Ecosystem engineering in the Quaternary of the West Coast of South Africa

Diversity-dependent speciation and extinction in hominins

The search for drivers of hominin speciation and extinction has tended to focus on the impact of climate change. Far less attention has been paid to the role of interspecific competition. However, research across vertebrates more broadly has shown that both processes are often correlated with species diversity, suggesting an important role for interspecific competition. Here we ask whether hominin speciation and extinction conform to the expected patterns of negative and positive diversity dependence, respectively. We estimate speciation and extinction rates from fossil occurrence data with preservation variability priors in a validated Bayesian framework and test whether these rates are correlated with species diversity. We supplement these analyses with calculations of speciation rate across a phylogeny, again testing whether these are correlated with diversity. Our results are consistent with clade-wide diversity limits that governed speciation in hominins overall but that were not quite reached by the Australopithecus and Paranthropus subclade before its extinction. Extinction was not correlated with species diversity within the Australopithecus and Paranthropus subclade or within hominins overall; this is concordant with climate playing a greater part in hominin extinction than speciation. By contrast, Homo is characterized by positively diversity-dependent speciation and negatively diversity-dependent extinction-both exceedingly rare patterns across all forms of life. The genus Homo expands the set of reported associations between diversity and macroevolution in vertebrates, underscoring that the relationship between diversity and macroevolution is complex. These results indicate an important, previously underappreciated and comparatively unusual role of biotic interactions in Homo macroevolution, and speciation in particular. The unusual and unexpected patterns of diversity dependence in Homo speciation and extinction may be a consequence of repeated Homo range expansions driven by interspecific competition and made possible by recurrent innovations in ecological strategies. Exploring how hominin macroevolution fits into the general vertebrate macroevolutionary landscape has the potential to offer new perspectives on longstanding questions in vertebrate evolution and shed new light on evolutionary processes within our own lineage.

Late Acheulean occupations at Montagu Cave and the pattern of Middle Pleistocene behavioral change in Western Cape, southern Africa

Patterns of so-called modern human behavior are increasingly well documented in an abundance of Middle Stone Age archaeological sites across southern Africa. Contextualized archives directly preceding the southern African Middle Stone Age, however, remain scarce. Current understanding of the terminal Acheulean in southern Africa derives from a small number of localities that are predominantly in the central and northern interior. Many of these localities are surface and deflated contexts, others were excavated prior to the availability of modern field documentation techniques, and yet other relevant assemblages contain low numbers of characteristic artifacts relative to volume of excavated deposit. The site of Montagu Cave, situated in the diverse ecosystem of the Cape Floral Region, South Africa, contains the rare combination of archaeologically rich, laminated and deeply stratified Acheulean layers followed by a younger Middle Stone Age occupation. Yet little is known about the site owing largely to a lack of contextual information associated with the early excavations. Here we present renewed excavation of Levels 21-22 at Montagu Cave, located in the basal Acheulean sequence, including new data on site formation and ecological context, geochronology, and technological variability. We document intensive occupation of the cave by Acheulean tool-producing hominins, likely at the onset of interglacial conditions in MIS 7. New excavations at Montagu Cave suggest that, while Middle Stone Age technologies were practiced by 300 ka in several other regions of Africa, the classic Acheulean persisted later in the Fynbos Biome of the southwestern Cape. We discuss the implications of this regionalized persistence for the biogeography of African later Middle Pleistocene hominin populations, for the ecological drivers of their technological systems, and for the pattern and pace of behavioral change just prior to the proliferation of the southern African later Middle Stone Age.

The revolution that still isn't: The origins of behavioral complexity in Homo sapiens

The behavioral origins of Homo sapiens can be traced back to the first material culture produced by our species in Africa, the Middle Stone Age (MSA). Beyond this broad consensus, the origins, patterns, and causes of behavioral complexity in modern humans remain debated. Here, we consider whether recent findings continue to support popular scenarios of: (1) a modern human 'package,' (2) a gradual and 'pan-African' emergence of behavioral complexity, and (3) a direct connection to changes in the human brain. Our geographically structured review shows that decades of scientific research have continuously failed to find a discrete threshold for a complete 'modernity package' and that the concept is theoretically obsolete. Instead of a continent-wide, gradual accumulation of complex material culture, the record exhibits a predominantly asynchronous presence and duration of many innovations across different regions of Africa. The emerging pattern of behavioral complexity from the MSA conforms to an intricate mosaic characterized by spatially discrete, temporally variable, and historically contingent trajectories. This archaeological record bears no direct relation to a simplistic shift in the human brain but rather reflects similar cognitive capacities that are variably manifested. The interaction of multiple causal factors constitutes the most parsimonious explanation driving the variable expression of complex behaviors, with demographic processes such as population structure, size, and connectivity playing a key role. While much emphasis has been given to innovation and variability in the MSA record, long periods of stasis and a lack of cumulative developments argue further against a strictly gradualistic nature in the record. Instead, we are confronted with humanity's deep, variegated roots in Africa, and a dynamic metapopulation that took many millennia to reach the critical mass capable of producing the ratchet effect commonly used to define contemporary human culture. Finally, we note a weakening link between 'modern' human biology and behavior from around 300 ka ago.

