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The genetics of African North Americans are complex amalgamations of various West and Central African peoples with modest gene flow from specific European and Amerindian peoples. A comprehensive understanding of African North American biohistory is a prerequisite for accurate interpretations of the ancestral genetics of this population. Too often, genetic interpretations falter with ahistorical reconstructions. The recently reported overrepresentation of Nigerian lineages in African North Americans reflects pronounced limitations in the African genomic database, the artificiality of the colonial maps of Africa, the contributions of multiple African empires and kingdoms into the transatlantic trade in enslaved Africans, and the overrepresentation of Yoruba peoples in the existing limited representation of West Africans in public genomic databases. This Matters Arising paper is in response to Micheletti et al. (2020), published in The American Journal of Human Genetics. See also the response by Micheletti et al. (2020), published in this issue. [ABSTRACT FROM AUTHOR]

Summary In a recent paper in Current Biology , Fennessy and colleagues [1] conclude that there are four species of giraffe and that their numbers are declining in Africa. Giraffes ( Giraffa camelopardalis ) are presently classified as one species, with nine subspecies, which are considered ‘Vulnerable’ on the IUCN Red List [2] . The present consensus of one species divided into nine subspecies has previously been questioned (Supplemental information), and Fennessy and colleagues [1] provide another viewpoint on giraffe taxonomy. The fundamental reason for different taxonomic interpretations is that they are based upon different datasets that adopt different statistical techniques and follow different criteria for nomenclature. [ABSTRACT FROM AUTHOR]

Sex-biased admixture can be inferred from ancestry-specific proportions of X chromosome and autosomes. In a paper published in the American Journal of Human Genetics, Micheletti et al. 1 used this approach to quantify male and female contributions following the transatlantic slave trade. Using a large dataset from 23andMe, they concluded that African and European contributions to gene pools in the Americas were much more sex biased than previously thought. We show that the reported extreme sex-specific contributions can be attributed to unassigned genetic ancestry as well as the limitations of simple models of sex-biased admixture. Unassigned ancestry proportions in the study by Micheletti et al. ranged from ∼1% to 21%, depending on the type of chromosome and geographic region. A sensitivity analysis illustrates how this unassigned ancestry can create false patterns of sex bias and that mathematical models are highly sensitive to slight sampling errors when inferring mean ancestry proportions, making confidence intervals necessary. Thus, unassigned ancestry and the sensitivity of the models effectively prohibit the interpretation of estimated sex biases for many geographic regions in Micheletti et al. Furthermore, Micheletti et al. assumed models of a single admixture event. Using simulations, we find that violations of demographic assumptions, such as subsequent gene flow and/or sex-specific assortative mating, may have confounded the analyses of Micheletti et al., but unassigned ancestry was likely the more important confounding factor. Our findings underscore the importance of using complete ancestry information, sufficiently large sample sizes, and appropriate models when inferring sex-biased patterns of demography. This Matters Arising paper is in response to Micheletti et al., 1 published in American Journal of Human Genetics. See also the response by Micheletti et al., 2 published in this issue., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)