Past Extinctions of Homo Species Coincided with Increased Vulnerability to Climatic Change

Flame-forged divergence? Ancient human fires and the evolution of diurnal and nocturnal lineages in moorish geckos

Using a multidisciplinary approach, we investigated whether human-controlled fire has historically influenced temporal niche partitioning between dark-diurnal and pale-nocturnal lineages of the Moorish gecko (Tarentola mauritanica). The pale-nocturnal variant exhibited lower skin melanin levels, smaller and fewer melanosomes, and lower plasma α-Melanocyte Stimulating Hormone levels than its dark-diurnal counterpart. Mitochondrial genome analyses indicated that the common ancestor of these gecko lineages diverged approximately 6,600 years ago, coinciding with the transition of modern humans from nomadic hunter-gatherers to settled agricultural societies. Species distribution models suggested coexistence between humans and geckos during the emergence of these lineages. Additionally, we demonstrated that fire attracts phototactic arthropods, concentrating prey resources. These findings imply that human-controlled fire may have created a novel foraging niche for pale-nocturnal geckos, likely driving the divergence of the two variants.

The evolution of human music in light of increased prosocial behavior: a new model

Together with language, music is perhaps our most distinctive behavioral trait. Following the lead of evolutionary linguistic research, different hypotheses have been proposed to explain why only humans perform music and how this ability might have evolved in the species. In this paper, we advance a new model of music evolution that builds on the theory of self-domestication, according to which the human phenotype is, at least in part, the outcome of a process similar to mammal domestication, triggered by a progressive reduction in reactive aggression levels in response to environmental changes. In the paper, we specifically argue that changes in aggression management through the course of human cultural evolution can account for the behaviors conducive to the emergence and evolution of music. We hypothesize 4 stages in the evolutionary development of music under the influence of environmental changes and evolution of social organization: starting from musilanguage, 1) proto-music gave rise to 2) personal and private forms of timbre-oriented music, then to 3) small-group ensembles of pitch-oriented music, at first of indefinite and then definite pitch, and finally to 4) collective (tonal) music. These stages parallel what has been hypothesized for languages and encompass the diversity of music types and genres described worldwide. Overall, music complexity emerges in a gradual fashion under the effects of enhanced abilities for cultural niche construction, resulting from the stable trend of reduction in reactive aggression towards the end of the Pleistocene, leading to the rise of hospitality codes, and succeeded by the increase in proactive aggression from the beginning of the Holocene onward. This paper addresses numerous controversies in the literature on the evolution of music by providing a clear structural definition of music, identifying its structural features that distinguish it from oral language, and summarizing the typology of operational functions of music and formats of its transmission. The proposed framework of structural approach to music arms a researcher with means to identify and comparatively analyze different schemes of tonal organization of music, placing them in the context of human social and cultural evolution. Especially valuable is the theory of so-called "personal song", described and analyzed here from ethological, social, cultural, cognitive, and musicological perspectives. Personal song seems to constitute a remnant of the proto-musical transition from animal communication to human music as we know it today. We interlink the emergence of personal song with the evolution of kinship, placing both of them on the timeline of cultural evolution - based on totality of ethnographic, archaeological, anthropological, genetic, and paleoclimatic data.

The evolving three-dimensional landscape of human adaptation

Over the past 3 million years, humans have expanded their ecological niche and adapted to more diverse environments. The temporal evolution and underlying drivers behind this niche expansion remain largely unknown. By combining archeological findings with landscape topographic data and model simulations of the climate and biomes, we show that human sites clustered in areas with increased terrain roughness, corresponding to higher levels of biodiversity. We find a gradual increase in human habitat preferences toward rough terrains until about 1.1 million years ago (Ma), followed by a 300 thousand-year-long contraction of the ecological niche. This period coincided with the Mid-Pleistocene Transition and previously hypothesized ancestral population bottlenecks. Our statistical analysis further reveals that from 0.8 Ma onward, the human niche expanded again, with human species (e.g., H. heidelbergensis, H. neanderthalensis, and H. sapiens) adapting to rougher terrain, colder and drier conditions, and toward regions of higher ecological diversity.

