Human Variation

Abstract:  Hispanics represent the largest and fastest growing minority in the United States. It is increasingly important to understand the skeletal morphology and regional variation within this diverse group. This research focuses on the eight cranial morphoscopic traits of Southwest Hispanics from Birkby et al. (J Forensic Sci 2008;53(1):29–33) and 18 additional traits. Frequency distributions assessed the prevalence of trait expressions in Southwest Hispanic, African-American, and European-American samples. Forward stepwise discriminant function analysis indicated the best traits for differentiating these three groups. Six of the Birkby et al.’s traits are prevalent in the Southwest Hispanic sample and the best traits to distinguish the three groups are as follows: incisor shoveling, anterior malar projection, nasal sill, oval window visualization, enamel extensions, anterior nasal spine, nasal aperture width, and alveolar prognathism. This research demonstrates the efficacy of morphoscopic traits in ancestry determinations and the utility of the aforementioned traits in discriminating Southwest Hispanics, African Americans, and European Americans.

We report the discovery of an African American Y chromosome that carries the ancestral state of all SNPs that defined the basal portion of the Y chromosome phylogenetic tree. We sequenced~240 kb of this chromosome to identify private, derived mutations on this lineage, which we named A00. We then estimated the time to the most recent common ancestor (TMRCA) for the Y tree as 338 thousand years ago (kya) (95% confidence interval ¼ 237-581 kya). Remarkably, this exceeds current estimates of the mtDNA TMRCA, as well as those of the age of the oldest anatomically modern human fossils. The extremely ancient age combined with the rarity of the A00 lineage, which we also find at very low frequency in central Africa, point to the importance of considering more complex models for the origin of Y chromosome diversity. These models include ancient population structure and the possibility of archaic introgression of Y chromosomes into anatomically modern humans. The A00 lineage was discovered in a large database of consumer samples of African Americans and has not been identified in traditional hunter-gatherer populations from sub-Saharan Africa. This underscores how the stochastic nature of the genealogical process can affect inference from a single locus and warrants caution during the interpretation of the geographic ___location of divergent branches of the Y chromosome phylogenetic tree for the elucidation of human origins.

Sex determination using mandible parameters is population dependent. In order to assess which measurements better characterize sex in prehispanic individuals from the Canary Islands, we blindly contrasted the results obtained by visual inspection and osteometric measurements with those obtained by molecular sexing using amelogenin ancient DNA analysis on teeth from the same material. Unambiguous sex classification was achieved by amplification of sex specific amelogenin alleles in 56 out of 76 mandibles (73.78% of the cases). Visual inspection led to a correct diagnosis in 66.04% of cases, with a greater proportion of errors for female (54.17%) than male (17.24%) mandibles. Osteometric measurements were able to assign sex correctly in 72.2% in the best of cases (mandibular height), a proportion similar to that obtained using a discriminant function (71.2%). By logistic regression analysis, ramus breadth, index ramus breadth/ramus height and mandibular length were the parameters independently related with a mistaken diagnosis of female sex, whereas bigonial width, ramus height and mandibular length were the parameters more closely and independently related to a mistaken diagnosis of male sex. In conclusion, diagnosis based on visual examination of the mandible or on its metric measurement only serves to roughly estimate sex with an accuracy of around 70% or less, at least among the prehispanic population from Gran Canaria. Amplification of amelogenin alleles leads to unambiguous identification of male and female alleles in 73.68% of cases, at least among the prehispanic population from Gran Canaria.

Abstract:  This paper presents data from a sample of 803 individuals (308 females and 495 males) from the Hamann-Todd collection testing Dwight’s century-old assertion that maximum height of the human scapula can be used for sex estimation—males being larger than 170 mm, females falling below 140 mm. The results of this project show Dwight’s method has high accuracy when scapular height falls either above or below the sex specific demarcation points (96.81%), but a vast majority of both males and females fall in between. The overall accuracy of the method is just 29.27%. By empirically demonstrating the limited usefulness of Dwight’s technique, the author hopes the rote republication of this method in introductory texts on the subject will cease, and draw attention to the need for multiple methods of sex estimation as a response to the overlap in both size and shape between males and females.

