Late pliocene faunal turnover in the turkana basin, kenya and ethiopia

Long-term biotic homogenization in the East African Rift System over the last 6 million years of hominin evolution

Eastern Africa preserves the most complete record of human evolution anywhere in the world but we have little knowledge of how long-term biogeographic dynamics in the region influenced hominin diversity and distributions. Here, we use spatial beta diversity analyses of mammal fossil records from the East African Rift System to reveal long-term biotic homogenization (increasing compositional similarity of faunas) over the last 6 Myr. Late Miocene and Pliocene faunas (~6-3 million years ago (Ma)) were largely composed of endemic species, with the shift towards biotic homogenization after ~3 Ma being driven by the loss of endemic species across functional groups and a growing number of shared grazing species. This major biogeographic transition closely tracks the regional expansion of grass-dominated ecosystems. Although grazers exhibit low beta diversity in open environments of the Early Pleistocene, the high beta diversity of Mio-Pliocene browsers and frugivores occurred in the context of extensive woody vegetation. We identify other key aspects of the Late Cenozoic biogeographic development of eastern Africa, their likely drivers and place the hominin fossil record in this context. Because hominins were undoubtedly influenced by many of the same factors as other eastern African mammals, this provides a new perspective on the links between environmental and human evolutionary histories.

Plio-Pleistocene environmental variability in Africa and its implications for mammalian evolution

We have developed an Africa-wide synthesis of paleoenvironmental variability over the Plio-Pleistocene. We show that there is strong evidence for orbital forcing of variability during this time that is superimposed on a longer trend of increasing environmental variability, supporting a combination of both low- and high-latitude drivers of variability. We combine these results with robust estimates of mammalian speciation and extinction rates and find that variability is not significantly correlated with these rates. These findings do not currently support a link between environmental variability and turnover and thus fail to corroborate predictions derived from the variability selection hypothesis.

Understanding the climatic drivers of environmental variability (EV) during the Plio-Pleistocene and EV’s influence on mammalian macroevolution are two outstanding foci of research in African paleoclimatology and evolutionary biology. The potential effects of EV are especially relevant for testing the variability selection hypothesis, which predicts a positive relationship between EV and speciation and extinction rates in fossil mammals. Addressing these questions is stymied, however, by 1) a lack of multiple comparable EV records of sufficient temporal resolution and duration, and 2) the incompleteness of the mammalian fossil record. Here, we first compile a composite history of Pan-African EV spanning the Plio-Pleistocene, which allows us to explore which climatic variables influenced EV. We find that EV exhibits 1) a long-term trend of increasing variability since ∼3.7 Ma, coincident with rising variability in global ice volume and sea surface temperatures around Africa, and 2) a 400-ky frequency correlated with seasonal insolation variability. We then estimate speciation and extinction rates for fossil mammals from eastern Africa using a method that accounts for sampling variation. We find no statistically significant relationship between EV and estimated speciation or extinction rates across multiple spatial scales. These findings are inconsistent with the variability selection hypothesis as applied to macroevolutionary processes.

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.

U-Pb-dated flowstones restrict South African early hominin record to dry climate phases

The Cradle of Humankind (Cradle) in South Africa preserves a rich collection of fossil hominins representing Australopithecus, Paranthropus and Homo¹. The ages of these fossils are contentious^2-4 and have compromised the degree to which the South African hominin record can be used to test hypotheses of human evolution. However, uranium-lead (U-Pb) analyses of horizontally bedded layers of calcium carbonate (flowstone) provide a potential opportunity to obtain a robust chronology⁵. Flowstones are ubiquitous cave features and provide a palaeoclimatic context, because they grow only during phases of increased effective precipitation^6,7, ideally in closed caves. Here we show that flowstones from eight Cradle caves date to six narrow time intervals between 3.2 and 1.3 million years ago. We use a kernel density estimate to combine 29 U-Pb ages into a single record of flowstone growth intervals. We interpret these as major wet phases, when an increased water supply, more extensive vegetation cover and at least partially closed caves allowed for undisturbed, semi-continuous growth of the flowstones. The intervening times represent substantially drier phases, during which fossils of hominins and other fossils accumulated in open caves. Fossil preservation, restricted to drier intervals, thus biases the view of hominin evolutionary history and behaviour, and places the hominins in a community of comparatively dry-adapted fauna. Although the periods of cave closure leave temporal gaps in the South African fossil record, the flowstones themselves provide valuable insights into both local and pan-African climate variability.