Estimating ancestral ranges and biogeographical processes in early hominins

Historical biogeography provides crucial insights into understanding the evolutionary history of hominins. We applied maximum-likelihood and biogeographical stochastic mapping to infer the ancestral ranges of hominins and estimate the frequency of biogeographical events. These events were inferred using two time-calibrated phylogenetic trees that differ in the position of Australopithecus sediba. Results suggest that regardless of which phylogeny was selected, Northcentral Africa was the preferred ancestral region for the ancestor of the Homo-Pan clade, as well as the ancestor of Sahelanthropus and later hominins. The northern and middle part of eastern Africa was the preferred ancestral region for several clades originating at subsequent deep nodes of the trees (∼5-4 Ma). The choice of tree topology had one important effect on results: whether hominin ancestors appearing after ∼4 Ma were widespread or endemic. These different patterns highlight the biogeographic significance of the phylogenetic relationships of A. sediba. Overall, the results showed that dispersal, local extinction, and sympatry played vital roles in creating the hominin distribution, whereas vicariance and jump dispersal were not as common. The results suggested symmetry in the directionality of dispersals. Distance probably influenced how rapidly taxa colonized a new region, and dispersals often followed the closest path. These findings are potentially impacted by the imperfection of the fossil record, suggesting that the results should be interpreted cautiously.

The Neanderthal niche space of Western Eurasia 145 ka to 30 ka ago

Neanderthals occupied Western Eurasia between 350 ka and 40 ka ago, during the climatically volatile Pleistocene. A key issue is to what extent Neanderthal populations expanded into areas of Western Eurasia and what conditions facilitated such range expansions. The range extent of Neanderthals is generally based on the distribution of Neanderthal material, but the land-altering nature of glacial periods has erased much of the already sparse material evidence of Neanderthals, particularly in the northern latitudes. To overcome this obstacle species distribution models can estimate past distributions of Neanderthals, however, most implementations are generally constrained spatially and temporally and may be artificially truncating the Neanderthal niche space. Using dated contexts from Neanderthal sites from across Western Eurasia, millennial-scale paleoclimate reconstructions, and a spatiotemporal species distribution model, we infer the fundamental climatic niche space of Neanderthals and estimate the extent of Neanderthal occupation. We find that (a.) despite the long timeframe, Neanderthals occupy a relatively narrow fundamental climatic niche space, (b.) the estimated projected potential Neanderthal niche space suggests a larger geographic range than the material record suggests, and (c.) that there was a general decline in the size of the projected potential Neanderthal niche from 145 ka ago onward, possibly contributing to their extinction.

The Persian plateau served as hub for Homo sapiens after the main out of Africa dispersal

A combination of evidence, based on genetic, fossil and archaeological findings, indicates that Homo sapiens spread out of Africa between ~70-60 thousand years ago (kya). However, it appears that once outside of Africa, human populations did not expand across all of Eurasia until ~45 kya. The geographic whereabouts of these early settlers in the timeframe between ~70-60 to 45 kya has been difficult to reconcile. Here we combine genetic evidence and palaeoecological models to infer the geographic location that acted as the Hub for our species during the early phases of colonisation of Eurasia. Leveraging on available genomic evidence we show that populations from the Persian Plateau carry an ancestry component that closely matches the population that settled the Hub outside Africa. With the paleoclimatic data available to date, we built ecological models showing that the Persian Plateau was suitable for human occupation and that it could sustain a larger population compared to other West Asian regions, strengthening this claim.

Open plains are not a level playing field for hominid consonant-like versus vowel-like calls

Africa's paleo-climate change represents an "ecological black-box" along the evolutionary timeline of spoken language; a vocal hominid went in and, millions of years later, out came a verbal human. It is unknown whether or how a shift from forested, dense habitats towards drier, open ones affected hominid vocal communication, potentially setting stage for speech evolution. To recreate how arboreal proto-vowels and proto-consonants would have interacted with a new ecology at ground level, we assessed how a series of orangutan voiceless consonant-like and voiced vowel-like calls travelled across the savannah. Vowel-like calls performed poorly in comparison to their counterparts. Only consonant-like calls afforded effective perceptibility beyond 100 m distance without requiring repetition, as is characteristic of loud calling behaviour in nonhuman primates, typically composed by vowel-like calls. Results show that proto-consonants in human ancestors may have enhanced reliability of distance vocal communication across a canopy-to-ground ecotone. The ecological settings and soundscapes experienced by human ancestors may have had a more profound impact on the emergence and shape of spoken language than previously recognized.