Climate is thought to be one of the factors affecting the distribution of nasal form as represented by the breadth and height of the skeletal nasal aperture. A model of nasal function is developed to predict influences on the skeletal nasal dimensions by selection acting upon the external nasal passage and aperture. Cranial series from Alaska and Australia, each series representing a climatic continuum from warmer and moister conditions to cooler and drier conditions, verify the predictions. These data suggest conditions for testing hypotheses about human variation.

This study incorporated a phlylogenetic approach to look for cranial differences between geographical distant pre-contact California Amerindian populations. A total of 162 female and 273 male crania representing 10 groups from 5 geographical areas (coastal, intermediate coastalvalley, valley, mountainous, and island) within California were used along with 16 cranial variables out of the 22 reported Gifford (1926) variables. A Neighbor Net analysis was used to look for genetic relationships showing either similarities and/or differences between the studied populations. The results analysis suggested that there are similarities among populations based on geographical distance, but also implied that there are differences between populations at greater geographical distances from themselves. This study does suggest there are differences in cranial morphology of pre-contact California Amerindian populations representing coastal, intermediate coastal-valley, valley, mountainous, and island geographical areas. It is essential for a future study to address the need for a larger sample size, a decrease in the amount of missing variables, a temporal distinction of Gifford (1926) reported remains and an appropriate method in converting continuous data to discrete characters in order to look for phylogenetic cranial relationships between pre-contact California Amerindians.

Sex estimation is the grounds for an accurate identification of unknown human skeletal elements. The need for reliable methods distinguishing males from females based upon various skeletal elements is evident in cases of commingled, eroded and/or missing remains. The aim of this work lays on establishing criteria for sex estimation from the scapula and the clavicle in modern Greeks.

Population data on the hypervariable regions of the mitochondrial DNA (mtDNA) genome are used to convey the relative rarity of mtDNA profiles obtained from evidence samples and of profiles used to identify missing persons. In this study, mtDNA profiles of Spanish individuals (n = 312) were analyzed to describe haplogroup distributions and to determine relevant single nucleotide polymorphisms (SNPs) of those haplogroups. All nine common European haplogroups were observed in the sample, and these were divided into subgroups when possible. Haplogroup H was the most common haplogroup. The haplogroups U, J, T, and V were the next most frequent groups, each occurring at a frequency of 6.4% or greater. In addition, African and Asian sequences were present though rare in the samples. The data were compared with and found to be similar to other published data sets. There were 109 SNPs observed in the data set, including 10 positions not previously reported. The most variable sites are consistent with other studies.

In order to better understand microevolutionary processes in Holocene Chinese craniofacial mor-phology, an analysis has been done on 21 metric traits on Neolithic (n=161), Bronze Age (n=423) and modern (n=134) adult male skulls from northern China. The results indicate that the physical characters of these Chinese populations evolved throughout the Holocene. From the Neolithic to Bronze Age to present day, general trends include: cranial and facial sizes decrease; the nose gets narrower and longer; the orbits become narrower and higher; the head is more globular. The expression of the cranial features varies between the different time periods. The decrease in cranial size primarily occurred from the Bronze Age to present day. However, the decrease in facial size, the narrowing of the nose, and the elevation of the orbits took place throughout the Holocene. These traits are likely still evolving. This evolving pattern of the cranial features for the Holocene Chinese populations is similar to that found elsewhere in the world. The decrease in overall craniofacial size is associated with changes in climate and diet. In addition, it is possible that the craniofacial morphological microevolution is controlled by human evolutionary mechanisms.

Cranial and postcranial research on East and Southeast Asians has shown population variability between and within these two regions. Moreover, as populations vary by sex, sex differences vary by population. The purpose of this study is to provide the first descriptive and comparative analysis of two recently curated samples of complete, documented, contemporary skeletons from Thailand (N=104) and Hong Kong (N=94) that have not been previously studied. Sex differences reveal Hong Kong males and females as larger but less dimorphic than Thais. Stepwise discriminant function analysis of the Thai humerus and femur allowed 94%-96% sex classification accuracy. In conclusion, this research has increased our knowledge of sex and population differences in Asia and has important applications to demographic and medicolegal investigations.

