Tropical forests and the genus Homo

Pliocene climatic change and the origins of Homo at Ledi-Geraru, Ethiopia

BACKGROUND

Long-term cooling and aridification are associated with the spread of grassland habitats and the appearance of new hominin adaptations starting in the late Miocene. However, limited fossil data during critical periods limits our ability to examine these climatic correlations further.

AIM

We set out to reconstruct potential habitat and climate conditions at the origin of our genus Homo.

SUBJECTS AND METHODS

Mammalian faunal lists and species trait data were collected for Ledi-Geraru localities dated from ∼2.78 to <2.59 million years ago (Ma). These were compared to a modern comparative dataset of mammal communities across Africa with known habitat and climate conditions, as well as to other fossil mammal data from eastern Africa in the time period leading up to and following shortly after the earliest known appearance of Homo at ∼2.78 Ma.

RESULTS

Early Homo is associated with ongoing aridification and increasing seasonality in the Afar Depression. While climate trends in eastern Africa parallel global models, local environmental variation persisted across fossil-bearing regions.

CONCLUSION

Climatic change (aridification and increasing seasonality) continues to be supported as a possible factor in the origins of our genus, although other fossil hominins continued to persist in these conditions.

Long legs and small joints: The locomotor capabilities of Homo naledi

The lower limb of Homo naledi presents a suite of primitive, derived and unique morphological features that pose interesting questions about the nature of bipedal movement in this species. The exceptional representation of all skeletal elements in H. naledi makes it an excellent candidate for biomechanical analysis of gait dynamics using modern kinematic software. However, virtual gait analysis software requires 3D models of the entire lower limb kinematic chain. No single H. naledi individual preserves all lower limb elements, and what material is preserved is fragmentary. As an antecedent to future kinematic analysis, a 3D lower limb skeleton was reconstructed from the most complete fossil bones of different H. naledi individuals. As both juvenile and adult H. naledi were used, we tested if the knee joint remained congruent throughout ontogeny in a sample of great apes (N = 143) and modern humans (N = 70). The reconstruction and subsequent comparative analysis reveal that H. naledi had remarkably small joint sizes for their body size, a hyper-elongated tibia, and a high crural index (90.2). We consider that the lower limb morphology of H. naledi could have improved locomotor economy, but the exceptionally small joints cast doubt on its capabilities for long distance travel, including endurance running. The unusual mixture of primitive and derived traits in H. naledi remains intriguing and might indicate that this hominin engaged both in bipedal walking and climbing, demonstrating that kinematic diversity in hominins persisted well into the Middle Pleistocene.

Extensive locomotor versatility across a global sample of hunter-gatherer societies

Studies of hunter-gatherer locomotion inform a wide range of academic fields, from human behavioural ecology and hominin evolution to sports science and evolutionary health. Despite celebrated ethnographic examples of hunter-gatherer locomotor proficiency in running, climbing, swimming and diving, there has been limited systematic analysis of cross-cultural variation in hunter-gatherer locomotor versatility. We conducted a systematic cross-cultural analysis of hunter-gatherer locomotion, coding locomotor behaviour from over 900 ethnographic documents. Our results indicated that high levels of locomotor versatility are common among hunter-gatherers, and that proficiency of running, climbing, swimming and diving is found in societies across the geographical and ecological breadth of the sample. Each locomotor modality was found to be relevant not only to food acquisition but also in leisure, ritual and violent conflict. Our results also indicated the prevalence of both male and female engagement within each locomotor modality, with climbing being the only modality to possess a notable bias towards male engagement in a substantial proportion of societies. The widespread habituality and functional significance of diverse locomotor proficiency in hunter-gatherers suggests that locomotor versatility represents a dimension of human adaptive lability, playing a major role in the ability of hunter-gatherers to thrive in almost every global ecology.

