Probable evidence of scurvy in subadults from archeological sites in Peru

Subadult scurvy is not well documented in archeological human remains despite the existence of many biomedical references indicating that bone changes do occur in some cases and, because of this, should be observable in human burials. There are several potential reasons for this gap in our knowledge of scurvy. Not all children who suffered from scurvy died of the disease or from other causes when they had scurvy. Scurvy may not leave characteristic bone changes in every case of the disease. Some of the pathological conditions associated with scurvy have been known for many years, but these features may be rare or difficult to differentiate from other pathological conditions. Recently a lesion of the skull has been described that is probably pathognomonic for scurvy, specifically porous and sometimes hypertrophic lesions of the greater wing of the sphenoid. This lesion is bilateral and highly associated with evidence of inflammation at other anatomical sites in the skull. A survey of subadult skulls (N = 363) in the human skeletal collection from Peru at the National Museum of Natural History, Smithsonian Institution, reveals a prevalence of 10% of skulls that exhibit plausible evidence of scurvy. Some cases of scurvy also have cribra orbitalia that has been attributed to anemia. In most of the Peruvian scurvy cases, anemia is an unlikely possibility because there is no evidence of marrow hyperplasia. This highlights the need for caution in using lesions of the orbit as an indicator of anemia when there is no other evidence of this disease elsewhere in the skeleton. Anatomical evidence of scurvy offers the potential of providing new and important evidence of diet in archeological human populations.     

Skeletal manifestations of infantile scurvy

Recent investigations of human skeletal material from the historic St. Martin's cemetery, England, found a range of abnormal lesions in six infants that are almost certainly related to scurvy. Porous and proliferative bone lesions affecting the cranial bones and scapulae were found, and this paper presents images obtained using both macroscopic and scanning electron microscope examination of the lesions. Previous work on infantile scurvy (Ortner et al., 1997-2001) relied heavily on changes at the sphenoid, which is often missing in archaeological bone, so the identification of changes attributable to scurvy on other cranial bones and the scapulae is encouraging. The ability to recognize changes related to scurvy on a range of bones will ensure an enhanced potential for recognition of this disease in future research involving archaeological bone. Research on historical documents from Birmingham dating to the eighteenth and nineteenth centuries, combined with the probable cases of scurvy identified, supports the view that the paucity of cases of infantile scurvy from the archaeological record reflects a lack of understanding and recognition of bone manifestations, rather than a lack of occurrence in this period. Changes linked to scurvy were only found in infants from the poorer sections of the community from St. Martin's, and this is almost certainly linked to patterns of food consumption and may be related to shortages of potatoes, due to blight, experienced during this period.     

Genetic variation in Native Americans, inferred from Latino SNP and resequencing data

Analyses of genetic polymorphism data have the potential to be highly informative about the demographic history of Native American populations, but due to a combination of historical and political factors, there are essentially no autosomal sequence polymorphism data from any Native American group. However, there are many resequencing studies involving Latinos, whose genomes contain segments inherited from their Native American ancestors. In this study, we introduce a new method for estimating local ancestry across the genomes of admixed individuals and show how this method, along with dense genotyping and targeted resequencing, can be used to assay genetic variation in ancestral Native American groups. We analyze roughly 6 Mb of resequencing data from 22 Mexican Americans to provide the first large-scale view of sequence level variation in Native Americans. We observe low levels of diversity and high levels of linkage disequilibrium in the Native American-derived sequences, consistent with a recent severe population bottleneck associated with the initial peopling of the Americas. Using two different computational approaches, one novel, we estimate that this bottleneck occurred roughly 12.5 Kya; when uncertainty in the estimation process is taken into account, our results are consistent with archeological estimates for the colonization of the Americas.     

