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Meneganzin A, Ramsey G, DiFrisco J. What is a trait? Lessons from the human chin. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART B, MOLECULAR AND DEVELOPMENTAL EVOLUTION 2024. [PMID: 38528769 DOI: 10.1002/jez.b.23249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Revised: 02/14/2024] [Accepted: 02/19/2024] [Indexed: 03/27/2024]
Abstract
The chin, a distinguishing feature of Homo sapiens, has sparked ongoing debates regarding its evolutionary origins and adaptive significance. We contend that these controversies stem from a fundamental disagreement about what constitutes a well-defined biological trait, a problem that has received insufficient attention despite its recognized importance in biology. In this paper, we leverage paleoanthropological research on the human chin to investigate the general issue of character or trait identification. First, we examine four accounts of the human chin from the existing literature: the mandibular differential growth byproduct, the bony prominence, the inverted T-relief, and the symphyseal angle. We then generalize from these accounts and propose a three-stage framework for the process of character identification: description, detection, and justification. We use this framework to reinterpret the four accounts, elucidating key points of contention surrounding the chin as well as other morphological characters. We show that debates over the chin carry broad and important biological implications that extend beyond this trait and that are not mere semantic issues of definition.
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Affiliation(s)
| | - Grant Ramsey
- Institute of Philosophy, KU Leuven, Leuven, Belgium
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2
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Bergmann I, Hublin JJ, Gunz P, Freidline SE. How did modern morphology evolve in the human mandible? The relationship between static adult allometry and mandibular variability in Homo sapiens. J Hum Evol 2021; 157:103026. [PMID: 34214909 DOI: 10.1016/j.jhevol.2021.103026] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 05/12/2021] [Accepted: 05/12/2021] [Indexed: 02/07/2023]
Abstract
Key to understanding human origins are early Homo sapiens fossils from Jebel Irhoud, as well as from the early Late Pleistocene sites Tabun, Border Cave, Klasies River Mouth, Skhul, and Qafzeh. While their upper facial shape falls within the recent human range of variation, their mandibles display a mosaic morphology. Here we quantify how mandibular shape covaries with mandible size and how static allometry differs between Neanderthals, early H. sapiens, and modern humans from the Upper Paleolithic/Later Stone Age and Holocene (= later H. sapiens). We use 3D (semi)landmark geometric morphometric methods to visualize allometric trends and to explore how gracilization affects the expression of diagnostic shape features. Early H. sapiens were highly variable in mandible size, exhibiting a unique allometric trajectory that explains aspects of their 'archaic' appearance. At the same time, early H. sapiens share a suite of diagnostic features with later H. sapiens that are not related to mandibular sizes, such as an incipient chin and an anteroposteriorly decreasing corpus height. The mandibular morphology, often referred to as 'modern', can partly be explained by gracilization owing to size reduction. Despite distinct static allometric shape changes in each group studied, bicondylar and bigonial breadth represent important structural constraints for the expression of shape features in most Middle to Late Pleistocene hominin mandibles.
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Affiliation(s)
- Inga Bergmann
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
| | - Jean-Jacques Hublin
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Philipp Gunz
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Sarah E Freidline
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
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3
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Sella Tunis T, Hershkovitz I, May H, Vardimon AD, Sarig R, Shpack N. Variation in Chin and Mandibular Symphysis Size and Shape in Males and Females: A CT-Based Study. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2020; 17:ijerph17124249. [PMID: 32545912 PMCID: PMC7345472 DOI: 10.3390/ijerph17124249] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Revised: 06/10/2020] [Accepted: 06/11/2020] [Indexed: 11/16/2022]
Abstract
The chin is a unique anatomical landmark of modern humans. Its size and shape play an important role from the esthetic perspective. However, disagreement exists in the dental and anthropological literature regarding the sex differences in chin and symphysis morphometrics. The "sexual selection" theory is presented as a possible reason for chin formation in our species; however, many other contradictory theories also exist. This study's aims were therefore to determine how chin and symphysis size and shape vary with sex, and to discuss "sexual selection" theory as a reason for its formation. Head and neck computed tomography (CT) scans of 419 adults were utilized to measure chin and symphysis sizes and shapes. The chin and symphysis measures were compared between the sexes using an independent-samples t-test, a Mann-Whitney test, and the F-statistic. The chin width was significantly greater in males than in females (p < 0.001), whereas the chin height, area, and size index were significantly greater in females (p < 0.001). Symphysis measures did not differ significantly between the sexes. Size accounted for 2-14% of the chin variance and between 24-33% of the symphysis variance. Overall, the chin was found to be a more heterogeneous anatomical structure than the symphysis, as well as more sexually dimorphic.
