OpenUCT :: Browsing by Author "Ackermann, Rebecca Rogers"

Browsing by Author "Ackermann, Rebecca Rogers"

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Open Access
Characterizing the Evolutionary Path(s) to Early Homo
(Public Library of Science, 2014) Schroeder, Lauren; Roseman, Charles C.; Cheverud, James M.; Ackermann, Rebecca Rogers
Numerous studies suggest that the transition from Australopithecus to Homo was characterized by evolutionary innovation, resulting in the emergence and coexistence of a diversity of forms. However, the evolutionary processes necessary to drive such a transition have not been examined. Here, we apply statistical tests developed from quantitative evolutionary theory to assess whether morphological differences among late australopith and early Homo species in Africa have been shaped by natural selection. Where selection is demonstrated, we identify aspects of morphology that were most likely under selective pressure, and determine the nature (type, rate) of that selection. Results demonstrate that selection must be invoked to explain an Au. africanus -- Au. sediba -- Homo transition, while transitions from late australopiths to various early Homo species that exclude Au. sediba can be achieved through drift alone. Rate tests indicate that selection is largely directional, acting to rapidly differentiate these taxa. Reconstructions of patterns of directional selection needed to drive the Au. africanus -- Au. sediba -- Homo transition suggest that selection would have affected all regions of the skull. These results may indicate that an evolutionary path to Homo without Au. sediba is the simpler path and/or provide evidence that this pathway involved more reliance on cultural adaptations to cope with environmental change.
Open Access
A comparison of statistical and geometric reconstruction techniques : guidelines for correcting fossil hominin crania
(2007) Neeser, Rudolph; Gain, James; Ackermann, Rebecca Rogers
The study of human evolution centres, to a large extent, around the study of fossil morphology, including the comparison and interpretation of these remains within the context of what is known about morphological variation within living species. However, many fossils suffer from environmentally caused damage (taphonomic distortion) which hinders any such interpretation: fossil material may be broken and fragmented while the weight and motion of overlaying sediments can cause their plastic distortion. To date, a number of studies have focused on the reconstruction of such taphonomically damaged specimens. These studies have used myriad approaches to reconstruction, including thin plate spline methods, mirroring, and regression-based approaches. The efficacy of these techniques remains to be demonstrated, and it is not clear how different parameters (e.g., sample sizes, landmark density, etc.) might effect their accuracy. In order to partly address this issue, this thesis examines three techniques used in the virtual reconstruction of fossil remains by statistical or geometrical means: mean substitution, thin plate spline warping (TPS), and multiple linear regression.
Open Access
Craniofacial variation, integration, and evolutionary diversification in baboons
(2009) Off, Eileen Catherine; Ackermann, Rebecca Rogers
This dissertation aims to increase our understanding of Papio by: 1) examining variation within and between baboon species; 2) investigating morphological integration in the cranium, and; 3) determining what evolutionary processes produce diversification among baboon crania. Twenty-five three-dimensional cranial landmarks on six-hundred and sixty four baboon crania from seven species were digitized. Forty-seven linear distances, chosen to cover the skull with minimal redundancy, were calculated from these coordinate data.
