DOCSLIB.ORG

QUANTIFYING SEXUAL DIMOPRHISM in the ADULT HUMAN CRANIUM Dissertation Presented in Partial Fulfillment of the Requirements for T

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
QUANTIFYING SEXUAL DIMOPRHISM in the ADULT HUMAN CRANIUM Dissertation Presented in Partial Fulfillment of the Requirements for T QUANTIFYING SEXUAL DIMOPRHISM IN THE ADULT HUMAN CRANIUM Dissertation Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School of The Ohio State University By Ana M. Casado Graduate Program in Anthropology The Ohio State University 2017 Dissertation Committee: Dr. Paul W. Sciulli, Advisor Dr. Samuel D. Stout, Co-Advisor Dr. Douglas Crews Copyright by Ana M. Casado 2017 ii ABSTRACT Biological anthropologists estimate sex from skeletal remains for forensic identification purposes or to reconstruct demographic profiles of past populations. Several features of the human cranium exhibit observable differences between males and females, known as sexual dimorphism. These sex-based differences are due to size disparities in muscle attachment sites as well as hormonal variations (Russell, 1985; Bass, 2005). A problem facing biological anthropologists is that of secular trends, or changes in physical traits over time; in the human skeleton. Most skeletal secular changes have been noted within the last 50 years (Jantz and Jantz, 1999, 2000). The most apparent secular trend is the increase in long bone length, and the consequent increase in height (Jantz and Jantz, 1999). Additionally, the human cranium has gotten taller and narrower, which can affect accurate sex estimation (Jantz et al., 2012). This research examines areas of the human skull that differ between the sexes and explores whether secular changes have affected sexually dimorphic areas of the cranium. The sample consists of 716 adult human crania of European European and African American ancestries from three skeletal collections: the Hamann-Todd Collection at the Cleveland Museum of Natural History, the Documented Skeletal Collection from the University of New Mexico’s Maxwell Museum, and the William M. Bass Donated Skeletal Collection housed at the University of Tennessee. The crania come from four defined generations, spanning birth years from 1864 to 1992. The ii individuals in the present sample were specifically chosen to fall between the ages of 20 and 60 to eliminate those who would not reflect pubertal changes and those who might show the most exaggeratedly robust cranial features in older age. To increase measurement accuracy, crania exhibiting fragmentation, trauma, or pathological conditions were not included. This dissertation includes skeletal samples from European American and African American individuals, and excludes crania of Hispanic, Asian, or any other ancestral affinity. The sample is limited to two groups due to underrepresentation of other populations in American skeletal collections. The six areas of the cranium analyzed here were specifically selected for their contribution to overall cranial robustness. These areas include: the external occipital protuberance, the nuchal area (or protuberances), the glabella, the mastoid processes, the supraorbital ridge(s) and frontal bossing. The novel measurement method proposed here quantitatively measures each trait (in millimeters), and considers the outward projection of each trait instead of the traditional method, which is to visually assess each feature and score its size and appearance on a scale of 1-5. To measure the cranial features, coordinate calipers were used, which provide an inexpensive and highly accessible alternative for three-dimensional skeletal data collection. Measurements were analyzed using a variety of statistical tests, including the measure of sexual dimorphism in a population, known as the calculation of D (after Bennett, 1981, and Chakraborty and Majumder, 1982). In addition, summary statistics, t- tests, analyses of variance, and discriminant function analyses were undertaken to test the hypotheses proposed in this dissertation. Results show that 12 features across the iii generations and ancestral groups exhibit sexual dimorphism (defined here as a D value of > 0.5). The sexual dimorphism associated with certain features, such as the supraorbital ridge, increased over the four generations, while the dimorphism associated with others stayed the same. No features experienced a decrease in sexual dimorphism over the four generations. From the discriminant function on the premodern dataset (Generations 1 and 2 combined), 77.8% of crania were correctly classified as males or females, a number which is roughly equivalent to the classification accuracy reported in most studies using traditional sex estimation methods. Only 51.1% of crania were correctly classified from the modern dataset (Generations 3 and 4 combined), and this may be because of secular trends affecting these areas of the