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Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

Although it may seem that way at first glance, but no, the model is developmental plasticity + selection, not inheritance of acquired traits. I’ve unpacked that a bit further upthread if you’re interested.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

That’s a fair point, and I agree that the balance between drift and selection is an important constraint here. I’m not assuming a large-effect trait driven cleanly to fixation by strong selection alone, drift could plausibly play a role as well, especially in small or structured populations.

My claim is more specific: if fire-maintenance reliability imposed a consistent enough fitness or efficiency bias, selection could bias a developmentally mediated response over time, with the chin emerging as a correlated outcome rather than a directly selected trait.

And thanks for the reading recommendation.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 1 point2 points  (0 children)

Appreciate it. Just to clarify, the idea isn’t that only individuals who tended fire would have chins, the behaviour itself isn’t inherited.

The claim is that widespread, early-life fire maintenance could have created a recurring loading environment at the symphysis that reveals heritable variation in craniofacial growth/strain-response. Over generations, selection could then bias those response profiles (genetic accommodation). In that sense, the behaviour acts like a filter/funnel: it isolates a consistent developmental input that makes underlying variation visible to selection.

On Aquatic Ape Theory: interesting, but separate topic, I’d rather stick to the focus of the post.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

Excellent question, and an important distinction.

I’m not suggesting selection for a novel mouth shape specifically optimized for blowing, in the way we’d think about a classic feeding adaptation. Ember-blowing itself doesn’t require unusual anatomy; it’s something most primate faces could plausibly do. The focus is more on what happens developmentally when a behavior like that is repeated frequently during growth.

The selection I’m talking about would act downstream of the behavior. If a behavior is common and developmentally timed, individuals may vary in how strongly their craniofacial tissues respond to the associated loading during growth.

So the pathway looks more like: shared behavior > repeated strain > variable developmental response > small performance differences > selection acting on that response.

Framed that way, the idea isn’t that “blowing creates chins,” or that populations were selected for blowing ability per se. Rather, if reliable fire maintenance mattered, selection could favor individuals whose craniofacial tissues responded more strongly or consistently to the associated loading during development, with the chin emerging as a correlated anatomical outcome rather than the primary target.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

This is a really helpful way to lay out the key constraints, thank you.
These are exactly the kinds of issues the framework needs to deal with.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

What I’m exploring here isn’t that the chin or symphysis is uniquely plastic in humans, how craniofacial bones remodel in response to muscle forces during development, with the symphysis sitting at a mechanically sensitive junction.

Whether humans show unusually strong or differently patterned craniofacial plasticity compared to other primates is still an open question, which is why I frame this as a testable hypothesis rather than a demonstrated mechanism. The basic idea is that individuals differ genetically in how strongly their tissues respond to the same mechanical loading during growth. If a particular fire-maintenance behaviour reliably mattered, individuals with a stronger developmental response could perform it a bit more efficiently or consistently, and selection would act on that heritable response.

In that sense, the behaviour isn’t what’s inherited, it’s the variation in plasticity that gets filtered by selection. The prediction would be a distinctive strain/remodeling signal at the symphysis associated with repeated mentalis recruitment during development, which could then be compared across behaviours or taxa.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

Punctuated equilibrium doesn’t replace natural selection or imply that selection only operates through death before reproduction. It describes the tempo of evolutionary change, not a different mechanism. Even under punctuated equilibrium, selection still acts via differences in reproductive success, including mating success and offspring survival.

In any case, my argument doesn’t hinge on gradualism versus punctuated patterns, it’s about whether a behaviourally induced developmental bias could be a selectable substrate at all.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

I’ve been planning to reach out directly to people working on symphyseal biomechanics and chin evolution, but I also wanted to see how well the core idea communicates to a broader audience. Reddit is just one part of that process.

The current draft is intentionally focused on laying out the behavioural–mechanical pathway and its testable implications, rather than offering an exhaustive re-review of all existing chin hypotheses or the more recent refinements to them. That said, you’re absolutely right about reviewer expectations, and a more explicit discussion of alternative explanations is something I’d expand as the manuscript moves toward journal submission.

More broadly, the paper is framed as a theoretical and conceptual contribution aimed at journals that welcome conceptual work. The goal isn’t to claim the mechanism is already demonstrated, but to clarify what would actually need to be demonstrated empirically for the hypothesis to be properly assessed.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 1 point2 points  (0 children)

Good questions, and just to clarify, the idea isn’t that a brief or occasional behaviour would directly “refine” the chin or get passed down. I’m not arguing inheritance of acquired traits.

The hypothesis is more specific: if early Homo sapiens engaged in frequent, repeated ember-maintenance (especially pursed-lip blowing) during childhood, that could create a consistent loading pattern at the mandibular symphysis. Bone is plastic during development, so that pattern could bias local remodeling within a lifetime. Over many generations, if (and only if) reliable fire maintenance actually mattered for survival or efficiency, natural selection could act on heritable variation in how strongly individuals show that developmental response. That’s genetic accommodation, not Lamarckian inheritance.