Chloroplast capture and range extension after hybridization in taro (Colocasia esculenta)

Complete chloroplast genomes of 17 samples from six species of Colocasia (Araceae) were sequenced, assembled, and aligned together with two previously reported complete genome sequences from taro (Colocasia esculenta). Analysis provides a well-supported phylogenetic tree for taro and closely-related wild Colocasia species in Southeast Asia. Two chloroplast lineages (CI and CII) form a well-defined haplotype group and are found in cultivated taros known as var. esculenta (dasheen, CI), var. antiquorum (eddoe, CII), and in a widespread, commensal wild form known as var. aquatilis (CI). A third lineage (CIII) is also found in wild taros known as var. aquatilis and in the wild species C. lihengiae, C. formosana, and C. spongifolia. We suggest three different scenarios to explain the grouping of CIII wild taros (C. esculenta) with other wild Colocasia species. Chloroplast lineages CI and CIII in C. esculenta and an unknown parent species may be involved in an as yet undated history of hybridization, chloroplast capture, and range extension. Substantial taxonomic revision may be needed for C. esculenta after further studies of morphological and genetic diversity within the crop, in wild populations, and in closely related wild species. The results also point to the Bengal delta as a region of key interest for future research on the origins of tropical wetland taros.

Palaeoenvironments and hominin evolutionary dynamics in southeast Asia

Secure environmental contexts are crucial for hominin interpretation and comparison. The discovery of a Denisovan individual and associated fauna at Tam Ngu Hao 2 (Cobra) Cave, Laos, dating back to 164-131 ka, allows for environmental comparisons between this (sub)tropical site and the Palearctic Denisovan sites of Denisova Cave (Russia) and Baishiya Karst Cave (China). Denisovans from northern latitudes foraged in a mix of forested and open landscapes, including tundra and steppe. Using stable isotope values from the Cobra Cave assemblage, we demonstrate that, despite the presence of nearby canopy forests, the Denisovan individual from Cobra Cave primarily consumed plants and/or animals from open forests and savannah. Using faunal evidence and proxy indicators of climates, results herein highlight a local expansion of rainforest at ~ 130 ka, raising questions about how Denisovans responded to this local climate change. Comparing the diet and habitat of the archaic hominin from Cobra Cave with those of early Homo sapiens from Tam Pà Ling Cave (46-43 ka), Laos, it appears that only our species was able to exploit rainforest resources.

Geochemical fingerprinting of Pleistocene stone tools from the Tràng An Landscape Complex, Ninh Bình Province, Vietnam

Raw material analyses of prehistoric stone tool assemblages can reveal insight into mobility and exchange patterns in hunter-gatherer populations by reconstructing the circulation of stone throughout ancient landscapes. In Pleistocene Southeast Asia, stone tools are generally thought to have been fashioned from easily accessible local raw materials. However, despite the consistent presence of stone tools made of igneous raw material at prehistoric sites throughout the Tràng An Landscape Complex in northern Vietnam, there are no sources of igneous raw material in the immediate vicinity. This paper presents the results of geochemical sourcing analysis of late Pleistocene igneous stone tools from Tràng An: the first analysis of its type in mainland Southeast Asia. The results shed light on mobility and raw material provisioning strategies in Pleistocene mainland Southeast Asian hunter-gatherer populations and raise questions surrounding the relationship between technological organization, raw material, and expediency in Southeast Asian stone tool assemblages.

Riddles wrapped inside an enigma. Lupemban MSA technology as a rainforest adaptation: revisiting the lanceolate point

The Central African Stone Age is very poorly known when compared to the higher-resolution records of East and Southern Africa. Early Stone Age (ESA) archaeology is effectively absent from the rainforest zone, with the early Middle Stone Age (MSA) Lupemban industry representing the earliest sustained archaeological signature. Uranium-series dates of approximately 265 ka BP for the Lupemban at Twin Rivers (Zambia), although queried, suggest a precocious late Middle Pleistocene dispersal of early Homo sapiens into the equatorial rainforest belt. Lupemban palaeohabitat interactions and attendant behavioural and technological repertoires are key to its evolutionary significance, but investigation is hampered by the widespread vertical disturbance of stratigraphic profiles and the formation of 'stone-lines'. The Lupemban takes in a range of implement types and technologies, including core-axes, prepared core technology (PCT) points, blades and backed blades. But it is the elongated bifacial lanceolate point-some exquisitely made and many exceeding 30 cm in length-that defines the industry. Remarkably, unequivocal examples of these iconic artefacts have never been the focus of detailed techno-typological scrutiny. In this paper, I advance understanding of the Lupemban by initiating a re-consideration of lanceolate points at Kalambo Falls, Zambia, and discuss their implications for the Lupemban's evolutionary significance. This article is part of the theme issue 'Tropical forests in the deep human past'.