cranium. Additionally, other discussions concerning changes in specific traits over time is included. Another two discriminant analyses were performed using the three traits exhibiting the highest levels of sexual dimorphism; classification accuracies were much higher for both premodern and modern datasets, and higher for premodern than the modern group of crania. This research is crucial for biological anthropologists and anatomists interested in skeletal change and human identification. Clearly, crania have changed over time, and the extent of those changes is somewhat quantified here, though more research is needed. As the modern human population changes, anthropologists must continue to improve their standards. This study will improve our understanding of cranial secular trends and will allow for more accurate skeletal identification. iv ACKNOWLEDGMENTS I wish to thank those who allowed me to access the skeletal collections used for this dissertation: Lyman Jellema, of the Cleveland Museum of Natural History, Dawnie Wolfe Steadman of the University of Tennessee’s Bass Collection, and Heather Edgar, of the Maxwell Museum at the University of New Mexico. I would also like to thank the members of my committee for advice and comments along the way, especially statistical advice. Special thanks to Meng Li and Stacy Porter for statistical guidance. Samantha Blatt, thank you for the beautiful drawings to supplement my method descriptions. Thanks to James Roberts, for supporting me and being willing to put up with the odd and hectic schedule of a graduate student. Y para Ben: Mi vida ha sido por tí. v VITA May 2003 .......................................................Farragut High School 2007................................................................B.A. Anthropology, University of Tennessee 2010................................................................M.A. Anthropology, The Ohio State University Publications Casado AM. 2017. Quantifying Sexual Dimorphism in the Human Cranium: A Novel Method. Journal of Forensic Sciences Fields of Study Major Field: Anthropology vi Table of Contents ABSTRACT ....................................................................................................................... ii ACKNOWLEDGMENTS ................................................................................................ v VITA.................................................................................................................................. vi List of Tables .................................................................................................................... ix List of Figures ................................................................................................................... xi CHAPTER 1 – INTRODUCTION .................................................................................. 1 Background: Literature Review and Previous Research .......................................... 1 Sexual Dimorphism: An Overview .............................................................................. 1 Causes for sexual dimorphism ..................................................................................... 2 Proximate Causes, or Extrinsic Factors for Sexual Dimorphism ......................... 3 Ultimate Causes, or Intrinsic Factors for Sexual Dimorphism ............................. 5 Measuring Sexual Dimorphism ................................................................................... 7 Sexual Dimorphism in the Human Skeleton ............................................................... 8 Sexual dimorphism in the human pelvis.................................................................. 9 Sexual dimorphism in the long bones .................................................................... 13 Sexual dimorphism in the human cranium ........................................................... 13 Sexual Dimorphism Across Populations................................................................ 15 Biological Ancestry and the Human Cranium ...................................................... 17 Sexual Dimorphism and Age-At-Death ................................................................. 19 Environmental Effects on the Human Cranium ...................................................... 21 Climate ...................................................................................................................... 21 Nutrition ................................................................................................................... 23 Mastication ............................................................................................................... 24 Growth and Development of the Human Cranium ................................................. 25 Cranial growth ........................................................................................................
