We're the Only Animals with Chins
I posted this on reddit last night:<p>Any time there&#x27;s a special feature on a bone, usually a muscle attaches to it. I googled, and found out that the mentalis muscle attaches to the chin.<p>Interestingly, wikipedia says &quot;In conjunction with orbicularis contraction, the mentalis muscle allows the lips to &#x27;pout.&#x27; Externally, mentalis contraction causes wrinkling of the chin skin, as used in expressions of doubt or displeasure. It is sometimes referred to as the &#x27;pouting muscle.&#x27;&quot; [Emphasis mine]<p>Humans have complex facial expressions, and I would say that the pout is part of the repertoire. When someone is pouting, they are in extreme emotional distress, on the verge of sobbing. Having such an obvious &quot;tell&quot; would be beneficial to a social species, probably leading to conciliatory behavior and promoting de-escalation and group cohesion during conflict.<p>I did some cursory googling to see of the mentalis is involved in speech production, but found nothing at my level. Offhand I can&#x27;t think of any particular speech sounds I can make when my lips are in pout formation.