Genetic admixture and gallbladder disease in Mexican Americans

Gallbladder disease is a common source of morbidity in the Mexican American population. Genetic heritage has been proposed as a possible contributor, but evidence for this is limited. Because gallbladder disease has been associated with Native American heritage, genetic admixture may serve as a useful proxy for genetic susceptibility to the disease in epidemiologic studies. The objective of our study was to examine the possibility that gallbladder disease is associated with greater Native American admixture in Mexican Americans. This study used data from the Hispanic Health and Nutrition Examination Survey and was based on 1,145 Mexican Americans who underwent gallbladder ultrasonography and provided usable phenotypic information. We used the GM and KM immunoglobulin antigen system to generate estimates of admixture proportions and compared these for individuals with and without gallbladder disease. Overall, the proportionate genetic contributions from European, Native American, and African ancestries in our sample were 0.575, 0.390, and 0.035, respectively. Admixture proportions did not differ between cases and noncases: Estimates of Native American admixture for the two groups were 0.359 and 0.396, respectively, but confidence intervals for estimates overlapped. This study found no evidence for the hypothesis that greater Native American admixture proportion is associated with higher prevalence of gallbladder disease in Mexican Americans. Reasons for the finding that Native American admixture proportions did not differ between cases and noncases are discussed. Improving our understanding of the measurement, use, and limitations of genetic admixture may increase its usefulness as an epidemiologic tool as well as its potential for contributing to our understanding of disease distributions across populations. Am. J. Phys. Anthropol. 106:361–371, 1998. Published 1998 Wiley-Liss, Inc.     

Temporal trends in femoral diaphyseal torsional asymmetry among the Arikara associated with postural behavior

Average femoral torsion has been reported to differ among populations, and several studies have observed a relatively high prevalence of femoral anteversion asymmetry in Native Americans, especially females. This study investigates sexual dimorphism and temporal trends in femoral torsional asymmetry among the Arikara from the seventeenth to the early nineteenth century. To establish if there are population differences, femoral torsion was first measured using a direct method on a diverse comparative sample of Native Americans from the Southwest, Midwest, and Great Plains as well as American Whites and Blacks. To examine temporal trends among the Arikara, femoral torsion was examined using the orientation of the maximum bending rigidity at subtrochanteric in 154 females and 164 males from three temporal variants of the Arikara Coalescent tradition. There is significant sexual dimorphism in femoral torsional directional and absolute asymmetry among most Native American samples, but not among American Whites and Blacks. Among the Arikara there is significant sexual dimorphism in femoral torsional asymmetry in all three temporal variants, and asymmetry in femoral torsional asymmetry increased significantly from the protohistoric to the early historic period among females. The increased femoral torsional asymmetry is likely associated with a common side‐sitting posture observed in historic photographs of Great Plains females. Historic Arikara females may have habitually sat in this compulsory position for extended periods while conducting domestic chores. The dramatic change from the protohistoric to historic period suggests a cultural change in sitting posture among females that was widespread across the Northern Plains. Am J Phys Anthropol 154:512–524, 2014. © 2014 Wiley Periodicals, Inc.     

Contact in the Andes: bioarchaeology of systemic stress in colonial Mórrope, Peru

The biocultural interchange between the Eastern and Western Hemispheres beginning in the late fifteenth century initiated an unprecedented adaptive transition for Native Americans. This article presents findings from the initial population biological study of contact in the Central Andes of Peru using human skeletal remains. We test the hypothesis that as a consequence of Spanish colonization, the indigenous Mochica population of Mórrope on the north coast of Peru experienced elevated systemic biological stress. Using multivariate statistical methods, we examine childhood stress reflected in the prevalence of linear enamel hypoplasias and porotic hyperostosis, femoral growth velocity, and terminal adult stature. Nonspecific periosteal infection prevalence and D(30+)/D(5+) ratio estimations of female fertility characterized adult systemic stress. Compared to the late pre-Hispanic population, statistically significant patterns of increased porotic hyperostosis and periosteal inflammation, subadult growth faltering, and depressed female fertility indicate elevated postcontact stress among both children and adults in Mórrope. Terminal adult stature was unchanged. A significant decrease in linear enamel hypoplasia prevalence may not indicate improved health, but reflect effects of high-mortality epidemic disease. Various lines of physiological, archaeological, and ethnohistoric evidence point to specific socioeconomic and microenvironmental factors that shaped these outcomes, but the effects of postcontact population aggregation in this colonial town likely played a fundamental role in increased morbidity. These results inform a model of postcontact coastal Andean health outcomes on local and regional scales and contribute to expanding understandings of the diversity of indigenous biological variation in the postcontact Western Hemisphere.     

