biostudies-literatureUnknown21(1)von Cramon-Taubadel NHumans are unique among primates in possessing a chin, yet it is currently unclear whether the form of the symphyseal region of the mandible where the chin is located is the product of direct selection or a by-product of evolutionary pressures on other craniomandibular features. Here, we conduct an evolutionary analysis of hominoid craniomandibular traits to test three hypotheses: symphyseal mandibular traits evolved (1) neutrally due to genetic drift, (2) under direct selection, and (3) as a by-product (or "spandrel") of selection on other craniomandibular traits. Evolutionary rates of morphological change, via Lande's generalized genetic distance, were estimated along each branch of a fully-resolved hominoid phylogeny to reveal patterns of neutral, stabilizing and directional selection. PloS onee0340278https://www.ebi.ac.uk/biostudies/studies/S-EPMC12854472biostudies-literatureIs the human chin a spandrel? Insights from an evolutionary analysis of ape craniomandibular form.PMC12854472Scott JESchroeder LRobinson CAvon Cramon-Taubadel NfalseIs the human chin a spandrel? Insights from an evolutionary analysis of ape craniomandibular form.Humans are unique among primates in possessing a chin, yet it is currently unclear whether the form of the symphyseal region of the mandible where the chin is located is the product of direct selection or a by-product of evolutionary pressures on other craniomandibular features. Here, we conduct an evolutionary analysis of hominoid craniomandibular traits to test three hypotheses: symphyseal mandibular traits evolved (1) neutrally due to genetic drift, (2) under direct selection, and (3) as a by-product (or "spandrel") of selection on other craniomandibular traits. Evolutionary rates of morphological change, via Lande's generalized genetic distance, were estimated along each branch of a fully-resolved hominoid phylogeny to reveal patterns of neutral, stabilizing and directional selection. 2026-01-01T00:00:00Z20262026-06-11T05:33:25.116Z2026-06-11T03:08:01.257ZS-EPMC128544724161012910.1371/journal.pone.0340278