The craniofacial skeleton carries out diverse functions served by hierarchically integrated developmental and functional modules. The craniofacial biologist is interested in how the skeleton of the cranium evolves and develops to integrate these functions while the clinician is more concerned with how function and development is altered in disease. The study of pathology is informative with respect to the control of development as is the study of normal variability. Particularly interesting are the paranasal sinuses which show marked variation within humans, in the human fossil record and among our close relatives. Their variations in humans are important clinically because they can be associated with increased susceptibility to disease and render sinus surgery more difficult. The extent and nature of variation within and between cranial structures is also informative with respect to normal developmental regulation since this can inform us about how their development is regulated. To fully understand the reasons we possess paranasal sinuses and why they vary it is necessary to relate their development to the temporally and spatially integrated development of the face from modules. Recent advances in morphometrics and mechanical modelling of the developing face have opened up new avenues of investigation likely to lead to such an understanding. They have the potential to test mechanical and spatial hypotheses of sinus ontogeny and so are likely to lead to new insights into craniofacial biology of importance to both evolutionary biologist and clinician.Es esqueleto facial cumple una serie de funciones distintas que se llevan a cabo a través de módulos tanto funcionales como módulos del desarrollo todos ellos organizados jerárquicamente. Mientras que el biólogo craneofacial está interesado en conocer la evolución y la ontogenia de la integración de esto módulos en el esqueleto craneofacial, el clínico se interesa mas por como la función y el desarrollo están alterados por enfermedad. El estudio de las patologías y el de la variación normal son interesantes en cuanto a los mecanismos de control ontogénico. Los senos paranasales que demuestran una variación marcada en humanos modernos, homínidos fósiles y nuestros parientes evolutivos más cercanos, los simios, son especialmente interesantes. La variación de los senos paranasales en humanos tiene elevada importancia clínica porque se asocia con una susceptibilidad elevada a infectarse y porque aumenta la dificultad de intervención cirujana. El grado y la naturaleza de esta variación entre determinadas módulos craneofaciales y dentro de aquellos contienen también información sobre la regulación ontogénica normal. Para un conocimiento completo de los motivos de la formación de los senos paranasales y su variación es necesario relacionar su desarrollo con las propiedades de la integración espacio-temporal de los componentes craneofaciales a lo largo de la ontogenia. Avances recientes en morfometría y en la modelización mecánica de la cara durante su ontogenia han abierto nuevas perspectivas para la investigación. Estas metodologías permiten testar hipótesis espaciales y funcionales de la ontogenia de los senos. Asimismo, contienen el potencial de incrementar nuestro conocimiento sobre la biología craneofacial, algo tan importante para el biólogo evolutivo como para el clínico.

Forensic anthropologists have typically relied on the cranium as the first resource for sexing human remains. However, there is a growing amount of literature on the utility and accuracy of using postcranial elements in sexing unknown remains (3, 8-16, 18).  A recent publication by Spradley and Jantz (J Forensic Sci 2011;56(1)) tested the accuracy of various discriminant functions using cranial and postcranial skeletal measurements from the Forensic Data Bank (FDB).  The purpose of the current study was to test their univariate and multivariate postcranial formulas against two regionally diverse White populations and compare classification rates between both samples.  The results of the current study strongly support and validate the Spradley and Jantz (1) equations and reiterate that postcranial measurements can be reliably used to estimate the sex of unidentified individuals.

Identification (ID) is of the utmost importance in any democratic society: every corpse must be positively identified. There has been significant scientific and technical progress in this field over the last several decades. Numerous circumstances may cause an individual to lose his or her identity: loss, theft, or destruction of identity papers, neurological and psychiatric disease, age, emigration, and so on. These factors may apply to living subjects as well as to the deceased.