Genetic relationships among Native American maize accessions of the Great Plains assessed by RAPDs

Genetic variation among 15 accessions of Native American maize from the Great Plains was investigated using random amplified polymorphic DNA (RAPD). RAPDs revealed very high levels of polymorphism among accessions. Banding patterns ranged in percentage polymorphism from 46.7% to 86.2% with an overall mean of 70.7% for the primers analyzed. The construction of genetic relationships using cluster analysis and principal coordinates analysis revealed that RAPDs are successful in confirming hypothesized relationships and in identifying misclassified specimens. Furthermore, the phenogram fails to reveal a strong correspondence between genetic relationships and the geographical position of Native Americans prior to contact. This provides support for the hypothesis that multiple introductions of maize into the Great Plains via trade may have resulted in the great morphological variation found among accessions in the region. Based on these data, it is unlikely that a separate Great Plains race of maize can be distinguished. In general, we conclude that RAPDs are potentially very useful in organizing seed collections and understanding intraspecific genetic differentiation. Received: 10 March 1999 / Accepted: 25 March 1999     

Toward Comprehensive Obesity Prevention Programs in Native American Communities

Obesity is a particularly important challenge to the health status of Native Americans. This challenge is manifest in the increasing rates of non-insulin-dependent diabetes mellitus among Native Americans. Most studies of Native American infants, preschool children, schoolchildren, and adults have confirmed a high prevalence of over weight Historical studies suggest that for many Native American communities the high rates of obesity are a relatively recent phenomenon. The specific reasons for the increase in obesity among Native Americans have not been determined, although it has been hypothesized that Native Americans have a genetic predisposition to over weight in a “westernized” environment of abundant food and decreased energy expenditure. Few detailed studies of diet or of physical activity levels of contemporary Native Americans have been published. Community-based interventions to modify diet and activity levels to prevent obesity in Native American communities are needed. Preliminary evidence from two formative school-based programs in the Southwest suggest that Native American communities are receptive to school-based interventions, and that such programs may be able to slow the rate of excess weight gain and to improve fitness in schoolchildren. Because of the cultural diversity among Native Americans, future studies should focus on collecting community- and region-specific data, and should emphasize the need for obesity prevention through culturally appropriate community-and school-based behavioral interventions.     

Patterns of demographic change in the Americas.

Considerable scholarly debate has focused on the nature of demographic change in the Americas before and after 1492. Recent research on human skeletal samples and related archeological materials suggests that morbidity and mortality were increasing throughout much of the Western Hemisphere before 1492 in response to increased population density, increased sedentism, and changing subsistence. The evidence suggests that after 1492 population reduction was caused not by continental pandemics but by localized or regional epidemics augmented by social and economic disruption. The twentieth century has witnessed remarkable Native American population recovery, fueled both by improvements in health care and changing definitions of "being Indian."     

Demography And Disease Patterns In A Protohistoric Plains Group: A Study ofthe Mobridge Site (39WW1)

Abstract

Epidemic disease has often been cited as the major factor causing historic depopulation of Native American groups. Because a range of infectious diseases introduced by Europeans struck different tribes at different times, the effects of these diseases or the outbreak of epidemics were not uniform for all groups. The Arikara of the American Plains wereamong the last North American Indian groups to experience direct contact with Europeans. However, indirect contact with introduced infectious diseases may have reduced these Plains protohistoric groups prior to established relations with Europeans. Historic depopulation of the Arikara and a demographic study of the skeletal remains from the Mobridge site (39WW1 l are the focus of this case study of the protohistoric population dynamics of a Native American group. Disease patterns are used in the demographic analysis to aid in the interpretation of observed mortality patterns. Evaluation of the skeletal remains from the Mobridge Site includes life table reconstruction and differential diagnosis of skeletal pathology complexes. Results of these analyses show that certain underlying disease processes evident skeletally correspond to deviations in the age distribution. Thus; the protohistoric mortality patterns of Mobridge appear to reflect the early stages of impact from introduced diseases.     

Evolutionary responses to a constructed niche: ancient Mesoamericans as a model of gene-culture coevolution

Culture and genetics rely on two distinct but not isolated transmission systems. Cultural processes may change the human selective environment and thereby affect which individuals survive and reproduce. Here, we evaluated whether the modes of subsistence in Native American populations and the frequencies of the ABCA1*Arg230Cys polymorphism were correlated. Further, we examined whether the evolutionary consequences of the agriculturally constructed niche in Mesoamerica could be considered as a gene-culture coevolution model. For this purpose, we genotyped 229 individuals affiliated with 19 Native American populations and added data for 41 other Native American groups (n?=?1905) to the analysis. In combination with the SNP cluster of a neutral region, this dataset was then used to unravel the scenario involved in 230Cys evolutionary history. The estimated age of 230Cys is compatible with its origin occurring in the American continent. The correlation of its frequencies with the archeological data on Zea pollen in Mesoamerica/Central America, the neutral coalescent simulations, and the F(ST)-based natural selection analysis suggest that maize domestication was the driving force in the increase in the frequencies of 230Cys in this region. These results may represent the first example of a gene-culture coevolution involving an autochthonous American allele.     

