On October 28th, 2015 we learned about

Learning human history from the dirty teeth of the dead

Your dentist reminds you to brush your teeth. She tells you that you should floss more. She says that sugary drinks are bad for your teeth. What you dentist probably doesn’t mention is that by cleaning your teeth, you’re possibly removing a record of your life that could help preserve a (slightly gross) slice of your biography for long after your eventual death.

Preserved in plaque

The plaque that develops on our teeth can actually harden and act as a sort of fossil record of what your mouth was doing when you were alive. Anthropologists have started looking at plaque found in skeletons’ mouths for samples of plants, bacteria, meat and even textile fibers. Beyond foreign debris, they’ve also been able to find out more about the genes of the person from their accumulated plaque than is often possible with the actual teeth.

Oral plaque is actually so robust that it’s being used as a source of DNA, holding 100 to 1000 times more nucleic acids per milligram than other available sources. This has allowed scientists to sequence genomes that weren’t in environments that would naturally preserve tissue, like permafrost. So far the oldest dental buildup to yield DNA has been 10,000 years old, and there’s hope that dirty mouths will make a wider set of samples useful for genetic studies.

Anthropology through oral history

The details trapped in plaque have been helping anthropologists in a number of different studies. By tracing beta-lactoglobulin protein in plaque from different human populations, we’re getting a better understanding of how lactose tolerance arose in humans. So far the oldest confirmed samples were from Bronze Age teeth, but Neolithic skulls may yield even older secrets. Other investigations closer to a dentist’s heart have looked at the evolution of periodontitis, a gum disease that affects many people today.

Source: Meet the Dentist to the Dead by Megan Gannon, Scientific American

On October 15th, 2015 we learned about

Rethinking which society has the superior sleep schedule

Supposedly, we all used to sleep better. Before our work schedules split from natural circadian rhythms, before electric lights artificially shortened our nights, and before various devices kept us transfixed long after we meant to “take a quick look” at our preferred social media site. Personally, I remember sleeping better before my kids were born, but even then I certainly wasn’t going to bed at sundown and starting my day refreshed at sunrise. Which may, it turns out, be completely normal.

Defining our inherent sleep schedule

It’s hard to know how humans used to sleep, since we’re still working on tracking how humans sleep today. Documents from Europe in the last few hundred years indicate that people used to go to bed earlier, wake for a bit at night, then sleep until dawn. Even if these notes were representative of the average human at the time, that’s not really long enough ago to necessarily be the last record of humans sleeping according to our evolutionarily-determined needs. For a different reference point, researchers have now tracked the sleep habits of three “traditional” lifestyles from Tanzania, Nambia and Bolivia to see how they rested up each night. They might not be the ultimate proxy for an undisrupted human schedule, but without any contact with each other, similarities would probably have stemmed from a basic need rather than current fashion.

Their day wasn’t quite the fabled experience described above. They generally went to bed two to three hours after sundown, which may have been influenced not by light but by the ambient temperature. They’d then sleep for around seven to eight and a half hours, waking up before sunrise to start their day. Again, the timing in the morning seemed to be tied to temperature— rather than pull the quilt back up for more snoozing, these people got out of bed. There was occasional napping, more often in warmer weather, but nothing that seemed to be core to their circadian rhythms.

Benefits of consistency

This isn’t to say that their sleep health was no better than the average westerner staying up past midnight to write a blog though. Insomnia was such a foreign concept to all three cultures that none of them even had a term to describe the idea. Researchers theorized that the keys to their consistent sleep were when they were exposed to sunlight, the responsiveness to temperature and just being consistent overall. Sunlight exposure seemed to be most concentrated when working outdoors in the morning hours around 9 am. By noon, all three cultures were likely to seek shade, but that earlier activity helped set their internal clocks.  Then by waking up at the same time each day, they were able to keep their body on regular and effective schedule.

So for anyone struggling to sleep, consistent light exposure and scheduling may be the easiest features of primitive human sleep to adopt. Which is good news, because if we all needed to shift to a schedule where we were up for an hour in the middle of the night, it’d be mighty hard to keep a lid on accidentally watching cat videos until dawn, ruining the whole concept.