When forensic anthropologists estimate the sex of Hispanic skeletal remains using nonpopulation specific metric methods, initial observations cause males to frequently misclassify as female. To help improve these methods, this research uses postcranial measurements from United States–Mexico border migrant fatalities at the Pima County Office of the Medical Examiner in Tucson, Arizona, as well as Hispanic individuals from the Forensic Anthropology Data Bank. Using a total of 114 males and 28 females, sectioning points and discriminant functions provide classification rates as high as 89.43% for Hispanic individuals. A test sample assessed the reliability of these techniques resulting in accuracy up to 99.65%. The clavicle maximum length measurement provides the best univariate estimate of sex, while the radius provides the best multivariate estimated of sex. The results of this research highlight the need for population specific data in the creation of a biological profile, especially when working with individuals considered Hispanic.

When modern humans left Africa ca. 60,000 years ago (60 kya), they were already infected with Helicobacter pylori, and these bacteria have subsequently diversified in parallel with their human hosts. But how long were humans infected by H. pylori prior to the out-of-Africa event? Did this co-evolution predate the emergence of modern humans, spanning the species divide? To answer these questions, we investigated the diversity of H. pylori in Africa, where both humans and H. pylori originated. Three distinct H. pylori populations are native to Africa: hpNEAfrica in Afro-Asiatic and Nilo-Saharan speakers, hpAfrica1 in Niger-Congo speakers and hpAfrica2 in South Africa. Rather than representing a sustained coevolution over millions of years, we find that the coalescent for all H. pylori plus its closest relative H. acinonychis dates to 88-116 kya. At that time the phylogeny split into two primary super-lineages, one of which is associated with the former hunter-gatherers in southern Africa known as the San. H. acinonychis, which infects large felines, resulted from a later host jump from the San, 43-56 kya. These dating estimates, together with striking phylogenetic and quantitative humanbacterial similarities show that H. pylori is approximately as old as are anatomically modern humans. They also suggest that H. pylori may have been acquired via a single host jump from an unknown, non-human host. We also find evidence for a second Out of Africa migration in the last 52,000 years, because hpEurope is a hybrid population between hpAsia2 and hpNEAfrica, the latter of which arose in northeast Africa 36-52 kya, after the Out of Africa migrations around 60 kya.

Background: Information on nucleotide diversity along completely sequenced human genomes has increased tremendously over the last few years. This makes it possible to reassess the diversity status of distinct receptor proteins in different human individuals. To this end, we focused on the complete inventory of human olfactory receptor coding regions as a model for personal receptor repertoires.

Aleš Hrdlička produced a tremendous amount of data in his career, much of which was published in a series of catalogs by the US National Museum. The Gulf States catalog, for example, contains raw craniometric data for over 700 individuals from the state of Florida alone. However, many of these skeletons are poorly sourced by Hrdlička, thus limiting their utility in modern bioarchaeological analyses where context is critical. In particular, the age of the skeletal material is often based solely on associated material culture and information on the sites themselves is not presented by Hrdlička. in Wiley Online Library (wileyonlinelibrary.com).

Vault sutures have proven their low reliability for estimating age at death in individual forensic science cases. We broke down the palatine sutures of 134 skulls (with known sex and age at time of death) into 15 subparts and 5 stages of fusion to obtain a mean coefficient of obliteration (Cp) which was then linked to five age classes. We completed this study with multiple regression equations of total palatine suture scores. We compared our results with those obtained using the Mann method on the one hand and classically segmented and scored ectocranial suture age determination methods on the other. Palatine sutures generally do not estimate age at death any better than cranial vault sutures. Despite the partly subjective aspect of suture study, palatine suture observation contributes additional information to age-range estimation, especially in old and very old subjects where other methods lose their effectiveness.

This study provides evidence of craniofacial growth variation between the sexes in juveniles of European descent. Data were collected from lateral cephalometric radiographs belonging to the Michigan Craniofacial Growth Study. The collection consists of longitudinal lateral radiographs that represent individuals 5-16 years of age. Each radiograph was manually traced on hyprint vellum from which eight craniometric points were identified. From these points, 20 craniofacial measurements were recorded and then analyzed by means of a canonical discriminant function analysis. Sex classification equations were then created by applying a backward stepwise procedure to the discriminant functions. The analysis demonstrates the presence of sexually dimorphic differences in craniofacial growth. The neurocranium is the most sexually dimorphic region of the juvenile craniofacial skeleton, until the onset of puberty. Size is the main source of variation with males having taller and longer heads than females. Overall, sex classification in the sample ranges from 78 to 89% accuracy.

