학술논문
Approaches for assessing whether the human hand evolved by natural selection in adaptation to stone tool use
Document Type
Dissertation/Thesis
Author
Source
TDX (Tesis Doctorals en Xarxa)
Subject
Language
English
Abstract
Los estudios en evolución humana han concluido en general que los rasgos derivados en humanos facilitaron comportamientos relacionados con el uso de herramientas y nos hicieron primates especialmente diestros. Cómo los humanos adquirimos esta configuración única de caracteres musculoesqueletales tiene profundas implicancias en nuestro entendimiento de la evolución humana en general, ya que la tecnología lítica es un elemento clave para definir culturas humanas. El propósito de esta tesis es evaluar si la mano humana evolucionó por selección natural en adaptación al uso de herramientas líticas, la que es la hipótesis más extendida para la evolución de la mano. Con este propósito, una muestra de manos de primates actuales, principalmente humanos, chimpancés y gorillas, fue analizada con distintos métodos que permiten relacionar forma y función biológica. El primer objetivo fue evaluar el comportamiento del pulgar bajo escenarios simulados de uso de un percutor en hominoideos, a través del análisis de elementos finitos. Los resultados indican que la distribución del estrés en los huesos probablemente no fue una presión selectiva suficientemente fuerte como para modelar la forma de los huesos de la mano en humanos. El segundo objetivo fue evaluar si los humanos muestran una estructura de covariación en los carpos que es diferente a la de chimpancés y gorilas. Los resultados indican que patrones de covariación distintos pueden haber modelado la evolución de la muñeca en estos primates, lo que puede estar relacionado con demandas funcionales distintas de locomoción y manipulación. El último objetivo fue probar si el tamaño de las entesis de ligamentos y músculos son proxis confiables para inferir patrones de actividad. Los resultados indican que el uso de herramientas líticas puede ser inferido en homininos analizando regiones de la mano donde se unen tendones (con entesis fibrocartilaginosas) y ligamentos. Esto puede servir para discutir desde cuándo y con qué frecuencia los homininos utilizaron herramientas líticas.
Studies in hand morphology have generally concluded that derived traits in humans facilitated stone tool-related behaviors and made us a highly dexterous primate. How humans acquired this unique configuration of musculoskeletal traits has profound implications for our understanding of human evolution overall, considering that stone technology is a key element defining culture in our species. The aim of this thesis was to evaluate whether the human hand evolved by natural selection in adaptation to stone tool use, which is the most widespread hypothesis for the evolution of the human hand. For this purpose, a comparative sample of hands of extant primates, mainly humans, chimpanzees and gorillas, were analyzed under different methods that relate biological form and function. The first objective of this thesis was to evaluate the performance of the thumb during simulated hammerstone use through a finite element analysis. The results that stress distribution in hand bones was unlikely to be a selective pressure strong enough to shape the hand of humans. The second objective was to evaluate whether humans have a different covariation structure at the wrist than that of chimpanzees and gorillas. Results indicate that different covariation patterns may be shaping the evolution of the wrist in these primates, which might be related to different functional demands of locomotion and manipulation. The last objective was to test whether entheseal size of ligaments and muscles are reliable for inferring activity patterns in the hand. The results indicate that stone tool use may be inferred in hominins by analyzing hand regions where tendons (with fibrocartilaginous entheses) and ligaments attach. This serves to discuss since when and to which extent hominins were using stone tools.
Studies in hand morphology have generally concluded that derived traits in humans facilitated stone tool-related behaviors and made us a highly dexterous primate. How humans acquired this unique configuration of musculoskeletal traits has profound implications for our understanding of human evolution overall, considering that stone technology is a key element defining culture in our species. The aim of this thesis was to evaluate whether the human hand evolved by natural selection in adaptation to stone tool use, which is the most widespread hypothesis for the evolution of the human hand. For this purpose, a comparative sample of hands of extant primates, mainly humans, chimpanzees and gorillas, were analyzed under different methods that relate biological form and function. The first objective of this thesis was to evaluate the performance of the thumb during simulated hammerstone use through a finite element analysis. The results that stress distribution in hand bones was unlikely to be a selective pressure strong enough to shape the hand of humans. The second objective was to evaluate whether humans have a different covariation structure at the wrist than that of chimpanzees and gorillas. Results indicate that different covariation patterns may be shaping the evolution of the wrist in these primates, which might be related to different functional demands of locomotion and manipulation. The last objective was to test whether entheseal size of ligaments and muscles are reliable for inferring activity patterns in the hand. The results indicate that stone tool use may be inferred in hominins by analyzing hand regions where tendons (with fibrocartilaginous entheses) and ligaments attach. This serves to discuss since when and to which extent hominins were using stone tools.