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Affiliation(s)
- Tatiana Sella Tunis
- Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel; (I.H.); (H.M.)
- Dan David Center for Human Evolution and Biohistory Research, Shmunis Family Anthropology Institute, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel;
- Department of Orthodontics, The Maurice and Gabriela Goldschleger School of Dental Medicine, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel; (A.D.V.); (N.S.)
- Correspondence: ; Tel.: +972-3-640-7310
| | - Israel Hershkovitz
- Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel; (I.H.); (H.M.)
- Dan David Center for Human Evolution and Biohistory Research, Shmunis Family Anthropology Institute, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel;
| | - Hila May
- Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel; (I.H.); (H.M.)
- Dan David Center for Human Evolution and Biohistory Research, Shmunis Family Anthropology Institute, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel;
| | - Alexander Dan Vardimon
- Department of Orthodontics, The Maurice and Gabriela Goldschleger School of Dental Medicine, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel; (A.D.V.); (N.S.)
| | - Rachel Sarig
- Dan David Center for Human Evolution and Biohistory Research, Shmunis Family Anthropology Institute, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel;
- Department of Orthodontics, The Maurice and Gabriela Goldschleger School of Dental Medicine, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel; (A.D.V.); (N.S.)
- Department of Oral Biology, The Maurice and Gabriela Goldschleger School of Dental Medicine, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel
| | - Nir Shpack
- Department of Orthodontics, The Maurice and Gabriela Goldschleger School of Dental Medicine, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv 69978, Israel; (A.D.V.); (N.S.)
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4
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Sánchez‐Villagra MR, van Schaik CP. Evaluating the self‐domestication hypothesis of human evolution. Evol Anthropol 2019; 28:133-143. [DOI: 10.1002/evan.21777] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2018] [Revised: 12/12/2018] [Accepted: 03/03/2019] [Indexed: 12/17/2022]
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5
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Pampush JD, Scott JE, Robinson CA, Delezene LK. Oblique human symphyseal angle is associated with an evolutionary rate-shift early in the hominin clade. J Hum Evol 2018; 123:84-95. [DOI: 10.1016/j.jhevol.2018.06.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Revised: 06/19/2018] [Accepted: 06/21/2018] [Indexed: 01/06/2023]
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6
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Raia P, Boggioni M, Carotenuto F, Castiglione S, Di Febbraro M, Di Vincenzo F, Melchionna M, Mondanaro A, Papini A, Profico A, Serio C, Veneziano A, Vero VA, Rook L, Meloro C, Manzi G. Unexpectedly rapid evolution of mandibular shape in hominins. Sci Rep 2018; 8:7340. [PMID: 29743608 PMCID: PMC5943523 DOI: 10.1038/s41598-018-25309-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 04/16/2018] [Indexed: 12/23/2022] Open
Abstract
Members of the hominins - namely the so-called 'australopiths' and the species of the genus Homo - are known to possess short and deep mandibles and relatively small incisors and canines. It is commonly assumed that this suite of traits evolved in early members of the clade in response to changing environmental conditions and increased consumption of though food items. With the emergence of Homo, the functional meaning of mandible shape variation is thought to have been weakened by technological advancements and (later) by the control over fire. In contrast to this expectation, we found that mandible shape evolution in hominins is exceptionally rapid as compared to any other primate clade, and that the direction and rate of shape change (from the ape ancestor) are no different between the australopiths and Homo. We deem several factors including the loss of honing complex, canine reduction, and the acquisition of different diets may have concurred in producing such surprisingly high evolutionary rates. This study reveals the evolution of mandibular shape in hominins has strong morpho-functional and ecological significance attached.