"The subadult age distribution for the Bab edh-Dhra' charnel house A22 collection, dated to the Early Bronze Age II/III period (2800-2300 BCE), was constructed using femoral diaphyseal length estimates. Vertical head diameter and mediolateral neck breadth were measured for 56 fragmented left subadult proximal femora in order to estimate diaphyseal lengths using a regression equation (Hoppa and Gruspier, 1996). These lengths were used to place femora into an age category (fetal, infant, young child, old child, and adolescent) based on dental or functional development scales. Diaphyseal length ranges for these categories were constructed using available studies of other skeletal collections, including the Bab edh-Dhra’ Early Bronze I cemetery (3150-2950 BCE).

Age distributions based on the two separate scales were not significantly different (x2=3.38, p=0.34). Using the dental scale, 10% of the remains were classified as fetal, 4% as infant, 19% as young child, 44% as old child, and 23% as adolescent. This profile was significantly different from four North American groups ranging in ___location and time period, but not to other comparative groups from around the world. The age profile was not significantly different from another constructed using mandible dental data for the Early Bronze II/III subadults (x2=2.16, p=0.54) indicating a robust estimate, but it was significantly different from the Early Bronze I group (x2=16.35, p=0.001). Preservation and conservation issues in A22 may have affected these estimates, or changes in settlement and subsistence strategies may have altered childhood mortality.

This research was supported by the NSF–REU program (SES 0649088) at the University of Notre Dame."

The genomic features of an organism can be defined as the structural and functional attributes of its genotype. Genome science has thus far provided a course-grained characterization of genomic regulatory organization and expression . However, a model can be used to approximate the underlying control mechanisms and functional processes behind a particular phenotype. Many current muscle and biomechanical models deal with activity at the whole-muscle level [2], which may not provide insight into developmental and evolutionary processes that alter the interactions between muscle mass and force production. The modeling approach presented here may also eventually inform the design of robotic and prosthetic devices.

The corpus callosum displays considerable morphological variability between individuals. Although some characteristics are thought to differ between male and female brains, there is no agreement regarding the source of this variation. Biomedical imaging and geometric morphometrics have provided tools to investigate shape and size variation in terms of integration and correlation. Here we analyze variations at the midsagittal outline of the corpus callosum in a sample of 102 young adults in order to describe and quantify the pattern of covariation associated with its morphology. Our results suggest that the shape of the corpus callosum is characterized by low levels of morphological integration, which explains the large variability. In larger brains, a minor allometric component involves a relative reduction of the splenium. Small differences between males and?females are associated with this allometric pattern, induced primarily by size variation rather than gender-specific characteristics.

Discriminant functions were developed using long-bone robusticity measurements of 82 individuals from the protohistoric Maya site of Tipu, Belize. All individuals were sexed using nonmetric morphological indicators, particularly those of the pelvis. These functions are designed to provide a means of determining the sex of fragmentary prehistoric Maya skeletons. The equations ranged in accuracy from 77.5% to 100%. The reliability of these equations was tested using a jackknife method on the Tipu sample and by applying the equations to small samples of prehistoric skeletons from the sites of Seibal, KOB Swamp, Laguna de On, and Chau Hiix. The vast majority of the equations applied to the test cases succeeded in correctly estimating the sex based on pelvic and cranial features. A more reliable technique for sex determination of poorly preserved skeletal remains will allow a whole new range of archaeological and bioanthropological hypotheses concerning sex and gender among the ancient Maya to be investigated and considered.

