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Bipedal trackways discovered in 1978 at Laetoli site G, Tanzania and dated to 3.66 million years ago are widely accepted as the oldest unequivocal evidence of obligate bipedalism in the human lineage1–3. Another trackway discovered two years earlier at nearby site A was partially excavated and attributed to a hominin, but curious affinities with bears (ursids) marginalized its importance to the paleoanthropological community, and the location of these footprints fell into obscurity3–5. In 2019, we located, excavated and cleaned the site A trackway, producing a digital archive using 3D photogrammetry and laser scanning. Here we compare the footprints at this site with those of American black bears, chimpanzees and humans, and we show that they resemble those of hominins more than ursids. In fact, the narrow step width corroborates the original interpretation of a small, cross-stepping bipedal hominin. However, the inferred foot proportions, gait parameters and 3D morphologies of footprints at site A are readily distinguished from those at site G, indicating that a minimum of two hominin taxa with different feet and gaits coexisted at Laetoli.

Effective ocean management and the conservation of highly migratory species depend on resolving the overlap between animal movements and distributions, and fishing effort. However, this information is lacking at a global scale. Here we show, using a big-data approach that combines satellite-tracked movements of pelagic sharks and global fishing fleets, that 24% of the mean monthly space used by sharks falls under the footprint of pelagic longline fisheries. Space-use hotspots of commercially valuable sharks and of internationally protected species had the highest overlap with longlines (up to 76% and 64%, respectively), and were also associated with significant increases in fishing effort. We conclude that pelagic sharks have limited spatial refuge from current levels of fishing effort in marine areas beyond national jurisdictions (the high seas). Our results demonstrate an urgent need for conservation and management measures at high-seas hotspots of shark space use, and highlight the potential of simultaneous satellite surveillance of megafauna and fishers as a tool for near-real-time, dynamic management.

Just as in clay moulding or glass blowing, physically sculpting biological structures requires the constituent material to locally flow like a fluid while maintaining overall mechanical integrity like a solid. Disordered soft materials, such as foams, emulsions and colloidal suspensions, switch from fluid-like to solid-like behaviours at a jamming transition1–4. Similarly, cell collectives have been shown to display glassy dynamics in 2D and 3D5,6and jamming in cultured epithelial monolayers7,8, behaviours recently predicted theoretically9–11and proposed to influence asthma pathobiology8and tumour progression12. However, little is known about whether these seemingly universal behaviours occur in vivo13and, specifically, whether they play any functional part during embryonic morphogenesis. Here, by combining direct in vivo measurements of tissue mechanics with analysis of cellular dynamics, we show that during vertebrate body axis elongation, posterior tissues undergo a jamming transition from a fluid-like behaviour at the extending end, the mesodermal progenitor zone, to a solid-like behaviour in the presomitic mesoderm. We uncover an anteroposterior, N-cadherin-dependent gradient in yield stress that provides increasing mechanical integrity to the presomitic mesoderm, consistent with the tissue transiting from a wetter to a dryer foam-like architecture. Our results show that cell-scale stresses fluctuate rapidly (within about 1 min), enabling cell rearrangements and effectively ‘melting’ the tissue at the growing end. Persistent (more than 0.5 h) stresses at supracellular scales, rather than cell-scale stresses, guide morphogenetic flows in fluid-like tissue regions. Unidirectional axis extension is sustained by the reported rigidification of the presomitic mesoderm, which mechanically supports posterior, fluid-like tissues during remodelling before their maturation. The spatiotemporal control of fluid-like and solid-like tissue states may represent a generic physical mechanism of embryonic morphogenesis.

The challenges of evolution in a complex biochemical environment, coupling genotype to phenotype and protecting the genetic material, are solved elegantly in biological systems by the encapsulation of nucleic acids. In the simplest examples, viruses use capsids to surround their genomes. Although these naturally occurring systems have been modified to change their tropism and to display proteins or peptides, billions of years of evolution have favoured efficiency at the expense of modularity, making viral capsids difficult to engineer. Synthetic systems composed of non-viral proteins could provide a ‘blank slate’ to evolve desired properties for drug delivery and other biomedical applications, while avoiding the safety risks and engineering challenges associated with viruses. Here we create synthetic nucleocapsids, which are computationally designed icosahedral protein assemblies with positively charged inner surfaces that can package their own full-length mRNA genomes. We explore the ability of these nucleocapsids to evolve virus-like properties by generating diversified populations using Escherichia coli as an expression host. Several generations of evolution resulted in markedly improved genome packaging (more than 133-fold), stability in blood (from less than 3.7% to 71% of packaged RNA protected after 6 hours of treatment), and in vivo circulation time (from less than 5 minutes to approximately 4.5 hours). The resulting synthetic nucleocapsids package one full-length RNA genome for every 11 icosahedral assemblies, similar to the best recombinant adeno-associated virus vectors. Our results show that there are simple evolutionary paths through which protein assemblies can acquire virus-like genome packaging and protection. Considerable effort has been directed at ‘top-down’ modification of viruses to be safe and effective for drug delivery and vaccine applications; the ability to design synthetic nanomaterials computationally and to optimize them through evolution now enables a complementary ‘bottom-up’ approach with considerable advantages in programmability and control.