Diversity analysis of Plio-Pleistocene large mammal communities in the Omo-Turkana Basin, eastern Africa

Knowing how the diversity of large mammal communities changes across space and time provides an important ecological framework for studying hominin evolution. However, diversity studies that apply methods currently used by neoecologists are rare in paleoanthropology and are also challenging due to diversity's unusual statistical properties. Here, we apply up-to-date analytical methods for understanding how species- and genus-level large mammalian diversity in the Omo-Turkana Basin changed through time and across space at multiple spatiotemporal scales (within each formation:10^2-3 km² and 10^4-5 years; and within the basin as a whole: 10³ km² and 10⁵ years). We found that, on average, Koobi Fora's large mammal community was more diverse than Nachukui's, which in turn was more diverse than Shungura's. Diversity was stable through time within each of these formations (alpha diversity), as was diversity in the basin as a whole (gamma diversity). Compositional dissimilarity between these three formations (beta diversity) was relatively low through time, with a 0.6 average proportion of shared species, suggesting dispersal acted to homogenize the region. Though alpha and gamma diversity were fairly stable through time, we do observe several notable peaks: during the KBS Member in Koobi Fora (30% increase), the Lokalalei Member in Nachukui (120% increase), and at 1.7 Ma in the entire basin (100% increase). We conclude by (1) demonstrating that habitat heterogeneity was an important factor influencing alpha diversity within each of the three formations, and (2) hypothesizing that diversity stability may have been driven by equilibrial dynamics in which overall diversity was constrained by resource availability, implying biotic interactions were an important factor in structuring the communities that included hominins as members. Our findings demonstrate the need to quantify how large mammal diversity changes across time and space in order to further our understanding of hominin ecology and evolution.

Photobiological Effects at Earth's Surface Following a 50 pc Supernova

We investigated the potential biological impacts at Earth's surface of stratospheric O3 depletion caused by nearby supernovae known to have occurred about 2.5 and 8 million years ago at about 50 pc distance. New and previously published atmospheric chemistry modeling results were combined with radiative transfer modeling to determine changes in surface-level solar irradiance and biological responses. We find that UVB irradiance is increased by a factor of 1.1 to 2.8, with large variation in latitude, and seasonally at high-latitude regions. Changes in UVA and PAR (visible light) are much smaller. DNA damage (in vitro) is increased by factors similar to UVB, while other biological impacts (erythema, skin cancer, cataracts, marine phytoplankton photosynthesis inhibition, and plant damage) are increased by smaller amounts. We conclude that biological impacts due to increased UV irradiance in this SN case are not mass-extinction level but might be expected to contribute to changes in species abundances; this result fits well with species turnover observed around the Pliocene-Pleistocene boundary. Key Words: UV radiation-Supernovae-Ozone-Radiative transfer. Astrobiology 18, 481-490.

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

The role of climate change in the origin and diversification of early hominins is hotly debated. Most accounts of early hominin evolution link observed fluctuations in species diversity to directional shifts in climate or periods of intense climatic instability. None of these hypotheses, however, have tested whether observed diversity patterns are distorted by variation in the quality of the hominin fossil record. Here, we present a detailed examination of early hominin diversity dynamics, including both taxic and phylogenetically corrected diversity estimates. Unlike past studies, we compare these estimates to sampling metrics for rock availability (hominin-, primate-, and mammal-bearing formations) and collection effort, to assess the geological and anthropogenic controls on the sampling of the early hominin fossil record. Taxic diversity, primate-bearing formations, and collection effort show strong positive correlations, demonstrating that observed patterns of early hominin taxic diversity can be explained by temporal heterogeneity in fossil sampling rather than genuine evolutionary processes. Peak taxic diversity at 1.9 million years ago (Ma) is a sampling artifact, reflecting merely maximal rock availability and collection effort. In contrast, phylogenetic diversity estimates imply peak diversity at 2.4 Ma and show little relation to sampling metrics. We find that apparent relationships between early hominin diversity and indicators of climatic instability are, in fact, driven largely by variation in suitable rock exposure and collection effort. Our results suggest that significant improvements in the quality of the fossil record are required before the role of climate in hominin evolution can be reliably determined.

