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Mark Collard

Publications and source records attributed to Mark Collard.

5 recordsLinked to original sources
PubMed2005

Do homoiologies impede phylogenetic analyses of the fossil hominids? An assessment based on extant papionin craniodental morphology.

Homoiologies are phylogenetically misleading resemblances among taxa that can be attributed to phenotypic plasticity. Recently, it has been claimed that homoiologies are widespread in the hominid skull, especially in those regions affected by mastication-related strain, and that their prevalence is a major reason why researchers have so far been unable to obtain a reliable estimate of hominid phylogeny. To evaluate this "homoiology hypothesis", we carried out analyses of a group of extant primates for which a robust molecular phylogeny is available-the papionins. We compiled a craniometric dataset from measurements that differ in their susceptibility to mastication-related strain according to developmental considerations and experimental evidence. We used the coefficient of variation and analysis of variance with post hoc least significant difference comparisons in order to evaluate the variability of the measurements. The prediction from the homoiology hypothesis was that dental measurements, which do not remodel in response to strain, should be less variable than low-to-moderate-strain measurements, and that the latter should be less variable than high-strain measurements. We then performed phylogenetic analyses using characters derived from the measurements and compared the resulting phylogenetic hypotheses to the group's consensus molecular phylogeny. The prediction was that, if the homoiology hypothesis is correct, the agreement between the craniometric and molecular phylogenies would be best in the analyses of dental characters, intermediate in the analyses of low-to-moderate-strain characters, and least in the analyses of high-strain characters. The results of this study support the suggestion that mastication-related mechanical loading can result in variation in hominid cranial characters. However, they do not support the hypothesis that homoiology is a major reason why phylogenetic analyses of hominid crania have so far yielded conflicting and weakly supported hypotheses of relationship. These findings are consistent with a recent test of the homoiology hypothesis using craniodental data from extant hominoids, and cast doubt on the validity of the homoiology hypothesis, as originally formulated.

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PubMed2004

On the reliability of recent tests of the Out of Africa hypothesis for modern human origins.

In this paper we critique two recent studies that have been claimed to disprove the Out of Africa hypothesis for modern human origins (Hawks et al., 2000; Wolpoff et al., 2001). We show that the test prediction employed by Hawks et al. (2000) and Wolpff et al. (2001) is not relevant to many versions of the Out of Africa hypothesis, and that the key specimens they used are problematic in terms of morphological representativeness. We also show that there are significant problems with the character state datasets employed in the studies. Lastly, we highlight evidence that the main method used in the studies (pairwise difference analysis) is not reliable when applied to the type of data employed by Hawks et al. (2000) and Wolpoff et al. (2001). In view of the foregoing, we contend that Hawks et al.'s (2000) and Wolpoff et al.'s (2001) claim to have disproved the Out of Africa hypothesis cannot be sustained.

Africa↗
PubMed2002

Pairwise difference analysis in modern human origins research.

Pairwise difference analysis is a phenetic method that groups taxa on the basis of the number of differences they exhibit. Recently, pairwise difference analysis has been used to investigate the phylogenetic relationships of hominid fossils at the centre of the modern human origins debate. It has been argued that the results of these analyses disprove the African replacement model of modern human origins, and support instead its competitor, the multiregional evolution model. However, this inference is problematic because the ability of pairwise difference analysis to recover phylogenetic information from morphological data has not been demonstrated. With this in mind, we conducted pairwise difference analyses of craniodental and soft tissue evidence from a group of extant primates for which a reliable molecular phylogeny is available, the hominoids. We found that the phylogenies yielded by the pairwise difference analyses were incompatible with the molecular phylogeny for the group. Given the robustness of the molecular phylogeny, these results suggest that pairwise difference analysis cannot be relied on to generate reliable estimates of primate phylogeny from morphological data. The corollary of this is that the results of published pairwise difference analyses of hominid fossils are not informative regarding the origin of modern humans.

Africa↗
PubMedDate not supplied

Impact of methodological choices on assessments of the reliability of fossil primate phylogenetic hypotheses.

It has been argued in several recent studies that conventional craniodental characters cannot be assumed to be reliable for the purposes of reconstructing primate phylogenetic relationships and that as a consequence little confidence can be invested in published fossil primate phylogenies. Here, we evaluate this claim by revisiting the analyses reported in one of these studies [Collard and Wood, 2000]. Specifically, we investigate whether the use of alternative methodological procedures would have altered their findings. We focus on three key issues: (1) size correction, (2) outgroup composition and (3) non-phylogenetic correlation among characters. Our analyses suggest that the results of Collard and Wood [2000] were not affected by the size correction method they used or by the outgroup they employed. Our analyses also suggest that their results were not affected by their decision to ignore developmental, functional and other non-phylogenetic correlations among the characters in their data sets. Accordingly, our study supports the assertion that conventional craniodental characters cannot be assumed to be reliable for reconstructing primate phylogenetic relationships. This in turn suggests that many published fossil primate phylogenies may be unreliable.

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