “We know that some of these people had health problems. One person had very serious pathology in the lower back and probably had troule walking and moving.” Someone had to be caring for these people before their deaths, she says.

And while it might not sound like a lovely funeral today, the fact that people living at the site buried bodies by dropping them down the same shaft indicates some sense of ceremonial burial or ritual—the dead weren’t merely dragged away from the campsite to decay.

Overall, the site paints a picture of ancient people who lived, loved—and sometimes fought—together.

Sala’s take on life with Homo heidelbergensis: “They’re not so bad—at least they have also good points.”



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Fast-Evolving Human DNA Leads to Bigger-Brained Mice

Between 5 and 7 million years of evolution separate us humans from our closest relatives—chimpanzees. During that time, our bodies have diverged to an obvious degree, as have our mental skills. We have created spoken language, writing, mathematics, and advanced technology—including machines that can sequence our genomes. Those machines reveal that the genetic differences that separate us and chimps are subtler: we share between 96 and 99 percent of our DNA.

Some parts of our genome have evolved at particularly high speed, quickly accumulating mutations that distinguish them from their counterparts in chimps. You can find these regions by comparing different mammals and searching for stretches of DNA that are always the same, except in humans. Scientists started identifying these “human-accelerated regions” or HARs about a decade ago. Many turned out to be enhancers—sequences that are not part of genes but that control the activity of genes, telling them when and where to deploy. They’re more like coaches than players.

It’s tempting to think these fast-evolving enhancers, by deploying our genes in new formations, drove the evolution of our most distinguishing traits, like our opposable thumbs or our exceptionally large brains. There’s some evidence for this. One HAR controls the activity of genes in the part of the hand that gives rise to the thumb. Many others are found near genes involved in brain development, and at least two are active in the growing brain. So far, so compelling—but what are these sequences actually doing?

To find out, J. Lomax Boyd from Duke University searched a list of HARs for those that are probably enhancers. One jumped out—HARE5. It had been identified but never properly studied, and it seemed to control the activity of genes involved in brain development. The human version differs from the chimp version by just 16 DNA ‘letters’. But those 16 changes, it turned out, make a lot of difference.

Boyd’s team introduced the human and chimp versions of HARE5 into two separate groups of mice. They also put these enhancers in charge of a gene that makes a blue chemical. As the team watched the embryos of their mice, they would see different body parts turning blue. Those were the bits where HARE5 was active—the areas where the enhancer was enhancing.

Embryonic mice start building their brains on their ninth day of life, and HARE5 becomes active shortly after. The team saw that the human version is more strongly active than the chimp one, over a larger swath of the brain, and from a slightly earlier start.

HARE5 seems to be particularly active in stem cells that produce neurons in the brain. The human version of the enhancer makes these stem cells divide faster—they take just 9 hours to split in two, compared to the usual 12. So in a given amount of time, the mice with human HARE5 developed more neural stem cells than those with the chimp version. As such, they accumulated more neurons.

And they developed bigger brains. On average, their brains were 12 percent bigger than those of their counterparts. “We weren’t expecting to get anything that dramatic,” says Debra Silver, who led the study.

“Ours stands as among the first studies to demonstrate any functional impact of one of these HARs,” she adds. “It shows that just having a few changes to our DNA can have a big impact on how the brain is built. We’ve only tested this in a mouse so we can’t say if it’s relevant to humans, but there’s strong evidence for a connection.”

“I’m really excited that people are following up [on these HARs] and finding out what they do,” says Katherine Pollard from the Gladstones Institutes, who was one of the scientists who first identified these sequences. “It’s been really daunting to figure out what the heck these things do. Each one takes years. These guys went the extra mile beyond what everyone else has been doing, by showing changes in the cell cycle and in brain size.”

“It’s a very clever use of mice as readouts for human-chimp differences,” says Arnold Kriegstein from the University of California, San Francisco. “The [brain] size difference isn’t terribly big, but it’s certainly in the correct direction.”