Environmental dynamics during the onset of the Middle Stone Age in eastern Africa

Development of the African Middle Stone Age (MSA) before 300,000 years ago raises the question of how environmental change influenced the evolution of behaviors characteristic of early Homo sapiens We used temporally well-constrained sedimentological and paleoenvironmental data to investigate environmental dynamics before and after the appearance of the early MSA in the Olorgesailie basin, Kenya. In contrast to the Acheulean archeological record in the same basin, MSA sites are associated with a markedly different faunal community, more pronounced erosion-deposition cycles, tectonic activity, and enhanced wet-dry variability. Aspects of Acheulean technology in this region imply that, as early as 615,000 years ago, greater stone material selectivity and wider resource procurement coincided with an increased pace of land-lake fluctuation, potentially anticipating the adaptability of MSA hominins.

An ecometric analysis of the fossil mammal record of the Turkana Basin

Although ecometric methods have been used to analyse fossil mammal faunas and environments of Eurasia and North America, such methods have not yet been applied to the rich fossil mammal record of eastern Africa. Here we report results from analysis of a combined dataset spanning east and west Turkana from Kenya between 7 and 1 million years ago (Ma). We provide temporally and spatially resolved estimates of temperature and precipitation and discuss their relationship to patterns of faunal change, and propose a new hypothesis to explain the lack of a temperature trend. We suggest that the regionally arid Turkana Basin may between 4 and 2 Ma have acted as a ‘species factory’, generating ecological adaptations in advance of the global trend. We show a persistent difference between the eastern and western sides of the Turkana Basin and suggest that the wetlands of the shallow eastern side could have provided additional humidity to the terrestrial ecosystems. Pending further research, a transient episode of faunal change centred at the time of the KBS Member (1.87–1.53 Ma), may be equally plausibly attributed to climate change or to a top-down ecological cascade initiated by the entry of technologically sophisticated humans.

This article is part of the themed issue ‘Major transitions in human evolution’.

Correlates and catalysts of hominin evolution in Africa

Hominin evolution in the African Pliocene and Pleistocene was accompanied and mediated by changes in the abiotic and biotic spheres. It has been hypothesized that such environmental changes were catalysts of hominin morphological evolution and speciations. Whereas there is little doubt that ecological changes were relevant to shaping the trajectories of mammalian evolution, testing specific hypotheses with data from the fossil record has yielded ambiguous results regarding environmental disruption as a primary catalyst. Proposed mechanisms for abiotic and biotic causes of evolution are not always consistent with the timing and trends exhibited by the African fossil record of hominins and other mammals. Analyses of fossil and genetic data suggest that much of hominin evolution, and by extension mammalian evolution, was autocatalytic, driven by feedback loops within a species or lineage, irrespective of changes in the external environment.

Discordant population histories of host and its parasite: A role for ecological permeability of extreme environment?

Biogeographical and ecological barriers strongly affect the course of micro-evolutionary processes in free living organisms. Here we assess the impact of a recently emerged barrier on populations of limnic fauna. Genetic diversity and population structure in a host-parasite system (Wenyonia virilis tapeworm, Synodontis schall catfish) are analyzed in the recently divided Turkana and Nile basins. The two basins, were repeatedly connected during the Holocene wet/dry climatic oscillations, following late Pleistocene dessication of the Turkana basin. Mitochondrial DNA sequences for cytochrome oxidase I gene (cox I) and a whole genome scanning method—amplified fragment length polymorphism (AFLP) were employed. A total of 347 cox I sequences (representing 209 haplotypes) and 716 AFLP fragments, as well as 120 cox I sequences (20 haplotypes) and 532 AFLP fragments were obtained from parasites and hosts, respectively. Although results indicate that host and parasite populations share some formative traits (bottlenecks, Nilotic origin), their population histories/patterns differ markedly. Mitochondrial analysis revealed that parasite populations evolve significantly faster and show remarkably higher genetic variability. Analyses of both markers confirmed that the parasites undergo lineage fission, forming new clusters specific for either freshwater or saline parts of Lake Turkana. In congruence with the geological history, these clusters apparently indicate multiple colonisations of Lake Turkana from the Nile. In contrast, the host population pattern indicates fusion of different colonisation waves. Although fish host populations remain connected, saline habitats in Lake Turkana (absent in the Nile), apparently pose a barrier to the gene flow in the parasite, possibly due to its multihost lifecycle, which involves freshwater annelids. Despite partially corroborating mitochondrial results, AFLP data was not sufficiently informative for analyzing populations with recently mixed biogeographic histories.

