The clade (a.k.a. twig of the Tree of Life) that includes modern humans includes all of the extinct species that are judged, on the basis of their morphology or their genotype, to be more closely related to modern humans than to chimpanzees and bonobos. Taxic diversity with respect to the hominin clade refers to evidence that it included more than one species at any one time period in its evolutionary history. The minimum requirement is that a single ancestor-descendant sequence connects modern humans with the hypothetical common ancestor they share with chimpanzees and bonobos. Does the hominin clade include just modern human ancestors or does it also include non-ancestral species that are closely related to modern humans? It has been suggested there is evidence of taxic diversity within the hominin clade back to 4.5 million years ago, but how sound is that evidence?
The main factor that would work to overestimate taxic diversity is the tendency for paleoanthropologists to recognize too many taxa among the site collections of hominin fossils. Factors that would work to systematically underestimate taxic diversity include the relative rarity of hominins within fossil faunas, the realities that many parts of the world where hominins could have been living are un- or under-sampled, and that during many periods of human evolutionary history, erosion rather than deposition predominated, thus reducing or eliminating the chance that animals alive during those times would be recorded in the fossil record. Finally, some of the most distinctive parts of an animal (e.g., pelage, vocal tract, scent glands) are not likely to be preserved in the hominin fossil record, which is dominated by fragments of teeth and jaws.
Article
K. Ann Horsburgh
Genetic analyses of southern African livestock have been limited and primarily focused on agricultural production rather than the reconstruction of prehistory. Attempts to sequence DNA preserved in archaeological remains of domestic stock have been hampered by the discovery of high error rates in the morphological identification of fauna. As such, much DNA sequencing effort that was directed at sequencing southern Africa’s domestic livestock has been expended sequencing wild forms. The few genetic data that are available from both modern and archaeological domestic stock show relatively low genetic diversity in maternally inherited mitochondrial lineages in both sheep and cattle. Analyses of modern stock show, in contrast, that the bi-parentally inherited nuclear genome is relatively diverse. This pattern is perhaps indicative of historic cross-breeding with stock introduced from outside Africa. Critically important to moving forward in our understanding of the prehistory of domesticates in southern Africa is attention to the high error rates in faunal analyses that have been documented both genetically and through ZooMS.
Article
Peregrine Horden
“An evil destiny of bubo and armpit” (CIG 8628), the plague of Justinian is the name given—unfairly, since the emperor did not cause it, himself contracted it, and was long outlasted by it—to the pandemic of “bubonic plague,” infection by Yersinia pestis, that struck western Eurasia and North Africa towards the middle of the 6th century
Article
Mary E. Prendergast, Elizabeth A. Sawchuk, and Kendra A. Sirak
Africa harbors the greatest human genetic diversity on the planet, a fact that has inspired extensive investigation of the population structure found across the continent and the demographic processes that shaped observed patterns of genetic variation. Since the 1980s, studies of the DNA of living people have repeatedly demonstrated that Africa is the cradle of human origins, in agreement with fossil and archaeological evidence. Since the first ancient human genome was published in 2010, ancient DNA (aDNA) has contributed additional possibilities for exploring population history, providing a direct window into genetic lineages that no longer exist or are barely discernible. Genetic data from both living and ancient people—when integrated with available archaeological, bioarchaeological, historical linguistic, and written or oral historical data—are important tools for contextualizing African genetic diversity and understanding the biological and cultural processes that have shaped it over time. While most studies to date have focused on humans, aDNA can also be obtained from plant and animal remains, sediments, and some artifacts, all of which can enable a more comprehensive understanding of human lives.
Genetic research on the African past often focuses on human origins and Pleistocene population structure, as well as on the origins, directionality, and tempo of demographic changes that accompanied Holocene transitions to herding and farming. The rise of cosmopolitan cities and states in the past two millennia has been examined with genetic evidence to a very limited extent, but this is a potentially rich vein of research. Increasingly, forced migrations of enslaved Africans and the development of the diaspora are the subjects of genetic study as well. Yet to date, Africa remains vastly understudied relative to parts of the world such as Eurasia, in terms of both ancient and present-day DNA. This shapes not only the study of the past but also medical innovations and public health.
While the bulk of published African genomes come from present-day people, there are problems with relying solely on this data to reconstruct the past, given the continent’s long and complex demographic history. Increasingly, aDNA is providing novel perspectives on a past largely invisible in the genomes of people living in the 20th and 21st centuries due to recent demographic shifts. A surge in African aDNA studies since 2015 has also renewed longstanding debates about the ethics of genetic research on people, both living and deceased. Researchers working in Africa today must consider ethical issues including stakeholder engagement, informed consent, and control of biological samples and data; in aDNA studies, descendant communities, museum curators, bioarchaeologists, and geneticists, among others, play critical roles in these discussions.