Open Access
Current issues in human origins research in South Africa
(Academy of Science of South Africa (ASSAf), 2003) Ackermann, Rebecca Rogers
Open Access
Dental morphology and variation across holocene Khoesan people of Southern Africa
(2014) Black, Wendy; Ackermann, Rebecca Rogers; Sealy, Judith
Dental analyses of the Holocene Khoesan populations of southern Africa can provide insight into the biological evolution of an anthropologically important people. There have been many studies of dental variation in Holocene populations of Europe and the Americas, but few of African populations. Despite the Khoesan being the focus of much osteological research over the last two decades, their dental morphology is understudied and we know little about their dental evolution. Here, I assess the metric and non-metric dental morphology and variation of Holocene Khoesan individuals across southern Africa (N=487). Due to the fragmentary nature of many archaeological skeletons, most previous work on Khoesan osteology has focused on the second half of the Holocene, because more recent skeletons tend to be better preserved. There are, however, relatively abundant and well-preserved dental remains from the early Holocene. These are studied in detail for the first time in this dissertation, adding to our understanding of the emergence of Holocene Khoesan dentition and providing insight into phenotypic (and presumably genetic) continuity in this region. In addition to examining similarities/differences among the Khoesan through space and time, comparisons are made between the teeth of Khoesan and those of Holocene archaeological skeletons from East Africa (Kenya) to provide a broader context for interpreting the Khoesan dentition. Comparisons are also made between Holocene Khoesan and Mid-Late Pleistocene teeth from southern Africa in order to provide insights into dental relationships deeper in time. There are six aims of this thesis: (1) to construct the population's dental map and with it, (2) evaluate the significance of Khoesan Late mid-Holocene body size fluctuations and (3) assess the question of population continuity or replacement ca. 2000 BP with the introduction of herding in South Africa, (4) to explore possible geographic differences among Khoesan dentitions (5) to investigate temporal differences within the Holocene, and also to compare Holocene and earlier hunter-gatherers to assess population continuity/discontinuity, and (6) to evaluate the position of Khoesan dentition in a global context. Up to 52 non-metric traits were scored using the Arizona State University Dental Anthropology System. To test for significant relationships between groups through time, chi-square statistics were employed on dichotomised data and the mean measure of divergence was assessed in order to identify phenetic similarities and dissimilarities between regions. Additionally, MANOVAs and Principal Components Analysis were used to investigate size and shape variation. Metric analyses demonstrate minor size/shape variation between temporal and regional groups. Increased metric variation is observed during the Late Holocene, coinciding with fluctuations in body size documented in previous studies. Although some differences in trait frequencies are observed during the Late Holocene, there is little variation in qualitative traits throughout the Khoesan sample. This suggests that the minor differences observed result from intrinsic factors such as geographic variation, rather than gene flow from outlying areas. Teeth from the Mid-Late Pleistocene demonstrate a degree of phenetic affinity to Holocene Khoesan dentition. Finally, the Khoesan dentition is significantly different from global dental complexes, as exemplified by a suite of twelve core Khoesan traits that distinguish Khoesan teeth from other dental patterns (including Afridonty). Taken together, these results support hypotheses of morphological and genetic continuity in southern African populations during the Holocene, with some evidence for continuity deeper in time. In addition, these results place the Khoesan dentition at the margins of the range of human dental variation and call into question the fit of this dental map into current sub-Saharan African dental models.
Open Access
Dietary ecology and niche separation among three closely related species (Parapapio jonesi, Pp. whitei and Pp. broomi) of South African Plio-Pleistocene Cercopithecoidea from Makapansgat Limeworks site
(2006) Fourie, Nicolaas Hofmeyer; Lee-Thorp, Julia A; Ackermann, Rebecca Rogers
Three sympatric, contemporaneous fossil cercopithecoid genera (Cercopithecoides, Parapapio and Theropithecus) are represented in assemblages from the Makapansgat Limeworks hominin locality in South Africa. The presence of such a variety of primate taxa in a single ecosystem at the same time suggests a certain degree of ecological and/or dietary differentiation between taxa. This research explores the possibility of dietary niche separation within this sample. Stable isotope (13C/12C, 180/160 ) and trace-element (Sr, Ba, Ca) techniques for palaeodietary analysis are employed to investigate papionin dietary ecology, and especially to search for evidence of subtle niche separation between the more closely related, morphologically similar taxa of the genus Parapapio. Previous studies of fossil cercopithecoid dietary ecology report disjunctions between dietary and taxonomic groupings, possibly as a result of the use of fragmentary specimens or isolated teeth and ensuing taxonomic uncertainty, or perhaps because of problems in the taxonomy itself. Because such taxonomic uncertainties impede the interpretation of dietary data, craniometric analyses were also performed to ground the dietary interpretations in a morphological context. Only complete or partially complete cranial specimens from which morphological craniometric measurements could also be taken were sampled. Dietary analyses indicated two widely differing dietary ecologies within the Cercopithecoides williamsi sample, consistent with published results for this taxon from Swartkrans and Sterkfontein. Results for Theropithecus darti indicated a predominantly C4 diet. Two overlapping dietary ecologies, loosely correlated to taxonomic groupings, were found within the genus Parapapio; specimens attributed to Pp. broomi tended to have C3-dominated diets with a larger rootstock component than Pp. whitei and Pp. jonesi, which included more C4 grasses in their diet. The morphological analyses found no clear taxonomic signal in the craniometric data for Parapapio, suggesting that the current taxonomic assignments of Parapapio specimens are problematic. Additionally, for all of the analysed anatomical regions, the Parapapio sample was no more variable than the single geographically circumscribed extant chacma baboon sample. To sum, while biogeochemical dietary indicators indicate distinct dietary ecologies within and between genera, disjunctions exist between the dietary categories and the taxonomic assignment of specimens. Given these results, and in light of the taxonomic concerns highlighted by the craniometric investigation, reinvestigation of papionin taxonomy at Makapansgat may be warranted.