Load more

Recommended publications
  • Evolutionary Trajectories Explain the Diversified Evolution of Isogamy And
    Evolutionary trajectories explain the diversified evolution of isogamy and anisogamy in marine green algae Tatsuya Togashia,b,c,1, John L. Barteltc,d, Jin Yoshimuraa,e,f, Kei-ichi Tainakae, and Paul Alan Coxc aMarine Biosystems Research Center, Chiba University, Kamogawa 299-5502, Japan; bPrecursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan; cInstitute for Ethnomedicine, Jackson Hole, WY 83001; dEvolutionary Programming, San Clemente, CA 92673; eDepartment of Systems Engineering, Shizuoka University, Hamamatsu 432-8561, Japan; and fDepartment of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, Syracuse, NY 13210 Edited by Geoff A. Parker, University of Liverpool, Liverpool, United Kingdom, and accepted by the Editorial Board July 12, 2012 (received for review March 1, 2012) The evolution of anisogamy (the production of gametes of dif- (11) suggested that the “gamete size model” (Parker, Baker, and ferent size) is the first step in the establishment of sexual dimorphism, Smith’s model) is the most applicable to fungi (11). However, and it is a fundamental phenomenon underlying sexual selection. none of these models successfully account for the evolution of It is believed that anisogamy originated from isogamy (production all known forms of isogamy and anisogamy in extant marine of gametes of equal size), which is considered by most theorists to green algae (12). be the ancestral condition. Although nearly all plant and animal Marine green algae are characterized by a variety of mating species are anisogamous, extant species of marine green algae systems linked to their habitats (Fig.
    [Show full text]
  • Hands-On Human Evolution: a Laboratory Based Approach
    Hands-on Human Evolution: A Laboratory Based Approach Developed by Margarita Hernandez Center for Precollegiate Education and Training Author: Margarita Hernandez Curriculum Team: Julie Bokor, Sven Engling A huge thank you to….. Contents: 4. Author’s note 5. Introduction 6. Tips about the curriculum 8. Lesson Summaries 9. Lesson Sequencing Guide 10. Vocabulary 11. Next Generation Sunshine State Standards- Science 12. Background information 13. Lessons 122. Resources 123. Content Assessment 129. Content Area Expert Evaluation 131. Teacher Feedback Form 134. Student Feedback Form Lesson 1: Hominid Evolution Lab 19. Lesson 1 . Student Lab Pages . Student Lab Key . Human Evolution Phylogeny . Lab Station Numbers . Skeletal Pictures Lesson 2: Chromosomal Comparison Lab 48. Lesson 2 . Student Activity Pages . Student Lab Key Lesson 3: Naledi Jigsaw 77. Lesson 3 Author’s note Introduction Page The validity and importance of the theory of biological evolution runs strong throughout the topic of biology. Evolution serves as a foundation to many biological concepts by tying together the different tenants of biology, like ecology, anatomy, genetics, zoology, and taxonomy. It is for this reason that evolution plays a prominent role in the state and national standards and deserves thorough coverage in a classroom. A prime example of evolution can be seen in our own ancestral history, and this unit provides students with an excellent opportunity to consider the multiple lines of evidence that support hominid evolution. By allowing students the chance to uncover the supporting evidence for evolution themselves, they discover the ways the theory of evolution is supported by multiple sources. It is our hope that the opportunity to handle our ancestors’ bone casts and examine real molecular data, in an inquiry based environment, will pique the interest of students, ultimately leading them to conclude that the evidence they have gathered thoroughly supports the theory of evolution.
    [Show full text]
  • Is the Skeleton Male Or Female? the Pelvis Tells the Story
    Activity: Is the Skeleton Male or Female? The pelvis tells the story. Distinct features adapted for childbearing distinguish adult females from males. Other bones and the skull also have features that can indicate sex, though less reliably. In young children, these sex-related features are less obvious and more difficult to interpret. Subtle sex differences are detectable in younger skeletons, but they become more defined following puberty and sexual maturation. What are the differences? Compare the two illustrations below in Figure 1. Female Pelvic Bones Male Pelvic Bones Broader sciatic notch Narrower sciatic notch Raised auricular surface Flat auricular surface Figure 1. Female and male pelvic bones. (Source: Smithsonian Institution, illustrated by Diana Marques) Figure 2. Pelvic bone of the skeleton in the cellar. (Source: Smithsonian Institution) Skull (Cranium and Mandible) Male Skulls Generally larger than female Larger projections behind the Larger brow ridges, with sloping, ears (mastoid processes) less rounded forehead Square chin with a more vertical Greater definition of muscle (acute) angle of the jaw attachment areas on the back of the head Figure 3. Male skulls. (Source: Smithsonian Institution, illustrated by Diana Marques) Female Skulls Smoother bone surfaces where Smaller projections behind the muscles attach ears (mastoid processes) Less pronounced brow ridges, Chin more pointed, with a larger, with more vertical forehead obtuse angle of the jaw Sharp upper margins of the eye orbits Figure 4. Female skulls. (Source: Smithsonian Institution, illustrated by Diana Marques) What Do You Think? Comparing the skull from the cellar in Figure 5 (below) with the illustrated male and female skulls in Figures 3 and 4, write Male or Female to note the sex depicted by each feature.