Different facets of the same niche: Integrating citizen science and scientific survey data to predict biological invasion risk under multiple global change drivers

Citizen science initiatives have been increasingly used by researchers as a source of occurrence data to model the distribution of alien species. Since citizen science presence-only data suffer from some fundamental issues, efforts have been made to combine these data with those provided by scientifically structured surveys. Surprisingly, only a few studies proposing data integration evaluated the contribution of this process to the effective sampling of species' environmental niches and, consequently, its effect on model predictions on new time intervals. We relied on niche overlap analyses, machine learning classification algorithms and ecological niche models to compare the ability of data from citizen science and scientific surveys, along with their integration, in capturing the realized niche of 13 invasive alien species in Italy. Moreover, we assessed differences in current and future invasion risk predicted by each data set under multiple global change scenarios. We showed that data from citizen science and scientific surveys captured similar species niches though highlighting exclusive portions associated with clearly identifiable environmental conditions. In terrestrial species, citizen science data granted the highest gain in environmental space to the pooled niches, determining an increased future biological invasion risk. A few aquatic species modelled at the regional scale reported a net loss in the pooled niches compared to their scientific survey niches, suggesting that citizen science data may also lead to contraction in pooled niches. For these species, models predicted a lower future biological invasion risk. These findings indicate that citizen science data may represent a valuable contribution to predicting future spread of invasive alien species, especially within national-scale programmes. At the same time, citizen science data collected on species poorly known to citizen scientists, or in strictly local contexts, may strongly affect the niche quantification of these taxa and the prediction of their future biological invasion risk.

Climate shifts orchestrated hominin interbreeding events across Eurasia

When, where, and how often hominin interbreeding happened is largely unknown. We study the potential for Neanderthal-Denisovan admixture using species distribution models that integrate extensive fossil, archaeological, and genetic data with transient coupled general circulation model simulations of global climate and biomes. Our Pleistocene hindcast of past hominins' habitat suitability reveals pronounced climate-driven zonal shifts in the main overlap region of Denisovans and Neanderthals in central Eurasia. These shifts, which influenced the timing and intensity of potential interbreeding events, can be attributed to the response of climate and vegetation to past variations in atmospheric carbon dioxide and Northern Hemisphere ice-sheet volume. Therefore, glacial-interglacial climate swings likely played an important role in favoring gene flow between archaic humans.

The earliest Ethiopian wolf: implications for the species evolution and its future survival

In 2017, a hemimandible (MW5-B208), corresponding to the Ethiopian wolf (Canis simensis), was found in a stratigraphically-controlled and radio-isotopically-dated sequence of the Melka Wakena paleoanthropological site-complex, on the Southeastern Ethiopian Highlands, ~ 2300 m above sea level. The specimen is the first and unique Pleistocene fossil of this species. Our data provide an unambiguous minimum age of 1.6-1.4 Ma for the species' presence in Africa and constitutes the first empirical evidence that supports molecular interpretations. Currently, C. simensis is one of the most endangered carnivore species of Africa. Bioclimate niche modeling applied to the time frame indicated by the fossil suggests that the lineage of the Ethiopian wolf faced severe survival challenges in the past, with consecutive drastic geographic range contractions during warmer periods. These models help to describe future scenarios for the survival of the species. Projections ranging from most pessimistic to most optimistic future climatic scenarios indicate significant reduction of the already-deteriorating territories suitable for the Ethiopian Wolf, increasing the threat to the specie's future survival. Additionally, the recovery of the Melka Wakena fossil underscores the importance of work outside the East African Rift System in research of early human origins and associated biodiversity on the African continent.

Human adaptation to diverse biomes over the past 3 million years

To investigate the role of vegetation and ecosystem diversity on hominin adaptation and migration, we identify past human habitat preferences over time using a transient 3-million-year earth system-biome model simulation and an extensive hominin fossil and archaeological database. Our analysis shows that early African hominins predominantly lived in open environments such as grassland and dry shrubland. Migrating into Eurasia, hominins adapted to a broader range of biomes over time. By linking the location and age of hominin sites with corresponding simulated regional biomes, we also find that our ancestors actively selected for spatially diverse environments. The quantitative results lead to a new diversity hypothesis: Homo species, in particular Homo sapiens, were specially equipped to adapt to landscape mosaics.