Open Access
The evolution and diversification of Pleistocene Homo
(2015) Schroeder, Lauren; Ackermann, Rebecca Rogers
The morphologically diverse and geographically expansive Pleistocene Homo fossil record continues to be a topic of debate. Recent fossil discoveries have highlighted the diversity, as well as the difficulty of identifying evolutionary relationships, within our lineage. Previous studies have focused on making distinctions between inter-and intra-specific variation, with relatively poor understanding of population structure or the evolutionary forces which have shaped the complex phenotypic diversity within our genus. The focus of this thesis is to expand our current understanding of the cranial and mandibular variation within Pleistocene Homo by assessing patterns of variation within our lineage, exploring the morphological link between newly discovered Homo (and Homo-like) fossil species and existing Homo taxa, investigating the evolutionary processes acting during the emergence and diversification of our genus, and considering the possible ancestor-descendant relationships at the transition from australopith to Homo. Analyses are performed on three-dimensional scan data (landmarks and interlandmark distances) collected from specimens of Pleistocene Homo. To provide context, robust and gracile australopiths are incorporated due to their temporal and/or spatial correspondence. The core of this thesis consists of four manuscripts. A suite of quantitative methods are utilized in these manuscripts to evaluate the morphological diversity within this hypodigm. These include statistical tests developed from quantitative evolutionary theory, Mahalanobis' distances, Generalised Procrustes Analysis, and Euclidean Distance Matrix Analysis. The results of these analyses emphasise the importance of neutral evolutionary forces in shaping morphological diversity during the evolution of Homo. However, they also indicate that adaptive evolution /selection contributed to the differences in masticatory morphology within our genus, played a significant role in the dispersal of Homo out of Africa, and may have been an important driver of diversification during the transition from Australopithecus to Homo, as well as between Homo rudolfensis and other Homo groups. Importantly, they show that specimen affiliations, the effect of selection, as well as patterns of variability vary depending on the skeletal region analysed and extant model choice. Finally, they highlight the large amount of morphological variability during the emergence and evolution of our genus, supporting the coexistence of a diversity of forms, and the presence of multiple lineages. Taken together, these results reveal a complex evolutionary scenario shaping the diversity within Pleistocene Homo and their possible ancestors, challenging previous notions of a linear evolutionary trajectory. This conclusion emphasises the need for future research on hominin diversity to incorporate evolutionary process into models of evolutionary change.
Open Access
Investigating the emergence and spread of tuberculosis in South Africa
(2019) Campbell, Tessa; Ackermann, Rebecca Rogers; Stone, Anne
Tuberculosis is the leading cause of death in South Africa and, while the disease is clearly very relevant today, little has been done to understand its emergence locally from a deep history perspective. Bioarchaeological investigations of tuberculosis have received much attention in Europe and North America but, with the exception of Egypt, the African continent has not been well-evaluated in this regard despite numerous genetic studies suggesting an African origin for the disease. This thesis aims to identify cases of skeletal tuberculosis in the archaeological record of South Africa and, aided by historical literature, trace its geographical and temporal origins in order to inform a broader local and global understanding of this ancient pathogen. Ancient DNA detection and analysis was also attempted in order to compliment skeletal diagnoses and obtain strain informative sequences. Preservation, demographic and paleopathological data were collected for 2321 individuals, representing the majority of South African Holocene and historical remains curated in local institutions, and a thorough description of this extensive dataset is presented. Only twelve individuals showing pathology suggestive of tuberculosis were identified. All potentially date to the colonial period; however, two individuals likely predate direct European contact. The association of these individuals with Iron Age populations may suggest a link between an early introduction of the disease and East African trade but caution in this interpretation is advised due to the tentative diagnoses in both cases. The skeletal record supports the major events identified in the literature; an early focus of disease along the Orange River and at the major port city of Cape Town, followed by a cluster of cases in Kimberley associated with mining activities and, finally, a spread to rural agricultural communities. Of the nine individuals subject to ancient DNA analysis using silicabased extraction protocols and quantitative PCR, Mycobacterium tuberculosis complex (MTBC) DNA was identified in only three. Attempts to obtain MTBC strain informative sequences through next generation sequencing were unsuccessful. This is the first study in South Africa to report the detection of ancient pathogen DNA; however, despite a possible African origin for tuberculosis, there is no evidence to support a pre-colonial presence of the disease in South Africa.