    [Show full text]
  • Establishing Sexual Dimorphism in Humans
    CORE Metadata, citation and similar papers at core.ac.uk Coll. Antropol. 30 (2006) 3: 653–658 Review Establishing Sexual Dimorphism in Humans Roxani Angelopoulou, Giagkos Lavranos and Panagiota Manolakou Department of Histology and Embryology, School of Medicine, University of Athens, Athens, Greece ABSTRACT Sexual dimorphism, i.e. the distinct recognition of only two sexes per species, is the phenotypic expression of a multi- stage procedure at chromosomal, gonadal, hormonal and behavioral level. Chromosomal – genetic sexual dimorphism refers to the presence of two identical (XX) or two different (XY) gonosomes in females and males, respectively. This is due to the distinct content of the X and Y-chromosomes in both genes and regulatory sequences, SRY being the key regulator. Hormones (AMH, testosterone, Insl3) secreted by the foetal testis (gonadal sexual dimorphism), impede Müller duct de- velopment, masculinize Wolff duct derivatives and are involved in testicular descent (hormonal sexual dimorphism). Steroid hormone receptors detected in the nervous system, link androgens with behavioral sexual dimorphism. Further- more, sex chromosome genes directly affect brain sexual dimorphism and this may precede gonadal differentiation. Key words: SRY, Insl3, testis differentiation, gonads, androgens, AMH, Müller / Wolff ducts, aromatase, brain, be- havioral sex Introduction Sex is a set model of anatomy and behavior, character- latter referring to the two identical gonosomes in each ized by the ability to contribute to the process of repro- diploid cell. duction. Although the latter is possible in the absence of sex or in its multiple presences, the most typical pattern The basis of sexual dimorphism in mammals derives and the one corresponding to humans is that of sexual di- from the evolution of the sex chromosomes2.
    [Show full text]
  • Sex-Specific Spawning Behavior and Its Consequences in an External Fertilizer
    vol. 165, no. 6 the american naturalist june 2005 Sex-Specific Spawning Behavior and Its Consequences in an External Fertilizer Don R. Levitan* Department of Biological Science, Florida State University, a very simple way—the timing of gamete release (Levitan Tallahassee, Florida 32306-1100 1998b). This allows for an investigation of how mating behavior can influence mating success without the com- Submitted October 29, 2004; Accepted February 11, 2005; Electronically published April 4, 2005 plications imposed by variation in adult morphological features, interactions within the female reproductive sys- tem, or post-mating (or pollination) investments that can all influence paternal and maternal success (Arnqvist and Rowe 1995; Havens and Delph 1996; Eberhard 1998). It abstract: Identifying the target of sexual selection in externally also provides an avenue for exploring how the evolution fertilizing taxa has been problematic because species in these taxa often lack sexual dimorphism. However, these species often show sex of sexual dimorphism in adult traits may be related to the differences in spawning behavior; males spawn before females. I in- evolutionary transition to internal fertilization. vestigated the consequences of spawning order and time intervals One of the most striking patterns among animals and between male and female spawning in two field experiments. The in particular invertebrate taxa is that, generally, species first involved releasing one female sea urchin’s eggs and one or two that copulate or pseudocopulate exhibit sexual dimor- males’ sperm in discrete puffs from syringes; the second involved phism whereas species that broadcast gametes do not inducing males to spawn at different intervals in situ within a pop- ulation of spawning females.