Virtual excavation and analysis of the early Neanderthal cranium from Altamura (Italy)

Complete Neanderthal skeletons are almost unique findings. A very well-preserved specimen of this kind was discovered in 1993 in the deepest recesses of a karstic system near the town of Altamura in Southern Italy. We present here a detailed description of the cranium, after we virtually extracted it from the surrounding stalagmites and stalactites. The morphology of the Altamura cranium fits within the Neanderthal variability, though it retains features occurring in more archaic European samples. Some of these features were never observed in Homo neanderthalensis, i.e. in fossil specimens dated between 300 and 40 ka. Considering the U-Th age we previously obtained (>130 ka), the morphology of Altamura suggests that the archaic traits it retains may have been originated by geographic isolation of the early Neanderthal populations from Southern Italy.

Ruminant inner ear shape records 35 million years of neutral evolution

Extrinsic and intrinsic factors impact diversity. On deep-time scales, the extrinsic impact of climate and geology are crucial, but poorly understood. Here, we use the inner ear morphology of ruminant artiodactyls to test for a deep-time correlation between a low adaptive anatomical structure and both extrinsic and intrinsic variables. We apply geometric morphometric analyses in a phylogenetic frame to X-ray computed tomographic data from 191 ruminant species. Contrasting results across ruminant clades show that neutral evolutionary processes over time may strongly influence the evolution of inner ear morphology. Extant, ecologically diversified clades increase their evolutionary rate with decreasing Cenozoic global temperatures. Evolutionary rate peaks with the colonization of new continents. Simultaneously, ecologically restricted clades show declining or unchanged rates. These results suggest that both climate and paleogeography produced heterogeneous environments, which likely facilitated Cervidae and Bovidae diversification and exemplifies the effect of extrinsic and intrinsic factors on evolution in ruminants.

Javanese Homo erectus on the move in SE Asia circa 1.8 Ma

The migration of Homo erectus in Southeast Asia during Early Pleistocene is cardinal to our comprehension of the evolution of the genus Homo. However, the limited consideration of the rapidly changing physical environment, together with controversial datings of hominin bearing sites, make it challenging to secure the robust timeline needed to unveil the behavior of early humans. Here, we reappraise the first appearance datum of Javanese H. erectus by adding the most reliable age constraints based on cosmogenic nuclides [Formula: see text]Be and [Formula: see text]Al produced in situ to a compilation of earlier estimates. We find that H. erectus reached Java and dwelled at Sangiran, Java, ca. 1.8 Ma. Using this age as a baseline, we develop a probabilistic approach to reconstruct their dispersal routes, coupling ecological movement simulations to landscape evolution models forced by reconstructed geodynamic and climatic histories. We demonstrate that the hospitable terra firma conditions of Sundaland facilitated the prior dispersal of hominins to the edge of Java, where they conversely could not settle until the Javanese archipelago emerged from the sea and connected to Sundaland. The dispersal of H. erectus across Sundaland occurred over at least tens to hundreds kyr, a time scale over which changes in their physical environment, whether climatic or physiographic, may have become primary forcings on their behavior. Our comprehensive reconstruction method to unravel the peopling timeline of SE Asia provides a novel framework to evaluate the evolution of early humans.

Ecosystem productivity affected the spatiotemporal disappearance of Neanderthals in Iberia

What role did fluctuations play in biomass availability for secondary consumers in the disappearance of Neanderthals and the survival of modern humans? To answer this, we quantify the effects of stadial and interstadial conditions on ecosystem productivity and human spatiotemporal distribution patterns during the Middle to Upper Palaeolithic transition (50,000-30,000 calibrated years before the present) in Iberia. First, we used summed probability distribution, optimal linear estimation and Bayesian age modelling to reconstruct an updated timescale for the transition. Next, we executed a generalized dynamic vegetation model to estimate the net primary productivity. Finally, we developed a macroecological model validated with present-day observations to calculate herbivore abundance. The results indicate that, in the Eurosiberian region, the disappearance of Neanderthal groups was contemporaneous with a significant decrease in the available biomass for secondary consumers, and the arrival of the first Homo sapiens populations coincided with an increase in herbivore carrying capacity. During stadials, the Mediterranean region had the most stable conditions and the highest biomass of medium and medium-large herbivores. These outcomes support an ecological cause for the hiatus between the Mousterian and Aurignacian technocomplexes in Northern Iberia and the longer persistence of Neanderthals in southern latitudes.