Eddy Rubin from the Joint Genome Institute is less convinced. His concern is that the team’s methods could have saddled the mice with multiple copies of HARE5 in various parts of their genome. As such, it’s not clear if the differences between the two groups are due to these factors, rather than to the 16 sequence differences between the human and chimp enhancers. “[That] casts major shadow on the conclusions,” says Rubin. “This is an interesting study pursuing an important issue, but the results should be taken with a grain of salt.”

Regardless, Silver’s team are now continuing to study HARE5. Now that their mice have grown up, they are designing tests to see if the adults behave differently thanks to their larger brains. This is important—bigger brains don’t necessarily mean smarter animals. They’re also looking into a few other enhancers. One of them, for example, seems to a control a gene that affects the growth of neurons.

“I think HARE5 is just the tip of the iceberg,” says Silver. “It is probably one of many regions that explain why our brains are bigger than those of chimps. Now that we have an experimental paradigm in place, we can start asking about these other enhancers.”

Reference: Boyd, Skove, Rouanet, Pilaz, Bepler, Gordan, Wray & Silver. 2015. Human-Chimpanzee Differences in a FZD8 Enhancer Alter Cell-Cycle Dynamics in the Developing Neocortex. Current Biology http://dx.doi.org/10.1016/j.cub.2015.01.041

More on enhancers:

Did a gene enhancer humanise our thumbs?

RNA gene separates human brains from chimpanzees

How to Pick up Pliocene Takeout

[Note: This post was originally published on January 7th, 2 million years before present.]

I’m sure you know the feeling. You’ve been digging up roots and tubers for days and they’re just not hitting the spot. Something more savory would be delightful, but, like they do, lions take their share of their kills, leaving what looks like just scraps for you and your family. Well don’t despair, my hominin friend. If you know what to look for, you can turn even a practially-skeletonized carcass into a feast.

The first step is picking the right place to dine. An open grassland just won’t do. There’s no place to hide out in the open, and nothing ruins a meal like an uninvited leopard showing up to dinner. And you’ll want to avoid the haunts of bone-crunching hyenas, too. Aside from the fact that you don’t want to wind up as an appetizer for them, they usually don’t leave much behind beyond scattered, splintered bones. What use is a bone-shard toothpick if you’ve nothing to pick out of your teeth?

You’ll want to look for a large carcass in a more closed habitat. Someplace wooded and a little more shady. This is where sabercats prowl, and, when spotting leftovers, big cats are practically your sous chefs.

Sigh. Goodbye, lunch. Photo by Mariomassone, CC BY-SA 2.0.

You can pinpoint a promising carcass by the way it looks.

Hyenas disarticulate and scatter skeletons, often carrying off the heavily-muscled limbs to consume elsewhere. Not to mention that they strip almost every piece of meat from the bones in the process. A disorganized clump of bones probably won’t hold much for you. But big cats are more interested in the softest and most accessible cuts, usually starting with the hind legs and continuing on to the thorax, head, and forelimbs. The skeletons of their kills are usually left relatively intact, and, depending on the habits of the local cats, there’s usually a good deal of flesh left on the skeleton.

Don’t fret if you can only see bones at a distance. There’s still plenty of good eating on that carcass. If you’re lucky, you’ll find large pieces of flesh still attached to spots like the skull, legs, and ribs. Those are easy enough to slice off with a handy stone tool – never leave home with out some cutlery in hand – but you’re more likely to find some smaller morsels. Some hominins look down their noses and call these “scraps”, but that’s just negativity. If you can pinch a piece of horse or antelope flesh between your thumb and forefinger, that’s big enough to give you a juicy mouthful.

Consider this: even a horse leg with 10% of the original amount of meat left on it still yields 2-4 pounds of flesh. And if the same is true of the rest of the skeleton, well, you’re looking at between 2,000 and 6,000 calories of protein! Even the lower range is enough to fulfill the caloric needs of at least one of your clever Homo erectus for an entire day. And that’s not even considering the marrow held inside those bones!

Don’t believe those uber-macho hominins who say you need to run leopards and hyenas off kills in order to enjoy a steak dinner. Natural selection will likely see them off sooner rather than later. If you’re patient and don’t mind a little cat saliva, you can have a meaty “cheat day” meal to mix up the routine of tubers and water plants.