    [Show full text]
  • Sexual Dimorphism in Four Species of Rockfish Genus Sebastes (Scorpaenidae)
    181 Sexual dimorphism in four species of rockfish genus Sebastes (Scorpaenidae) Tina Wyllie Echeverria Soiithwest Fisheries Center Tihurori Laboratory, Natioriril Maririe Fisheries Service, NOAA, 3150 Paradise Drive) Tibirron, CA 94920, U.S.A. Keywords: Morphology, Sexual selection. Natural selection, Parental care. Discriminant analysis Synopsis Sexual dimorphisms, and factors influencing the evolution of these differences, have been investigated for four species of rockfish: Sebastcs melanops, S. fluvidus, S.mystiriiis. and S. serranoides. These four species, which have similar ecology. tend to aggregate by species with males and females staying together throughout the year. In all four species adult females reach larger sizes than males, which probably relates to their role in reproduction. The number of eggs produced increases with size, so that natural selection has favored larger females. It appears malzs were subjected to different selective pressures than females. It was more advantageous for males to mature quickly, to become reproductive, than to expend energy on growth. Other sexually dimorphic features include larger eyes in males of all four species and longer pectoral fin rays in males of the three piscivorous species: S. rnelanops, S. fhvidiis. and S. serranoides. The larger pectoral fins may permit smaller males to coexist with females by increasing acceleration and, together with the proportionately larger eye, enable the male to compete successfully with the female tb capture elusive prey (the latter not necessarily useful for the planktivore S. niy.ftiriiis). Since the size of the eye is equivalent in both sexes of the same age, visual perception should be comparable for both sexes. Introduction tails (Xiphophorus sp.) and gobies (Gobius sp.) as fin variations, in guppies (Paecilia sp.) and wrasses Natural selection is a mechanism of evolution (Labrus sp.) as color variations, in eels (Anguilla which can influence physical characteristics of a sp.) and mullets (Mugil sp.) as size differences.
    [Show full text]
  • A Description of the Geological Context, Discrete Traits, and Linear Morphometrics of the Middle Pleistocene Hominin from Dali, Shaanxi Province, China
    AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 150:141–157 (2013) A Description of the Geological Context, Discrete Traits, and Linear Morphometrics of the Middle Pleistocene Hominin from Dali, Shaanxi Province, China Xinzhi Wu1 and Sheela Athreya2* 1Laboratory for Human Evolution, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China 2Department of Anthropology, Texas A&M University, College Station, TX 77843 KEY WORDS Homo heidelbergensis; Homo erectus; Asia ABSTRACT In 1978, a nearly complete hominin Afro/European Middle Pleistocene Homo and align it fossil cranium was recovered from loess deposits at the with Asian H. erectus.Atthesametime,itdisplaysa site of Dali in Shaanxi Province, northwestern China. more derived morphology of the supraorbital torus and It was subsequently briefly described in both English supratoral sulcus and a thinner tympanic plate than and Chinese publications. Here we present a compre- H. erectus, a relatively long upper (lambda-inion) occi- hensive univariate and nonmetric description of the pital plane with a clear separation of inion and opis- specimen and provide comparisons with key Middle thocranion, and an absolute and relative increase in Pleistocene Homo erectus and non-erectus hominins brain size, all of which align it with African and Euro- from Eurasia and Africa. In both respects we find pean Middle Pleistocene Homo. Finally, traits such as affinities with Chinese H. erectus as well as African the form of the frontal keel and the relatively short, and European Middle Pleistocene hominins typically broad midface align Dali specifically with other referred to as Homo heidelbergensis.Specifically,the Chinese specimens from the Middle Pleistocene Dali specimen possesses a low cranial height, relatively and Late Pleistocene, including H.
    [Show full text]
  • How Sexually Dimorphic Are Human Mate Preferences?