Source: What You Can Learn From Hunter-Gatherers' Sleeping Patterns by Ed Yong, The Atlantic

On September 10th, 2015 we learned about

Cramped cavern yields colossal clutch of hominid fossils

The human family tree was recently confirmed to have a new branch. Or perhaps an addition to the trunk? It’s hard to say, as Homo naledi seems to have features that would be at home on a human, but others that are a better match for a more primitive relation. Their brain was around the size of an orange, but their feet were stiffer and more suitable for walking like ours. Their jaws were small, like an Australopithecus, but their molars were a better match for Homo sapiens. While there are still a number of questions to be answered, we have an amazing amount of data to work with thanks to the somewhat amazing story of how H. naledi was discovered.

Loosely buried but well hidden

Anthropologist Lee Berger was exploring caves in South Africa, explicitly for the sake of exploring new territory. There was reason to suspect the Rising Star cave might be interesting, but what transpired was nearly worthy of Indiana Jones, or maybe the Goonies if you removed the booby traps. An accidentally discovered crevice led to a nearly 40-foot shaft so narrow Berger himself couldn’t fit through it. A caver assisting the exploration managed to get through it, and immediately found bone fragments sitting out in the open. A proper investigation was needed, but it required the assembly of a special team first.

The team Berger put together didn’t need a demolition specialist, but they were otherwise a very elite group. They needed some field experience with paleontology or archaeology, they needed to have caving experience, they couldn’t be claustrophobic, and they needed to be small enough to fit through the narrow shaft without too much difficulty. Oh, and they needed to be ready to go within the month. The all female-team was brought together with amazing ease, and then went on to be the front line of the excavation, working in six-hour shifts, often on their hands and knees in the dark cave. They were supported by a 60-member team at camp, communicating via fiber optic cable while they carefully dug out what was a treasure trove of fossils.

Enough fossils to span generations

While many ancient animals are identified only from single bones, H. naledi was represented by over 1,500 pieces of bone from 15 individuals. The group of skeletons were young and old, male and female, and showed no signs of serious injury. The range and scope of the fossils allow for an unprecedented amount of detail in the analysis of the new species. It also raises the question as to why such a robust collection of bodies was in this cave in the first place.

The site was obviously fairly inaccessible, and there were no signs that it had been a lair for a large predator of some sort, leaving its left-overs for our eventual discovery. The bodies weren’t obviously injured, and there wasn’t evidence of cave-ins or flooding depositing them in that location. It was also a very clean site, without the usual scraps and debris left by hominid occupants, indicating that they hadn’t really been living there (and with adult H. naledi being around five-feet tall, they probably could have made it through the narrow caves.)

Family burial plot?

While scientists try to to ascribe motivation to their finds, it’s hard to ignore remaining possibilities that point to deliberate placement. Did these relatively small-brained creatures treat this as a burial site? Were the bodies placed there for a purpose? If so, it might demand we rethink the timeline of human development, since ritual burial wasn’t thought to have been invented until the Paleolithic Neanderthals or possibly Homo heidelbergensis. This should be clearer once the fossils from Rising Star Cave are finally dated. At this point, they’ve strangely been unable to ascribe a date to the bones, but it’s hoped that Berger’s team will be able to fill in this critical information as they continue to excavate the cave.

Source: 6 Tiny Cavers, 15 Odd Skeletons, and 1 Amazing New Species of Ancient Human by Ed Yong, The Atlantic

On May 24th, 2015 we learned about

Australopithecus may have created humanity’s first tools

The human species is quite young, only going back 2.5 million years or so. Our species has made a huge impact on the world since then, spreading to every continent on the planet. As such, we often like to tout our accomplishments as a species, like we’re proud of being such prodigies. However, new discoveries in Kenya are showing that crafting tools may not be yet another feather in the cap of Homo sapiens, having instead been invented before we even existed as a species.

The tools were dated at being 3.3 million years old, predating modern humans by hundreds of thousands of years. This would mean that they predate even early proto-humans named Homo habilis, which means “handy man,” for their tool use. Instead, these tools would have been crafted by a much more apelike species, Australopithecus. The most famous specimen from this era, Lucy, was only 4 feet tall, and probably was part of our ancestors’ transition out of the trees to the ground.

