Let’s start with a day in the life of your skeleton. Many people think that once they reach adulthood and stop growing, their skeletons never change. Anyone who has broken a bone knows that can’t be true, though, because bones can repair themselves. Even if you’ve been spared the pain of a complete fracture, your bones suffer for you daily. Every time you take a step, your muscles pull on their bony attachments, your body mass weighs down your skeleton, and all your weight-bearing bones (spine, hips, legs and feet) develop tiny little micro-fractures. If those micro-fractures kept building up, they’d eventually cause a complete break in the bone. But your body can sense when those micro-fractures occur, and it sends in special bone-building cells to repair the damage. These cells, called osteoblasts for you etymology fans out there, are responsible for detecting exactly how much strain you’re putting on your bones and repairing it. If you insist on running or jumping or hitting things on a regular basis, your muscles will hypertrophy (get bigger), but so will your bones. One famous study found that the upper arms bones of tennis players were significantly different sizes—their serving arm bones dwarfed their non-serving arm bones. Swimmers and golfers also strain their upper bodies, maintaining or increasing bone mass there.

If bones respond to extreme loading by getting bigger, what about if you spend too much time in front of your computer writing blog posts and forget to load your bones at all? In a classic case of “use it or lose it,” extreme unloading (i.e., computer potato behavior) causes the atrophy of bones. Without exercise, the body senses that the bones don’t need to be so strong, and so it begins to dismantle the skeleton (with cells called osteoclasts), which while it sounds awful, is actually very efficient. The materials locked up in bone (calcium, among other useful minerals) can be used elsewhere, so if they aren’t needed in the bones to support intense physical activity, the body breaks down those bones. Astronauts experience both muscle atrophy and decreased bone density due to the lack of gravity in space. Without the resistance provided by gravity, muscles don’t have to work very hard to move them around, so the bones don’t get strained. The muscles and bones both atrophy, becoming weaker and smaller. Bed-ridden individuals experience similar problems.

Thus, the link between weight and bone mass is slightly more complicated. Yes, underweight individuals are more likely to suffer from osteoporosis. They don’t load their bones as heavily with every step, and if their low body weight is supported by inadequate nutrition, their body may be dismantling their bones simply to get at the calcium inside. But if they’re skinny because they run marathons and they drink enough milk, their bones are likely loaded sufficiently to prevent (or at least) slow osteoporosis. On the flip side, overweight individuals build stronger bones with each step, but if their diet lacks adequate nutrients, their bones might still be in danger. While I am not licensed to offer health advice of any kind, in this case, it seems pretty straight-forward: go for a walk or a swim or dance around your living room, but eat that cookie afterward. With your bones, as with life, balance is key.

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Recent news reported that the amazing finding of preserved blood vessels and other soft tissue in fossilized dinosaur bones first reported in 2005 was independently confirmed by another lab. The 68 million-year-old collagen molecules are remarkably similar to those found in modern-day chickens. The claim of un-fossilized material dating to the Cretaceous Epoch ran so counter to accepted knowledge about the fossilization process when it was first announced that many scientists dismissed the report out of hand. In the past four years, however, it has become clear that soft tissue preservation is more widespread than anyone imagined – the problem is just that no one really ever looked for it before!

Bone is made of both organic and inorganic material. The inorganic mineral hydroxyapatite gives bone its strength and rigidity. The organic material, containing proteins such as collagen, provides that stiff skeleton some flexibility, preventing bones from shattering with each movement. The fossilization process is simply the transformation of the organic part of bone into rock (inorganic material). Muscles and organs rarely fossilize because they have so little inorganic material to start with. Bones are easier to fossilize, given that they start already 70% mineralized. Teeth, made of enamel and dentin with very little collagen, are already 95% mineralized, so are the most frequently preserved elements in the fossil record.

Conventional understanding of fossilization held that unless the organic material in bone rapidly turned into rock, it would decay. “Very old” preserved soft-tissue before 2005 had been found in Ice Age megafauna like mammoths, dating back 50,000 years. This material was preserved because it was buried in ice, slowing the decay process. “Subfossil” material such as giant lemurs from Madagascar and the “hobbit” species from Indonesia retains soft tissue because it dates to younger than 20,000 years ago and has not yet had time to fully mineralize. The Tyrannosaurus rex fossil excavated in 2003 was dated to 68 million years ago and was not preserved in ice. However, after one of the femora was broken during transportation, the internal contents were visible. The lab examining the material then took the unorthodox step of dissolving the mineralized part of the bone with a weak acid. I’m confused by this step, since if the fossil were truly entirely mineralized as everyone expected, it would have entirely disappeared. And who does that to T. rex fossils? But in this case, some soft tissue remained after the mineralized portion was removed. And it is from this that the genetic signal of the collagen protein was found to resemble modern-day chickens, initially in 2007 and confirmed last week.