    PSPXXX10.1177/0146167215590987Personality and Social Psychology BulletinConroy-Beam et al. 590987research-article2015 Article Personality and Social Psychology Bulletin How Sexually Dimorphic Are Human 2015, Vol. 41(8) 1082 –1093 © 2015 by the Society for Personality and Social Psychology, Inc Mate Preferences? Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/0146167215590987 pspb.sagepub.com Daniel Conroy-Beam1, David M. Buss1, Michael N. Pham2, and Todd K. Shackelford2 Abstract Previous studies on sex-differentiated mate preferences have focused on univariate analyses. However, because mate selection is inherently multidimensional, a multivariate analysis more appropriately measures sex differences in mate preferences. We used the Mahalanobis distance (D) and logistic regression to investigate sex differences in mate preferences with data secured from participants residing in 37 cultures (n = 10,153). Sex differences are large in multivariate terms, yielding an overall D = 2.41, corresponding to overlap between the sexes of just 22.8%. Moreover, knowledge of mate preferences alone affords correct classification of sex with 92.2% accuracy. Finally, pattern-wise sex differences are negatively correlated with gender equality across cultures but are nonetheless cross-culturally robust. Discussion focuses on implications in evaluating the importance and magnitude of sex differences in mate preferences. Keywords mate selection, sex differences, multivariate analysis, cross-cultural analysis Received February 9, 2015;
    [Show full text]
  • Human Sexual Selection
    Available online at www.sciencedirect.com ScienceDirect Human sexual selection David Puts Sexual selection favors traits that aid in competition over Here, I review evidence, focusing on recent findings, mates. Widespread monogamous mating, biparental care, regarding the strength and forms of sexual selection moderate body size sexual dimorphism, and low canine tooth operating over human evolution and consider how sexual dimorphism suggest modest sexual selection operating over selection has shaped human psychology, including psy- human evolution, but other evidence indicates that sexual chological sex differences. selection has actually been comparatively strong. Ancestral men probably competed for mates mainly by excluding The strength of human sexual selection competitors by force or threat, and women probably competed Some evidence suggests that sexual selection has been primarily by attracting mates. These and other forms of sexual relatively weak in humans. Although sexual dimorphisms selection shaped human anatomy and psychology, including in anatomy and behavior may arise from other selective some psychological sex differences. forces, the presence of sexually dimorphic ornamentation, Address weaponry, courtship displays, or intrasexual competition Department of Anthropology and Center for Brain, Behavior and indicates a history of sexual selection [3]. However, men’s Cognition, Pennsylvania State University, University Park, PA 16802, 15–20% greater body mass than women’s is comparable to USA primate species with a modest degree of mating competi- tion among males, and humans lack the canine tooth Corresponding author: Puts, David ([email protected]) dimorphism characteristic of many primates with intense male competition for mates [4]. Moreover, humans exhibit Current Opinion in Psychology 2015, 7:28–32 biparental care and social monogamy, which tend to occur This review comes from a themed issue on Evolutionary psychology in species with low levels of male mating competition [5].