Female excellence in rock climbing likely has an evolutionary origin

The human body is exceptional for many reasons, not the least of which is the wide variety of movements it is capable of executing. Because our species is able to execute so many discrete activities, researchers often disagree on which were the movements most essential to the evolution of our species. This paper continues a recently introduced analysis, that the performance gap between female and male athletes narrows in sports which most reflect the movements humans evolved to do. Here, I examine the performance gap in rock climbing. Female climbers are some of the best in the world irrespective of gender, a trend that is not found in any other major sport. I conclude that the exceptional ability of female rock climbers relative to male rock climbers is further evidence of the existence of sex-blind musculoskeletal adaptations, which developed over the course of human evolution – as a result of external (non-sexual) selection forces – to facilitate essential movements. These adaptations abate some of the general physical sexual dimorphism which exists in humans. This paper provides more evidence that the human body was shaped, in part, by pressure to climb well.

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Rock climbing is the sport most similar to tree climbing, a movement essential to human development.

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Multiple women can be found in the list of top 100 rock climbers, a trend not found in any other major sport.

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Sports with a higher degree of gender equity, may reflect movements with a greater degree of evolutionary importance.

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Rock climbing’s gender gap provides further evidence that early humans faced external selection pressure to climb well.

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Thus, the importance of climbing to the survival of humans - even after the onset of genus Homo - may be understated.

A multi-proxy approach to exploring Homo sapiens' arrival, environments and adaptations in Southeast Asia

The capability of Pleistocene hominins to successfully adapt to different types of tropical forested environments has long been debated. In order to investigate environmental changes in Southeast Asia during a critical period for the turnover of hominin species, we analysed palaeoenvironmental proxies from five late Middle to Late Pleistocene faunas. Human teeth discoveries have been reported at Duoi U'Oi, Vietnam (70-60 ka) and Nam Lot, Laos (86-72 ka). However, the use of palaeoproteomics allowed us to discard the latter, and, to date, no human remains older than ~ 70 ka are documented in the area. Our findings indicate that tropical rainforests were highly sensitive to climatic changes over that period, with significant fluctuations of the canopy forests. Locally, large-bodied faunas were resilient to these fluctuations until the cooling period of the Marine Isotope Stage 4 (MIS 4; 74-59 ka) that transformed the overall biotope. Then, under strong selective pressures, populations with new phenotypic characteristics emerged while some other species disappeared. We argue that this climate-driven shift offered new foraging opportunities for hominins in a novel rainforest environment and was most likely a key factor in the settlement and dispersal of our species during MIS 4 in SE Asia.

Memory for medicinal plants remains in ancient and modern environments suggesting an evolved adaptedness

Adaptive memory is the propensity of human memory to easily store and retrieve important information to deal with challenges related to the Pleistocene. Recent evidence shows that humans have had a multiregional evolution across the African continent, including the rainforests and deciduous forests; however, there is little evidence regarding the implications of these origins and the relevant and recurring challenges of these environments on survival processing advantage in memory. In this study, we conducted an experiment with volunteers to analyze whether adaptive memory operates in the retrieval of important information to solve challenges of using medicinal plants to treat diseases in the ancestral environments of the savanna, rainforests, and deciduous forests compared to the modern environments of desert, tundra, coniferous forest, and urban areas. We used simulated survival environments and asked volunteers (30 per simulated scenario) to imagine themselves sick in one of these environments, and needing to find medicinal plants to treat their disease. The volunteers rated the relevance of 32 words to solve this challenge, followed by a surprise memory test. Our results showed no ancestral priority in recalling relevant information, as both ancestral and modern environments showed a similar recall of relevant information. This suggests that the evolved cognitive apparatus allows human beings to survive and can create survival strategies to face challenges imposed in various environments. We believe that this is only possible if the human mind operates through a flexible cognitive mechanism. This flexibility can reflect, for example, the different environments that the first hominids inhabited and the different dangerous situations that they faced.

