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1 This article reprinted from: McMahon, K. A Ratio. Investigation of a Sexually Dimorphic Trait in the Human Skeleton. Page(s) , in Tested Studies for Laboratory Teaching, Volume 31 (K.L. Clase, Editor). Proceedings of the 31st Workshop/Conference of the Association for Biology Laboratory Education (ABLE), 534 pages. Compilation copyright 2010 by the Association for Biology Laboratory Education (ABLE) ISB All rights reserved. o part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyright owner. Use solely at one s own institution with no intent for profit is excluded from the preceding copyright restriction, unless otherwise noted on the copyright notice of the individual chapter in this volume. Proper credit to this publication must be included in your laboratory outline for each use; a sample citation is given above. Upon obtaining permission or with the sole use at one s own institution exclusion, ABLE strongly encourages individuals to use the exercises in this proceedings volume in their teaching program. Although the laboratory exercises in this proceedings volume have been tested and due consideration has been given to safety, individuals performing these exercises must assume all responsibilities for risk. The Association for Biology Laboratory Education (ABLE) disclaims any liability with regards to safety in connection with the use of the exercises in this volume. The focus of ABLE is to improve the undergraduate biology laboratory experience by promoting the development and dissemination of interesting, innovative, and reliable laboratory exercises. Visit ABLE on the Web at:

2 495 RATIO IVESTIGATIO OF A SEXUALLY DIMORPHIC TRAIT I THE HUMA SKELETO Karen A. McMahon Biological Science The University of Tulsa Tulsa OK karen-mcmahon@utulsa.edu RESULTS ITRODUCTIO The ratio between the 2nd digit (index finger) and 4th digit (ring finger) length () is a sexually dimorphic trait. Males tend to have a lower ratio because the 2nd digit is usually shorter than the 4th digit. Females tend to have a higher ratio because the 2nd and 4th digits are approximately of equal length. (Fig. 1) The ratio is established by the week of gestation. The higher the fetal testosterone levels, the lower the ratio. 14th Homeobox genes Hoxa and Hoxd control development of both genitals and digits. Variations in ratios have been correlated with certain diseases, athletic ability, mental skills, and career choices. Students can easily measure digit length directly or from photocopies using a metric ruler or digital calipers. o significant differences were found in measuring finger length directly or from photocopies with either a ruler or digital calipers (Table1). right ratio for female students () was significantly different from mean right ratio for male students (0.94). Left ratios for female () students were slightly higher than male (0.97) students (Table 2). In the general population males have a mean ratio of and women a mean digit ratio of 1.0. right () and left (0.96) ratios for the women s soccer team were slightly lower from the mean ratios (0.99 and 0.97 respectively) for college female students (Table 3). Previous studies of woman professional teams had shown ratios approaching the masculine digit ratio. right and left ratios for college-age males (right 0.94, left 0.97) were not significantly different from ratios for older male faculty and staff (right 0.95, left 0.96). right and left ratios for college-age females (right, left ) were slightly lower than ratios (right 1.00, left 0.99) for female faculty and staff (Table 4). It was thought that younger males would have a digit ratio approaching the female mean because of the recent abundance of estrogen-mimicking chemicals in the environment. Table 1. Comparison of mean 2D, 4D, and ratio for right and left hands when measured by ruler and digital calipers directly or from xeroxed copies. =2. +/-standard deviation. DISCUSSIO & FUTURE WORK 2D and 4D lengths are easily measured directly or from photocopies by either ruler or digital calipers. ratios for college males were <1; ratios for college females were higher and approached 1. 2D;4D ratios for women soccer players were slightly lower than college females from the general population. ratios for college-age males and females did not differ significantly from those of older college faculty and staff. The ratio will be used to investigate fluctuating asymmetry during This exercise brings an investigative approach to the study of the human skeleton and introduces provocative discussions about development. MEA R2D MEA R 4D MEA R MEA L2D MEA L4D MEA L METHOD MATERIALS & METHODS Ruler Directly ± ± ± ± ± ±0.00 Metric rulers (150 mm) preferably transparent vinyl Ruler Xerox Digital calipers, resolution of 0.01 mm (optional) ± ± ± ± ± ±0.02 Photocopies of hands (optional) Students measure the length (in mm) of the 2nd (index finger) and 4th (ring finger) digits of each hand (palm side) from the basal crease (metacarpophalangeal joint) to the finger tip (Fig 2). Calipers Directly Calculate the right and left ratio. Calipers Xerox Compare ratio means in populations - males vs. females, athletes vs. non-athletes, older faculty/staff vs. college-age students, etc ± ± ± ± ± ± ± ± ± ± ±0.01 REFERECES Honekopp, Johannes, Luise Bartholdt, Lothar Beier, and Andreas Liebert Second to fourth digit length ratio () and adult sex hormone levels: new data and a meta-analytic review. Psychoneuroendocrinology 32: Lutchmaya, S. S. Baron-Cohen, P. Raggatt, R. Knickmeyer, and J. T. Manning nd to 4th digit ratios, fetal testosterone and estradiol. Early Human Development 77: Malas, Mehmet Ali, Sevkinaz Dogan, E. Hilal Evcil, and Kadir Desdicioglu Fetal development of the hand, digits and digit ratio (). Early Human Development 82: Manning, John T Digit ratio: a pointer to fertility, behavior, and health. Rutgers University Press, ew Brunswick J, 173 pp. Putz, David A., Steven J. C. Gaulin, Robert J. Sporter, and Donald H. McBurney Sex hormones and finger length: What does indicate? Evolution and Human Behavior 25: Fig.1. Left hand of a female (a) and male (b). a) In females, the 2nd digit is typically near equal in length to the 4th digit and the ratio = 1. b) In males, the 2nd digit is usually noticeably shorter than the 4th digit and the ratio < 1. a Table 2. ratios for right and left hands of male college students compared to female college students (spring 09). *AOVA Single Factor p<0.0065, +/standard deviation. Table 3. ratios for right and left hands of female college students (fall 08) compared to female college soccer players. +/- standard deviation. SUPPLIES & SOURCES MEA R * MEA L POPULATIO MEA R MEA L Rulers, transparent vinyl (150 mm), $ each Digital calipers (0.01 mm resolution), $70-$100 POPULATIO MALE STUDETS ± ±0.20 FEMALE STUDETS ± ±0.05 FEMALE STUDETS 14 ±0.03 WOME S SOCCER TEAM ±0.03 Carolina Biological Supply Company Edmund Scientifics scientificsonline.com Ward s atural Science wardsci.com b ACKOWLEDGEMETS Fig. 2. Measuring digit length. a) Basal crease to finger tip of the 4th digit. b) Metacarpophalangeal joint to tip of distal phalanx of the 4th digit. Measuring digital length by transparent metric ruler (c) or by digital calipers (d). c Table 4. ratios for right and left hands of college students compared to faculty and staff. YOB = year of birth, +/-standard deviation. a b d MEA R MEA L COLLEGE AGE MALES YOB ± ±0.20 OLDER MALES YOB COLLEGE AGE FEMALES YOB ±0.03 OLDER FEMALES YOB ± ±0.02 Many thanks to the students, faculty, staff, and the Women s Golden Hurricane Soccer Team at The University of Tulsa for participating in this study. POPULATIO 31st AUAL ABLE (ASSOCIATIO OF BIOLOGY LABORATORY EDUCATIO) COFERECE University of Delaware, ewark, DE June 9-13, 2009