The Stone Age’s first factory

Now, simply using tools isn’t thought to have been an invention of humans, as many other animals are known to do so. But the tools in question here are much more sophisticated than a found stick, and in fact seem to be an entire tool kit or primitive workshop. One stone appeared to have been the table or anvil that was used to support the “core” stones. The core stones were the sort of raw material that sharp flakes of stone were chipped off of, and those flakes were the final product to be used for cutting or stabbing. The number of components in this small knife-factory alone shows that their creator could plan and gather components needed for an unseen and thus conceptualized end-product. (Modern humans still struggle with this!)

Difficulties of the early adopter

Despite this impressive toolkit, it doesn’t mean that Homo habilis added nothing to human evolution. Later variations on this kind of kit have been found to be much more refined and sophisticated, and more widespread. It’s quite possible that while someone like Australopithecus could produce these tools, they were not widely adopted. Part of that may have been ergonomics— at this time, hands were still better suited for tree branches than tightly gripping and manipulating rocks. It may have been a case of early brains who could come up with these ideas waiting for evolution to provide the thumbs to use them.

Source: Chipping Away At The Mystery Of The Oldest Tools Ever Found by Chris Joyce, NPR

On April 16th, 2015 we learned about

Our preferences for chins may reveal their purpose

What separates humans from apes? Humans have tried to establish our distinction from other animals for thousands of years, claiming our everything from tool usage (nope) to temporal abstraction (sorry). The list of unique human traits has been getting winnowed down the more we learn about the world around us. But one critical trait has yet to be matched by our primate cousins: our chins.

No other primate has a chin like ours. This is undisputed, and no other primate species looks like they’re trying to knock humans off this pedestal any time soon. It’s just that, it’d be so much easier to proud of our chins if we were sure why we had them in the first place.

Many possible purposes for our facial protrusion

Many theories have been proposed. Does it help with speech, allowing attachment points for specialized muscle groups? Does the chin help absorb stress caused by our otherwise smaller jaws and teeth?  This was supported a bit by comparisons to Neanderthal jaws, but it ignores a key pattern in our chin-structures, and that’s the sexual dimorphism visible in most human faces.

The newest theory is based entirely around sexual selection as the motivation behind our current chins. Men generally have taller, more pronounced chins which may be read as a sign of good genetics to potential mates. Women then have narrower chins, possibly corresponding to having more estrogen. Proponents of this theory argue that if chins were needed for a universal, mechanical need like chewing, we’d all have the same chins, because… eating is pretty important. The fact that dimorphism exists indicates that jaw support is not the need driving these boney knobs at the bottom of our faces. And compared to the dimorphism in other parts of our bodies, or especially other species, a broader or narrower chin isn’t that big of a stretch.

Detractors, however, ask why chins couldn’t have started as jaw support, and branched off from there? Does any of this dimorphism go so far as to undo mechanical gains of having a chin? The timeline needs to be fleshed out further to see what came first— our bite, our speech or our dashing good looks.

Source: Why Do Humans Have Chins? by Erin Wayman, Smithsonian.com

On April 14th, 2015 we learned about

European genes assembled by a need for vitamin D

When humans moved into Europe 40,000 years ago, it’s assumed they arrived with dark skin. It’s also been assumed that they quickly started selecting for lighter skin in their new, Northern climate. Then, the thinking continued, after figuring out farming, this population started propagating genes for lactose tolerance, taking advantage of milk from the newly domesticated livestock. But DNA studies of European populations have been unraveling this tidy little story, revealing a more complicated and more recent timeline.

The genes researchers were looking for were those involved in a few different, and apparently discrete, traits. These included the LCT gene allowing the digestion of sugars in milk, SLC24A5 and SLC45A2, leading to pale skin, and HERC2/OCA2, which is the source of blue eyes, as well as possibly influencing lighter hair and skin pigmentation. And while it could have been possible to have all of these genetic changes sweep newly-settled Europeans all together, they seem to have come in multiple waves of influence from multiple sources.

Eating cheese and milk a fresher concept than previously understood

The new timeline starts with hunter-gatherers 8000 years ago, who were confirmed to not carry the LCT gene allowing lactose tolerance. This genetic variation wouldn’t take root until 2200 BCE, 5000 years after Europeans had been practicing agriculture. Two waves of immigrants that did bring many farming practices also lacked the gene upon arrival, indicating it may have developed in Europe. The advantage of consuming dairy went beyond gaining another source of calories- vitamin D was relatively scarce in Europe compared to humans’ original habitat further south, and milk products would have helped compensate for the loss of sunlight.

