Moody, Brittany Leigh Staff (2017-12). An Analysis of Morphological Differences in the Femoral Diaphyseal Midshaft Between Fossil and Modern Humans. Master's Thesis. Thesis uri icon

abstract

  • The understanding of morphological variation between fossil and modern humans is critical to the discussion of evolutionary processes within the Homo lineage. Neanderthals are recognizably distinct in their morphology from Late Pleistocene Homo sapiens and recent modern humans, especially in the femoral midshaft cross-section. These lineages are often assumed to be independent when applying statistical methods to account for these morphological differences. The shared evolutionary history of fossil and modern humans, however, increases the likelihood that the distinction in observable traits cannot entirely be attributed to divergent selective pressures; morphological variation is obscured by phylogenetic signal and therefore violates assumptions of statistical independence. In order to understand the observed variation between these groups, phylogenetic signal must be taken into account. To test for phylogenetic signal in the femoral cross-section in recent human evolution, geometric morphometric shape data was taken from fossil groups (Neanderthals and Late Pleistocene Homo sapiens) and compared to a global recent modern human sample. This shape data was isolated from other morphological constraints through Procrustes superimposition and mapped onto a phylogeny created from mitochondrial genomes from geographic and temporally comparable populations. The trends in femoral midshaft cross-sectional shape variation were examined through Principal Component Analyses and Canonical Variate Analyses and showed concentrated shape change in the region of the pilaster. A permutation test indicated that phylogenetic signal is present in the femoral midshaft shape. The presence of this signal between fossil and modern human groups stresses the importance of taking into account, and controlling for, shared evolutionary history in comparative analyses. In order to understand the nature of the phylogenetic signal present in the femoral midshaft, independent contrasts were calculated and a multivariate regression was performed to test for the impact of evolutionary allometry. The results showed that allometric changes throughout modern and fossil human evolutionary history had an insignificant impact on changes in shape, explaining only 20% of shape variation. This, therefore, suggests that the observed shape changes at the femoral midshaft between these groups are not due to evolutionary allometry but can be attributed to other factors, such as behavioral, genetic, or environmental pressures.
  • The understanding of morphological variation between fossil and modern humans
    is critical to the discussion of evolutionary processes within the Homo lineage.
    Neanderthals are recognizably distinct in their morphology from Late Pleistocene Homo
    sapiens and recent modern humans, especially in the femoral midshaft cross-section.
    These lineages are often assumed to be independent when applying statistical methods to
    account for these morphological differences. The shared evolutionary history of fossil
    and modern humans, however, increases the likelihood that the distinction in observable
    traits cannot entirely be attributed to divergent selective pressures; morphological
    variation is obscured by phylogenetic signal and therefore violates assumptions of
    statistical independence. In order to understand the observed variation between these
    groups, phylogenetic signal must be taken into account.

    To test for phylogenetic signal in the femoral cross-section in recent human
    evolution, geometric morphometric shape data was taken from fossil groups
    (Neanderthals and Late Pleistocene Homo sapiens) and compared to a global recent
    modern human sample. This shape data was isolated from other morphological
    constraints through Procrustes superimposition and mapped onto a phylogeny created
    from mitochondrial genomes from geographic and temporally comparable populations.
    The trends in femoral midshaft cross-sectional shape variation were examined through
    Principal Component Analyses and Canonical Variate Analyses and showed
    concentrated shape change in the region of the pilaster. A permutation test indicated that
    phylogenetic signal is present in the femoral midshaft shape. The presence of this signal
    between fossil and modern human groups stresses the importance of taking into account,
    and controlling for, shared evolutionary history in comparative analyses. In order to
    understand the nature of the phylogenetic signal present in the femoral midshaft,
    independent contrasts were calculated and a multivariate regression was performed to
    test for the impact of evolutionary allometry.

    The results showed that allometric changes throughout modern and fossil human
    evolutionary history had an insignificant impact on changes in shape, explaining only
    20% of shape variation. This, therefore, suggests that the observed shape changes at the
    femoral midshaft between these groups are not due to evolutionary allometry but can be
    attributed to other factors, such as behavioral, genetic, or environmental pressures.

publication date

  • December 2017