This analysis is not one that a paleoanthropologist would readily perform. Dinosaur fossils, while millions of years older than any human fossil, are far more plentiful. Perhaps as many as 700 species of dinosaur existed during their 160 million year reign, and many of those species lived in fossilization-promoting environments. Even the most species-friendly anthropologists (who belong to a group called the “splitters” due to their fondness for naming multiple species) only designates ~20 hominin fossil species, spanning only the past seven million years. Our ancestors also had the annoying habit of living in tropical rainforests and along ancient coastlines, assuring their remains would be lost to modern scientists forever. The abundance of dinosaur fossils perhaps explains why one brave researcher undertook such a potentially destructive experiment – even if one fossil was dissolved completely, there were plenty of others around. This unorthodox experiment paid off, however, and will hopefully inspire similar investigation in other fossils. After all, if 45-million-year-old yeast can still be brewed into beer, and T. rex proteins can be sequenced after 68 million years, we’re two steps closer to Jurassic Park becoming a reality – but with drunk dinosaurs.

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This week brought news of a dinosaur and a fossil fish up for auction as well. The debate over who “owned” Sue, the most complete T. rex ever found, raged for seven years, and the state of South Dakota is back in court over another T. rex named Tinker. Are fossils public property? Can they be kept by private collectors or should they be held only by museums and made available to researchers?

Even when fossils are kept in museums, not all researchers have been allowed access to them. Claiming intellectual priority, those who obtained funding and provided the labor for fossil excavations can prohibit their “competitors” from accessing their prized finds until they have adequately examined them. While this rule seems fair, who determines what “adequate” examination time is? Can it be limited to one year? Ten? Twenty?

A related problem involves the display and transportation of original fossil material. After a 1983 exhibit called Ancestors: Four Million Years of Humanity brought together 40 original fossils of human ancestors at the American Museum of Natural History, paleoanthropologists came to a de facto agreement that original fossil material should generally be left in its country of origin. Fossil hominins are much rarer than fossil dinosaurs, and the originals absolutely irreplaceable.

However, in 2006 the government of Ethiopia announced plans to send Lucy, perhaps the most famous and recognizable fossil hominid the world over, on a tour of the United States. As the “owners” of the fossil, the country was completely within its rights to do so, although most anthropologists were horrified at the thought of the potential disasters that could befall her scientifically invaluable remains. Should the exhibition be lauded for presenting a once-in-a-lifetime opportunity for school children to see original fossils, or be derided for putting those fossils at risk? To add to the debate is the fact that, unfortunately, the tour has not done particularly well.

So what’s a scientific community to do? On the one hand, we argue that fossils should not be sold to private collectors, but should remain in the public sphere. But who should get to see original fossils? Just those researchers who found them? Any scientifically interested party willing to travel to a regional museum in Kenya? The entire population of Seattle? Much like parents trying to strike a balance between keeping our children safe and being overprotective, paleontologists much find a way to preserve the treasures from the past without diminishing their potential to inspire.

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First, in February, a team from the University of Michigan published a remarkable find—a female whale that died 48 million years ago with a term fetus still in utero. The article discusses what can be learned about the species’ behavior based on body and tooth size differences between the female and an adult male found nearby, but just briefly mentions that the birth position of the fetus is also important. (In the image to the right, the maternal bones are colored pink, and the fetal bones are colored blue, illustrating the head-first position of birth, unusual for aquatic whales since they are born tail-first.) Since whales are marine mammals, infants are born tail-first, so they can end up swimming in the same direction as their mother immediately, a clear evolutionary advantage for both mother and offspring. Terrestrial mammals tend to be born head first, since our easily-splayed limbs can make any other position exceptionally dangerous. This fossil whale was giving birth like a terrestrial mammal, indicating that it was one of the first whale species to emerge from the ocean—a “missing link” between aquatic and terrestrial mammals if ever there was one (and there wasn’t!).

