Neandertal Introgression Sheds Light on Modern Human Endocranial Globularity

Hybridization in human evolution: Insights from other organisms

During the late Pleistocene, isolated lineages of hominins exchanged genes thus influencing genomic variation in humans in both the past and present. However, the dynamics of this genetic exchange and associated phenotypic consequences through time remain poorly understood. Gene exchange across divergent lineages can result in myriad outcomes arising from these dynamics and the environmental conditions under which it occurs. Here we draw from our collective research across various organisms, illustrating some of the ways in which gene exchange can structure genomic/phenotypic diversity within/among species. We present a range of examples relevant to questions about the evolution of hominins. These examples are not meant to be exhaustive, but rather illustrative of the diverse evolutionary causes/consequences of hybridization, highlighting potential drivers of human evolution in the context of hybridization including: influences on adaptive evolution, climate change, developmental systems, sex-differences in behavior, Haldane's rule and the large X-effect, and transgressive phenotypic variation.

A catalog of single nucleotide changes distinguishing modern humans from archaic hominins

Throughout the past decade, studying ancient genomes has provided unique insights into human prehistory, and differences between modern humans and other branches like Neanderthals can enrich our understanding of the molecular basis of unique modern human traits. Modern human variation and the interactions between different hominin lineages are now well studied, making it reasonable to go beyond fixed genetic changes and explore changes that are observed at high frequency in present-day humans. Here, we identify 571 genes with non-synonymous changes at high frequency. We suggest that molecular mechanisms in cell division and networks affecting cellular features of neurons were prominently modified by these changes. Complex phenotypes in brain growth trajectory and cognitive traits are likely influenced by these networks and other non-coding changes presented here. We propose that at least some of these changes contributed to uniquely human traits, and should be prioritized for experimental validation.

A virtual assessment of the proposed suprainiac fossa on the early modern European calvaria from Cioclovina, Romania

OBJECTIVES

The calvaria from Cioclovina (Romania) has been argued to possess some traits commonly ascribed to individuals belonging to the Neanderthal lineage, including a suprainiac fossa. However, its supranuchal morphology has only been evaluated with a qualitative analysis of the ectocranial surface. We evaluate whether the morphology of the supranuchal area of this specimen is homologous to the Neanderthal condition.

MATERIALS AND METHODS

We described in detail the external morphology, and, using computed tomography, investigated the internal morphology of the Cioclovina supranuchal area. We took measurements of the internal structures and calculated their relative contributions to total cranial vault thickness, which were compared to published data and evaluated with a principal component analysis (PCA).

RESULTS

The Cioclovina supranuchal region is characterized by superficial resorption present on the outer layer of the external table. Neither the diploic layer nor the external table decrease in relative thickness in the area above inion. In the PCA, Cioclovina falls within the convex hulls of recent modern Homo sapiens.

DISCUSSION

Our results show that the morphology of the Cioclovina supranuchal region does not correspond to the external and internal morphology of the typical Neanderthal suprainiac fossa. It cannot be characterized as a depression but rather as an area presenting superficial bone turnover. Together with earlier results, there is little phenotypic evidence that Cioclovina has high levels of Neanderthal ancestry. Our study demonstrates the usefulness of this quantitative method in assessing proposed Neanderthal-like suprainiac depressions in Upper Paleolithic and other fossil specimens.