Climate effects on archaic human habitats and species successions

It has long been believed that climate shifts during the last 2 million years had a pivotal role in the evolution of our genus Homo^1–3. However, given the limited number of representative palaeo-climate datasets from regions of anthropological interest, it has remained challenging to quantify this linkage. Here, we use an unprecedented transient Pleistocene coupled general circulation model simulation in combination with an extensive compilation of fossil and archaeological records to study the spatiotemporal habitat suitability for five hominin species over the past 2 million years. We show that astronomically forced changes in temperature, rainfall and terrestrial net primary production had a major impact on the observed distributions of these species. During the Early Pleistocene, hominins settled primarily in environments with weak orbital-scale climate variability. This behaviour changed substantially after the mid-Pleistocene transition, when archaic humans became global wanderers who adapted to a wide range of spatial climatic gradients. Analysis of the simulated hominin habitat overlap from approximately 300–400 thousand years ago further suggests that antiphased climate disruptions in southern Africa and Eurasia contributed to the evolutionary transformation of Homo heidelbergensis populations into Homo sapiens and Neanderthals, respectively. Our robust numerical simulations of climate-induced habitat changes provide a framework to test hypotheses on our human origin.

A new model simulation of climate change during the past 2 million years indicates that the appearances and disappearances of hominin species correlate with long-term climatic anomalies.

Estimating origination times from the early hominin fossil record

The age of the earliest recovered fossil evidence of a hominin taxon is all too often equated with that taxon's origination. However, the earliest known fossil record nearly always postdates, sometimes by a substantial period of time, the true origination of a taxon. Here we evaluate the first appearance records of the earliest potential hominins (Sahelanthropus, Ardipithecus, Orrorin), as well as of the genera Australopithecus, Homo, and Paranthropus, to illustrate the considerable uncertainty regarding the actual timing of origin of these taxa. By placing confidence intervals on the first appearance records of early hominin taxa, we can better evaluate patterns of hominin diversity, turnover, and potential correlations with climatic and environmental changes.

Rethinking the ecological drivers of 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.

How can evolutionary and biological anthropologists engage broader audiences?

OBJECTIVES

With our diverse training, theoretical and empirical toolkits, and rich data, evolutionary and biological anthropologists (EBAs) have much to contribute to research and policy decisions about climate change and other pressing social issues. However, we remain largely absent from these critical, ongoing efforts. Here, we draw on the literature and our own experiences to make recommendations for how EBAs can engage broader audiences, including the communities with whom we collaborate, a more diverse population of students, researchers in other disciplines and the development sector, policymakers, and the general public. These recommendations include: (1) playing to our strength in longitudinal, place-based research, (2) collaborating more broadly, (3) engaging in greater public communication of science, (4) aligning our work with open-science practices to the extent possible, and (5) increasing diversity of our field and teams through intentional action, outreach, training, and mentorship.

CONCLUSIONS

We EBAs need to put ourselves out there: research and engagement are complementary, not opposed to each other. With the resources and workable examples we provide here, we hope to spur more EBAs to action.

A Major Change in Rate of Climate Niche Envelope Evolution during Hominid History

Homo sapiens is the only species alive able to take advantage of its cognitive abilities to inhabit almost all environments on Earth. Humans are able to culturally construct, rather than biologically inherit, their occupied climatic niche to a degree unparalleled within the animal kingdom. Precisely, when hominins acquired such an ability remains unknown, and scholars disagree on the extent to which our ancestors shared this same ability. Here, we settle this issue using fine-grained paleoclimatic data, extensive archaeological data, and phylogenetic comparative methods. Our results indicate that whereas early hominins were forced to live under physiologically suitable climatic conditions, with the emergence of H. heidelbergensis, the Homo climatic niche expanded beyond its natural limits, despite progressive harshening in global climates. This indicates that technological innovations providing effective exploitation of cold and seasonal habitats predated the emergence of Homo sapiens.

•

Homo sapiens oversteps our ecological niche limits by means of culture

•

The origin of Homo niche-construction ability is unknown

•

We found Homo species other than H. sapiens were able to construct their own niche