A second amazing whale find was published just last week. Paleontologists reported finding a partially healed broken jaw in a 14-million-year old fossil whale. The injury mimicked those seen in modern whales hit by large fishing boats, but Miocene apes weren’t driving boats around modern-day Virginia. The jaw was broken on the left side, indicating that perhaps the animal collided with something while turning left. Bottom-feeding whales (less common than the filter feeding types) could have come into with large objects on the sea floor with enough force to break bones. Interestingly, 80% of bottom-feeding marine mammals alive today consistently turn to the right when trolling sediment from the ocean floor for food. This individual must have been turning to the left if the colliding-with-something-big-while-feeding hypothesis holds. This may seem like a bit of a stretch (and not just to you—other paleontologists aren’t embracing the idea fully), but it’s a fascinating example of the possible conclusions that can be drawn from a single partially healed fossil.

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During the 2008 presidential campaign, I found a fail-proof cure for low blood pressure—I just listened to any of the candidates talk about the wasteful spending in science. “They spent 3 million dollars on bear genetics” was one favorite phrase for the politicians, and every time I heard it, I felt the desire to throw something bear-sized at the wall (or a politician). “Do they not know how expensive science is? What is wrong with them that they don’t see how important that study is?” were my most frequent utterances.

The months following the numbing onslaught of talking heads gave me some time to think, though, and I concluded that while I could spend energy accusing politicians of being idiots, it might be more productive to understand the role scientists play in the debate about science policy. Unfortunately, that role is limited. Scientists, as a group, tend to be more interested in doing science than taking about that science—egoism (“this is far too complicated for the plebians to understand”) is most definitely involved, although limitations posed by the number of hours in a day play a role as well. However this separation between scientists and non-scientists is created and maintained, it serves neither group in the long run. Scientists must do better at explaining both how we go about doing science and why what we do is important (and exciting), or we can expect the 2012 presidential election to be as full of misleading anti-science sound bites as was 2008. One of my favorite questions to ask when I learn new information is “But how do we know that?” Usually, the answer is so obvious to the expert presenting the information that he or she hadn’t even considered someone might be curious about it.

For example, at a science fair a few years ago, a visitor to my table was learning about Lucy, a 3.2 million year old fossil human ancestor, and asked me, “How do you know she wasn’t carved out of stone by a faker?” At the time, I stuttered through a response, so taken aback by the question that I couldn’t form a very coherent answer. But a few hours later, I thought, “Actually, that’s a pretty good question—how do I know that?” The biggest scandal in paleoanthropological history was the 1912 discovery of a fossil skull in Piltdown, England that was revealed to be a hoax only after decades of shaping the opinions of scientists as to the evolutionary history of humankind. Why should a visitor to a science festival accept that the fossils I brought were actually the remains of long-dead ancestors?

The answer for Lucy’s species, Australopithecus afarensis, is fairly straightforward. We have fossil fragments representing more than 300 individuals, found at several sites by many different scientists over the past forty years, and the techniques used to date the fossils replicate the 3-4 million-year-old age range again and again.

But the more complicated the science, the more important it is for scientists to translate the answer to the “how do we know?” question into words everyone can understand. We can’t expect politicians untrained in the scientific method to respect (or fund) what goes on in our labs if we lock ourselves in and refuse them entry. A study of bear genetics is an easy target for accusations of wasteful spending when people don’t understand all that goes into such a study or why it’s important., I’d like politicians to have a better understanding of science so my walls can stay safe from flying objects come next election.

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It costs thousands of dollars to run a summer-long paleontological excavation with a small crew in a developed country. If the dig continues for more than one field season, employs more than three people or takes place in a hard-to-reach locale, budgets climb into the millions. All scientists need sponsors and grants to cover these costs, and those with money like some assurance that their funding is going to making Important Discoveries. Thus, it has become common for new fossil finds to be announced via press conference with all the pomp and circumstance of current events—you know, those news-worthy tidbits that haven’t been sitting around underground for millions of years. In the scramble to get more people interested in these new fossils (which have neither the bulk of a T. rex nor the cuteness factor of a baby dwarf hippo), a small handful of buzz-words pops up again and again. You can play matching games with these words and come up with every major fossil find reported in the past decade. Want to meet the First Tree-Dwelling Vertebrate? How about the Earliest European Human Ancestor? You can explore the Oldest Asian Monkey, the Human “Hobbits”, and the most overused of all, The Missing Link.

