Rethinking the ecological drivers of hominin evolution

doi:10.1016/j.tree.2021.04.011

Trends in Ecology & Evolution

Volume 36, Issue 9, September 2021, Pages 797-807

https://doi.org/10.1016/j.tree.2021.04.011 Get rights and content

Highlights

Research aiming to understand the role of ecological change in hominin evolution has fueled the generation of paleoclimatic and paleoenvironmental records across Africa.
Limitations of conventional methods for inferring ecology–evolution relationships mean that more data have not always led to a deeper understanding of hominin evolution.
We outline several challenges that have hindered progress, and highlight how recent research is addressing them.
This research is confronting the limitations of the fossil record, contending with proxy records spanning a range of spatiotemporal scales, and providing a stronger inferential approach to hypothesis testing.
Addressing the obstacles that have hindered progress will enable a more robust understanding of the relationships between ecological change and 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.

Section snippets

Challenges and progress in hominin paleoecology

Hominin paleoecology seeks to understand the relationships between the evolutionary history of fossil hominins and the ecosystems in which they lived. Key questions include: (i) was global-scale climate change a major driving force in hominin diversification? (ii) Did paleoenvironmental dynamics influence hominin morphological and behavioral adaptations? (iii) Were changes in community structure and biotic interactions important in shaping hominin evolution and extinction? Attempts to answer

Confronting an incomplete fossil record

To begin to understand why hominin paleoecology is not providing more informative evolutionary insights, a frank appraisal of the limitations of the hominin fossil record, and their implications for the types of questions we can answer, is warranted. These limitations stem from a hominin fossil record derived from the few places where (i) hominins were present, (ii) their remains were buried in a depositional environment conducive to preservation, (iii) tectonic forces and erosion are currently

Aligning the scales of the questions and the data

A second fundamental challenge involves acknowledging the scales of the research questions and the empirical evidence. The paleoecological data bearing on hominin evolution span a massive range of spatial, temporal, and taxonomic scales (Figure 3). Paying attention to these scales is crucial because ecological patterns and processes vary across them [34,35]. For example, if researchers followed a herd of zebras across a grassy floodplain, they would notice that the herd avoids places frequented

Building stronger inferences

A final challenge in hominin paleoecology relates to how we infer causal relationships between ecological and evolutionary change. Conventional strategies often begin with reconstructing paleoecological change through time at a given location (e.g., site, depositional basin, or region) using one or more forms of proxy evidence. These proxies are derived from the paleontological and geological record, and include fossil faunas and plant microfossils (pollen and phytoliths), as well as the

Concluding remarks

Over the past several decades researchers have focused their efforts on reconstructing late Cenozoic paleoclimatic and paleoenvironmental changes and fleshing out aspects of hominin evolution that demand explanation. This wealth of data, which is the outcome of efforts by numerous international teams, deserves a research agenda that extends beyond the pattern-matching paradigm that has dominated hominin paleoecology. An expanding body of research is adopting strategies to (i) adapt our analyses

Acknowledgments

We acknowledge our late friend and colleague, Andrew Hill, whose thoughts on 'why study paleoecology?' provided the motivation for this work. We are indebted to the many people and institutions across Africa who have contributed to the evidence that is allowing a new phase of research in understanding hominin evolution. Brian Codding, Kate Fish, Nick Hebdon, Kristen Hawkes, Randy Irmis, Kaedan O'Brien, Jim O'Connell, Andrea Stephens, and two anonymous referees provided helpful feedback on

Declaration of interests

The authors have no interests to declare.