‘Moving South’: Late Pleistocene Plant Exploitation and the Importance of Palm in the Colombian Amazon

The role of plants in early human migrations across the globe has received little attention compared to big game hunting. Tropical forests in particular have been seen as a barrier for Late Pleistocene human dispersals due to perceived difficulties in obtaining sufficient subsistence resources. Archaeobotanical data from the Cerro Azul rock outcrop in the Colombian Amazon details Late Pleistocene plant exploitation providing insight into early human subsistence in the tropical forest. The dominance of palm taxa in the assemblage, dating from 12.5 ka BP, allows us to speculate on processes of ecological knowledge transfer and the identification of edible resources in a novel environment. Following the hypothesis of Martin Jones from his 2009 work, “Moving North: archaeobotanical evidence for plant diet in Middle and Upper Paleolithic Europe”, we contend that the instantly recognizable and economically useful palm family (Arecaceae) provided a “gateway” to the unknown resources of the Amazon forest.

Plant wax biomarkers in human evolutionary studies

Plant wax biomarkers are an innovative proxy for reconstructing vegetation composition and structure, rainfall intensity, temperature, and other climatic and environmental dynamics. Traditionally used in earth sciences and climate studies from "off-site" ocean and lake records, biomarker research is now incorporated in archeology and paleoanthropology to answer questions relating to past human-environment interactions and human evolution. Biomarker research is generating new and exciting information on the ecological context in which Homo and its closest relatives evolved, adapted, and invented stone tool technologies. In this review, we examine plant wax biomarkers and their use in reconstructing past plant landscapes and hydroclimates. We summarize the applications of plant wax molecular proxies in archeological research, assess challenges relating to taphonomy, consider the role of modern plant ecosystems in interpreting ancient habitats, and examine case studies conducted at key paleoanthropological locations in eastern and southern Africa and Europe.

Human Evolution and Dietary Ethanol

The "drunken monkey" hypothesis posits that attraction to ethanol derives from an evolutionary linkage among the sugars of ripe fruit, associated alcoholic fermentation by yeast, and ensuing consumption by human ancestors. First proposed in 2000, this concept has received increasing attention from the fields of animal sensory biology, primate foraging behavior, and molecular evolution. We undertook a review of English language citations subsequent to publication of the original paper and assessed research trends and future directions relative to natural dietary ethanol exposure in primates and other animals. Two major empirical themes emerge: attraction to and consumption of fermenting fruits (and nectar) by numerous vertebrates and invertebrates (e.g., Drosophila flies), and genomic evidence for natural selection consistent with sustained exposure to dietary ethanol in diverse taxa (including hominids and the genus Homo) over tens of millions of years. We also describe our current field studies in Uganda of ethanol content within fruits consumed by free-ranging chimpanzees, which suggest chronic low-level exposure to this psychoactive molecule in our closest living relatives.

The Performance Gap in Sport Can Help Determine Which Movements Were Most Essential to Human Evolution

Men outperform women in sports that require muscular strength and endurance, but the magnitude of this performance gap (PG) does not appear to be constant; that is, the PG between men and women is greater in some sports than it is in others. Here, we examine the size of this gap within the realm of track and field by comparing the top 50 world-record performances of men to the top 50 records set by women in a number of long-distance running, medium-distance running, short-distance running, and jumping events. While women do not perform at the level of men in any track and field event, the magnitude of the PG trends up or down depending on the type of event. Jumping events exhibit a larger gap between the sexes than do running events, and short-distance running events show a smaller disparity between the sexes than do medium- or long-distance running events. This difference suggests that general sexual dimorphism does not explain why female performance is relatively closer to male performance at some track and field events than others. We hypothesize that this trend can be explained by the presence of sex-blind musculoskeletal adaptations (SBMA's), which accumulate over generations to reduce the size of the PG in certain movements. We conclude that the selection trend favoring in humans should be explored further to determine whether the PG in sport can indeed be used to determine movements to which the human body is adapted.