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Affiliation(s)
- P Raia
- Università degli Studi di Napoli Federico II, Department of Earth Sciences, Environment and Resources, L.go San Marcellino 10, 80138, Naples, Italy.
| | - M Boggioni
- Università degli Studi di Roma La Sapienza, Department of Environmental Biology, Piazzale Aldo Moro, 5, 00185, Roma, Italy
| | - F Carotenuto
- Università degli Studi di Napoli Federico II, Department of Earth Sciences, Environment and Resources, L.go San Marcellino 10, 80138, Naples, Italy
| | - S Castiglione
- Università degli Studi di Napoli Federico II, Department of Earth Sciences, Environment and Resources, L.go San Marcellino 10, 80138, Naples, Italy
| | - M Di Febbraro
- Università degli Studi del Molise, Department of Biosciences and The Territory, Contrada Fonte Lappone, 86090, Pesche, Isernia, Italy
| | - F Di Vincenzo
- Università degli Studi di Roma La Sapienza, Department of Environmental Biology, Piazzale Aldo Moro, 5, 00185, Roma, Italy.,Istituto Italiano di Paleontologia Umana, Via Ulisse Aldrovandi, 18, 00197, Roma, Italy
| | - M Melchionna
- Università degli Studi di Napoli Federico II, Department of Earth Sciences, Environment and Resources, L.go San Marcellino 10, 80138, Naples, Italy
| | - A Mondanaro
- Università degli Studi di Napoli Federico II, Department of Earth Sciences, Environment and Resources, L.go San Marcellino 10, 80138, Naples, Italy.,Università degli Studi di Firenze, Department of Earth Sciences, Via Giorgio La Pira, 4, 50121, Florence, Italy
| | - A Papini
- Università degli Studi di Roma La Sapienza, Department of Environmental Biology, Piazzale Aldo Moro, 5, 00185, Roma, Italy
| | - A Profico
- Università degli Studi di Roma La Sapienza, Department of Environmental Biology, Piazzale Aldo Moro, 5, 00185, Roma, Italy
| | - C Serio
- Università degli Studi di Napoli Federico II, Department of Earth Sciences, Environment and Resources, L.go San Marcellino 10, 80138, Naples, Italy
| | - A Veneziano
- Università degli Studi di Roma La Sapienza, Department of Environmental Biology, Piazzale Aldo Moro, 5, 00185, Roma, Italy
| | - V A Vero
- Università degli Studi di Napoli Federico II, Department of Earth Sciences, Environment and Resources, L.go San Marcellino 10, 80138, Naples, Italy
| | - L Rook
- Università degli Studi di Firenze, Department of Earth Sciences, Via Giorgio La Pira, 4, 50121, Florence, Italy
| | - C Meloro
- Liverpool John Moores University, School of Natural Science and Psychology, Byrom Street, L3 3AF, Liverpool, UK
| | - G Manzi
- Università degli Studi di Roma La Sapienza, Department of Environmental Biology, Piazzale Aldo Moro, 5, 00185, Roma, Italy
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Godinho RM, Fitton LC, Toro-Ibacache V, Stringer CB, Lacruz RS, Bromage TG, O'Higgins P. The biting performance of Homo sapiens and Homo heidelbergensis. J Hum Evol 2018; 118:56-71. [DOI: 10.1016/j.jhevol.2018.02.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Revised: 02/18/2018] [Accepted: 02/19/2018] [Indexed: 01/10/2023]
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8
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Martinón-Torres M, Wu X, Bermúdez de Castro JM, Xing S, Liu W. Homo sapiens in the Eastern Asian Late Pleistocene. CURRENT ANTHROPOLOGY 2017. [DOI: 10.1086/694449] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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9
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Sandel AA, Miller JA, Mitani JC, Nunn CL, Patterson SK, Garamszegi LZ. Assessing sources of error in comparative analyses of primate behavior: Intraspecific variation in group size and the social brain hypothesis. J Hum Evol 2016; 94:126-33. [PMID: 27178464 DOI: 10.1016/j.jhevol.2016.03.007] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2015] [Revised: 03/11/2016] [Accepted: 03/12/2016] [Indexed: 10/21/2022]
Abstract
Phylogenetic comparative methods have become standard for investigating evolutionary hypotheses, including in studies of human evolution. While these methods account for the non-independence of trait data due to phylogeny, they often fail to consider intraspecific variation, which may lead to biased or erroneous results. We assessed the degree to which intraspecific variation impacts the results of comparative analyses by investigating the "social brain" hypothesis, which has provided a framework for explaining complex cognition and large brains in humans. This hypothesis suggests that group life imposes a cognitive challenge, with species living in larger social groups having comparably larger neocortex ratios than those living in smaller groups. Primates, however, vary considerably in group size within species, a fact that has been ignored in previous analyses. When within-species variation in group size is high, the common practice of using a mean value to represent the species may be inappropriate. We conducted regression and resampling analyses to ascertain whether the relationship between neocortex ratio and group size across primate species persists after controlling for within-species variation in group size. We found that in a sample of 23 primates, 70% of the variation in group size was due to between-species variation. Controlling for within-species variation in group size did not affect the results of phylogenetic analyses, which continued to show a positive relationship between neocortex ratio and group size. Analyses restricted to non-monogamous primates revealed considerable intraspecific variation in group size, but the positive association between neocortex ratio and group size remained even after controlling for within-species variation in group size. Our findings suggest that the relationship between neocortex size and group size in primates is robust. In addition, our methods and associated computer code provide a way to assess and account for intraspecific variation in other comparative analyses of primate evolution.