In this paper we present a pilot survey focusing on the chiropractors’ views on possible racial differences in their patients’ response to treatment. A questionnaire was developed and validated through this study. Results of this pilot survey show that the majority of respondents did not see biological race as a significant factor in chiropractic treatment and response to it. Thus, one may hypothesize that the race concept in chiropractic might not be as critical and contentious as it seems to be in the “mainstream” medicine. The inclusion of questions on patients’ cultural differences is suggested for future surveys. Further studies, based on bigger and more diverse samples of chiropractors could shed more light on this issue..

Introduction: Secular changes in the head and body dimensions of the Japanese population were recorded during the last century, but studies on Japanese adult facial shape were poorly documented. This study aimed to document the secular changes in facial shape and their association with craniofacial measures of Japanese adult female students. Methods: Data were collected from 1998-2001 and 1975-1979 from institutions in Tokyo and Kyoto. The prosopic index (PI) was derived from morphological facial height (n-gn) and bizygomatic breadth (zy-zy). Multiple regression analysis was used to determine the association between PI (facial form) and craniofacial measures. Results: Larger mean values for morphological facial height (n-gn) and for PI, but smaller values for bizygomatic breadth (zy-zy) and bigonial breadth (go-go) were observed in the current sample compared to their predecessors 21 years ago. The most prevalent facial shapes were mesoprosopic (30.53 percent) and euryprosopic (45.14 percent) for the current and previous series, respectively. There was a significant positive relationship between the PI and head length (g-op) (p less than 0.01), head breadth (eu-eu) (p less than 0.01) and head height (v-po) (p less than 0.05), and a negative relationship between the PI and head circumference (g-g) (p less than 0.01) and minimum frontal breadth (ft-ft) (p less than 0.01). Conclusion: Our results suggest that a narrowing of facial shape has been occurring for approximately 21 years in adult Japanese females. The best predictor variables for PI were head length, head circumference, head breadth, minimum frontal breadth and head height.

This study, and others, are being carried out in order to establish a Forensic Anthropology databank on age estimation and sex determination of skeletonized remains in Ghana. An osteometric study of sexual dimorphism in the sternal end of the right fourth rib on 346 consecutive coroner's autopsy cases (221 males, 125 females) of known age, sex, and race was conducted. The height and width of the sternal end of the rib were measured in each case. The sample was analyzed in three groups: young (Ͻ30 years), old (Ն30 years), and total sample (total group). Stepwise discriminant function analysis showed that the accuracy of sex determination varied from 80% in the young and 74% in the old groups to 78% for the total group. Statistical analysis of the results obtained when the functions derived from the study were tested using another batch of ribs showed the functions to be effective and reliable in determining sex. When functions derived from a previous study of American Whites were used to determine sex in our study sample, the vast majority of males were misclassified as females. This is the first time, to our knowledge, that a Black African population has been studied osteometrically to evaluate sexual dimorphism in the sternal end of the fourth rib.

Despite great progress in identifying genetic variants that influence human disease, most inherited risk remains unexplained. A more complete understanding requires genome-wide studies that fully examine less common alleles in populations with a wide range of ancestry. To inform the design and interpretation of such studies, we genotyped 1.6 million common single nucleotide polymorphisms (SNPs) in 1,184 reference individuals from 11 global populations, and sequenced ten 100-kilobase regions in 692 of these individuals. This integrated data set of common and rare alleles, called 'HapMap 3', includes both SNPs and copy number polymorphisms (CNPs). We characterized population-specific differences among low-frequency variants, measured the improvement in imputation accuracy afforded by the larger reference panel, especially in imputing SNPs with a minor allele frequency of #5%, and demonstrated the feasibility of imputing newly discovered CNPs and SNPs. This expanded public resource of genome variants in global populations supports deeper interrogation of genomic variation and its role in human disease, and serves as a step towards a high-resolution map of the landscape of human genetic variation.

"It is argued in this article that the human body both in health and disease cannot be fully understood without adequately accounting for the different levels of human variation.The article focuses on variation due to ancestry, arguing that the inclusion of information pertaining to ancestry in human anatomy teaching materials and courses should be carried out and implemented with care and in line with latest developments in biological
anthropology and related sciences. This seems to be of particular importance in the education of health professionals, as recent research suggests that better knowledge of human variation can improve clinical skills. It is also argued that relatively small curricular changes relating to the teaching of human variation can produce significant educational
gains."