Faunal response to sea-level and climate change in a short-lived seaway: Jurassic of the Western Interior, USA

Understanding how regional ecosystems respond to sea-level and environmental perturbations is a main challenge in palaeoecology. Here we use quantitative abundance estimates, integrated within a sequence stratigraphic and environmental framework, to reconstruct benthic community changes through the 13 myr history of the Jurassic Sundance Seaway in the western United States. Sundance Seaway communities are notable for their low richness and high dominance relative to most areas globally in the Jurassic, and this probably reflects steep temperature and salinity gradients along the 2000 km length of the Seaway that hindered colonization of species from the open ocean. Ordination of samples shows a main turnover event at the Middle-Upper Jurassic transition, which coincided with a shift from carbonate to siliciclastic depositional systems in the Seaway, probably initiated by northward drift from subtropical latitudes to more humid temperate latitudes, and possibly global cooling. Turnover was not uniform across the onshore-offshore gradient, but was higher in offshore environments. The higher resilience of onshore communities to third-order sea-level fluctuations and to the change from a carbonate to a siliciclastic system was driven by a few abundant eurytopic species that persisted from the opening to the closing of the Seaway. Lower stability in offshore facies was instead controlled by the presence of more volatile stenotopic species. Such increased onshore stability in community composition contrasts with the well-documented onshore increase in taxonomic turnover rates, and this study underscores how ecological analyses of relative abundance may contrast with taxonomically based analyses. We also demonstrate the importance of a stratigraphic palaeobiological approach to reconstructing the links between environmental and faunal gradients, and how their evolution through time produces local stratigraphic changes in community composition.

Testing Dietary Hypotheses of East African Hominines Using Buccal Dental Microwear Data

There is much debate on the dietary adaptations of the robust hominin lineages during the Pliocene-Pleistocene transition. It has been argued that the shift from C3 to C4 ecosystems in Africa was the main factor responsible for the robust dental and facial anatomical adaptations of Paranthropus taxa, which might be indicative of the consumption of fibrous, abrasive plant foods in open environments. However, occlusal dental microwear data fail to provide evidence of such dietary adaptations and are not consistent with isotopic evidence that supports greater C4 food intake for the robust clades than for the gracile australopithecines. We provide evidence from buccal dental microwear data that supports softer dietary habits than expected for P. aethiopicus and P. boisei based both on masticatory apomorphies and isotopic analyses. On one hand, striation densities on the buccal enamel surfaces of paranthropines teeth are low, resembling those of H. habilis and clearly differing from those observed on H. ergaster, which display higher scratch densities indicative of the consumption of a wide assortment of highly abrasive foodstuffs. Buccal dental microwear patterns are consistent with those previously described for occlusal enamel surfaces, suggesting that Paranthropus consumed much softer diets than previously presumed and thus calling into question a strict interpretation of isotopic evidence. On the other hand, the significantly high buccal scratch densities observed in the H. ergaster specimens are not consistent with a highly specialized, mostly carnivorous diet; instead, they support the consumption of a wide range of highly abrasive food items.

TERRESTRIAL EFFECTS OF NEARBY SUPERNOVAE IN THE EARLY PLEISTOCENE

Recent results have strongly confirmed that multiple supernovae happened at distances of ∼100 pc, consisting of two main events: one at 1.7-3.2 million years ago, and the other at 6.5-8.7 million years ago. These events are said to be responsible for excavating the Local Bubble in the interstellar medium and depositing 60Fe on Earth and the Moon. Other events are indicated by effects in the local cosmic ray (CR) spectrum. Given this updated and refined picture, we ask whether such supernovae are expected to have had substantial effects on the terrestrial atmosphere and biota. In a first look at the most probable cases, combining photon and CR effects, we find that a supernova at 100 pc can have only a small effect on terrestrial organisms from visible light and that chemical changes such as ozone depletion are weak. However, tropospheric ionization right down to the ground, due to the penetration of ⩾TeV CRs, will increase by nearly an order of magnitude for thousands of years, and irradiation by muons on the ground and in the upper ocean will increase twentyfold, which will approximately triple the overall radiation load on terrestrial organisms. Such irradiation has been linked to possible changes in climate and increased cancer and mutation rates. This may be related to a minor mass extinction around the Pliocene-Pleistocene boundary, and further research on the effects is needed.