Embryonic development is driven by tightly regulated patterns of gene expression, despite extensive genetic variation among individuals. Studies of expression quantitative trait loci (eQTL) indicate that genetic variation frequently alters gene expression in cell-culture models and differentiated tissues. However, the extent and types of genetic variation impacting embryonic gene expression, and their interactions with developmental programs, remain largely unknown. Here we assessed the effect of genetic variation on transcriptional (expression levels) and post-transcriptional (3′ RNA processing) regulation across multiple stages of metazoan development, using 80 inbred Drosophila wild isolates, identifying thousands of developmental-stage-specific and shared QTL. Given the small blocks of linkage disequilibrium in Drosophila, we obtain near base-pair resolution, resolving causal mutations in developmental enhancers, validated transcription-factor-binding sites and RNA motifs. This fine-grain mapping uncovered extensive allelic interactions within enhancers that have opposite effects, thereby buffering their impact on enhancer activity. QTL affecting 3′ RNA processing identify new functional motifs leading to transcript isoform diversity and changes in the lengths of 3′ untranslated regions. These results highlight how developmental stage influences the effects of genetic variation and uncover multiple mechanisms that regulate and buffer expression variation during embryogenesis.

THE living pandas are restricted to the mountains of south-eastern Asia where both the giant panda (Aeluropoda) and the lesser panda (Ailurus) occur. They overlap in geographical range only in Szechuan, China, and there they are separated altitudinally, with the lesser panda favouring higher elevations1. Pleistocene records extend the range of the giant panda into Burma and eastern China, but the lesser panda has apparently not had a significantly wider range during the Quaternary2. Considerable controversy surrounds the phylogenetic relationships of both genera as they represent some of the most derived of terrestrial Carnivora. Recent marshalling of anatomical evidence on the giant panda has demonstrated its fundamental affinity with other members of the Ursidae3. The position of the lesser panda is equivocal although it is usually assigned to the Procyonidae. Procyonids are widely thought to be restricted to the New World, but recent work on various Oligocene and early Miocene forms in Europe4and North America5indicate that the procyonids had a Holarctic distribution at that time. Regardless of its broader phylogenetic affinity, the presence of medial and late Miocene relatives of the lesser panda in Pakistan and western Europe (Sivanasua Pilgrim, 1931=Schlossericyon Crusafont, 1959)6and their absence in the New World makes an Old World origin for this group highly likely. Thus the discovery of a single tooth in North America almost identical to European specimens of the extinct lesser panda Parailurus is unexpected, and must be explained by immigration from Asia.

Deep-space probes offer excellent opportunities to study interstellar grains streaming into the Solar System. Direct detection of such particles would considerably add to our knowledge in many areas of cosmic dust research and could also provide information on the characteristics of both the interstellar medium and the interacting solar wind. Here we present the results of a theoretical study of the interaction between interstellar grains and the solar wind, including the effects of solar cycle variations in the interplanetary magnetic field. The latter is shown to influence significantly regions of concentration and depletion of interstellar grains within the Solar System.

STUDIES from our laboratories have shown that ruthenium red, empirical formula [Ru3O2(NH3)14]Cl6·4H2O, M.W. 858.5 (ref. 1), reacts specifically with mast cell granules2. These organelles are stained red and rendered electron dense, probably as a consequence of a reaction between the stain and granule acid glycosaminoglycan2. After vital staining or staining at fixation, the electron density is usually intense but irregular and sometimes varies from one experiment to another. The variation might be caused by differences in the content of glycosaminoglycan, blocking substances or poor penetration of the stain3. With vital staining it is also obvious that ruthenium red can function as a poly-cation histamine releaser, although at temperatures greater than 4° C this stain did not degranulate mast cells as markedly as did astra blau, a copper containing polyammonium stain.

THEORETICALLY, a particle moving without friction on the surface of a rotating planet should describe a circular path in the course of twelve ‘pendulum hours’, that is, with a period given by where ω is the angular velocity of the rotation and φ is the latitude. It is generally assumed, that these movements are insignificant compared to the currents actually existing in the ocean.

WE recently reported1that washed, killed suspensions of Leptotrichia buccalis were lethal to rabbits on intravenous injection. Endotoxin, which possesses potent biological activity2,3, was extracted from L. buccalis with hot phenol according to the technique of Westphal and Lüderitz4. Further purification was accomplished by differential centrifugation.

WE have measured the flight altitudes of homing pigeons and swifts using a new type of altimeter carried by the birds. The altimeter is based on the fact that the range in air of α-particles from a radioactive substance is inversely proportional to the density of the air and that air density decreases in a regular way with altitude. The altimeter used with the pigeons consists of a lucite tube with outer dimensions of 50 × 8 × 5 mm3(Fig. 1). The α-particle source (210Po) is protected by a thin plastic film and inserted through slits in one end of the tube. The detectors are sheets of cellulose acetate plastic placed in the two 45° slits in the other end of the tube, making it possible to measure the maximum range and range distribution of the α-particles. The altimeter weighs about 1.0 g and is open at both ends so that the air may pass through freely without significant heating. Experiments performed by the Aeronautical Research Institute of Sweden have shown that pressures inside and outside the tube are nearly equal, representing an error in altitude of only 10 m (too high). There is no systematic error in the air density determinations. The precision in a determination of the maximum range depends on the source strength and the duration of the flight. The error amounts to about 0.2–0.4 mm, which corresponds to an error of about 100–200 m in flight altitude in the homing pigeon experiments.

THE experiments by von Friesen and Kristiansson described in the preceding communication indicate that, at the same velocity, π-mesons give a smaller track width than protons, and μ-mesons smaller than π-mesons. The pertinent velocities, c/5–c/3, lie below those of the Čerenkov effect.

THE ‘λ-limiting process’, given by Wentzel and improved by Dirac, gives a finite classical theory for the interaction of a point-charge with its own field. A new mathematical method due to M. Riesz1,2of solving the wave equation by means of analytical continuation gives the same finite equation of motion for a point-charge as this ‘λ-limiting process’.

A DIVERGENCE-FREE theory of the classical electron has been given by Wentzel, and then, with other methods, by Dirac. In quantum theory these methods give an elimination of part of the infinite expressions. Making further the assumption of positive- and negative-energy photons, Dirac eliminates all the infinite expressions.