Open Access
Khoe, San, Coloured, controvert or conform: Physical attributes influencing the formation of cultural identity in ""Coloured"" women of the Western and Northern Cape
(2024) Kotze, Annelize; Ackermann, Rebecca Rogers
This study sets out to investigate how physical attributes such as hair texture, the colour of your skin and even body structure, influences one's sense of self and ultimately, how this informs cultural identity formulation. The focus of the study was on women from the Northern and the Western Cape to gauge whether these formulations of cultural identity are also influenced by geographical spaces. The Khoe and San have been studied, misrepresented and misinterpreted for many years, to the extent that they have become protective of their time and their information, and rightfully so. This also holds for people classified under the Apartheid regime as Coloured. Racist, derogatory past classificatory terms which refer to Khoe and San persons, still haunt many people to the extent that they have chosen to disassociate from their indigenous ancestry and internalize and embrace the Apartheid classificatory term Coloured. This very same classification and categorisation which today, under the new dispensation, is still used to marginalise people of colour on a racial basis. In certain communities the Khoisan revivalist movement has seen an uprising in individuals claiming their indigenous Khoisan identity and their rights as indigenous people in the postapartheid South Africa. This study was performed through oral interviews with over 100 women, and a few men, from various geographical areas and age groups. Data was obtained through focus group, zoom and telephonic interviews to see how past classificatory systems still persist in a democratic South Africa and whether democracy allows people the freedom to choose how they want to be classified. It is a study about cultural identity which aimed to hear the stories from the women themselves, providing space for them to talk about their past as women of colour, their present situations, and how both of these affect them and the cultural identity of future generations. Overarching themes that emerged were that of historical traumas related to colonialism, slavery and apartheid; traumas of having to comply with certain standards of beauty and traumas of place, who we are and our place in the world. This study showed that discussions regarding something as seemingly insignificant as hair is important. Hair is not just hair. It is a journey, a trauma, a story and a huge part of our identity to heal from silenced and untold histories. It is a conversation that must be had. It is a story that must be told.
Open Access
Of mice and hominins: using the craniomandibular morphology of hybrid mice to better understand hybrid morphologies in the Hominin fossil record
(2017) Warren, Kerryn Ashleigh; Ackermann, Rebecca Rogers
Since the sequencing of the Neanderthal genome in 2010, there has been an explosion of molecular research into hybridization and gene flow among hominin taxa in the Late Pleistocene. However, little research has focussed on how hybridization affects skeletal morphology. In regions and time periods where the recovery of ancient DNA is not possible, a thorough understanding of hybrid morphologies is essential for truly understanding hominin interactions in the past. This thesis examines the cranio-mandibular morphologies of hybrid mice across different degrees of phylogenetic relatedness (three sub-specific hybrids and one specific hybrid) and through several generations (F1s, B1s and F2s for the sub-specific hybrids), in order to build an animal model for better understanding hybrid morphologies. Cranio-mandibular size, form and shape are compared between parents and hybrids (N=634), as are frequencies of unusual non-metric traits. Morphometric analyses show that all first generation (F1) hybrids are intermediate in cranial and mandibular shape, and larger in size than the mid-parental mean, or sometimes even larger than parents. However, the expression of these differences in hybrids appears to be dependent on phylogenetic distances between parents, with sub-specific F1 hybrids often appearing transgressive (outside the range of both parents), and specific hybrids more intermediate. Subsequent hybrid generations (B1s and F2s) are highly variable in cranio-mandibular size and shape depending on the generation of the cross, possibly reflecting the degree of heterozygosity. B1s and F2s are highly variable, with examples of both parental morphologies as well as hybrid heterotic size being retained in some individuals. Models based on these data show that it is possible to detect hybridization in samples (as opposed to sampling sympatric non-hybridizing taxa) on the basis of morphological variability. In terms ofnon-metric cranial traits, hybrids are more likely to express unusual sutural anomalies and atypical bilateral foramina. Two specimens (intra-specific F1 and B1 individuals) showed extensive wormion bones. These data corroborate current research on hybrids, providing further evidence for the patterns seen in other animal hybrids. Furthermore, results of this study support morphological evidence for hybridization in several hominin specimens, including Oase II (cranium associated with a known multigenerational recombinant) and potentially other Middle Pleistocene hominins.