Digital data collection in paleoanthropology

Understanding patterns of human evolution across space and time requires synthesizing data collected by independent research teams, and this effort is part of a larger trend to develop cyber infrastructure and e-science initiatives. At present, paleoanthropology cannot easily answer basic questions about the total number of fossils and artifacts that have been discovered, or exactly how those items were collected. In this paper, we examine the methodological challenges to data integration, with the hope that mitigating the technical obstacles will further promote data sharing. At a minimum, data integration efforts must document what data exist and how the data were collected (discovery), after which we can begin standardizing data collection practices with the aim of achieving combined analyses (synthesis). This paper outlines a digital data collection system for paleoanthropology. We review the relevant data management principles for a general audience and supplement this with technical details drawn from over 15 years of paleontological and archeological field experience in Africa and Europe. The system outlined here emphasizes free open-source software (FOSS) solutions that work on multiple computer platforms; it builds on recent advances in open-source geospatial software and mobile computing.

Paleodietary reconstruction using stable isotopes and abundance analysis of bovids from the Shungura Formation of South Omo, Ethiopia

Preservation of the stable carbon isotopic composition of fossil tooth enamel enables us to estimate the relative proportion of C3 versus C4 vegetation in an animal's diet, which, combined with analysis of faunal abundance, may provide complementary methods of paleoenvironmental reconstruction. To this end, we analyzed stable carbon isotopic composition (δ(13)C values) of tooth enamel from four bovid tribes (Tragelaphini, Aepycerotini, Reduncini, and Alcelaphini) derived from six members of the Shungura Formation (Members B, C, D, F, G, and L; ages from ca. 2.90-1.05 Ma (millions of years ago) in the Lower Omo Valley of southwestern Ethiopia. The bovids show a wide range of δ(13)C values within taxa and stratigraphic members, as well as temporal changes in the feeding strategies of taxa analyzed throughout the middle to late Pliocene and early Pleistocene. Such variation suggests that the use of actualistic approaches for paleoenvironmental reconstruction may not always be warranted. Alcelaphini was the only taxon analyzed that retained a consistent dietary preference throughout the sequence, with entirely C4-dominated diets. Reduncini had a mixed C3/C4 to C4-dominated diet prior to 2.4 Ma, after which this taxon shifted to a largely C4-dominated diet. Aepycerotini generally showed a mixed C3/C4 diet, with a period of increased C4 diet from 2.5 to 2.3 Ma. Tragelaphini showed a range of mixed C3/C4 diets, with a median value that was briefly nearer the C4 end member from 2.9 to 2.4 Ma but was otherwise towards the C3 end member. These isotopic results, combined with relative abundance data for these bovids, imply that the environment of the Lower Omo Valley consisted of a mosaic of closed woodlands, with riverine forests and open grasslands. However, our data also signify that the overall environment gradually became more open, and that C4 grasses became more dominant. Finally, these results help document the range and extent of environments and potential diets that were available to the four hominin species encountered in the Shungura sequence.

Continuous evolutionary change in Plio-Pleistocene mammals of eastern Africa

Much debate has revolved around the question of whether the mode of evolutionary and ecological turnover in the fossil record of African mammals was continuous or pulsed, and the degree to which faunal turnover tracked changes in global climate. Here, we assembled and analyzed large specimen databases of the fossil record of eastern African Bovidae (antelopes) and Turkana Basin large mammals. Our results indicate that speciation and extinction proceeded continuously throughout the Pliocene and Pleistocene, as did increases in the relative abundance of arid-adapted bovids, and in bovid body mass. Species durations were similar among clades with different ecological attributes. Occupancy patterns were unimodal, with long and nearly symmetrical origination and extinction phases. A single origination pulse may be present at 2.0-1.75 Ma, but besides this, there is no evidence that evolutionary or ecological changes in the eastern African record tracked rapid, 100,000-y-scale changes in global climate. Rather, eastern African large mammal evolution tracked global or regional climatic trends at long (million year) time scales, while local, basin-scale changes (e.g., tectonic or hydrographic) and biotic interactions ruled at shorter timescales.

