THE CEREBELLUM AND COGNITIVE EVOLUTION IN PLIOCENE AND PLEISTOCENE HOMINIDS BY ANNE GENEVIEVE HERA WEAVER B. A. Fine Arts Metropolitan State College 1976 M.S. Biological Anthropology University of New Mexico 1995 Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY BIOLOGICAL ANTHROPOLOGY The University of New Mexico Albuquerque, New Mexico August, 2001 DEDICATION To the Company of Scholars. iii ACKNOWLEDGEMENTS I am deeply grateful for the generous assistance and support of the following individuals and institutions, who helped me weave the web of “distributed cognition” from which the pattern of my research emerged. Flaws in the design are mine alone. The L.S.B. Leakey Foundation (Grant No. 33-15171), the University of New Mexico Graduate and Professional Student Association (Student Research and Allocations Committee), and the Wenner-Gren Foundation for Anthropological Research (Grant No. 6528) funded my research. Dr. John Csernansky, of Washington University Department of Psychiatry Instruction and Research, provided me with a beautiful set of modern human MRI scans. Dr. Jean-Jacques Hublin, then of the Musée de l’Homme, and Dr. Marc Braun, H ôpital St. Julien, Nancy, France, allowed me to measure the Neandertal CTs. Dr. Thomas Insel and Dr. James Rilling, of Emory University provided the primate MRIs. Dr. Katerina Semendeferi, designer of the primate MRI project, allowed me to measure the scans, and provided lab facilities and support at the University of California at San Diego. Fred Spoor introduced me to NIH Image, and provided valuable advice about how to proceed with the project at its inception. Dr. Chris Coulon, of the GAIA Group; Nicol Drouin, of Polyworks; Erwan Kerrien at the H ôpital St. Julien in Nancy; Bob Knapp, then of the Mallinkrodt Institute of Radiology at Washington University, and Dr. Lei Wang, at the Center for Imaging Sciences at Washington University, all helped me with the resolution of software and hardware incompatibilities that repeatedly threatened to sabotage the project. Several members of the UNM Medical School Faculty met with me in the early stages of the project and allowed me access to CT scanning facilities at UNM Hospital, including Dr. Blaine Hart and Dr. Fred Mettler, Jr., Department of Radiology. Cathy Jernigan, Radiology Technologist, spent many hours scanning skulls for me. Dr. John Sanders, of the NM Institute of Neuroimaging also met with me and provided information about radiographic computer software. Dr. Ruth Ramsey, of the University of Chicago Medical School, aided my research for suitable MRI materials. Dr. Jeff Clark, of North Dakota State University, was open to my unorthodox proposal to lease the Minolta portable scanner, allowing me to expand my fossil data base, and opening up the opportunity for fruitful collaboration beyond the duration of the dissertation research. He and his wife, Ann, were generous hosts, providing many delicious meals and excellent company, summer and winter, in Fargo. iv Aaron Bergstrom, of North Dakota State University, trained me in the use of the digitizer, talked me through many frustrating confrontations with recalcitrant computers, tracked down thousands of renegade pixels, and produced the beautiful digital endocast scans that are the foundation of my data. My research could never have been completed without his expertise in digital manipulation, his ingenuity, and his commitment to a job well done. Jessica Thompson’s good-humored company and careful measurements saved me many long and tedious hours in measuring MRIs. George Lawrence helped me to illustrate the “Adjustment for Scan Angle” and provided the initial drawing for Figure 10-1. Ereka Gerety, Carla Sarracino and Karen Marty of UNM’s Anthropology Department helped me to navigate the treacherous shoals of bureaucracy. John Anderson, Bettina Behrens, Steve Byers, Anne Carson, Steve Churchill, Tom Estenson, Bob Franciscus, Chuck Hilton, Trent Holliday, Carol MacLeod, Wes Niewoehner (my role model), Marsha Ogilvie, Meg Rhodes, Jan Shapiro, and Vince Stefan provided companionship along the way. “The Girls,” Cate Fitzmaurice, and Michael Yuan helped me to retain a sense of perspective, encouraged me in the face of the grimmest obstacles and celebrated with me when the end was in sight. I am especially grateful for the intellectual inspiration, patience, and guidance of my committee members: Dr. Heather Murray met with me for many hours, led me through the intricacies of neuroanatomy, showed me how to read MRIs, provided me with literature and materials, and shared the benefit of her long experience with me. Dr. Joe Powell’s encouragement and feedback kept me on track. He was there to “hood” me and congratulate me at one of the high points of