3 496 THE RATIO IVESTIGATIO OF A SEXUALLY DIMORPHIC TRAIT I THE HUMA SKELETO Karen A. McMahon Biological Science The University of Tulsa Tulsa OK karen-mcmahon@utulsa.edu Abstract The ratio () between 2 nd digit and 4 th digit length is sexually dimorphic in humans. Males have <1 because the 2 nd digit is shorter whereas in females, = 1. This dimorphism reflects relative testosterone:estrogen levels during fetal development and is observable by week 14. The ratio has been correlated with certain diseases, careers, athletic ability, and mental skills. Students predicted ratios for a population subset. Digit lengths were measured directly or from a photocopy with either a ruler or calipers. was lower for female athletes; no trend in was detected between age groups. Introduction The ratio () between the 2 nd digit (index finger) and the 4 th digit (ring finger) length is a sexually dimorphic trait of the human skeleton. In many females, = 1 because the 2nd and 4th digits are approximately of equal length (Fig. 1a). In most males, <1 because the 2nd digit is usually shorter than the 4 th digit (Fig. 1b). Low ratios are correlated to higher fetal testosterone levels whereas high ratios are indicative of higher fetal estrogen levels. Relatively higher fetal testosterone levels promote the growth of the 4 th digit, resulting in a low. The ratio is established by the 14 th week of gestation and is not correlated with circulating sex hormones in adults. Homeobox genes Hoxa and Hoxd control development of both the urogenital system and digits and may explain the connection between prenatal sex hormones and digit growth (Manning, 2002; Honekopp et al., 2007; Lutchmaya, et al., 2004; and Malas et al., 2006). Several studies have correlated ratios with certain diseases, genetic disorders, athletic ability, mental skills, and career choices (Manning, 2002; Putz et al., 2004). Students predict ratios for a specific group. This exercise offers an investigative approach to the study of the human skeleton in the Human Anatomy & Physiology laboratory course.

4 497 a b Figure 1. The is typically 1 in females (a) whereas males (b) usually have a less than 1 because the second digit is shorter than the fourth. Student Outline Learning Objectives 1. Learn about a sexually dimorphic trait in the human skeleton. 2. Understand how may be correlated with certain skills and disorders. 3. Design a scientific investigation correlating to certain characteristics in a defined population. Materials eeded Metric Rulers (150 mm, preferably transparent vinyl) Digital calipers (0.01 mm resolution, optional) Photocopies of palm side of hands (optional) Protocol 1. Turn the hand to be measured palm side up. Look for the basal crease at the attachment of the finger to the palm. Align the ruler or calipers from the basal crease to the fingertip (Fig. 2). In the human skeleton, the basal crease corresponds to the metacarpophalangeal joint on the skeleton and the fingertip corresponds to the distal end of the distal phalanx. (Fig.3). Measure the length in mm of the second and fourth digits of each hand. Record in Table Calculate the right, left, and overall and record in Table 1. Calculate the mean right, left, and overall for the each subset of the population measured. 3. Are there any differences in between the tested groups? Is your hypothesis supported? Explain.