Heading north: Late Pleistocene environments and human dispersals in central and eastern Asia

The adaptability of our species, as revealed by the geographic routes and palaeoenvironmental contexts of human dispersal beyond Africa, is a prominent topic in archaeology and palaeoanthropology. Northern and Central Asia have largely been neglected as it has been assumed that the deserts and mountain ranges of these regions acted as 'barriers', forcing human populations to arc north into temperate and arctic Siberia. Here, we test this proposition by constructing Least Cost Path models of human dispersal under glacial and interstadial conditions between prominent archaeological sites in Central and East Asia. Incorporating information from palaeoclimatic, palaeolake, and archaeological data, we demonstrate that regions such as the Gobi Desert and the Altai Mountain chains could have periodically acted as corridors and routes for human dispersals and framing biological interactions between hominin populations. Review of the archaeological datasets in these regions indicates the necessity of wide-scale archaeological survey and excavations in many poorly documented parts of Eurasia. We argue that such work is likely to highlight the 'northern routes' of human dispersal as variable, yet crucial, foci for understanding the extreme adaptive plasticity characteristic of the emergence of Homo sapiens as a global species, as well as the cultural and biological hybridization of the diverse hominin species present in Asia during the Late Pleistocene.

Persistent Early to Middle Holocene tropical foraging in southwestern Amazonia

The Amazon witnessed the emergence of complex societies after 2500 years ago that altered tropical landscapes through intensive agriculture and managed aquatic systems. However, very little is known about the context and conditions that preceded these social and environmental transformations. Here, we demonstrate that forest islands in the Llanos de Moxos of southwestern Amazonia contain human burials and represent the earliest settlements in the region between 10,600 and 4000 years ago. These archaeological sites and their contents represent the earliest evidence of communities that experienced conditions conducive to engaging with food production such as environmental stability, resource disturbance, and increased territoriality in the Amazonian tropical lowlands.

The Influence of the Evolutionary Past on the Mind: An Analysis of the Preference for Landscapes in the Human Species

According to some evolutionary psychologists, landscapes preferences in the human species are influenced by their evolutionary past. Because the Pleistocene savanna is the least inhospitable landscape, it was the most suitable environment for survival and influenced the evolution of hominids in such a way that even today the human being has a universal preference for these environments. However, there is controversy regarding this statement, because in some studies it was evidenced that people prefer images of landscapes that are similar to those of the environment where they live. In this sense, we want to test whether there is indeed a preference for images of the savanna landscape and how the current environmental context may influence this preference. We performed a study in three environmental contexts with different landscapes in order to be able to observe the influence of the familiar landscape on landscape preference, of which two rural communities - one presenting a landscape similar to the deciduous seasonal forest and another presenting a savanna-like landscape - that totaled 132 participants and one urban community with 189 participants. The stimulus consisted of 12 images representing the six major terrestrial biomes and two images of urban landscapes. The variables analyzed were the emotional responses and the preference of the participants in relation to the images of landscapes. We analyzed the data using the Kruskal-Wallis test. The obtained result did not corroborate the idea of universal preference for images of savanna landscape. The image of Rainforest landscape was the preferred one among all the three environmental contexts studied. In this way, the preference for landscape may have been shaped at different periods of human evolutionary history, and not just during the period when hominids lived on the savannah. As much as selective pressures of the Pleistocene savanna have shaped the human mind during the evolutionary history, other factors and different types of environments may have influenced human preferences for landscapes. Thus, evolutionary psychologists who analyze human preferences for images of landscapes, guided by the idea of the past influencing the present, must be cautious before generalizing their results, especially if other variables such as the cultural ones are not controlled.