This post is based on a new Journal of Human Evolution paper by National Museum of Natural History anthropologist Briana Pobiner. Read her paper for fully fleshed-out details of how she determined how much meat some lions leave behind and what this means for the menu of our Plio-Pleistocene forebears. Top photo from here.


Pobiner, B. 2015. New actualistic data on the ecology and energetics of hominin scavenging opportunities. Journal of Human Evolution. doi: 10.1016/j.jhevol.2014.06.020

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What tree-climbing pygmies tell us about foot evolution

At some point in human history, our ancestors descended from the trees and started walking permanently on two legs. In the process, our feet evolved from the grasping appendages of other apes into sturdy levers. We lost an opposable big toe, our ankles became stiffer, and our bones formed an arch that runs from our ankle to our toes. We sacrificed the ability to grip in return for a springy, shock-absorbent step.

These changes were already in place 3.5 million years ago. One of our ancient relatives, Australopithecus afarensis, had a remarkably human foot and was clearly already walking around on two legs. Some scientists have taken this to mean that hominins such as Lucy (the most famous A.afarensis specimen) necessarily walked on the ground. After all, human feet are supposedly ill-suited for life in the trees.

But try telling that to the gentleman in the video below. He’s one of the Twa pygmies—a group of Ugandan hunter-gatherers who often climb trees in search of food, such as honey and fruit. Like other Twa men, he started from an early age. And he’s clear proof that a human foot is no impediment to walking straight up a trunk.

The footage was shot by Vivek Venkataraman, Thomas Kraft and Nathaniel Dominy from Dartmouth College. The trio originally started studying the Twa to understand the evolution of their short five-foot stature but were awestruck at how adeptly they could climb. “We tried to climb the same trees, but we found it extremely difficult,” says Venkataraman. “The Twa were quicker, more agile, and highly coordinated.”

That’s because their ankles are so extraordinarily flexible that their feet can make up to 45 degree angles with their shins. You can clearly see this in the video. It’s a level of flexibility comparable to wild chimpanzees, which walk up trees in much the same way. They plant their soles flat against the trunk, allowing them to hold their bodies closer to the trees and reducing the energy it takes to climb.

For comparison, most people can only bend their feet by 15 to 20 degrees. If you or I tried to match the flexion of a Twa climber, our ankles would rupture catastrophically and we wouldn’t be walking, much less effortlessly scaling a thick vine.

From Venkataraman et al, 2013

But the Twa’s secret isn’t in their ankles, which are indistinguishable from those of other people. Instead, the team found that the Twa’s flexibility stems from calf muscles (gastrocnemius) with unusually long fibres—far longer than those of the Bakiga, a group of neighbouring Ugandan farmers who don’t climb trees. The team found the same differences in the Philippines. The tree-climbing Agta hunter-gatherers have far longer gastrocnemius fibres than the non-climbing Manobo farmers.

Venkataraman suspects that their calf muscles aren’t born this way. Instead, their fibres lengthen with practice. “People who frequently wear high heels have short calf muscle fibres, and their ankles are stiffer as a result,” he says. Regular tree-climbing does the opposite for the Twa.

The stark lesson from this hard-won research is that there’s nothing about a human foot that precludes us from the trees. And equally, the fact that A.afarensis had a human-like foot doesn’t mean that it was a bad climber. The muscles, which don’t fossilise, can make a huge difference. With the right calves, Lucy could have scampered up a trunk as well as striding across a savannah.

Lucy at the Smithsonian Natural History Museum., by Ryan Somma

Venkataraman’s study lobs some much-needed data into a longstanding debate about how A.afarensis actually moved. “Our field has been arguing about tree climbing in A.afarensis for 30 years,” says Jeremy DeSilva from Boston University. “Remarkably, this is the first study to thoroughly investigate the tree-climbing habits of its closest living relative: humans! It is not that no one ever thought to do this; data such as these are just very difficult to obtain.”

