Microhabitat Variability in Human Evolution

Abstract

Climate variability and hominin evolution are inextricably linked. Yet, hypotheses examining the impact of large-scale climate shifts on hominin landscape ecology are often constrained by proxy data coming from off-site lake and ocean cores and temporal offsets between paleoenvironmental and archaeological records. Additionally, landscape response data (most commonly, records of vegetation change), are often used as a climate proxy. This is problematic as it assumes that vegetation change signifies global or regional climate shifts without accounting for the known non-linear behavior of ecological systems and the often-significant spatial heterogeneity in habitat structure and response. The exploitation of diverse, rapidly changing habitats by Homo by at least two million years ago highlights that the ability to adapt to landscapes in flux had emerged by the time of our genus’ African origin. To understand ecosystem response to climate variability, and hominin adaptations to environmental complexity and ecological diversity, we need cross-disciplinary datasets in direct association with stratified archaeological and fossil assemblages at a variety of temporal and spatial scales. In this article, we propose a microhabitat variability framework for understanding Homo’s adaptability to fluctuating climates, environments, and resource bases. We argue that the exploitation of microhabitats, or unique ecologically and geographically defined areas within larger habitats and ecoregions, was a key skill that allowed Homo to adapt to multiple climates zones and ecoregions within and beyond Africa throughout the Pleistocene.

Human adaptation to diverse biomes over the past 3 million years

“…Several single-site studies have alluded to the fact that hominins may have favored heterogeneous habitats ( 45 – 47 ), leading to the formulation of the microhabitat variability hypothesis ( 48 ). Combined with our large-scale results, we conclude that Pleistocene hominins selected for increasing regional biome heterogeneity.…”

A spatiotemporally explicit paleoenvironmental framework for the Middle Stone Age of eastern Africa

“…Moreover, Lake Victoria, which is relatively young but estimated to exist by 500–400 kya 45 , is the source of the White Nile, and therefore its refugial position could also have interesting implications for dispersals from the region out of the continent 46 . Together, this highlights the potential role of refugia in structuring MSA cultural and biological diversity 3 , 4 , laying the critical foundations for later human evolution, with microhabitat variability in refugial zones likely being a key component in creating resource-rich landscapes 32 , 47 .…”

“…To classify the biomes occupied by each occupation, we used the modelled biome dataset 32 . To increase the resolution of the data to 2.5’, we resampled the raster layers using the nearest neighbour method, which is most suitable for categorical data.…”

“…However, as also stressed in a recent review by Patalano et al . 32 , lake cores offer very limited insights into spatial patterns of climate change due to the inability to extrapolate across the wider landscape, the difficulty of translating relative wet and dry proxies into tangible climatic or ecological parameters, the non-linear relationship between different proxies and the phenomena they represent and the lack of directly associated, stratigraphically secure archaeological assemblages. Conversely, studies that rely on simplistic arid-humid simulated datasets 9 – 11 or use modern biogeographic zones to represent Pleistocene environments 13 lack chronological precision, and assume uniformity across successive glacial / interglacial cycles.…”

Homo heterogenus: Variability in early Pleistocene Homo environments

“…n. 11–12) are described to be less open than east African habitats, with woody cover up to 70% in the basin localities 36,105 . However, even the classic sites in the eastern African Rift such as Olduvai Gorge, show significant habitat heterogeneity and, at least local importance of habitats with dense woody cover 37,43,45,117 …”