Variation among early North American crania

The limited morphometric work on early American crania to date has treated them as a single, temporally defined group. This paper addresses the question of whether there is significant variability among ancient American crania. A sample of 11 crania (Spirit Cave, Wizards Beach, Browns Valley, Pelican Rapids, Prospect, Wet Gravel male, Wet Gravel female, Medicine Crow, Turin, Lime Creek, and Swanson Lake) dating from the early to mid Holocene was available. Some have recent accelerator mass spectrometry (AMS) dates, while others are dated geologically or archaeologically. All are in excess of 4500 BP, and most are 7000 BP or older. Measurements follow the definitions of Howells [(1973) Cranial variation in man, Cambridge: Harvard University). Some crania are incomplete, but 22 measurements were common to all fossils. Cranial variation was examined by calculating the Mahalanobis distance between each pair of fossils, using a pooled within sample covariance matrix estimated from the data of Howells. The distance relationships among crania suggest the presence of at least three distinct groups: 1) a middle Archaic Plains group (Turin and Medicine Crow), 2) a Paleo/Early Archaic Great Lakes/Plains group (Browns Valley, Pelican Rapids, Lime Creek), and 3) a spatially and temporally heterogeneous group that includes the Great Basin/Pacific Coast (Spirit Cave, Wizards Beach, Prospect) and Nebraska (Wet Gravel specimens and Swanson Lake). These crania were also compared to Howells' worldwide recent sample, which was expanded by including six additional American Indian samples. None of the fossils, except for the Wet Gravel male, shows any particular affinity to recent Native Americans; their greatest similarities are with Europe, Polynesia, or East Asia. Several crania would be atypical in any recent population for which we have data. Browns Valley, Pelican Rapids, and Lime Creek are the most distinctive. They provide evidence for the presence of an early population that bears no similarity to the morphometric pattern of recent American Indians or even to crania of comparable date in other regions of the continent. The heterogeneity among early American crania makes it inadvisable to pool them for purposes of morphometric analysis. Whether this heterogeneity results from different early migrations or one highly differentiated population cannot be established from our data. Our results are inconsistent with hypotheses of an ancestor-descendent relationship between early and late Holocene American populations. They suggest that the pattern of cranial variation is of recent origin, at least in the Plains region.     

New approaches to the study of disease in archeological New World populations.

One of the objectives of paleopathology is to clarify the role of disease in the evolution of human groups. The recovery of DNA and immunoglobulins from archeological human skeletal tissue offers a method for enhancing and expanding our knowledge about the presence and significance of disease in past human populations. DNA also might reveal the presence of genetic disease. Immunoglobulins recovered from archeological bone indicate some of the diseases to which an individual was exposed during life. This information also provides supporting evidence for anatomical observations of skeletal disease. This is illustrated by the identification of treponemal antibody in an archeological skeleton that has gross lesions suggestive of treponematosis. Similar biochemical methods could be applied to other research problems to clarify the presence of various syndromes of the inflammatory erosive arthropathies, such as rheumatoid arthritis, in New World archeological populations. Some of these syndromes are associated with DNA sequences and specific proteins that are recoverable from archeological skeletal tissue.     

Estimates of African, European and Native American ancestry in Afro-Caribbean men on the island of Tobago

BACKGROUND/AIMS: The Tobago Afro-Caribbean population is a valuable resource for studying the genetics of diseases that show significant differences in prevalence between populations of African descent and populations of other ancestries. Empirical confirmation of low European and Native American admixture may help in clarifying the ethnic variation in risk for such diseases. We hypothesize that the degree of European and Native American admixture in the Tobago population is low. METHODS: Admixture was estimated in a random sample of 220 men, from a population-based prostate cancer screening survey of 3,082 Tobago males, aged 40 to 79 years. We used a set of six autosomal markers with large allele frequency differences between the major ethnic populations involved in the admixture process, Europeans, Native Americans and West Africans. RESULTS: The ancestral proportions of Tobago population are estimated as 94.0+/-1.2% African, 4.6+/-3.4% European and 1.4+/-3.6% Native American. CONCLUSIONS: We conclude that Tobago Afro-Caribbean men are predominantly of West African ancestry, with minimal European and Native American admixture. The Tobago population, thus, may carry a higher burden of high-risk alleles of African origin for certain diseases than the more admixed African-American population. Conversely, this population may benefit from a higher prevalence of protective alleles of African origin.     

