Cochlear shape distinguishes southern African early hominin taxa with unique auditory ecologies

Insights into potential differences among the bony labyrinths of Plio-Pleistocene hominins may inform their evolutionary histories and sensory ecologies. We use four recently-discovered bony labyrinths from the site of Kromdraai to significantly expand the sample for Paranthropus robustus. Diffeomorphometry, which provides detailed information about cochlear shape, reveals size-independent differences in cochlear shape between P. robustus and Australopithecus africanus that exceed those among modern humans and the African apes. The cochlea of P. robustus is distinctive and relatively invariant, whereas cochlear shape in A. africanus is more variable, resembles that of early Homo, and shows a degree of morphological polymorphism comparable to that evinced by modern species. The curvature of the P. robustus cochlea is uniquely derived and is consistent with enhanced sensitivity to low-frequency sounds. Combined with evidence for selection, our findings suggest that sound perception shaped distinct ecological adaptations among southern African early hominins.

Sensational Science, Archaic Hominin Genetics, and Amplified Inductive Risk

More than a decade of exacting scientific research involving paleontological fragments and ancient DNA has lately produced a series of pronouncements about a purportedly novel population of archaic hominins dubbed “the Denisova.” The science involved in these matters is both technically stunning and, socially, at times a bit reckless. Here I discuss the responsibilities which scientists incur when they make inductively risky pronouncements about the different relative contributions by Denisovans to genomes of members of apparent subpopulations of current humans (i.e., the so-called “races”). This science is sensational: it is science which empirically speculates, to the public delight’s and entertainment, about scintillating topics such as when humans evolved, where we came from, and who else we were having sex with during our early hominin history. An initial characterization of sensational science emerges from my discussion of the case, as well as a diagnosis of an interactive phenomenon termed amplified inductive risk.

Naïve, unenculturated chimpanzees fail to make and use flaked stone tools

Background: Despite substantial research on early hominin lithic technologies, the learning mechanisms underlying flake manufacture and use are contested. To draw phylogenetic inferences on the potential cognitive processes underlying the acquisition of both of these abilities in early hominins, we investigated if and how one of our closest living relatives, chimpanzees (Pan troglodytes), could learn to make and use flakes. Methods: Across several experimental conditions, we tested unenculturated, naïve chimpanzees from two independent populations (n=11) for their abilities to spontaneously make and use their own flakes as well as to use pre-made flakes made by a human experimenter. Results: Despite the fact that the chimpanzees demonstrated an understanding of the requirements of the task and that subjects were sufficiently motivated and had ample opportunities to develop these behaviours, none of the chimpanzees tested, made or used flakes in any of the experimental conditions. Conclusions: These results differ from all previous ape flaking experiments, which found flake manufacture and use in bonobos and one orangutan. However, these earlier studies tested human-enculturated apes and provided the test subjects with flake making and using demonstrations. The contrast between these earlier positive findings and our negative findings (despite using a much larger sample size) suggests that human enculturation and/or human demonstrations may be necessary for chimpanzees to acquire these abilities. The data obtained in this study are consistent with the hypothesis that flake manufacture and use might have evolved in the hominin lineage after the split between Homo and Pan 7 million years ago, a scenario further supported by the initial lack of flaked stone tools in the archaeological record after this split. We discuss possible evolutionary scenarios for flake manufacture and use in both non-hominin and hominin lineages.

Preliminary paleohistological observations of the StW 573 (‘Little Foot’) skull

Numerous aspects of early hominin biology remain debated or simply unknown. However, recent developments in high-resolution imaging techniques have opened new avenues in the field of paleoanthropology. More specifically, X-ray synchrotron-based analytical imaging techniques have the potential to provide crucial details on the ontogeny, physiology, biomechanics, and biological identity of fossil specimens. Here we present preliminary results of our X-ray synchrotron-based investigation of the skull of the 3.67-million-year-old Australopithecus specimen StW 573 (‘Little Foot’) at the I12 beamline of the Diamond Light Source (United Kingdom). Besides showing fine details of the enamel (i.e., hypoplasias) and cementum (i.e., incremental lines), as well as of the cranial bone microarchitecture (e.g., diploic channels), our synchrotron-based investigation reveals for the first time the 3D spatial organization of the Haversian systems in the mandibular symphysis of an early hominin.

When Did Archaic Humans Control Fire?

A familiar geochemical technique shines a new spotlight on early hominin use of fire.