Open Access
Phylogeny and phylogeography of the Chacma Baboon (Papio ursinus): the role of landscape in shaping contemporary genetic structure in the southern African baboon
(2011) Sithaldeen, Riashna; Ackermann, Rebecca Rogers; Bishop, Jacqueline
This thesis contributes to our understanding of the role of climate and landscape change in structuring diversity within chacma baboons (Papio ursinus). The data set comprises molecular sequences from two mitochondrial DNA markers: the Brown region and the hypervariable D-loop. DNA was extracted from faecal samples of 261 free living chacma baboons across southern Africa. Phylogenetic and phylogeographic techniques, including coalescent modeling, were used to examine past and present population dynamics of chacma baboon populations. Bayesian tree constructions provide a timeline of diversification for the sample. Although the ecological drivers of ongoing differentiation remain unclear, it was shown that population contractions and expansions have also played a significant role in driving regional genetic structure within the species.
Open Access
Pleistocene aridification cycles shaped the contemporary genetic architecture of southern african baboons
(Public Library of Science, 2015) Sithaldeen, Riashna; Ackermann, Rebecca Rogers; Bishop, Jacqueline M
Plio-Pleistocene environmental change influenced the evolutionary history of many animal lineages in Africa, highlighting key roles for both climate and tectonics in the evolution of Africa’s faunal diversity. Here, we explore diversification in the southern African chacma baboon Papio ursinus sensu lato and reveal a dominant role for increasingly arid landscapes during past glacial cycles in shaping contemporary genetic structure. Recent work on baboons ( Papio spp.) supports complex lineage structuring with a dominant pulse of diversification occurring 1-2Ma, and yet the link to palaeoenvironmental change remains largely untested. Phylogeographic reconstruction based on mitochondrial DNA sequence data supports a scenario where chacma baboon populations were likely restricted to refugia during periods of regional cooling and drying through the Late Pleistocene. The two lineages of chacma baboon, ursinus and griseipes , are strongly geographically structured, and demographic reconstruction together with spatial analysis of genetic variation point to possible climate-driven isolating events where baboons may have retreated to more optimum conditions during cooler, drier periods. Our analysis highlights a period of continuous population growth beginning in the Middle to Late Pleistocene in both the ursinus and the PG2 griseipes lineages. All three clades identified in the study then enter a state of declining population size (Ne f ) through to the Holocene; this is particularly marked in the last 20,000 years, most likely coincident with the Last Glacial Maximum. The pattern recovered here conforms to expectations based on the dynamic regional climate trends in southern Africa through the Pleistocene and provides further support for complex patterns of diversification in the region’s biodiversity.
Open Access
A quantitative assessment of variation in Holocene Khoesan crania from South Africa's western, south-western, southern and south-eastern coasts and coastal forelands
(2006) Stynder, Deano Duane; Ackermann, Rebecca Rogers; Sealy, Judith
Includes bibliographical references (leaves 274-325).