Mitochondrial DNA studies of Native Americans: Conceptions and misconceptions of the population prehistory of the Americas

A decade ago, the first reviews of the collective mitochondrial DNA (mtDNA) data from Native Americans concluded that the Americas were peopled through multiple migrations from different Asian populations beginning more than 30,000 years ago. 1 These reports confirmed multiple‐wave hypotheses suggested earlier by other sources and rejected the dominant Clovis‐first archeological paradigm. Consequently, it appeared that molecular biology had made a significant contribution to the study of American prehistory. As Cann 2 comments, the Americas held the greatest promise for genetics to help solve some of the mysteries of prehistoric populations. In particular, mtDNA appeared to offer real potential as a means of better understanding ancient population movements. A decade later, none of the early conclusions remain unequivocal. Nevertheless, in its maturity, the study of Native American mtDNA has produced a volume of reports that still illuminate the nature and timing of the first peopling and postcolonization population movements within the New World.     

An assessment of health and disease in the prehistoric inhabitants of the Mariana Islands

Using a variety of skeletal and dental stress indicators, an assessment of the health and disease of the indigenous inhabitants of the Mariana Islands, the Chamorro, is made. The major hypothesis to be tested is that the Chamorro were relatively healthy and that deviations from the expected, as well as inter-island variation, may reflect environmental, ecological, and cultural differences. The major skeletal series surveyed include sites on Guam (N = 247 individuals), Rota (N = 14), Tinian (N = 20), and Saipan (N = 102). The majority of the specimens are from the transitional pre-Latte (AD 1–1000) and Latte (AD 1000–1521) periods. These data derive primarily from unpublished osteological reports. The indicators of health and disease surveyed include mortality and paleodemographic data, stature, dental paleopathology, cribra orbitalia, limb bone fractures, degenerative osteoarthritis, and infectious disease (including treponemal infection). Where appropriate, tests of significance are calculated to determine the presence of any patterning in the differences observed within and between the skeletal series. Information recorded in prehistoric Hawaiians provides a standard for external comparisons. Several of the larger skeletal series surveyed have paleodemographic features that are consistent with long-term cemetery populations. Females and subadults are typically underrepresented. Most subadult deaths occur in the 2–5 year age interval. Life expectancy at birth ranges from 26.4 to 33.7 years. A healthy fertility rate is indicated for these series. The prehistoric inhabitants of the Mariana Islands were relatively tall, exceeding living Chamorros measured in the early part of the present century. The greater prevalence of developmental defects in the enamel suggests that the Chamorro were exposed to more stress than prehistoric Hawaiians. The low frequency of cribra orbitalia further indicates iron deficiency anemia was not a problem. There are generally low frequencies of dental pathology in the remains from the Mariana Islands. Betel-nut staining is relatively common in all series which may help to explain the relatively low prevalence of dental pathology. Healed limb bone fractures are rare in these skeletal series; the frequency and patterns of fractures suggest accidental injury as the main cause. Greater physical demands involving the lower back region are indicated by a high frequency of spondylolysis, or stress fracture in the lumbar vertebrae in the Chamorro. Likewise, advanced degenerative bone changes, while of low occurrence, are significantly greater in the Chamorro than Hawaiians. The prevalence of skeletal and dental indicators of stress was generally higher in the smaller islands of the Marianas chain (e.g., Rota), islands with fewer resources to buffer environmental catastrophe. Bony changes suggestive of treponemal (probably yaws) disease are common in most of these Marianas Islands skeletal series. Am J Phys Anthropol 104:315–342, 1997. © 1997 Wiley-Liss, Inc.     

