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- All Subjects: Human Evolution
- Creators: Reed, Kaye
Description
Many of the derived features of the human skeleton can be divided into two adaptive suites: traits related to bipedalism and traits related to encephalization. The cervical spine connects these adaptive suites and is itself unique in its marked lordosis. I approach human cervical evolution from three directions: the functional significance of cervical curvature, the identification of cervical lordosis in osteological material, and the representation of the cervical spine in the hominin fossil record.
ContributorsFatica, Lawrence Martin (Author) / Kimbel, William (Thesis director) / Reed, Kaye (Committee member) / Schwartz, Gary (Committee member) / Barrett, The Honors College (Contributor) / School of Human Evolution and Social Change (Contributor) / School of Life Sciences (Contributor)
Created2014-05
Description
Early weaning, slow somatic and dental growth, and late age at reproduction are all part of a suite of energetic trade-offs that have shaped human evolution. A similar suite of energetic trade-offs has shaped the evolution of the indriid-palaeopropithecid clade, though members of this clade exhibit extremely fast dental development and nearly vestigial deciduous teeth. The development and functional occlusion of the primary postcanine dentition (i.e., deciduous premolars and molars) coincides with several life history parameters in great apes and indriids. This dissertation explored great ape dental macrowear, molar development in indriids, and molar size in lemurs with a broader goal of improving reconstructions of life history profiles in extinct primates. To this aim, macrowear and dental development were analyzed in apes and lemurs, respectively. Occlusal casts (six great ape species; N=278) were scanned to track mandibular fourth deciduous premolar (dp4) macrowear. Utilizing dental topographic analyses, changes in occlusal gradient and terrain were quantified. A subset of the great ape data (four species; n=199) was analyzed to test if differences in dp4 wear correlate with age at weaning. Using dental histology, molar development was reconstructed for Indri indri (n=1) and Avahi laniger (n=1). Life history and molar size data were collected from the literature. The results of this dissertation demonstrate that most great apes exhibited evidence of topographic maintenance, suggesting dp4s wear in a manner that maintain functional efficiency during growth and development; however, the manner in which maintenance is achieved (e.g., preservation of relief or complexity) is species specific. Dp4 macrowear is not correlated with age at weaning in great apes and is probably unreliable to reconstruct age at weaning in hominins. The pace of molar development in members of the indriid- palaeopropithecid clade did not correlate with body or brain size, an association present in several other primates. Associations of molar size with age at weaning suggest that expanding other developmental models (e.g., the inhibitory cascade) to life history is worth consideration. The broad variation in macrowear, dental development, and size highlights how the primary dentition may correlate with different life history parameters depending on the species and ecological setting, an important consideration when using teeth to reconstruct life history profiles.
ContributorsCatlett, Kierstin Kay (Author) / Schwartz, Gary (Thesis advisor) / Barton, Michael (Committee member) / Godfrey, Laurie (Committee member) / Reed, Kaye (Committee member) / Arizona State University (Publisher)
Created2016
Description
Understanding the evolution of cooperation is a central goal in animal behavior research. In several animal taxa, socioecological environments that promote frequent interaction and social tolerance have favored the evolution of strong, equitable, and enduring social bonds, which facilitate cooperation and confer fitness benefits. Among males, strong bonds are believed to have evolved in the context of long-term alliances that help individuals compete for dominance status and mating access, but it remains unclear in some species what factors predict the strength and quality of bonds and how sociality relates to adaptive outcomes. To fill these gaps, this dissertation presents three studies of male chimpanzees at Gombe National Park, Tanzania, addressing the form, function, and development of male social relationships. Maternal brothers who were close in age formed the strongest bonds, strong bonds were associated with more reciprocal grooming relationships, and the strength of bonds were stable for an average of two years, while lasting up to 13 years. For other males, similarity in age and rank had negligible effects on bond strength, suggesting that bond strength results from a more complex process than a simple accounting of basic characteristics. Additionally, these social bonds, identified using both association in small groups and grooming activity, showed positive relationships with changes in dominance. In combination with prior studies, these results suggest that having strong bonds is a valuable strategy for achieving higher rank and, ultimately, increased reproductive success. Lastly, immature males who associated more with particular adult males while growing up were more likely to both associate and groom with those same males after entering adulthood. By contrast, association rates among immature male peers were not correlated with bond strength as adults. These findings suggest that the persistence of social relationships beyond those between mothers and offspring are more likely to evolve in long-lived species where young males enter adult hierarchies comprised of stronger or more socially experienced competitors. Overall, these studies reinforce the notion that social bonds are a chimpanzee universal, fill in gaps about the relationship between sociality and fitness, and emphasize the utility of a prolonged immature period.
ContributorsBray, Joel (Author) / Gilby, Ian C (Thesis advisor) / Silk, Joan B (Committee member) / Langergraber, Kevin E (Committee member) / Machanda, Zarin P (Committee member) / Arizona State University (Publisher)
Created2021