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The entrance to Shanidar Cave in northern Iraq. Image courtesy of Flickr user Kurdistan Photo كوردستان

Iraq is the home of the Fertile Crescent, the Cradle of Civilization. But the country’s importance in human history goes back even further, to the time of the Neanderthals. In 1951, American archaeologist Ralph Solecki discovered Neanderthal remains in Shanidar Cave. The cave sits in the Zagros Mountains in the Kurdistan region of northern Iraq, about 250 miles north of Baghdad. From 1951 to 1960, Solecki and colleagues excavated the cave and recovered fossils belonging to 10 individuals dating to between 65,000 and 35,000 years ago. Politics prevented further archaeological work, but the Shanidar fossils still provide important insights on the Neanderthals of West Asia. Here are a few of the most intriguing finds:

Shanidar 1: Nicknamed Nandy, Shanidar 1 lived sometime between 45,000 and 35,000 years ago. He had a hard life. A blow to the head in his youth probably blinded him in his left eye. A withered right arm and leg suggest the head injury probably also caused brain damage that paralyzed the right side of Nandy’s body. He also fractured his foot at some point. Yet his bones all show signs of healing, and Nandy lived to be a senior citizen by Neanderthal standards, dying sometime between the ages of 35 and 45. The find revealed that Neanderthals must have taken care of their sick and wounded.

Shanidar 3: Also an adult male, Shanidar 3 had plenty of problems of his own. In addition to suffering from arthritis, the Neanderthal seems to have been violently attacked. A tiny groove on one of his ribs indicates he was probably struck in the chest. A 2009 analysis (PDF) points to a modern human, Homo sapiens, as the assailant. Based on experimental stabbings of pig carcasses, a team led by Steven Churchill of Duke University determined that the most likely weapon was some kind of dart, shot from long range. Because modern humans are the only hominids known to have made projectile weapons, the researchers blamed our species for the wound. The wound may have harmed Shandiar 3′s lungs, but it’s possible he survived the attack. A callous that formed over the groove shows that he must have lived at least a few week after the incident. And modern people with similar injuries can survive even with little medical care.

Today, you can examine Shanidar 3 for yourself at Smithsonian’s National Museum of Natural History, where the fossil is on display.

Shanidar 4: Yet another adult male, Shanidar 4 was found on his side curled up in the fetal position. An analysis of the ancient pollen found in association with the fossilized skeleton revealed bright flowers had been brought into the cave. Solecki interpreted the pollen studies as evidence that Neanderthals buried their dead and adorned the graves with flowers, suggesting Neanderthals had rituals. Skeptical anthropologists say natural forces—perhaps burrowing rodents—introduced the pretty flora into the cave. Although Neanderthals might not have decorated the graves, they were responsible for burying at least some of the individuals in Shanidar.

This skull from the Petralona Cave is one of the few hominid fossils found in Greece that date to the Middle Pleistocene. Image courtesy of Wikicommons

Greece should be filled with hominid bones and stone tools. Its location makes it the perfect gateway to Europe for the earliest hominids leaving Africa, and even during dry and cold spells that made many other parts of the world uninhabitable, Greece remained pleasant. Yet the country’s archaeological record is bare from 1.8 million to 125,000 years ago, a period known as the Early to Middle Pleistocene.

And here’s why: Only 2 to 5 percent of Greece’s paleoanthropological record from this period has survived. That’s the conclusion of the authors of a new study in Quaternary Science Reviews that looks at the geological processes that preserve or destroy bones and artifacts.

To be fair, Greece’s record isn’t completely empty. Anthropologists have found some handaxes and a few skulls, a Homo heidelbergensis in the cave of Petralona and two Neanderthals in Apidima. The problem is that these finds are poorly dated. Many of the discoveries have been made on the surface, meaning there’s no geological context or stratigraphy—the depositional layers that build up in a sequence over time—to help researchers figure out when the fossils and tools were left behind. And without dates, these pieces of evidence are hard to interpret.

One explanation for the lack of discoveries is that hominids never really set down roots in the area. If they didn’t live there, there was nothing to leave behind. Vangelis Tourloukis of the University of Tübingen in Germany and Panagiotis Karkanas of Ephoreia of Palaeoanthropology–Speleology of Southern Greece don’t buy this explanation. So they looked to the  region’s geology to solve the puzzle of the missing hominids, reviewing a range of previous studies.

