MISRYOUM newsroom reported that a paper published in January is putting a spotlight on something most people only notice when it’s huge, cartoonish, or suddenly in a mirror.
Chins, researchers say, are a distinctly human trait among primate kin. Even our closest ancestor, Neanderthals, did not have a chin. That makes the question feel oddly persistent: why does this bony “mental protuberance” show up here, and not there?
Misryoum newsroom reported findings from paleoanthropologist Lauren Schroeder and colleagues, and the answer is… not the kind you’d expect if you’ve been told your chin is there for one simple job. Schroeder, who studies how form evolves as an integrated whole, described how the team tested three broad possibilities: direct selection (the chin as an adaptation), a byproduct of evolution acting on other jaw and cranium structures, and genetic drift—evolution driven by random changes rather than purpose. They compared humans with a range of primates, measuring jaw and cranium traits and then tracing patterns across the primate lineage using an evolutionary tree.
What stood out is the mismatch between the upper and lower parts of the face. In the human lineage, the work shows strong evidence that direct selection was shaping evolution of the cranium and the jaw. But when the researchers looked specifically at chin traits, they didn’t see the signature of strong directional selection. In other words: the chin appears to have emerged as an indirect result—something that “came along” while other parts were being reshaped.
One analogy from the conversation made it click, even if it’s a little ridiculous. Schroeder likened the process to choosing one behavior and ending up with a secondary outcome—like selecting alcohol and only getting the Taco Bell later. The point wasn’t taste or cravings, obviously, but the logic of cause and side-effect. Misryoum editorial desk noted that the strongest directional-selection signatures were tied to dental reduction: humans evolved smaller teeth and smaller jaws. As the tooth-bearing part of the jaw—called the alveolar region—shrank, the researchers think byproduct forces rippled into the lower jaw, eventually shaping the chin. At the same time, the study connects face change to other direct selection signals, including a flatter, less-projecting face and more gracile-looking jaws over time.
So what pushed all that change in the first place? Schroeder pointed to diet and cooking, the shift that came as humans started relying on prepared food. She also mentioned the structural effects of becoming upright and, yes, the fact that brains became much larger. All of those pressures were acting on the cranium in ways that left signatures of direct selection—but apparently not in the same way for the lower jaw.
The paper’s title calls the chin a “spandrel,” and that word has an architecture vibe for a reason. Schroeder explained that evolution doesn’t always design traits for their own sake. The spandrel concept comes from Stephen J. Gould and Richard Lewontin, who argued that not every trait is an adaptation; some arise as byproducts of other evolutionary forces on different structures. Misryoum analysis indicates the chin may fit that logic: a space or feature that appears when other structural changes—arch-like changes in this metaphor—come together. Schroeder even said the door isn’t locked forever on chin research, but she plans to move on to other traits next.
Small real-world detail: when she paused to laugh mid-explanation, you could almost hear the casual rhythm in the room—like someone shifting in a chair while thinking “okay, that’s the part.” It’s the kind of moment that makes the science feel less like a verdict and more like a trail. The chin might not be the main character after all—maybe it’s more of a footprint left behind while other parts of the face were being rewritten.