my life. Dr. Lawrence Straus introduced me to the rich literature of Paleolithic archeology. His dynamic lectures provided the structure for understanding the theoretical issues that Paleolithic archeologists must grapple with. His meticulous feedback helped me to polish both my ideas and my presentation. Dr. Straus also allowed me to gain hands-on archeological experience at beautiful El Miron Cave. And, thanks to him, I had a once-in-a-lifetime chance for a breathtaking glimpse of Altamira. Dr. Ralph Holloway, of Columbia University, has been a generous mentor in countless ways. He gave me access to the sanctum sanctorum of the Brain Casting Lab, and allowed me to scan the endocasts there. Most important of all, he blazed the trail, established the standards, and enumerated the issues and obstacles to understanding hominid brain evolution. v Dr. Erik Trinkaus changed me life. He showed me how to transform my enthusiasms into intellectual riches by subjecting them to the fire of rigorous critical thinking. He has been a model for academic excellence and integrity. He read and critiqued my work from its lumbering beginnings to its final revised form. And he has lit the way with wit and wisdom. Steve, Jessica, and James made it all worthwhile. Year after year and day after day, their love, good cheer, and faith heartened and sustained me. Offering backrubs and words of encouragement, they accepted the laptop computer as one of the family on every single outing of the past five years. Thanks for letting me follow my dream. vi THE CEREBELLUM AND COGNITIVE EVOLUTION IN PLIOCENE AND PLEISTOCENE HOMINIDS By Anne Genevieve Hera Weaver B.A. Fine Arts M.S. Biological Anthropology Ph. D. Biological Anthropology ABSTRACT In the course of hominid evolution, the both the cerebellum and the neocortex have expanded, but they have done so at different rates. Differences in relative cerebellar volume with respect to overall brain and body size among Pliocene and Pleistocene hominids correlate with archeological and skeletal indicators of cognitive evolution. The cerebellum and the neocortex process information in different but complementary ways. The neocortex manipulates mental representations of objects, concepts, and events using data-rich “declarative” learning and memory processes. The cerebellum, on the other hand, uses “procedural,” rule-based and hierarchically organized functions to coordinate a continuum of sensory-motor and cognitive neural representations (Parkins 1997; Ullman in press). vii The present study used integrated data from Magnetic Resonance Images of living human and non-human primate endocrania and three-dimensional virtual models of hominid endocasts. Reduced major axis and least squares regression were used to calculate actual/predicted cerebellar volume with respect to brain volume (“cerebellar quotient” = “CQ”) for a sample of living primates, including recent humans, and fossil hominids. The evidence supports a three-stage model of hominid cerebellar evolution. In the first stage, brain mass expanded non-allometrically with respect to body mass (encephalization). CQ increased in parallel with encephalization, as H. habilis and H. erectus gradually developed a high level of technological competence, reflecting well-developed procedural cognitive processes and cultural mechanisms for disseminating technological information. In the second stage, represented by Middle Pleistocene, Late Archaic, and Early Modern Homo sapiens , absolute cerebellar volume increased only slightly, accompanied by a dramatic expansion of the neocortex, resulting in a marked decline in CQ. Neocortical expansion supported declarative knowledge with respect to the rich repertory of objects and activities and their mental representations. In the third stage, after the emergence of early anatomically modern humans, both brain and body mass were reduced, but absolute and relative cerebellar volume increased. Cerebellar algorithms for manipulating sensory-motor representations were extended to manipulation of conceptual representations as well. Computational efficiency was increased without an increase in overall brain mass. viii TABLE OF CONTENTS DEDICATION iii ACKNOWLEDGEMENTS iv ABSTRACT vii TABLE OF CONTENTS ix LIST OF FIGURES xvii LIST OF TABLES xviii 1 INTRODUCTION 1 PURPOSE 1 SIGNIFICANCE OF RESEARCH 1 ROLE OF THE CEREBELLUM IN COGNITION 1 RESEARCH HYPOTHESES 2 Overview of Question 2 Research Hypotheses 3 MODEL OF HOMINID COGNITIVE EVOLUTION INCORPORATING CHANGES IN RELATIVE CEREBELLAR VOLUME 4 DESCRIPTION OF MODEL 5 THREE STAGES IN HOMINID CEREBELLAR AND COGNITIVE EVOLUTION 6 STAGE I: OVERALL ENCEPHALIZATION 6 Phase 1-I (6 mya – 2.5 mya) – earliest hominids 6 Phase 1-II (2.5 mya – 1 mya) – early Homo