    [Show full text]
  • Download Poster
    Sutural Variability in the Hominoid Anterior Cranial Fossa Robert McCarthy, Monica Kunkel, Department of Biological Sciences, Benedictine University Email contact information: [email protected]; [email protected] SAMPLE ABSTRACT Table 2. Results split by age. Table 4. Specimens used in scaling analyses. Group Age A-M434; M555 This study Combined In anthropoids, the orbital plates of frontal bone meet at a “retro-ethmoid” Species Symbol FMNH CMNH USNM % Contact S-E S-E S-E % % % frontal suture in the midline anterior cranial fossa (ACF), separating the contact/n contact/n contact/n presphenoid and mesethmoid bones. Previous research indicates that this Hylobatid 0 0 23 13.0 Hylobatid Adult 0/6 0 4/13 30.8 4/19 21.1 configuration appears variably in chimpanzees and gorillas and infrequently in modern humans, with speculation that its incidence is related to differential Juvenile 0/2 0 3/10 30.0 3/12 25.0 Orangutan 6 0 37 100.0 growth of the brain and orbits, size of the brow ridges or face, or upper facial Combined 0/9 0 7/23 30.4 7/32 21.9 prognathism. We collected qualitative and quantitative data from 164 Gorilla 3 0 4 28.6 previously-opened cranial specimens from 15 hominoid species in addition to A Orangutan Adult 12/12 100.0 21/21 100.0 21/21 100.0 Chimpanzee 1 0 7 57.1 qualitative observations on non-hominoid and hominin specimens in order to Juvenile 13/13 100.0 13/13 100.0 13/13 100.0 (1) document sutural variability in the primate ACF, (2) rethink the evolutionary trajectory of frontal bone contribution to the midline ACF, and Combined 26/26 100.0 34/34 100.0 34/34 34/34 Human 0 83 0 91.8 (3) create a database of ACF observations and measurements which can be Gorilla Adult 3/7 42.9 1/2 50.0 3/7 42.9 used to test hypotheses about structural relationships in the hominoid ACF.
    [Show full text]
  • Sexual Dimorphism in Human Arm Power and Force: Implications for Sexual Selection on Fighting Ability Jeremy S
    © 2020. Published by The Company of Biologists Ltd | Journal of Experimental Biology (2020) 223, jeb212365. doi:10.1242/jeb.212365 RESEARCH ARTICLE Sexual dimorphism in human arm power and force: implications for sexual selection on fighting ability Jeremy S. Morris1,*, Jenna Link2, James C. Martin2 and David R. Carrier3 ABSTRACT characteristics of the primate order (Talebi et al., 2009; Wrangham Sexual dimorphism often arises from selection on specific and Peterson, 1996). Within this group, the great apes are also – musculoskeletal traits that improve male fighting performance. characterized by intense male male competition (Carrier, 2007; In humans, one common form of fighting includes using the fists as Puts, 2016; Wrangham and Peterson, 1996) and pronounced male- weapons. Here, we tested the hypothesis that selection on male biased sexual dimorphism in traits that improve fighting fighting performance has led to the evolution of sexual dimorphism in performance. Fighting among male chimpanzees, which can lead the musculoskeletal system that powers striking with a fist. We to severe injury and death, involves the use of the forelimbs to compared male and female arm cranking power output, using it as a grapple, strike and slam an opponent to the ground (Goodall, 1986). proxy for the power production component of striking with a fist. Using Selection on male fighting performance in chimpanzees may be backward arm cranking as an unselected control, our results indicate associated with the evolution of sexual dimorphism, with males the presence of pronounced male-biased sexual dimorphism in being 27% larger (Smith and Jungers, 1997) and having broader muscle performance for protracting the arm to propel the fist forward.
    [Show full text]
  • The Influence of Body Size on Sexual Dimorphism
    University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Masters Theses Graduate School 12-2017 The Influence of Body Size on Sexual Dimorphism Haley Elizabeth Horbaly University of Tennessee, Knoxville, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_gradthes Part of the Biological and Physical Anthropology Commons Recommended Citation Horbaly, Haley Elizabeth, "The Influence of Body Size on Sexual Dimorphism. " Master's Thesis, University of Tennessee, 2017. https://trace.tennessee.edu/utk_gradthes/4970 This Thesis is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Masters Theses by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a thesis written by Haley Elizabeth Horbaly entitled "The Influence of Body Size on Sexual Dimorphism." I have examined the final electronic copy of this thesis for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Master of Arts, with a major in Anthropology. Dawnie W. Steadman, Major Professor We have read this thesis and recommend its acceptance: Benjamin M. Auerbach, Michael W. Kenyhercz Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) The Influence of Body Size on Sexual Dimorphism A Thesis Presented for the Master of Arts Degree The University of Tennessee, Knoxville Haley Elizabeth Horbaly December 2017 Copyright © 2017 by Haley Elizabeth Horbaly All rights reserved.
    [Show full text]