One thing they considered was the changing sea level over time. During cold periods, more of the world’s water is locked in polar ice sheets and glaciers, and sea level recedes, exposing parts of the seafloor. When it gets warm again, the ice melts and the ocean rises. Tourloukis and Karkanas found that during parts of the Early and Middle Pleistocene, much of the Aegean Sea, east of Greece, was dry land. In fact, the total area that was exposed then equals the area of the Greek Peninsula today (more than 50,000 square miles). If you assume all dry land was a possible living site of hominids, that means half of the potential archaeological record is now gone, submerged beneath the Aegean, the researchers say.

Back on dry land, a range of climatic and geologic factors influenced the likelihood that bones and artifacts were preserved. One of the biggest contributors was water: Rivers and streams eroded the landscape, washing sediments (and artifacts) away and piling them up somewhere else. In the Early and Middle Pleistocene, climatic conditions led to periodic catastrophic flooding, the researchers noted, and “archaeological assemblages [were] subjected to disturbance, reworking or total destruction every few thousands, hundreds or even tens of years.”

Tectonic activity, the movement within Earth’s crust and mantle that shapes topography, caused further problems. Greece is a very tectonically active region, and in the Early and Middle Pleistocene, the crust was being stretched. At one point, the stretching changed directions, raising blocks of earth and exposing bones and artifacts to destructive erosion for thousands of years. (Meanwhile, some blocks were buried, which helped protect artifacts. Such basins are probably where most potential archaeological sites are today.)

Another issue is Greece’s rugged, steep terrain. More than half of the country is mountainous or hilly, where landslides can easily bury or destroy archaeological sites.

After reviewing this geological evidence, the pair’s final step was to estimate how much of Greece’s archaeological record from this period may still exist. This takes a little bit of math. Here are the important numbers:

10 percent: Not all of Greece’s land is composed of Early to Middle Pleistocene-aged deposits. Sediments from other time periods also make up the landscape. The researchers estimated about 10 percent of the Greek Peninsula is dated to this period.

40 percent: This is the area of Greece that isn’t too steep and mountainous for fossils and tools to be preserved over time.

50 percent: Right off the bat, the researchers eliminated half of the potential archaeological record because it’s now at the bottom of the Aegean Sea.

So, the amount of the potential archaeological record that may still be out there is 10 percent of the 40 percent of the 50 percent—or just 2 percent. With some tweaks in their expectations and assumptions, the researchers say it could be as high as 5 percent.

These odds don’t seem great, but Tourloukis and Karkanas have an optimistic outlook. Because so much more land was exposed in the past, forming a natural land bridge with Turkey, hominids dispersing from North Africa through the Sinai Peninsula and the Middle East could have easily followed the southern coast of Turkey into coastal Greece and then on to Italy and the rest of Europe. And the geological evidence suggests the landscape would have been home to numerous lakes, lagoons, marshes and streams rich in valuable plant and animal resources. Why wouldn’t hominids have wanted to live there?

With this new assessment, archaeologists now have a better chance of finding traces of these hominid Shangri-Las.

Someone painted this rhinoceros on a wall in France's Chauvet Cave about 30,000 years ago. Image courtesy of Wikicommons

In 1940, a group of teenagers discovered the paintings of bison, bulls and horses adorning the walls of France’s Lascaux Cave. Roughly 17,000 years old, the paintings are Europe’s most famous cave art, but hardly the oldest. This week archaeologists announced finding in another cave in France art dating to about 37,000 years ago, making it a candidate for Europe’s most ancient artwork. Here’s a look at the new discovery and the other top contenders for the title of Europe’s oldest work of art.

Nerja Caves (possibly about 43,000 years ago): In February, José Luis Sanchidrián of Spain’s University of Cordoba declared he had found paintings of seals on stalactites in southern Spain’s Nerja Caves. The paintings themselves have not yet been dated. But if they match the age of charcoal found nearby, then the art might be 43,500 to 42,3000 years old, New Scientist reported. That would make the Nerja Cave art the oldest known in Europe—and the most sophisticated art created by Neanderthals, the hominids that lived in this part of Spain some 40,000 years ago.

Abri Castanet (about 37,000 years ago): In 2007, among the rubble from a collapsed rock shelter at the Abri Castanet site in southwestern France just six miles from Lascaux, archaeologists found an engraved chunk of rock. The engravings on the 4-foot-by-3-foot slab, once part of the rock shelter’s ceiling, depict female genitalia and part of an animal. With the help of radiocarbon dating, Randall White of New York University and colleagues estimate the art was made sometime between 36,940 and 36,510 years ago by the Aurignacians, the modern humans who lived in Europe at this time. The researchers reported their findings this week in the Proceedings of the National Academy of Sciences.