The study helps to make sense of some A.afarensis’s contrasting anatomy—it had the feet of a committed biped, but the long arms, curved fingers, and ape-like shoulder blades of a competent tree-climber. “[It adds] to the growing body of evidence that the supposedly unique human foot is not quite as distinct from that of other great apes as we have tended to believe, and that human bipedalism had arboreal origins,” says Robin Crompton from the University of Liverpool.

Of course, Venkataraman’s study doesn’t mean that A.afarensis climbed trees, just that we shouldn’t rule out that possibility on the basis of its bones. “Maybe not having an opposable big toe isn’t as catastrophic for climbing trees as we commonly assume, especially if you change your climbing style,” he says.

“My guess is that the A.afarensis was mostly a terrestrial biped, living and feeding on the ground. At night, I suspect that they may have climbed slowly and carefully into the trees to build night nests,” says DeSilva. “But that scenario is really tough to test without more fossils and a better idea of what anatomies allow an upright walker to safely and effectively climb a tree.”

Update: A last-minute comment. Claude Owen Lovejoy from Kent State University says that the study misses the point. “No one has ever claimed that A.afarensis did not climb trees. I’m sure they did. Modern humans climb trees, but so what? The argument is not about behaviour but about principal adaptation.” And that was for bipedality. “Bipedality was so central to A.afarensis’ adaptation even if it climbed trees regularly,” says Lovejoy.

Reference: Venkataraman, Kraft & Dominy. 2012. Tree climbing and human evolution. http://dx.doi.org/10.1073/pnas.1208717110

More on human evolution:

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Q: Why don’t apes have bigger brains? A: They can’t eat enough to afford them

As animals get bigger, so do their brains. But the human brain is seven times bigger than that of other similarly sized animals. Our close relative, the chimpanzee, has a brain that’s just twice as big as expected for its size. And the gorilla, which can grow to be three times bigger than us, has a smaller brain than we do.

Many scientists ask why our brains have become so big. But Karina Fonseca-Azevedo and Suzana Herculano-Houzel from the Federal University of Rio de Janeiro have turned that question on its head—they want to know why other apes haven’t evolved bigger brains. (Yes, humans are apes; for this piece, I am using “apes” to mean “apes other than us”).

Their argument is simple: brains demand exceptional amounts of energy. Each gram of brain uses up more energy than each gram of body. And bigger brains, which have more neurons, consume more fuel. On their typical diets of raw foods, great apes can’t afford to fuel more neurons than they already have. To do so, they would need to spend an implausible amount of time on foraging and feeding. An ape can’t evolve a brain as big as a human’s, while still eating like an ape. Their energy budget simply wouldn’t balance.


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Why the genome project missed a gene that shaped our brains

The Human Genome Project was officially completed in 2003, but our version of the genome is far from truly complete. Scientists are still finishing the last parts, correcting errors in the official sequence, and discovering new genes. These new genes did not go unnoticed because they are useless or insignificant. Some of them may be key players in our evolutionary story.

Two groups led by Evan Eichler and Franck Polleux have found that humans, alone among all animals, have three extra copies of a gene called SRGAP2, which is involved in brain development. The second of these copies, SRGAP2C, is particularly interesting because it affects the development of neurons, and produces features that are distinctively human. It also emerged between 2 and 3 million years ago, during the time when our brains became much bigger.


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The Peking Man, and other lost treasures that science wants back

New Scientist had a great new feature on nine lost treasures that science wants back. I wrote about one of them – the bones of Peking Man.

In September 1941, Hu Chengzhi placed several skulls into two wooden crates. Around him, China was at war with Japan, so he was sending the skulls to the US for safekeeping. They never arrived. Hu was among the last people to see one of the most important palaeontological finds in history. These lost skulls belonged to Homo erectus pekinensis, known as Peking Man.

You can read all of them free online, which include the Maxberg Archaeopteryx, Nixon’s moon rocks, the recipe for Damascus steel and moon trees.