Soaking up any available sun

The need for vitamin D likely drove the propagation of genes for pale skin as well. Darker skin blocks more ultraviolet light than lighter skin, which, when less sunlight is available at higher latitudes, leads to a drop in the body’s synthesis of vitamin D. So while Southern Europeans were had dark skin until at least 5800 years ago, populations in the north were found to carry genes for lighter skin and lighter eyes as far back as 7700 years ago. It wasn’t until farmers from the Near East, who also had genes for lighter skin, immigrated to Europe that these variations started to spread across the whole continent.

So the piecemeal story of both diary consumption and pale pigments may still have the one common thread— vitamin D. While vitamin D does play a role in our immune system, other genes for immune response didn’t seem to be pressured or propagated in the European population in the same way, even with the introduction of farming, animal husbandry, and new populations. All that mattered was making up for the loss of sunshine.

Source: How Europeans evolved white skin by Ann Gibbons, Science

On April 6th, 2015 we learned about

Seeing snakes was a top primate priority

Humans have notably good vision, especially among mammals. We see more colors and in higher resolution than the average dog or deer. And of course, our forward-facing eyes give us depth perception, similar to hunters like lions or owls. But we’re not chasing down much colorful prey with our bare hands, so what was the initial advantage for our primate ancestors to develop better vision?

Seeing prey or predators

The answer may not be what we were after, but what may have been after us. Multiple forms of evidence have been gathered that point to the need to avoid venomous snakes as a reason for our visual abilities, the most recent of which was a survey of snakes in chimpanzee country.

Researchers spent four years documenting snakes they encountered in areas where chimpanzees live. 64% of the snake species encountered were venomous, and the researchers generally sense that their encounter rate is likely lower than what our ancestors would have faced. They also noted that their detection rate is likely lower than a group of chimps working together, just based on the number of eyes keeping watch alone.

More evidence for the Snake Detection Theory

The Snake-Detection Theory (SDT) is built on more a lot of snakes though. Championed by anthropologist Lynne Isbell, the number of snakes in an area has been compared to the visual abilities of local primates, and they show a strong correlation. For instance, lemurs on Madagascar have the worst primate vision, but they have no venomous snakes to contend with.

Primate brains provide more evidence for SDT. Neuroscientists looked at macaque monkeys, and found that their brain registered visual stimulus from snakes faster than to any other objects. What’s more, that recognition was even faster if the snake was seen in a coiled, threatening posture.

All together, this suggests that the need to quickly see the shape and color of a snake among the forest leaves, and then recognize it as a threat, was a significant advantage for our primate ancestors. Our visual capabilities have obviously bestowed other benefits since then, but a fear of serpents may have kicked it all off.


My kindergartner says: Another experiment should be done with the  macaque monkeys, wherein they are placed in a “tent” with pictures or projections of a real jungle inside it. An image or video of a snake would be hidden somewhere in that virtual jungle, and the test would be to see how quickly the monkey could pick the snake out of that scene. And there would be “a window so we could watch the monkey” of course.

Source: We May Have Snakes To Thank For Our Acute Vision by Barbara J. King, Cosmos & Culture

On March 3rd, 2015 we learned about

The History of Lucky Dolls

March 3rd is Hinamatsuri in Japan, also known as Girl Day and Doll Day. Since the Heian period approximately 1200 years ago, people have created and displayed dolls to ensure good luck.

The dolls represent the Emperor, Empress, and their attending court. They are traditionally set upon rows of platforms covered in red carpet, with a set hierarchy for each tier. While setup can begin in February, the dolls are to be taken down by March 4th to avoid causing a late marriage for one’s daughter.

Earlier versions of Hinamatsuri show more connections to Shinto beliefs, with the dolls being created out of straw in order to contain bad spirits people wanted to drive away. The straw dolls were floated down the river on a boat, putting distance between their owners and the spirits. After fisherman complained about catching too many dolls in their nets, the ritual was moved to the sea side, where they could be recaptured en mass, and then disposed of in a fire.

Source: Hinamatsuri, Wikipedia