Venus of Hohle Fels (35,000-40,000 years ago): In Nature in 2009, Nicholas Conrad of Germany’s University of Tübingen described the discovery of a 2-inch figurine carved from a mammoth tusk. The tiny sculpture was recovered from Hohle Fels cave in southern Germany’s Swabian Jura mountain range. The figure depicts a woman with large, exaggerated breasts, buttocks and genitalia. Radiocarbon dated to at least 35,000 years ago, it is the earliest known Venus figurine. Also in the Swabian Jura, archaeologists have found the Lion Man of Hohlenstein Stadel, an ivory sculpture dated to roughly 30,000 years ago.

Chauvet Cave (about 30,000 years ago): Discovered in 1994, Chauvet Cave’s paintings stand out among Europe’s cave art for their subject matter. In addition to depicting animals that Stone Age people hunted, such as horses and cattle, the wall art shows predators like cave bears, lions and rhinos. The cave’s paintings are exceptionally well preserved because tourists—and the damaging microbes they bring—aren’t allowed inside. But you can still enjoy the breathtaking art by taking a virtual tour of the cave or watching Werner Herzog’s 2011 documentary Cave of Forgotten Dreams.

Adult male orangutans have large cheek pads and a big throat pouch, but it can take decades to develop such traits. Image courtesy of Flickr user nebarnix

In Interview with the Vampire, Claudia, portrayed by Kirsten Dunst in the movie version, becomes a vampire at age 6. Six decades later, she still has the body of a child but the thoughts and desires of a grown woman.

In this way, orangutans are kind of like vampires. They have their own form of arrested development.

When male orangutans hit puberty, they develop distinct traits known as secondary sex characteristics that separate them from females. In addition to being much bigger, males grow longer, shaggier hair on their arms and back and sport giant cheek pads. They also have throat pouches that resemble large double chins, allowing males to beckon females with loud long calls.

Some males are late bloomers, not acquiring these traits until as late as age 30. But looks can be deceiving. Even though these males appear to be youngsters, they are sexually mature and capable of siring offspring.

Scientists think the two different types of adult males—those with secondary sex characteristics and those without—are two alternative mating strategies that evolved in orangutans. A new study published online in the American Journal of Physical Anthropology tries to pinpoint the circumstances under which orangutan arrested development emerges.

To do this, Gauri Pradhan of the University of South Florida and Maria van Noordwijk and Carel van Schaik, both of the University of Zurich, considered the differences between orangutans living in Borneo and those in Sumatra. These Indonesian islands are the only two places in the world where orangutans are still found in the wild. But arrested development is largely limited to Sumatra.

Orangutans in both locations are mostly solitary. They roam the treetops alone, but they live in home ranges that overlap with those of other orangutans. In Sumatra, a female prefers to mate with the dominant male that lives in her neck of the woods. This male always has his full set of male features. A female finds the dominant male by following the sound of his long call, and when she’s ready to be pregnant, the two enjoy a sort of honeymoon—traveling and mating together for up to three weeks. Other adult-looking males may live in the same area, but females actively avoid their calls and stay hidden from them.

Because the dominant male is so popular, he can be choosy about mates. These males tend to pass over inexperienced females who haven’t yet had a baby. With younger adult females, it’s hard to tell if they are truly ready to become mothers, so it’s a better bet to stick with females who are already moms.

Yet some males are interested in these naïve females: the sexually mature males lacking adult traits. Unlike the other male orangutans, these guys don’t wait for females to come to them. They search the forest for receptive females, and Pradhan and his colleagues speculate that these males might father a lot of the children of first-time orangutan moms.

The sex lives of orangutans on Borneo are quite different. Here, no single adult-looking male is dominant. Many full-fledged males mate with an area’s females. Orangutan honeymoons are much shorter, and males may fight with each over a potential mate. Because the competition is so fierce, males aren’t choosy about who they mate with—and sometimes, even if a female’s not in the mood for mating, a male might force her to copulate.

Pradhan’s team incorporated these differences, as well as some assumptions about male growth, into a mathematical model. Their equations allowed them to determine which factors best explain the presence of immature-looking adult males in a population. The most important variable, they conclude, is the ability for one male to dominate an area. When this happens, as in Sumatra, it becomes beneficial for other males to have a covert mating strategy.