5 498 Figure 2. Digit length is measured in millimeters from the basal crease to the finger tip with either a ruler or a digital caliper. Figure 3. The basal crease corresponds to the metacarpophalangeal joint of the hand (blue arrows) and the fingertip to the distal end of the distal phalanx (red arrows). Table 1. Record the length in mm of the right 2D,4D, and the left 2D,4D. Calculate the right, left, and overall. Subject R 2D R4D R L2D L 4D L Overall Instructor s otes o significant differences in the ratio were found when measuring hands directly or from photocopies by ruler or digital calipers (Table 2). Some students found it difficult to identify the basal crease from a photocopy. Others found locating the endpoint of the fingertip much easier on a

6 499 photocopy. I found that if the vinyl rulers were transparent it made it easier for students to line up from the basal crease to the fingertip. Digital calipers were easy to use and are more accurate than the rulers. Photocopies provided a record to check students accuracy of measurement. Table 2. Comparison of mean 2D, 4D, and for right and left hands when measured by ruler and digital calipers directly or from xeroxed copies. o significant differences were found among measurement techniques. = 4, +/- standard deviation, AOVA p= Method R2D R4D R L2D L4D L Overall Ruler Directly Ruler Xerox Calipers Directly Calipers Xerox 70.50± ± 3.77 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±0.01 right for female students () was significantly different from mean right ratio for male students (0.94). Left for female () students was slightly higher (0.97) than the mean left ratio for male students (Table 3). Table 3. for right and left hands of male college students compared to female college students (spring 09). *AOVA Single Factor p<0.0065, +/- standard deviation. Population R * L Male Students ± ± 0.20 Female Students 14 ±0.03 Since testosterone is correlated with good visual and spatial skills and these are skills which are valued in many sports, it was hypothesized that the women in the university soccer team would have lower ratios than college age women who were not athletes. right () and left (0.96) s for the women s soccer team were slightly lower from the mean s (0.99 and 0.97

7 500 respectively) for college female students (Table 4). Previous studies of woman professional teams had shown the approaching the masculine digit ratio. Table 4. ratios for right and left hands of female college students compared to female soccer players (fall 08). +/- standard deviation Students Soccer Team R L ± ± ±0.03 It was hypothesized that younger males would have a digit ratio approaching the female mean because of the increasing abundance of estrogen-mimicking chemicals in the environment but overall mean for college-age males (0.95) was identical to the overall mean for male faculty/staff (0.95). Overall mean for college-age females () was slightly lower than the overall mean (0.99) for female faculty/staff (Table 5). Table 5. for right and left hands in college-age students as compared to older university faculty and staff. R L Overall mean College Age Males YOB ± ± ±0.20 Older Males YOB College Age Females YOB Older Females YOB ±0.03 ± ± ± ±0.03 Suppliers Transparent vinyl rulers (150 mm) cost from $0.55 -$0.75 each. Digital calipers (0.01 mm resolution) cost from $50 -$100 and both are available at science supply houses such as Carolina

8 501 Biological Supply Company ( Edmund Scientifics (scientificsonline.com) or Ward s atural Science (wardsci.com). Acknowledgments Many thanks to the Women s Golden Hurricane Soccer Team and to the students, faculty, and staff, at The University of Tulsa for participating in this study. Literature Cited Honekopp, Johannes, Luise Bartholdt, Lothar Beier, and Andreas Liebert Second to fourth digit length ratio () and adult sex hormone levels: new data and a meta-analytic review. Psychoneuroendocrinology 32: Lutchmaya, S. S. Baron-Cohen, P. Raggatt, R. Knickmeyer, and J. T. Manning nd to 4th digit ratios, fetal testosterone and estradiol. Early Human Development 77: Malas, Mehmet Ali, Sevkinaz Dogan, E. Hilal Evcil, and Kadir Desdicioglu Fetal development of the hand, digits and digit ratio (). Early Human Development 82: Manning, John T Digit ratio: a pointer to fertility, behavior, and health. Rutgers University Press, ew Brunswick J, 173 pp. Putz, David A., Steven J. C. Gaulin, Robert J. Sporter, and Donald H. McBurney Sex hormones and finger length: What does indicate? Evolution and Human Behavior 25: About the Author Karen A. McMahon is an instructor at The University of Tulsa who has taught the laboratory for introductory Human Anatomy & Physiology since She is indebted to the faculty, staff, and students who have supported her interest in developing investigative activities for the A&P laboratory.