Landscape modification by Last Interglacial Neanderthals

Little is known about the antiquity, nature, and scale of Pleistocene hunter-gatherer impact on their ecosystems, despite the importance for studies of conservation and human evolution. Such impact is likely to be limited, mainly because of low population densities, and challenging to detect and interpret in terms of cause-effect dynamics. We present high-resolution paleoenvironmental and archaeological data from the Last Interglacial locality of Neumark-Nord (Germany). Among the factors that shaped vegetation structure and succession in this lake landscape, we identify a distinct ecological footprint of hominin activities, including fire use. We compare these data with evidence from archaeological and baseline sites from the same region. At Neumark-Nord, notably open vegetation coincides with a virtually continuous c. 2000-year-long hominin presence, and the comparative data strongly suggest that hominins were a contributing factor. With an age of c. 125,000 years, Neumark-Nord provides an early example of a hominin role in vegetation transformation.

Modeling a primate technological niche

The ability to modify the environment through the transport of tools has been instrumental in shaping the evolutionary success of humans. Understanding the cause-and-effect relationships between hominin behavior and the environment ultimately requires understanding of how the archaeological record forms. Observations of living primates can shed light on these interactions by investigating how tool-use behaviors produce a material record within specific environmental contexts. However, this requires reconciling data derived from primate behavioral observations with the time-averaged nature of the Plio-Pleistocene archaeological record. Here, we use an agent-based model to investigate how repeated short-distance transport events, characteristic for primate tool use, can result in significant landscape-scale patterning of material culture over time. Our results illustrate the conditions under which accumulated short-distance transport bouts can displace stone tools over long distances. We show that this widespread redistribution of tools can also increase access to tool require resources over time. As such, these results elucidate the niche construction processes associated with this pattern of tool transport. Finally, the structure of the subsequent material record largely depends on the interaction between tool transport and environmental conditions over time. Though these results have implications for inferring hominin tool transports from hominin archaeological assemblages. Furthermore, they highlight the difficulties with connecting specific behavioral processes with the patterning in the archaeological record.

Rethinking the ecological drivers of hominin evolution

A central goal of paleoanthropology is understanding the role of ecological change in hominin evolution. Over the past several decades researchers have expanded the hominin fossil record and assembled detailed late Cenozoic paleoclimatic, paleoenvironmental, and paleoecological archives. However, effective use of these data is precluded by the limitations of pattern-matching strategies for inferring causal relationships between ecological and evolutionary change. We examine several obstacles that have hindered progress, and highlight recent research that is addressing them by (i) confronting an incomplete fossil record, (ii) contending with datasets spanning varied spatiotemporal scales, and (iii) using theoretical frameworks to build stronger inferences. Expanding on this work promises to transform challenges into opportunities and set the stage for a new phase of paleoanthropological research.

The ripples of modernity: How we can extend paleoanthropology with the extended evolutionary synthesis

Contemporary understandings of paleoanthropological data illustrate that the search for a line defining, or a specific point designating, "modern human" is problematic. Here we lend support to the argument for the need to look for patterns in the paleoanthropological record that indicate how multiple evolutionary processes intersected to form the human niche, a concept critical to assessing the development and processes involved in the emergence of a contemporary human phenotype. We suggest that incorporating key elements of the Extended Evolutionary Synthesis (EES) into our endeavors offers a better and more integrative toolkit for modeling and assessing the evolution of the genus Homo. To illustrate our points, we highlight how aspects of the genetic exchanges, morphology, and material culture of the later Pleistocene complicate the concept of "modern" human behavior and suggest that multiple evolutionary patterns, processes, and pathways intersected to form the human niche.