Glossary

Biomarkers: molecular fossils (e.g., organic compounds) that are preserved in soils and sedimentary records, and which are indicative of past environments, climates, and fire regimes.
Depositional basin: in geology, a region of the Earth's surface where there is net accumulation of sedimentary deposits over time that may also preserve a fossil record.
Depositional environment: in geology, the physical environment in which sedimentary rocks are formed (e.g., floodplains, rivers, lakes, oceans) that are

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Eastern Africa and Arabia were major hominin hotspots and critical crossroads for migrating towards Asia during the late Pleistocene. To decipher the role of spatiotemporal environmental change on human occupation and migration patterns, we remeasured the marine core from Meteor Site KL 15 in the Gulf of Aden and reanalyzed its data together with the aridity index from ICDP Site Chew Bahir in eastern Africa and the wet-dry index from ODP Site 967 in the eastern Mediterranean Sea using linear and nonlinear time series analysis. These analyses show major changes in the spatiotemporal paleoclimate dynamics at 400 and 150 ka BP (thousand years before 1950), presumably driven by changes in the amplitude of the orbital eccentricity. From 400 to 150 ka BP, eastern Africa and Arabia show synchronized wet-dry shifts, which changed drastically at 150 ka BP. After 150 ka BP, an overall trend to dry climate states is observable, and the hydroclimate dynamics between eastern Africa and Arabia are negatively correlated. Those spatio-temporal variations and interrelationships of climate potentially influenced the availability of spatial links for human expansion along those vertices. We observe positively correlated network links during the supposed out-of-Africa migration phases of H. sapiens. Furthermore, our data do not suggest hominin occupation phases during specific time intervals of humid or stable climates but provide evidence of the so far underestimated potential role of climate predictability as an important factor of hominin ecological competitiveness.
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The Tugen Hills Succession of the Baringo Basin (Kenya) is a nearly continuous geologic succession spanning from the Middle Miocene (∼15.5 Ma) to the Late Pleistocene (∼240 ka) that includes one of the largest concentrations of fossil hominoids from 14 to 4 Ma. Paleoecological data from this succession are highly relevant to determining the nature and mode of environmental change during ape and human evolution, and while much work has characterized these environments in the Plio-Pleistocene, less has been done for those from the Miocene and early Pliocene. This study offers the first mesowear dataset for the Tugen Hills Succession and is one of the largest focused specifically on Miocene/Plio-Pleistocene bovids in eastern Africa. These data reflect the general diversity and increase in mixed-feeding behaviors of post-Miocene bovid diets in the THS, and while they can sometimes be extrapolated to describe an ‘opening’ of environments after the late Miocene, the enigmatic influence of spatial and temporal scale limit assemblage-level claims of paleoenvironment. The diversification of mesowear scores in the Plio-Pleistocene data is generally supported by bovid δ 13C values from the late Cenozoic of eastern and southern Africa and underscores the utility of combining both proxies in the characterization of bovid dietary ecology.
Aridity, availability of drinking water and freshwater foods, and hominin and archeological sites during the Late Pliocene–Early Pleistocene in the western region of the Turkana Basin (Kenya): A review
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Although the Turkana Basin is one of the driest regions of the East African Rift, its Plio–Pleistocene sediments are rich in freshwater vertebrates and invertebrates, providing evidence that freshwater resources were available to hominins in this region during the Plio–Pleistocene (4.2–0.7 Ma). Here we provide an overview of the hydroconnectivity of the Turkana Basin. We then review the period during which freshwater river and lake systems expanded into the western region of the Turkana Basin, where hominin and archeological sites have been discovered in sediments dating back to the Late Pliocene–Pleistocene. Freshwater conditions are reconstructed from river and lake sediments and the flora and micro- and macofauna they contain. Data synthesis suggests that drinking water and freshwater foods prevailed in the western region of the Turkana Basin at 4.20–3.98 Ma, 3.70–3.10 Ma, 2.53–2.22 Ma, then between 2.10 and 1.30 Ma and intermittently from 1.27 to 0.75 Ma. Milestones in hominin evolution occurred in this context, such as the first occurrence of Australopithecus anamensis (4.20–4.10 Ma) and Kenyanthropus platyops (3.50 Ma and 3.30–3.20 Ma), the presence of Paranthropus aethiopicus (2.53–2.45 Ma), early Homo (2.33 Ma), Paranthropus boisei (2.25 Ma and 1.77–1.72 Ma) and Homo ergaster/Homo erectus (1.75 Ma, 1.47–1.42 Ma and 1.10–0.90 Ma). Developments in hominin behavior also occurred during this timeframe, including the first known stone tools (3.30 Ma), the oldest Oldowan sites (2.34 Ma and 2.25 Ma) in the Turkana Basin, the earliest known evidence for the emergence of bifacial shaping in eastern Africa (1.80 Ma), and the first known Acheulean site (1.76 Ma). Our synthesis suggests that, diachronic variation in hydroconnectivity played a role on the amount of drinking water and freshwater foods available in the western region of the Turkana Basin, despite regional aridity.
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Trends in Ecology & Evolution