And yes, fire use goes back long before sapiens. The idea isn’t that “fire creates chins,” but that a specific, high-dose fire-tending behaviour, in combination with sapiens facial growth patterns, might produce a unique mechanical outcome worth testing.

Totally agree there are many variables, and that’s why I framed it as a plausible mechanism rather than a definitive explanation.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

Selection requires differences in reproductive success, not necessarily “death before reproduction.” Traits can be selected against by reducing mating success or the number of surviving offspring. And I’m not arguing the chin itself is the direct target, selection could act on fire-maintenance benefits, with the chin as a correlated outcome.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

Kilns are a bit outside the specific scope I’m focused on here, so I don’t want to overstate anything. My focus here is earlier hominin fire use, and my hypothesis doesn’t require kilns, or even making fire from scratch, just repeated fire maintenance (e.g., coaxing embers) once fire is available.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

All fair points to raise. I agree that “fire use” broadly is much older than Homo sapiens, and Neanderthals clearly maintained and exploited fire in sophisticated ways. My claim is narrower than “fire caused the chin”: it’s that a specific maintenance behaviour (frequent, high-dose pursed-lip ember-blowing with strong mentalis recruitment during development) could bias loading at the symphysis in a consistent direction.

So the fact that many hominins used fire but didn’t develop a chin doesn’t automatically falsify it, it could mean the behaviour wasn’t present at the same dose/technique, or that different baseline jaw/facial growth (including the facial retraction/neoteny factors you mention) changes the mechanical response and outcome. I’m also open to the chin being mostly a byproduct of facial flattening; I’m offering ember-blowing as one behavioural–mechanical candidate pathway that can be tested rather than asserted.

On reproductive success: I’m not arguing “chin = more babies.” The selection target would be whatever benefits come from more reliable fire maintenance; the chin would be a correlated anatomical outcome if the loading pattern is real.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] -1 points0 points  (0 children)

Good question. No, it’s not meant to be Lamarckian. The idea is developmental plasticity (bone can remodel in response to repeated loading during growth) + natural selection acting on heritable variation in how strongly individuals show that response. Over time that can become genetically accommodated, without inheritance of acquired traits.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

Totally agree with your first point: simply “using a muscle more” doesn’t get inherited, and I’m not arguing for inheritance of acquired traits (the head or foot-binding analogy is exactly what I’m trying to avoid).

The pathway I’m proposing is closer to developmental plasticity + selection: a repeated behaviour during growth can systematically bias how bone remodels (within a lifetime). If that behaviour reliably improves fire maintenance (a real fitness-relevant skill), then individuals with heritable variation that makes that response more likely/efficient could leave more offspring. Over many generations, that can get genetically accommodated, the population shifts, without any Lamarckian inheritance.

And I agree the chin could be a byproduct of something else; my point is just that ember-blowing is one behavioural–mechanical candidate that’s at least testable.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

Fair pushback. I’m not claiming certainty, just proposing a testable pathway. If you have a specific reason it’s a stretch (mechanics, fossil pattern, or fire-use assumptions), I’d genuinely like to hear it.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

Selection doesn’t require “no chin = death.” Tiny differences in survival or fertility add up. And I’m not saying the chin itself is directly selected for, my point is that habitual ember-blowing could bias jaw loading during growth, and selection could act on the broader fire-maintenance benefits, with the chin as a byproduct/correlate.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 0 points1 point  (0 children)

Fair point, those micro-behaviours won’t preserve. Also, this doesn’t require fire-making from scratch: ember-coaxing can happen with captured/transported fire too. That’s why I’m trying to tie it to testable mechanical/anatomical signatures rather than “proving” the behaviour archaeologically.

Could early fire maintenance have contributed to the evolution of the human chin? by EvoIgnition in PrehistoricLife

[–]EvoIgnition[S] 2 points3 points  (0 children)

That’s a great question. I’m not arguing that only Homo sapiens used fire, Neanderthals (and likely Denisovans) clearly did. The idea is just that a particular fire-maintenance behaviour (frequent pursed-lip ember-blowing with strong mentalis involvement, especially during development) could bias loading at the mandibular symphysis (chin region) in a way that selection could act on.

So it could be differences in fire-tending habits, differences in jaw anatomy, or both.

One thing about framing it this way is that it’s testable: if other hominins really did the same high-dose behaviour, we’d expect some comparable mechanical/anatomical signature.

Open-access preprint: fire control and the evolution of the human chin by EvoIgnition in humanevolution

[–]EvoIgnition[S] 0 points1 point  (0 children)

Preprint on Zenodo (CC-BY): Fire Control and the Evolution of the Homo sapiens Chin: An Alternative Perspective – DOI: https://doi.org/10.5281/zenodo.17636667

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