But if there is a lot of direct competition among males, as in Borneo, then it’s better to be a full-fledged male, who will always beat out immature males. No one male can monopolize females in Borneo because males tend to travel more on the ground there, the researchers say. That improves their mobility and makes it easier to quickly find females, even those who may not want to be found.

Thousands of years ago, orangutans once lived throughout much of Southeast Asia, even on the mainland. I wonder how pervasive arrested development was back then. Even if we had large bone samples, would anthropologists ever be able to detect such behavior in the fossil record?

A grandmother in Ethiopia carries her grandchild. Image courtesy of Wikicommons

As Mother’s Day approaches, let’s take a moment to celebrate grandmothers. Grandmothers have traditionally been important members of the family who help their daughters raise children. Some anthropologists have suggested that the evolutionary benefits of grandmothering may explain why women have such long post-menopausal lives. You don’t see that in other primates. The idea is controversial, but it has been the center of numerous research studies.

Now, Jack da Silva of Australia’s University of Adelaide adds a new twist to the grandmother effect: It may have helped keep harmful breast cancer mutations at bay.

Mutations in the BRCA1 and BRCA2 genes are risk factors for breast cancer. The genes normally keep a cell’s growth in check. When certain mutations arise in these genes, cells grow out of control and cancer develops in the breasts or reproductive organs. These mutations are among the main causes of hereditary breast cancer. According to the National Cancer Institute, about 12 percent of women in the general population get breast cancer compared to 60 percent of women carrying BRCA1 or BRCA2 mutations.

A grandmother and her grandson in New York City in 1947. Image courtesy of Wikicommons

Last fall, a study published in the Proceedings of the Royal Society B reported an unexpected benefit of the BRCA1 and BRCA2 mutations. In a sample of women born in Utah before 1930, those who carried the mutated genes had greater fertility than those who didn’t. Carriers had on average 6.22 children, while non-carriers had 4.19 kids. That’s almost a 50 percent increase in fertility. Exactly how these mutations improve fertility is not known, but women carrying the mutations had more reproductive years and shorter intervals between births.

In a paper published online today in Proceedings of the Royal Society B, da Silva considers the paradox of the BRCA1 and BRCA2 mutations—that they are both good and bad from an evolutionary perspective. They are an example of what biologists call antagonistic pleiotropy. Pleiotropy occurs when a gene influences more than one trait. Antagonistic pleiotropy explains why otherwise harmful mutations can stick around in the gene pool. In the game of evolution, the goal is to pass on your DNA. Any mutation that helps an individual reproduce will be selected for, even if that mutation is harmful later in life. That seems to be what happens with these breast cancer mutations, which tend to cause cancer after a woman’s reproductive years are over.

Based on estimated mutation rates and the mutations’ reproductive benefits, da Silva calculates that the BRCA1 and BRCA2 mutations should be much more common (one estimate suggests the BRCA1 mutations occur in about 1 in 3,000 women in the United States). This is where grandmothers come in.

Grandmothers can help ensure the survival of their grandchildren (and by extension, the survival of their own DNA) by helping raise them. A study of Finnish and Canadian women living on farms in the 18th and 19th centuries found that a woman produced an extra 0.2 grandchild for every year that she lived beyond age 50. If grandmothering is really that vital, then it might give women who don’t carry the breast cancer mutations an evolutionary edge over women who do and are therefore less likely to live as long.

Three generations of Black H'mong in Vietnam: grandmother, mother and grandson. Image courtesy of Wikicommons

Taking into account several factors about women’s reproductive lives and the effects of grandmothering, and with a little bit of math, da Silva argues that grandmothering would have limited the spread of the BRCA1 and BRCA2 mutations in the distant past, when more people lived in traditional hunter-gatherer societies. Based on this, he calculates that the mutations should occur in 0.275 percent of the population. He points out that that’s close to the worldwide average of 0.227 percent.

To get to this conclusion, da Silva made many assumptions about fertility, life span and the usefulness of grandmothers in hunter-gatherers. Those assumptions need to be validated by data from a variety of real-world groups for his conclusions to hold up.

Grandmothers’ effects on breast cancer mutations are smaller today because many people live in societies where birth control, fertility treatments, day care, nannies, etc. play big roles in reproduction and child rearing (and where breast cancer can be treated). But even if grandmothers had only a small part in limiting the spread of BRCA1 and BRCA2 mutations, it’s still one more reason to be thankful for them this Mother’s Day.