Differing Evolutionary Histories of the ACTN3*R577X Polymorphism among the Major Human Geographic Groups

It has been proposed that the functional ACTN3*R577X polymorphism might have evolved due to selection in Eurasian human populations. To test this possibility we surveyed all available population-based data for this polymorphism and performed a comprehensive evolutionary analysis of its genetic diversity, in order to assess the action of adaptive and random mechanisms on its variation across human geographical distribution. The derived 577X allele increases in frequency with distance from Africa, reaching the highest frequencies on the American continent. Positive selection, detected by an extended haplotype homozygosisty test, was consistent only with the Eurasian data, but simulations with neutral models could not fully explain the results found in the American continent. It is possible that particularities of Native American population structure could be responsible for the observed allele frequencies, which would have resulted from a complex interaction between selective and random factors.     

Can paleopathology provide evidence for “compassion”?

Paleopathological analyses of skeletal remains have provided significant information about diet and health in prehistoric populations. A number of individuals have been recovered whose remains show evidence of impairments that would have precluded "normal" functioning, resulting in a disability. The most famous example is Shanidar I; more recent discoveries include the Romito 2 dwarf from Italy and a boy with spina bifida from the Windover site in Florida. These finds have been interpreted by some writers as evidence for compassion and "moral decency" among the other members of the community, who would have had to support these nonproductive individuals. However, these interpretations are based on a number of implicit assumptions: about the number of nonproductive members normally present in any population, about the abilities of disabled individuals to contribute to society, about the treatment of disabled individuals by other members of the group, and about the "moral rightness" of facilitating the survival of a disabled individual under all circumstances. These assumptions are not justified by the evidence from the archeological record or by reference to ethnographic analogy. A tendency to focus on physical traits as the sole measure of productive ability, images of Rousseau's "noble savage" transported to the past, and unexamined beliefs about the disabled in modern societies have influenced these archeological interpretations. We are not justified in drawing conclusions either about the quality of life for disabled individuals in the past or about the motives or attitudes of the rest of the community from skeletal evidence of physical impairment.     

Did Native Americans influence the northward migration of plants during the Holocene?

Abstract Long‐distance plant dispersal explains the rapid northward migration of plant species during the Holocene but the mechanisms by which it occurred are poorly understood. Given that Native Americans spread numerous cultigens over thousands of kilometres during the late Holocene, I examined historical literature for evidence of non‐cultigen dispersal or cultivation in North America's eastern woodlands. Cultivation references are included because a strong relationship between dispersal and indigenous flora husbandry is assumed. Sixty‐seven texts describing Native American lifestyle, cultural activities, and land management reported some form of plant use. Most accounts, however, focus on cultigen production or the use of indigenous flora for medicine or food without mention of dispersal. Twenty‐four of the texts described the trade, transport, or cultivation of plants indigenous to eastern North American woodlands. Most accounts focus on the informal production of food plants, especially trees and shrubs. Confounding these reports was clear evidence of observer bias, limited botanical knowledge, acculturation, and secrecy by Native American informants. Because of these shortcomings, the likelihood of widespread long‐distance plant dispersal by Native Americans could not be determined using historical literature. This activity was either not widespread or was not observed by, or revealed to, Europeans. To adequately test the Native American plant dispersal hypothesis, direct evidence from other sources (e.g. archaeobotancial data) will be required.     

Population Genetic Inference from Personal Genome Data: Impact of Ancestry and Admixture on Human Genomic Variation

Full sequencing of individual human genomes has greatly expanded our understanding of human genetic variation and population history. Here, we present a systematic analysis of 50 human genomes from 11 diverse global populations sequenced at high coverage. Our sample includes 12 individuals who have admixed ancestry and who have varying degrees of recent (within the last 500 years) African, Native American, and European ancestry. We found over 21 million single-nucleotide variants that contribute to a 1.75-fold range in nucleotide heterozygosity across diverse human genomes. This heterozygosity ranged from a high of one heterozygous site per kilobase in west African genomes to a low of 0.57 heterozygous sites per kilobase in segments inferred to have diploid Native American ancestry from the genomes of Mexican and Puerto Rican individuals. We show evidence of all three continental ancestries in the genomes of Mexican, Puerto Rican, and African American populations, and the genome-wide statistics are highly consistent across individuals from a population once ancestry proportions have been accounted for. Using a generalized linear model, we identified subtle variations across populations in the proportion of neutral versus deleterious variation and found that genome-wide statistics vary in admixed populations even once ancestry proportions have been factored in. We further infer that multiple periods of gene flow shaped the diversity of admixed populations in the Americas—70% of the European ancestry in today’s African Americans dates back to European gene flow happening only 7–8 generations ago.