OpinionRethinking the ecological drivers of hominin evolution

Highlights

Section snippets

Challenges and progress in hominin paleoecology

Confronting an incomplete fossil record

Aligning the scales of the questions and the data

Building stronger inferences

Concluding remarks

Acknowledgments

Declaration of interests

Glossary

Palaeogeogr. Palaeoclimatol. Palaeoecol.

J. Hum. Evol.

J. Hum. Evol.

J. Hum. Evol.

J. Hum. Evol.

J. Hum. Evol.

J. Hum. Evol.

Rev. Paleobotany Palynol.

J. Hum. Evol.

Quat. Sci. Rev.

J. Anthropol. Archaeol.

J. Archaeol. Sci.

Ecol. Model.

J. Theor. Biol.

J. Hum. Evol.

Quat. Sci. Rev.

Physiol. Behav.

Earth Planet. Sci. Lett.

Quat. Sci. Rev.

Environment and climate of early human evolution

Annu. Rev. Earth Planet. Sci.

The hominin sites and paleolakes drilling project: high-resolution paleoclimate records from the East African Rift System and their implications for understanding the environmental context of hominin evolution

Paleoanthropology

Increased ecological resource variability during a critical transition in hominin evolution

Sci Adv.

Early hominins evolved within non-analog ecosystems

Proc. Natl. Acad. Sci. U. S. A.

Aridity and hominin environments

Proc. Natl. Acad. Sci. U. S. A.

The ecological niche and distribution of Neanderthals during the last interglacial

J. Biogeog.

Past extinctions of Homo species coincided with increased vulnerability to climatic change

One Earth

A new research strategy for integrating studies of paleoclimate, paleoenvironment, and paleoanthropology

Evol. Anthropol.

Shifting adaptive landscapes: progress and challenges in reconstructing early hominid environments

Yearb. Phys. Anthropol.

Climate change and human evolution

Science

Why study paleoecology?

Nature

Primate origins: plugging the gaps

Nature

Sporadic sampling, not climatic forcing, drives early hominin diversity

Proc. Natl. Acad. Sci. U.S.A.

Hominin taxic diversity

Ecology of Plio-Pleistocene mammals in the Omo-Turkana Basin and the emergence of Homo

Australopithecus sediba: a new species of Homo-like Australopith from South Africa

Science

Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa

Elife

Evolution of early Homo: an integrated biological perspective

Science

Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia

Science

Fossils from Mille-Logya, Afar, Ethiopia, elucidate the link between Pliocene environmental changes and Homo origins

Nat. Commun.

Estimating times of extinction in the fossil record

Biol. Lett.

Using confidence intervals to quantify the uncertainty in the end-points of stratigraphic ranges

Paleontol. Soc. Pap.

Temporal evidence shows Australopithecus sediba is unlikely to be the ancestor of Homo

Sci. Adv.

Optimal estimators on the position of a mass extinction when recovery potential is uniform

Paleobiology

Confidence intervals on stratigraphic ranges

Paleobiology

Stratigraphic tests of cladistic hypotheses

Opinion
Rethinking the ecological drivers of hominin evolution