Open Access
Using a mouse model to understand the effect of hybridization on skeletal and pelage trait variation in mammalian hybrids
(2018) Humphreys, Robyn; Ackermann, Rebecca Rogers
Hybridization is thought to have played an important role in human evolution, with hybridizing groups having significant differences in soft tissue trait variation. Ectodermal trait variation is of interest because primate hybrids show increased atypical non-metric dental and cranial trait variation thought to be the result of interactions between parental genomes which have diverged for ectodermal trait development (including hair and tooth development). There were also differences between hybridizing hominin groups for limb measurements which have changed significantly throughout human evolution. Here a mouse model is used to look at the effect of hybridization on coat morphology and long bone length. Using standardized photographs, the differences in mean RGB values for the dorsal and ventral coat were used to determine whether the hybrids were different from their parents for pelage colour of different regions of the body, dorsal ventral colour contrast, and levels of variation in coat colour. The sample is composed of parents from one specific and three sub-specific crosses, as well as F1, F2 and first generation backcrossed (B1) hybrids. Long bone measurements of the forelimbs and hind-limbs were collected from micro-CT scans of the sub-specific F1 hybrids and their parents. Previous data have shown that hybridization can have variable morphological outcomes: hybrids can look like one of the parents, they can be intermediate, or they can have extreme traits outside of the range of variation of the parents. Our results indicate that morphological outcomes for coat colour in F1 hybrids depends on factors such as genetic distance. However, the genetic background of one of the strains used for this experiment might contribute the transgressive phenotype of some of the F1 hybrids. Hybrid morphology also changes in subsequent generations (F2 and B1) as new recombinants formed, with transgressive coat colour phenotypes sometimes appearing even if they are not present in the F1 hybrid groups. Phenotypes produced in F1 hybrids are also seen in subsequent generations of hybrids. All sub-specific F1 hybrids were transgressive for long bone length. Compared to parental groups hybrids have a different relationship between the long bones of the forelimb (ratio of humerus to ulna). This is in line with previous data from primate hybrids, that shows that changes in the relationships between different regions of the body occurs in hybrids producing novel phenotypes. The inter-membral indexes are not significantly different from one of the parents for two of the crosses. This data shows that hybridization can produce novel pelage phenotypes over multiple generations. There were many transitions in hair/skin morphology during human evolution and these tissue groups were and are under a great deal of selective pressure due to their direct interaction with the environment. Thus, understanding how these traits are impacted by hybridization will be important for disentangling how hybridization affected our evolutionary trajectory and ability to occupy new regions of the world. Post cranial data, indicates that F1 hominin hybrids might have longer limbs in relation to parental populations, more work needs to be done on the post cranial remains of posited hominin hybrids as well as pedigreed mammalian hybrids to determine if this is a pattern which can be used to identify hybrids in the fossil record.
Open Access
Using extant morphological variation to understand fossil relationships: A cautionary tale
(Academy of Science of South Africa (ASSAf), 2003) Ackermann, Rebecca Rogers
Recent studies of variation in living monkeys, apes, and humans have produced a number of insights that are pertinent to how we evaluate relationships among our fossil human ancestors. Here I summarize four such insights. I then use a fossil hominid example to illustrate how our understanding of variation can alter our interpretation of the past. Results show that our assessments of the relationships among fossil hominids can differ depending on which extant model of variation is used as a variation ‘yardstick.’ Additionally, our interpretations of these relationships can be swayed considerably by how we evaluate significance.
Open Access
Variation and the evolutionary drivers of diversity in the genus Paranthropus
(2018) Hlazo, Nomawethu; Ackermann, Rebecca Rogers; Ritzman, Terrence
Craniodental robusticity in Paranthropus has led many researchers to posit that all the species in this genus share a common adaptation to a diet of hard foods. Recent research on craniodental morphology, microwear, biomechanics, and isotopes, by contrast, has suggested that substantial variation exists within the genus Paranthropus, both in terms of ecological niches occupied by the three recognized species within the genus and the amount of consumed hard and compliant foods. Rather than pointing to a common adaptive suite, these studies suggest that the species were adaptively distinct from each other. However, current approaches to understanding craniodental morphology do not present a clear picture of how these speciesspecific adaptations differ. It is also not clear whether all aspects of morphology that have been attributed to adaptation are indeed adaptive, rather than the products of non-adaptive processes. This study examines variation across the three known Paranthropus taxa (P. aethiopicus, P. boisei and P. robustus; N=39) using an approach that tests for adaptive morphology against a null hypothesis of random change (i.e. drift). Extant species (Homo sapiens (N=150), Gorilla gorilla (N=150), Pan troglodytes (N=143) act as analogues for Paranthropus variance/covariance (V/CV). Results reveal a high magnitude of variation within and between species across mandibular and cranial regions, especially when including the P. robustus individuals DNH 7 & 8 from Drimolen. Drift cannot be rejected for the bulk of comparisons. Neutrality tests detect adaptive divergence between P. robustus and the other two species, but not between P. aethiopicus and P. boisei. Reconstructed selection vectors indicate that both positive and negative directional selection have driven diversification in mandibular and tooth dimensions and in the cranium, resulting in variable morphological responses including considerable evidence for correlated selection.

Browsing by Author "Ackermann, Rebecca Rogers"

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