55 research outputs found
Biomechanics and the origins of human bipedal walking: the last 50 years.
Motion analysis, as applied to evolutionary biomechanics, has experienced its own evolution over the last 50 years. Here we review how an ever-increasing fossil record, together with continuing advancements in biomechanics techniques, have shaped our understanding of the origin of upright bipedal walking. The original, and long-established hypothesis held by Lamarck (1809), Darwin (1859) and Keith (1934), amongst others, maintained that bipedality originated in an arboreal context. However, the first field studies of gorilla and chimpanzees from the 1960's, highlighted their so-called 'knucklewalking' quadrupedalism, leading scientists to assume, semi-automatically, that knucklewalking must have been the precursor to bipedality. It would not be until the discovery of skeletons of early human relatives Australopithecus afarensis and Australopithecus prometheus, and the inclusion of methods of analysis from computer science, biomechanics, sports science and medicine, that the knucklewalking hypothesis would be most robustly challenged. Their short, but human-like lower limbs and human-like hand indicated that knucklewalking was not part of our ancestral locomotor repertoire. Rather, most current research in evolutionary biomechanics agrees it was a combination of climbing and bipedalism, both in an arboreal context, which facilitated upright, terrestrial, bipedal walking over short distances
EDGE -- Dark matter or astrophysics? Clear prospects to break dark matter heating degeneracies with HI rotation in faint dwarf galaxies
Low-mass dwarf galaxies are expected to showcase pristine `cuspy' inner dark
matter density profiles compared to their stellar sizes, as they form too few
stars to significantly drive dark matter heating through supernovae-driven
outflows. Here, we study such simulated faint systems () drawn from high-resolution (3 pc)
cosmological simulations from the `Engineering Dwarf Galaxies at the Edge of
galaxy formation' (EDGE) project. We confirm that these objects have steep and
rising inner dark matter density profiles at , little affected by galaxy
formation effects. But five dwarf galaxies from the suite showcase a detectable
HI reservoir (),
analogous to the observed population of faint, HI-bearing dwarf galaxies. These
reservoirs exhibit episodes of ordered rotation, opening windows for rotation
curve analysis. Within actively star-forming dwarfs, stellar feedback easily
disrupts the tenuous HI discs (), making rotation short-lived () and
more challenging to interpret for dark matter inferences. Contrastingly, we
highlight a long-lived () and easy-to-interpret HI
rotation curve extending to in a quiescent
dwarf, that has not formed new stars since . This stable gas disc is
supported by an oblate dark matter halo shape that drives high angular momentum
gas flows. Our results strongly motivate further searches for HI rotation
curves in the observed population of HI-bearing low-mass dwarfs, that provide a
key regime to disentangle the respective roles of dark matter microphysics and
galaxy formation effects in driving dark matter heating.Comment: Main text 10 pages, submitted to MNRAS. Comments welcome
Deciphering Lyman- Emission Deep into the Epoch of Reionisation
A major event in cosmic history is the genesis of the first starlight in our
Universe, ending the ''Dark Ages''. During this epoch, the earliest luminous
sources were enshrouded in neutral and pristine gas, which was gradually
ionised in a process called ''reionisation''. Hence, one of the brightest
emission lines in star-forming galaxies, Lyman- (Ly-), was
predicted to emerge only towards the end of the epoch of reionisation, about
one billion years after the Big Bang. However, this picture has been challenged
over the past decade by the surprising detection of Ly- in galaxies
less than 500 million years old. Here we show, by taking advantage of both
high-resolution and high-sensitivity images from the James Webb Space Telescope
programs PRIMER, CEERS and FRESCO, that all galaxies in our sample of
Ly- emitters deep in the epoch of reionisation have close companions.
To understand the physical processes that lead to the observed Ly-
emission in our sample, we take advantage of novel on-the-fly radiative
transfer magnetohydrodynamical simulations with cosmic ray feedback. We find
that in the early Universe, the rapid build up of mass through frequent
galactic mergers leads to very bursty star formation which in turn drives
episodes of high intrinsic Ly- emission and facilitates the escape of
Ly- photons along channels cleared of neutral gas. These merging
galaxies reside in clustered environments thus creating sufficiently large
ionised bubbles. This presents a solution to the long-standing puzzle of the
detection of Ly- emission deep into the epoch of reionisation.Comment: Submitted to Nature. 38 pages, 9 figures, 2 table
Low-mass bursty galaxies in JADES efficiently produce ionising photons and could represent the main drivers of reionisation
© 2023 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We study galaxies in JADES Deep to study the evolution of the ionising photon production efficiency, , observed to increase with redshift. We estimate for a sample of 677 galaxies at using NIRCam photometry. Specifically, combinations of the medium and wide bands F335M-F356W and F410M-F444W to constrain emission lines that trace : H and [OIII]. Additionally, we use the spectral energy distribution fitting code \texttt{Prospector} to fit all available photometry and infer galaxy properties. The flux measurements obtained via photometry are consistent with FRESCO and NIRSpec-derived fluxes. Moreover, the emission-line-inferred measurements are in tight agreement with the \texttt{Prospector} estimates. We also confirm the observed trend with redshift and M, and find: . We use \texttt{Prospector} to investigate correlations of with other galaxy properties. We see a clear correlation between and burstiness in the star formation history of galaxies, given by the ratio of recent to older star formation, where burstiness is more prevalent at lower stellar masses. We also convolve our relations with luminosity functions from the literature, and constant escape fractions of 10 and 20\%, to place constraints on the cosmic ionising photon budget. By combining our results, we find that if our sample is representative of the faint low-mass galaxy population, galaxies with bursty star formation are efficient enough in producing ionising photons and could be responsible for the reionisation of the Universe.Peer reviewe
The PhanSST global database of Phanerozoic sea surface temperature proxy data
