Sporadic sampling, not climatic forcing, drives observed early hominin diversity

Abstract

SignificancePaleoanthropologists have long been intrigued by the observed patterns of human evolution, including species diversity, and often invoked climatic change as the principal driver of evolutionary change. Here, we investigate whether the early hominin fossil record is of suitable quality to test these climate-forcing hypotheses. Specifically, we compare early hominin diversity to sampling metrics that quantify changes in fossil preservation and sampling intensity between 7 and 1 million years ago. We find that observed diversity patterns are governed by sporadic sampling and do not yield a genuine evolutionary signal. Many more fossil discoveries are required before existing hypotheses linking climate and evolution can be meaningfully tested.

Different environmental variables predict body and brain size evolution in Homo

“…Given the sparse nature of the fossil record and dating uncertainties, it is important to assess the power of our analyses given the limitations of the available datasets (e.g., ref. 26 ). We designed a power analysis to assess the strength of relationships that we could conceivably detect, as well as which variables (and thus hypotheses) we had sufficient information to test.…”

“…However, we need to be careful in interpreting these negative results. The fossil hominin record is scarce and patchy in space and time, confounding the ability to find patterns in our data 26 . We thus modeled and analyzed synthetic datasets to assess the degree to which the intrinsic nature of the fossil record biases and distorts associations of body and brain size with environmental variables.…”

“…24 ) on global averages is particularly problematic, as climate change has different impacts in different geographical areas and across time, even on geological time scales 25 . Consequently, more empirical work on the relation between hominin body/brain size and paleoenvironmental variables 18 , while also considering sampling issues for the fossil record 26 , has been called for.…”

Early Pleistocene faunivorous hominins were not kleptoparasitic, and this impacted the evolution of human anatomy and socio-ecology

“…They also counter-argument that grassland expansion could be responsible of such extinctions. However, it has been shown that it is sampling biases (i.e., number of sites and fossiliferous localities per period and collection intensity) that can account for specific taxic diversity and not climatic forcing, especially for the 1.9 Ma period 86 . No climatic explanation currently can be used to account for mammal evolution without taphonomic calibration 86 .…”

Defining humanity on the basis of its diversity: epistemological questions and philosophical issues

“…D'autres biais relatifs à la paléontologie conduisent à sous-estimer la diversité des hominines : la restriction de l'hypodigme à un petit nombre de spécimens fossiles, qui peuvent être déformés et fragmentés, ne permet pas toujours de se prononcer sur le statut d'espèce de l'échantillon considéré (Smith, 2005). La limitation du nombre de sites connus, ainsi que les aléas liés à l'exposition de la roche et à l'effort de collection (Maxwell, 2018), contribuent également à altérer la perception de la diversité des hominines.…”