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The semi-naked ape, or why peach fuzz makes it harder for parasites

We humans are often known as “naked apes”. It might seem like a deserved nickname; after all, we lack the lush coats of body hair that chimps, bonobos and gorillas have in abundance. But we are not naked. We actually have the same density of body hair as other apes of our size, but ours is largely fine and colourless rather than thick and dark. We are coated with a layer of short, fine hair, known technically as vellus hair and colloquially as peach fuzz.
Many scientists have speculated about why we humans have lost a thick coat of body hair. But very few of them have offered answers to an equally mysterious question: why have we kept our vellus coat? The fine hairs aren’t very good at preserving body heat, and they don’t make us more or less sexually attractive. They look like the results of a half-hearted evolutionary stab at becoming hairless. Some have suggested that they have no role at all.

But Isabelle Dean and Michael Siva-Jothy from the University of Sheffield have an intriguing possible answer: they think that the vellus hairs help us to spot parasites.


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Did humans trade guts for brains?

Humans are remarkably fuel-efficient, or at least, our brains are. The lump of tissue inside our skulls is three times larger than that of a chimp, and it needs a lot more energy to run. But for our size, we burn about as much energy as a chimp. We’re no gas-guzzlers, so how did we compensate for the high energy demands of our brains? In 1995, Leslie Aiello and Peter Wheeler proposed an answer – we sacrificed guts for smarts.

The duo suggested that during our evolution, there was a trade-off between the sizes of two energetically expensive organs: our guts and our brain. We moved towards a more energy-rich diet of meat and tubers, and we took a lot of the digestive work away from our bowels by cooking our food before eating it. Our guts can afford to be much smaller than expected for a mammal of our size, and the energy freed up by these shrunken bowels can power our mighty brains.

This attractive and intuitive idea – the so-called “expensive tissue hypothesis” became a popular one. But Ana Navarrete from the University of Zurich thinks she has disproved it.


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Humans and Neanderthals had sex, but not very often

Tens of thousands of years ago, our ancestors spread across the world, having sex with Neanderthals, Denisovans and other groups of ancient humans as they went. Today, our genes testify to these prehistoric liaisons. Last year, when the Neanderthal genome was finally sequenced, it emerged that everyone outside of African can trace 1 and 4 percent of their DNA from Neanderthals.

The discovery was a vindication for some and a surprise to others. For decades, palaeontologists had fought over different visions of the rise of early humans. Some championed the “Out of Africa” model, which says that all of us descend from a small group of ancestors who came out of Africa, swept the world, and replaced every other group of early humans. The most extreme versions of this model said that these groups never had sex, or at least, never bred successfully. The alternative – the multiregional model – envisages these prehistoric groups as part of a single population that met and mated extensively.

To an extent, these are caricatured versions of the two models, and there are subtler variants of each. Still, early evidence seemed to support the extreme Out of Africa version. When scientists sequenced the mitochondrial genome of Neanderthals (a small secondary set of genes set apart from the main pack), they found no evidence that any of these sequences had invaded the modern human genome. The conclusion: Neanderthals and humans never bred.

The full Neanderthal genome disproved that idea, but it also shifted the question from whether humans had sex with Neanderthals to just how much sex they had. As I mentioned in New Scientist earlier this year, modern humans were spreading into areas where Neanderthals existed. “It doesn’t necessarily take a lot of sex for genes from a resident population to infiltrate the genomes of colonisers. When an incoming group mates with an established one, the genes they pick up quickly rise to prominence as their population grows.”

Now, Mathias Currat from the University of Geneva and Laurent Excoffier from the University of Berne have weighed into the debate. They simulated the spread of modern humans from Africa and their encounters with Neanderthals throughout Europe and Asia, to work out the levels of sex that would have transferred Neanderthal genes to modern genomes at their current level.


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Did sex with Neanderthals and Denisovans shape our immune systems? The jury’s still out

The Neanderthals may be extinct, but they live on inside us. Last year, two landmark studies from Svante Paabo and David Reich showed that everyone outside of Africa can trace 1-4 percent of their genomes to Neanderthal ancestors. On top of that, people from the Pacific Islands of Melanesia owe 5-7 percent of their genomes to another group of extinct humans – the Denisovans, known only from a finger bone and a tooth. These ancient groups stand among our ancestors, their legacy embedded in our DNA.