The issue of human variation has recently become of great interest in medical research and practice, but numerous disagreements and misunderstandings surround this complex subject. It might be argued that these negative aspects could be reduced significantly if elements of human variation were taught to medical students. Even small changes in curriculum, if efficiently implemented, could produce considerable gains.

Anthropology Richard Bridges Biomedical and Pharmaceutical Sciences ii Christy, Bonny, M.A., Spring 2009 Anthropology Multivariate Statistical Analysis of Three Crania Housed at the University of Montana Physical Anthropology Lab Chairperson: Noriko Seguchi

Recombination varies greatly among species, as illustrated by the poor conservation of the recombination landscape between humans and chimpanzees. Thus, shorter evolutionary time frames are needed to understand the evolution of recombination. Here, we analyze its recent evolution in humans. We calculated the recombination rates between adjacent pairs of 636,933 common single-nucleotide polymorphism loci in 28 worldwide human populations and analyzed them in relation to genetic distances between populations. We found a strong and highly significant correlation between similarity in the recombination rates corrected for effective population size and genetic differentiation between populations. This correlation is observed at the genome-wide level, but also for each chromosome and when genetic distances and recombination similarities are calculated independently from different parts of the genome. Moreover, and more relevant, this relationship is robustly maintained when considering presence/absence of recombination hotspots. Simulations show that this correlation cannot be explained by biases in the inference of recombination rates caused by haplotype sharing among similar populations. This result indicates a rapid pace of evolution of recombination, within the time span of differentiation of modern humans.

Natural variation plays an important but subtle and often ignored role in neuromechanical systems. This is especially important when designing for living or hybrid systems which involve a biological or self-assembling component. Accounting for natural variation can be accomplished by taking a population phenomics approach to modeling and analyzing such systems. I will advocate the position that noise in neuromechanical systems is partially represented by natural variation inherent in user physiology. Furthermore, this noise can be augmentative in systems that couple physiological systems with technology. There are several tools and approaches that can be borrowed from computational biology to characterize the populations of users as they interact with the technology. In addition to transplanted approaches, the potential of natural variation can be understood as having a range of effects on both the individual's physiology and function of the living/hybrid system over time. Finally, accounting for natural variation can be put to good use in human-machine system design, as three prescriptions for exploiting variation in design are proposed.

Human intraspecific variation is a complex problem, but may be better understood by using computational models in tandem with knowledge about the genetic bases of phenotypic traits. These results can be used in a multitude of settings. To move closer to this goal, biologically-realistic mappings between genotype and phenotype are constructed using genetic algorithm and neural network-like models. These models allow for gene-gene and gene-environment interactions to be characterized in the resulting phenotype. Two types of model are introduced: a simple, two-layer model, and a more complex model. The final section will focus on trends of growth and development in relation to relationship to modeling anthropometric traits and other morphological phenomena.

We examined the affect of tissue depth variation on the reconstruction of facial form, through the application of the American method, utilizing published tissue depth measurements for emaciated, normal, and obese faces. In this preliminary study, three reconstructions were created on reproductions of the same skull for each set of tissue depth measurements. The resulting morphological variation was measured quantitatively using the anthropometric craniofacial variability index (CVI). This method employs 16 standard craniofacial anthropometric measurements and the results reflect ‘‘pattern variation’’ or facial harmony. We report no appreciable variation in the quantitative measure of the pattern facial form obtained from the three different sets of tissue depths. Facial similarity was assessed qualitatively utilizing surveys of photographs of the three reconstructions. Surveys indicated that subjects frequently perceived the reconstructions as representing different individuals. This disagreement indicates that size of the face may blind observers to similarities in facial form. This research is significant because it illustrates the confounding effect that normal human variation contributes in the successful recognition of individuals from a representational three-dimensional facial reconstruction. Research results suggest that successful identification could be increased if multiple reconstructions were created which reflect a wide range of possible outcomes for facial form. The creation of multiple facial images, from a single skull, will be facilitated as computerized versions of facial reconstruction are further developed and refined.