Scientists Are Comparing Our Modern Sinuses to Ancient Humans
Yet, experts are still mystified about why we evolved sinuses at all
Hiya!
I imagine sinuses aren’t something you’ve spent much time thinking about. Yeah, me either. Other than during Spring, when my allergies act up, I don’t think about my sinuses at all. But I’ve recently learned that sinuses are actually pretty cool, mysterious even. Given how much we know about human anatomy, I assumed that sinuses are a relatively simple feature to study.
It turns out, though, that while experts have a pretty good idea of the role sinuses play, there’s no consensus about why we evolved them in the first place. But now, a new study compared the sinuses of over 20 human species and found sinuses can help reveal more about our evolution.
What Are Sinuses?
I’ll admit, before learning about this, I didn’t know much about our sinuses other than their general location around my face and that sometimes they can get infected or plugged. But actually, sinuses are interconnected, air-filled caverns lined with mucous inside the bones of our skull.
You, me, and most of the rest of humankind have four pairs of sinuses, or eight total. There are two large ones called ethmoidal sinuses between your eyes and nose — aka the ones we squeeze during a brain freeze. Then there’s the maxillary sinus duo under your eyes but behind your cheekbones, which are the largest. The second largest pair is your frontal sinuses, just above your eyes, and lastly, the ethmoid sinuses are between your eyes and behind your nose.
Scientists have mostly figured out the role of sinuses which is taught in most anatomy classes. For instance, the mucous coating the sinus cavities help warm the air we breathe and drains dust, dirt, and other pollutants out of our sinuses and down the throat to be extinguished by our stomach acid. As a whole, our sinuses protect our health by preventing microorganisms and bacteria from entering our bodily systems. However, and this one surprised me, sinuses also lighten the weight of our head’s bone structure and gives tone to our voices.
Yet, despite knowing all of this, some aspects of sinuses remain unknown. Like, how or why they evolved at all. Some researchers suggest sinuses may be an example of an evolutionary spandrel, or evolved as the result of something else, then formed a function over time. They argue that just because sinuses may humidify our air and protect us from illness doesn’t mean that was their initial purpose for developing.
Still, their existence is prevalent throughout many species, so there must be an essential reason. All mammals have sinuses, though not all have four pairs as we do. Research on primates and bovids (cattle-type animals) shows that sinuses vary between species — and this made some researchers wonder if sinuses might vary between ancient human species, too.
After all, there’s plenty of debate about our human evolution. We know we, Homo sapiens, are just one of many Human species to have existed — we even coexisted with a few of them several thousand years ago. But the exact path of our evolution is hotly debated, and so is the exact number of human relatives we’ve had.
Now, an international team of researchers thinks analyzing the sinuses of ancient humans might help answer some questions. Co-author of the study I’m about to tell you about and human evolution expert at the Natural History Museum, Prof Chris Stringer explains:
"Sinuses are interesting morphological features in fossils but they have been neglected. Many papers that describe new species don't mention them, and they are often only illustrated incidentally to the rest of the specimen."
New Study
Antoine Balzeau of the Muséum National d’Histoire Naturelle led the team of international researchers in examining 94 hominin fossils from over 20 species to learn more about the variation in sinuses and what they may tell us about human evolution. They published their paper in Science Advances in October 2022, which includes the largest selection of fossil sinus data ever collected.
More specifically, they focused on the frontal and maxillary sinuses because they are only found in humans and our closest primate relatives, including gorillas and chimpanzees.
The team created 3-D models of the frontal sinuses using CT scans of the samples, which were measured and compared between the various species. They found that the small cavities just above our nose link to the size of our frontal lobe, which is responsible for our expressive language, voluntary movement, and managing higher-level functions such as self-monitoring ourselves or creating a plan.
This connection between the frontal sinuses and the frontal lobe provides a new way for scientists to investigate the evolution of this part of our brain. It also allows experts to learn more about the relationships between various ancient Human species.
For instance, tracking the sinuses may help us finalize the Human evolution timeline or settle debates about whether a species belongs to our genus or a different one. There’s disagreement right now about Homo naledi, which has some more prehuman characteristics, and whether they should be included within the Homo genus.
Results
After comparing the models, the researchers found that the sinus size couldn’t distinguish between super early hominins such as the Australopithecus, the same family as the beloved Lucy. However, the sinuses could identify more recent Homo species over the past two million years. Dr. Laura Buck, formerly of the Museum but now at Liverpool John Moores University and Co-author of the paper, explains:
"In early hominins and non-human apes, the size and shape of frontal sinuses is directly related to the amount of space available for them to grow into. The step change we see between these species and later hominins, including ourselves, suggests a shift in the way the skull is organized and develops. It may be relevant that this is happening at the same point as we start to see substantial brain expansion in these taxa (species)."
They found that Homo erectus, Homo neanderthalensis (Neanderthals), and us, Homo sapiens, all possess distinct ranges of sinus size. The researchers suggest this might have a connection to evolutionary constraints due to evolving larger brains.
The team also added support for Homo naledi to be included in the Human club, even though they have a mix of human and non-human features because Homo naledi’s sinuses were similar to the Homo erectus sinuses. And as for our H. sapiens evolution, the team found a link between the sinuses and the frontal lobe size from Homo erectus onward.
Perspective Shift
Who knew sinuses could tell us so much! Eight small pockets of air nestled in our facial bones are unique to our species of Humans, and we don’t even know why we evolved them. Did our bodies somehow decide they needed tiny holes in our bones to protect us from disease and pollutants, or are they the result of some other feature?
Regardless, it just goes to show that we don’t know everything — even with our advanced technology. Our modern cities and gadgets often create the illusion that we know everything we need to know. The truth is, we have no idea how much we don’t know. We could discover something at any time that could change everything we thought we knew. Even something as small as our sinuses have the potential to teach us about our evolution and what makes us, us.
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Joke's on us if it was just to make our heads lighter, like it often was for dinosaurs.