Paabo and Reich’s studies clearly showed that early modern humans must have bred with other ancient groups as they left Africa and swept around the world. But while they proved that Neanderthal and Denisovan genes are still around, they said little about what these genes are doing. Are they random stowaways or did they bestow important adaptations?


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Our patchwork origins – my new feature in New Scientist

The sequencing of the complete Neanderthals genome was one of the highlights of last year, not just because of the technical achievement involved, but because it confirmed something extraordinary about our own ancestry. It showed that everyone outside of Africa can trace around 1-4% of their genes to Neanderthals. Our ancestors must have bred with Neanderthals on their way out of Africa.

Then, later in the year, the same team revealed another ancient genome. This one belonged to a group of people called Denisovans, known only from a single finger bone and a tooth. They too had left genetic heirlooms in modern people. Around 5-7% of the genes of Melanesians (people from Papua New Guinea, Fiji and other Pacific islands) came from the Denisovans.

In this week’s issue of New Scientist, I’ve got a feature that explores our patchwork origins. I looked at what these ancient genomes mean for our understanding of human evolution. I also considered some intriguing questions like whether other Denisovan fossils have already been found, whether this human pattern is applicable to other animal species, how much you can tell from modern genomes alone, and whether we’ll ever get DNA from the ‘hobbits’ of Flores. Do check it out – it contains some great viewpoints from Svante Paabo and David Reich, two of the scientists who spearheaded the sequencing efforts, along with Chris Stringer, Milford Wolpoff, Alan Cooper and John Hawks.

The magazine’s on the stands for the next week, or you can read the piece online if you have a New Scientist subscription to read the full thing. If  get round to it, I’ll try and stick up some of the transcripts from the interviews that I did for the piece. There’s some great stuff there.

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Humans have a magnetic sensor in our eyes, but can we detect magnetic fields?

Many birds have a compass in their eyes. Their retinas are loaded with a protein called cryptochrome, which is sensitive to the Earth’s magnetic fields. It’s possible that the birds can literally see these fields, overlaid on top of their normal vision. This remarkable sense allows them to keep their bearings when no other landmarks are visible.

But cryptochrome isn’t unique to birds – it’s an ancient protein with versions in all branches of life. In most cases, these proteins control daily rhythms. Humans, for example, have two cryptochromes – CRY1 and CRY2 – which help to control our body clocks. But Lauren Foley from the University of Massachusetts Medical School has found that CRY2 can double as a magnetic sensor.


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Twinning is winning – mothers of twins live longer, raise larger families

For every hundred babies born in Europe, one or two of them are quickly followed by a twin. From a cold evolutionary point of view, twins look like a win for their mother. History, after all, is written by individuals who are best at passing on their genes, so having more children at once seems like a good strategy. So why are twins so rare?

The standard answer is that giving birth to twins, and raising them, is difficult. Complications during pregnancy and delivery could kill both mother and children. In a classic 1990 paper, a bird specialist called David Anderson expanded on this idea. He suggested that twins are the result of an evolutionary bet-hedging strategy gone wrong.

Anderson knew that birds will commonly lay several eggs as insurance, to make sure that they get at least one strong chick. After hatching, the parents (or the strongest chick) will kill the weaker babies. In humans, a similar (but less brutal) competition happens in the womb. Mothers will often produce several eggs, with the others acting as insurance in case the first doesn’t make it. If two eggs are fertilised, one embryo is often lost – this is why many more twins are conceived than are born, the so-called “vanishing twin” effect. If this process fails, you get twins. That’s a problem, because having twins exacts a physical toll upon the mother.

According to this fairly bleak view, mums with twins have taken an evolutionary gamble that has backfired. But Shannen Robson and Ken Smith don’t agree. In a new study, the two scientists from the University of Utah have painted the birth of twins in a more positive light. To them, the very fact that some mothers can bring twins to term is a sign that they are strong and fit. The presence of twins singles out mums who can bear the extra cost of having twins.