Paleotemperature proxy data form the cornerstone of paleoclimate research and are integral to understanding the evolution of the Earth system across the Phanerozoic Eon. Here, we present PhanSST, a database containing over 150,000 data points from five proxy systems that can be used to estimate past sea surface temperature. The geochemical data have a near-global spatial distribution and temporally span most of the Phanerozoic. Each proxy value is associated with consistent and queryable metadata fields, including information about the location, age, and taxonomy of the organism from which the data derive. To promote transparency and reproducibility, we include all available published data, regardless of interpreted preservation state or vital effects. However, we also provide expert-assigned diagenetic assessments, ecological and environmental flags, and other proxy-specific fields, which facilitate informed and responsible reuse of the database. The data are quality control checked and the foraminiferal taxonomy has been updated. PhanSST will serve as a valuable resource to the paleoclimate community and has myriad applications, including evolutionary, geochemical, diagenetic, and proxy calibration studies
Lake salinization drives consistent losses of zooplankton abundance and diversity across coordinated mesocosm experiments
Human-induced salinization increasingly threatens inland waters; yet we know little about the multifaceted response of lake communities to salt contamination. By conducting a coordinated mesocosm experiment of lake salinization across 16 sites in North America and Europe, we quantified the response of zooplankton abundance and (taxonomic and functional) community structure to a broad gradient of environmentally relevant chloride concentrations, ranging from 4 to ca. 1400 mg Cl- L-1. We found that crustaceans were distinctly more sensitive to elevated chloride than rotifers; yet, rotifers did not show compensatory abundance increases in response to crustacean declines. For crustaceans, our among-site comparisons indicate: (1) highly consistent decreases in abundance and taxon richness with salinity; (2) widespread chloride sensitivity across major taxonomic groups (Cladocera, Cyclopoida, and Calanoida); and (3) weaker loss of functional than taxonomic diversity. Overall, our study demonstrates that aggregate properties of zooplankton communities can be adversely affected at chloride concentrations relevant to anthropogenic salinization in lakes.Peer reviewe
Widespread variation in salt tolerance within freshwater zooplankton species reduces the predictability of community-level salt tolerance
The salinization of freshwaters is a global threat to aquatic biodiversity. We quantified variation in chloride (Cl-) tolerance of 19 freshwater zooplankton species in four countries to answer three questions: (1) How much variation in Cl- tolerance is present among populations? (2) What factors predict intraspecific variation in Cl- tolerance? (3) Must we account for intraspecific variation to accurately predict community Cl- tolerance? We conducted field mesocosm experiments at 16 sites and compiled acute LC(50)s from published laboratory studies. We found high variation in LC(50)s for Cl- tolerance in multiple species, which, in the experiment, was only explained by zooplankton community composition. Variation in species-LC50 was high enough that at 45% of lakes, community response was not predictable based on species tolerances measured at other sites. This suggests that water quality guidelines should be based on multiple populations and communities to account for large intraspecific variation in Cl- tolerance.Peer reviewe
Current water quality guidelines across North America and Europe do not protect lakes from salinization
Human-induced salinization caused by the use of road deicing salts, agricultural practices, mining operations, and climate change is a major threat to the biodiversity and functioning of freshwater ecosystems. Yet, it is unclear if freshwater ecosystems are protected from salinization by current water quality guidelines. Leveraging an experimental network of land-based and in-lake mesocosms across North America and Europe, we tested how salinization-indicated as elevated chloride (C-) concentration-will affect lake food webs and if two of the lowest Cl- thresholds found globally are sufficient to protect these food webs. Our results indicated that salinization will cause substantial zooplankton mortality at the lowest Cl- thresholds established in Canada (120 mg Cl-/L) and the United States (230 mg Cl-/L) and throughout Europe where Cl- thresholds are generally higher. For instance, at 73% of our study sites, Cl- concentrations that caused a >= 50% reduction in cladoceran abundance were at or below Cl thresholds in Canada, in the United States, and throughout Europe. Similar trends occurred for copepod and rotifer zooplankton. The loss of zooplankton triggered a cascading effect causing an increase in phytoplankton biomass at 47% of study sites. Such changes in lake food webs could alter nutrient cycling and water clarity and trigger declines in fish production. Current Cl- thresholds across North America and Europe clearly do not adequately protect lake food webs. Water quality guidelines should be developed where they do not exist, and there is an urgent need to reassess existing guidelines to protect lake ecosystems from human-induced salinization.Peer reviewe
The PhanSST global database of Phanerozoic sea surface temperature proxy data
Paleotemperature proxy data form the cornerstone of paleoclimate research and are integral to understanding the evolution of the Earth system across the Phanerozoic Eon. Here, we present PhanSST, a database containing over 150,000 data points from five proxy systems that can be used to estimate past sea surface temperature. The geochemical data have a near-global spatial distribution and temporally span most of the Phanerozoic. Each proxy value is associated with consistent and queryable metadata fields, including information about the location, age, and taxonomy of the organism from which the data derive. To promote transparency and reproducibility, we include all available published data, regardless of interpreted preservation state or vital effects. However, we also provide expert-assigned diagenetic assessments, ecological and environmental flags, and other proxy-specific fields, which facilitate informed and responsible reuse of the database. The data are quality control checked and the foraminiferal taxonomy has been updated. PhanSST will serve as a valuable resource to the paleoclimate community and has myriad applications, including evolutionary, geochemical, diagenetic, and proxy calibration studies
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