Stature, body mass, and brain size: a two-million-year odyssey

Physical size has been critical in the evolutionary success of the genus Homo over the past 2.4 million-years. An acceleration in the expansion of savannah grasslands in Africa from 1.6Ma to 1.2Ma witnessed concomitant increases in physical stature (150-170cm), weight (50-70kg), and brain size (750-900cm(3)). With the onset of 100,000year Middle Pleistocene glacial cycles ("ice ages") some 780,000years ago, large-bodied Homo groups had reached modern size and had successfully dispersed from equatorial Africa, Central, and Southeast Asia to high-latitude localities in Atlantic Europe and North East Asia. While there is support for incursions of multiple Homo lineages to West Asia and Continental Europe at this time, data does not favour a persistence of Homo erectus beyond ∼400,000years ago in Africa, west and Central Asia, and Europe. Novel Middle Pleistocene Homo forms (780,000-400,000years) may not have been substantially taller (150-170cm) than earlier Homo (1.6Ma-800,000years), yet brain size exceeded 1000cm(3) and body mass approached 80kg in some males. Later Pleistocene Homo (400,000-138,000years) were 'massive' in their height (160-190cm) and mass (70-90kg) and consistently exceed recent humans. Relative brain size exceeds earlier Homo, yet is substantially lower than in final glacial H. sapiens and Homo neanderthalensis. A final leap in absolute and relative brain size in Homo (300,000-138,000years) occurred independent of any observed increase in body mass and implies a different selective mediator to that operating on brain size increases observed in earlier Homo.

Temporal change in functional richness and evenness in the eastern African plio-pleistocene carnivoran guild

We analyze functional richness and functional evenness of the carnivoran guild in eastern Africa from 3.5 Ma to 1.5 Ma, and compare them to the present day. The data consist of characters of the craniodental apparatus of 76 species of fossil and extant carnivorans, divided into four 0.5 Ma time slices from 3.5 to 1.5 Ma, together with the modern fauna. Focus is on large (>21.5 kg) carnivores. Results show that the large carnivore guild has lost nearly 99% of its functional richness since 3.5 Ma, in a process starting prior to 2 Ma. Measurement of functional evenness shows the modern large carnivore guild to be unique in being randomly distributed in morphospace while in all past time slices there is significant clustering of species. The results are analyzed in the light of known changes to climate and environment in eastern Africa. We conclude that climate change is unlikely to explain all of the changes found and suggest that the evolution of early hominins into carnivore niche space, especially the evolution of derived dietary strategies after 2 Ma, played a significant part in the reduction of carnivore functional richness.

Fossil mammals and paleoenvironments in the Omo-Turkana Basin

Although best known for its fossil hominins, the Omo-Turkana Basin of Kenya and Ethiopia is the source of one of the best records of vertebrate evolution from the Late Cenozoic of Africa. Located near the heart of the East African Rift Valley, the basin serves as an important frame of reference for the continent. The fossil record from this region plays a key role in our efforts to understand the environmental and ecological context of human evolution in Africa. The Omo-Turkana faunal data shed light on key questions of human evolution: What kinds of environments did early humans inhabit? How did these environments change over time? What is the relationship between faunal change in East Africa and broader patterns of climatic change?

Rejecting strictly allopatric speciation on a continental island: prolonged postdivergence gene flow between Taiwan (Leucodioptron taewanus, Passeriformes Timaliidae) and Chinese (L. canorum canorum) hwameis

Allopatry is conventionally considered the geographical mode of speciation for continental island organisms. However, strictly allopatric speciation models that assume the lack of postdivergence gene flow seem oversimplified given the recurrence of land bridges during glacial periods since the late Pliocene. Here, to evaluate whether a continental island endemic, the Taiwan hwamei (Leucodioptron taewanus, Passeriformes Timaliidae) speciated in strict allopatry, we used weighted-regression-based approximate Bayesian computation (ABC) to analyse the genetic polymorphism of 18 neutral nuclear loci (total length: 8500 bp) in Taiwan hwamei and its continental sister species, the Chinese hwamei (L. canorum canorum). The nonallopatry model was found to fit better with observed genetic polymorphism of the two hwamei species (posterior possibility = 0.82). We also recovered unambiguous signals of nontrivial bidirectional postdivergence gene flow (N(e)m >> 1) between Chinese hwamei and Taiwan hwamei until 0.5 Ma. Divergence time was estimated to be 3.5 to 2 million years earlier than that estimated from mitochondrial cytochrome b sequences. Finally, using the inferred nonallopatry model to simulate genetic variation at 24 nuclear genes examined showed that the adiponectin receptor 1 gene may be under divergent adaptation. Our findings imply that the role of geographical barrier may be less prominent for the speciation of continental island endemics, and suggest a shift in speciation studies from simply correlating geographical barrier and genetic divergence to examining factors that facilitate and maintain divergence, e.g. differential selection and sexual selection, especially in the face of interpopulation gene flow.