Making paleontology relevant to the public may be a prerequisite to securing funding for additional explorations, but the concept of descent with modification, a central tenet to understanding evolutionary theory, is complicated enough without misleading headlines like “Early Human Relative Predates Dinosaurs.” Yes, humans share a common ancestor with all vertebrates, with all mammals, with all primates, and with all apes. But all mammals alive today are equally closely related to the synapsid “mammal-like reptile” found to be living in trees during the age of the dinosaurs. Linking the fossil uniquely to humans is both naive (causing eye-rolling amongst scientists) and scientifically speaking, utterly incorrect.

Ultimately, though, if these titles (mis)lead internet skimmers to read an article they wouldn’t have otherwise considered, I can see some benefit. I’ve had some great classroom conversations inspired by overenthusiastic headlines in the popular press that caught my students’ eyes. I worry about those who don’t have a friendly neighborhood science interpreter ready to explain the intricacies of the new find glossed over by the headline writers, but in the end, if paleontologists receive the funding needed to excavate new fossils and the public learns something about those fossils, the benefit outweighs the damage.

Photo: The skeleton of the tree-climbing synapsid Suminia getmanov via Discovery.com

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Paleoanthropologists I know seem pleased that the insurance giant Geico has been doing its part to bring caveman awareness to modern Americans. But since Neandertals are both the most recognized fossil human ancestor and remain sadly misunderstood, I’m going to provide some additional background on our much-maligned cousins.

The first fossil Neandertal was found in the Neander valley. Perhaps you think I mean Neanderthal. As is happens, “thal” is “valley” in German, but pronounced “tal,” leading to years of pronunciation-confusion until the Americanized spelling recently started dropping the “h.”

One of the first nearly complete skeletons of a Neandertal was found in 1899 in France. When Marcellin Boule reconstructed the skeleton, he unfortunately failed to recognize that its hunch-back was caused by old age and arthritis, and assumed that all Neandertals had been stooped, club-wielding idiots. Hundreds of reproductions used his reconstruction (left) and the image quickly became popularized by movies and comics. Most Neandertals stood slightly shorter than many modern humans, but weren’t all arthritic, or stupid for that matter: the average brain size in Neandertals was equal to that of modern humans. They do show more broken and healed fractures than most modern humans, similar to levels seen in rodeo riders. Their hunting tools consisted of short-range spears, which had to be thrust into prey (mostly mammoth) from a close distance. Modern humans invented a spear thrower called an atl-atl, which allowed them to stay a safer distance from their prey and thus keep more of their bones in tact.

Neandertals and Homo sapiens (a.k.a. modern humans) co-existed on the planet for 170,000 years. For the most part, Neandertals were hanging out in Europe while modern humans were in Africa, but around 40,000 years ago, Homo sapiens moved into Europe, too. Just 10,000 years later, Neandertals were extinct.

What happened? Perhaps if Neandertals and humans had mated regularly, the species might have survived. It’s often noted that modern human males will mate with just about anything, so how could two large-brained, bipedal apes living at the same place and time not engage in some hanky panky? Ancient DNA obtained from Neandertals seems to contradict this scenario—most modern humans are far more similar to each other than any is to a Neandertal. The average number of differences in mitochondrial DNA between humans is around 8 base pairs (the basic unit of the gene), while the difference between any human and a Neandertal is closer to 25. For comparison, the difference between humans and chimpanzees, our closest living relatives, is around 55. This indicates that if any inter-species infidelity occurred in the Pleistocene, it left little genetic evidence in the philanderer’s descendants.

If they didn’t make love, what about war? While no Neandertal has ever been found with a modern human spear point in its back, a recent paper investigated the cause of a Neandertal’s broken rib and found the anatomical details reflect the wound was likely caused by a thrown spear rather than a spear thrust at close-range. This implicates modern humans and their atl-atls, but of course, one case does not a hypothesis prove.

The best-supported theory is one that isn’t nearly as sexy as the Jean Auel’s Clan of the Cave Bear scenarios or as gruesome as all-out Planet of the Apes warfare. The lack of thrown hunting weapons probably increased the death rate of Neandertals during any hunting raid. (They often minimized their risk of death by chasing herds of prey off cliffs, wiping out far more meat than they needed.) The slightly higher death rate combined with drastic overkill, as well as the change in environment brought on by the end of the Ice Age, is what more likely spelled disaster for the Neandertals.

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