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Affiliation(s)
- Aaron A Sandel
- Department of Anthropology, University of Michigan, Ann Arbor, MI 48109, USA.
| | - Jordan A Miller
- Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC 20052, USA
| | - John C Mitani
- Department of Anthropology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Charles L Nunn
- Department of Evolutionary Anthropology and the Duke Global Health Institute, Duke University, Durham, NC 27708, USA
| | - Samantha K Patterson
- School of Human Evolution and Social Change, Arizona State University, Tempe, AZ 85287, USA
| | - László Zsolt Garamszegi
- Department of Evolutionary Ecology, Estación Biológica de Doñana-CSIC, 41092, Seville, Spain
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10
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Pampush JD, Daegling DJ. The enduring puzzle of the human chin. Evol Anthropol 2016; 25:20-35. [DOI: 10.1002/evan.21471] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Indexed: 11/12/2022]
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11
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Baker J, Meade A, Pagel M, Venditti C. Positive phenotypic selection inferred from phylogenies. Biol J Linn Soc Lond 2015. [DOI: 10.1111/bij.12649] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Joanna Baker
- School of Biological Sciences; University of Reading; Reading RG6 6BX UK
| | - Andrew Meade
- School of Biological Sciences; University of Reading; Reading RG6 6BX UK
| | - Mark Pagel
- School of Biological Sciences; University of Reading; Reading RG6 6BX UK
- Santa Fe Institute; Santa Fe NM 87501 USA
| | - Chris Venditti
- School of Biological Sciences; University of Reading; Reading RG6 6BX UK
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12
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Pampush JD, Daegling DJ. Symphyseal surface strain during in vitro human mandibular wishboning. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2015; 159:256-66. [PMID: 26381610 DOI: 10.1002/ajpa.22863] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2015] [Revised: 08/25/2015] [Accepted: 08/30/2015] [Indexed: 11/11/2022]
Abstract
OBJECTIVES This research theoretically models and empirically records symphyseal surface strain during in vitro human mandibular wishboning (lateral transverse bending) in order to test one aspect of the hypothesis that the chin is an adaptive response to masticatory stresses. From a perspective of optimality, three questions were tested: 1) Do human mandibles function as curved beams during wishboning? 2) Is the presence of a chin associated with lower than predicted curved beam effects? 3) Are there relatively low strain gradients on the lingual and labial symphyseal surfaces respectively? MATERIALS AND METHODS Based on morphometric criteria, theoretical wishboning strains were calculated for five dentate adult human mandibles. The same mandibles were fitted with strain gauges and subjected to simulated wishboning loads. From the empirically-recorded strains, relative strains were calculated by dividing all strains by the absolute lowest strain in a given specimen. The theoretical and empirical results were compared in order to address the three related questions guiding this research. RESULTS Human mandibles behave as curved beams during wishboning (question 1). Empirical strain measures showed greater disparity both between and within the labial and lingual symphyseal surfaces than the theoretical models predictions (questions 2 and 3). DISCUSSION Human symphyseal form, with its distinctive chin, is unlikely to be adapted for countering wishboning loads. Chins are associated with larger than expected strain gradients within and between symphyseal surfaces, which runs counter to the optimality criterion typically invoked in assessing trait performance for signs of adaptation. The implications are twofold: 1) wishboning may not, in fact, be a regular feature of human mastication or 2) wishboning may not pose the same structural risks in human jaws as this load does in other anthropoid primates.
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Affiliation(s)
- James D Pampush
- Department of Evolutionary Anthropology, Duke University, Durham, NC.,Department of Anthropology, University of Florida, Gainesville, FL
| | - David J Daegling
- Department of Anthropology, University of Florida, Gainesville, FL
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