Flaked stones and old bones: biological and cultural evolution at the dawn of technology

The appearance of Oldowan sites ca. 2.6 million years ago (Ma) may reflect one of the most important adaptive shifts in human evolution. Stone artifact manufacture, large mammal butchery, and novel transport and discard behaviors led to the accumulation of the first recognized archaeological debris. The appearance of the Oldowan sites coincides with generally cooler, drier, and more variable climatic conditions across Africa, probably resulting in a net decrease in woodland foods and an increase in large mammal biomass compared to the early and middle Pliocene. Shifts in plant food resource availability may have provided the stimulus for incorporating new foods into the diet, including meat from scavenged carcasses butchered with stone tools. Oldowan artifact form varies with clast size, shape, raw material physical properties, and flaking intensity. Oldowan hominins preferred hard raw materials with good fracture characteristics. Habitual stone transport is evident from technological analysis, and raw material sourcing to date suggests that stone was rarely moved more than 2-3 km from source. Oldowan debris accumulation was spatially redundant, reflecting recurrent visitation of attractive points on the landscape. Thin archaeological horizons from Bed I Olduvai Gorge, Tanzania, were probably formed and buried in less than 10 years and document hominin processing of multiple carcasses per year. Transport beyond simple refuging behavior is suggested by faunal density at some site levels. By 2.0 Ma, hominin rank within the predatory guild may have been moderately high, as they probably accessed meaty carcasses through hunting and confrontational scavenging, and hominin-carnivore competition appears minimal at some sites. It is likely that both Homo habilis sensu stricto and early African H. erectus made Oldowan tools. H. habilis sensu stricto was more encephalized than Australopithecus and may foreshadow H. erectus in lower limb elongation and some thermoregulatory adaptations to hot, dry climatic conditions. H. erectus was large and wide-ranging, had a high total energy expenditure, and required a high-quality diet. Reconstruction of H. erectus reproductive energetics and socioeconomic organization suggests that reproductively active females received assistance from other group members. This inference, combined with archaeological evidence for acquisition of meaty carcasses, suggests that meat would have been a shared food. This is indirectly confirmed by nutritional analysis suggesting that the combination of meat and nutritionally dense plant foods was the likely diet fueling body size increase and encephelization in Homo. Most discussion of Oldowan hominin behavior and ecology, including that presented here, is based on materials from a few sites. There is a critical need to analyze additional large, primary-context lithic and faunal assemblages to better assess temporal, geographic, and environmental variability in Oldowan behavior.

Natural history of Homo erectus

Our view of H. erectus is vastly different today than when Pithecanthropus erectus was described in 1894. Since its synonimization into Homo, views of the species and its distribution have varied from a single, widely dispersed, polytypic species ultimately ancestral to all later Homo, to a derived, regional isolate ultimately marginal to later hominin evolution. A revised chronostratigraphic framework and recent work bearing either directly or indirectly on reconstructions of life-history patterns are reviewed here and, together with a review of the cranial and postcranial anatomy of H. erectus, are used to generate a natural history of the species. Here I argue that H. erectus is a hominin, notable for its increased body size, that originates in the latest Pliocene/earliest Pleistocene of Africa and quickly disperses into Western and Eastern Asia. It is also an increasingly derived hominin with several regional morphs sustained by intermittent isolation, particularly in Southeast Asia. This view differs from several current views, most especially that which recognizes only a single hominin species in the Pleistocene, H. sapiens, and those which would atomize H. erectus into a multiplicity of taxa. Following Jolly ([2001] Yrbk Phys Anthropol 44:177-204), the regional morphs of H. erectus may be productively viewed as geographically replacing allotaxa, rather than as the focus of unresolvable species debates. Such a view allows us to focus on the adaptations and biology of local groups, including questions of biogeographic isolation and local adaptation. A number of issues remain unresolved, including the significance of diversity in size and shape in the early African and Georgian records.