Long-term patterns of body mass and stature evolution within the hominin lineage

Body size is a central determinant of a species' biology and adaptive strategy, but the number of reliable estimates of hominin body mass and stature have been insufficient to determine long-term patterns and subtle interactions in these size components within our lineage. Here, we analyse 254 body mass and 204 stature estimates from a total of 311 hominin specimens dating from 4.4 Ma to the Holocene using multi-level chronological and taxonomic analytical categories. The results demonstrate complex temporal patterns of body size variation with phases of relative stasis intermitted by periods of rapid increases. The observed trajectories could result from punctuated increases at speciation events, but also differential proliferation of large-bodied taxa or the extinction of small-bodied populations. Combined taxonomic and temporal analyses show that in relation to australopithecines, early Homo is characterized by significantly larger average body mass and stature but retains considerable diversity, including small body sizes. Within later Homo, stature and body mass evolution follow different trajectories: average modern stature is maintained from ca 1.6 Ma, while consistently higher body masses are not established until the Middle Pleistocene at ca 0.5-0.4 Ma, likely caused by directional selection related to colonizing higher latitudes. Selection against small-bodied individuals (less than 40 kg; less than 140 cm) after 1.4 Ma is associated with a decrease in relative size variability in later Homo species compared with earlier Homo and australopithecines. The isolated small-bodied individuals of Homo naledi (ca 0.3 Ma) and Homo floresiensis (ca 100-60 ka) constitute important exceptions to these general patterns, adding further layers of complexity to the evolution of body size within the genus Homo. At the end of the Late Pleistocene and Holocene, body size in Homo sapiens declines on average, but also extends to lower limits not seen in comparable frequency since early Homo.

The deep human prehistory of global tropical forests and its relevance for modern conservation

Significant human impacts on tropical forests have been considered the preserve of recent societies, linked to large-scale deforestation, extensive and intensive agriculture, resource mining, livestock grazing and urban settlement. Cumulative archaeological evidence now demonstrates, however, that Homo sapiens has actively manipulated tropical forest ecologies for at least 45,000 years. It is clear that these millennia of impacts need to be taken into account when studying and conserving tropical forest ecosystems today. Nevertheless, archaeology has so far provided only limited practical insight into contemporary human-tropical forest interactions. Here, we review significant archaeological evidence for the impacts of past hunter-gatherers, agriculturalists and urban settlements on global tropical forests. We compare the challenges faced, as well as the solutions adopted, by these groups with those confronting present-day societies, which also rely on tropical forests for a variety of ecosystem services. We emphasize archaeology's importance not only in promoting natural and cultural heritage in tropical forests, but also in taking an active role to inform modern conservation and policy-making.

Fruits of the forest: Human stable isotope ecology and rainforest adaptations in Late Pleistocene and Holocene (∼36 to 3 ka) Sri Lanka

Sri Lanka has yielded some of the earliest dated fossil evidence for Homo sapiens (∼38-35,000 cal. years BP [calibrated years before present]) in South Asia, within a region that is today covered by tropical rainforest. Archaeozoological and archaeobotanical evidence indicates that these hunter-gatherers exploited tropical forest resources, yet the contribution of these resources to their overall subsistence strategies has, as in other Late Pleistocene rainforest settings, remained relatively unexplored. We build on previous work in this tropical region by applying both bulk and sequential stable carbon and oxygen isotope analysis to human and faunal tooth enamel from the sites of Batadomba-lena, Fa Hien-lena, and Balangoda Kuragala. Tooth enamel preservation was assessed by means of Fourier Transform Infrared Spectroscopy. We use these data to produce a detailed stable isotope ecology for Late Pleistocene-Holocene foragers in Sri Lanka from ∼36-29,000 to 3000 cal. years BP, allowing us to test the degree of human tropical forest resource reliance over a considerable time period. Given that non-human primates dominate the mammalian assemblages at these sites, we also focus on the stable isotope composition of three monkey species in order to study their ecological preferences and, indirectly, human hunting strategies. The results confirm a strong human reliance on tropical forest resources from ∼36-29,000 cal. years BP until the Iron Age ∼3 cal. years BP, while sequential tooth data show that forest resources were exploited year-round. This strategy was maintained through periods of evident environmental change at the Last Glacial Maximum and upon the arrival of agriculture. Long-term tropical forest reliance was supported by the specialised capture of non-human primates, although the isotopic data revealed no evidence for niche distinction between the hunted species. We conclude that humans rapidly developed a specialisation in the exploitation of South Asia's tropical forests following their arrival in this region.