Volume 534 Number 7606

Editorials

Humanity’s forgotten family p.151

Hominin fossils discovered near the site of the 'hobbit' Homo floresiensis provide yet more evidence that the human lineage is more diverse than was ever imagined.

doi: 10.1038/534151a

Second chances p.152

The line between compliance and misconduct is finer than you might think.

doi: 10.1038/534152b

Energy hit p.152

Germany’s decision to slow the expansion of green-energy production is a reasonable move.

doi: 10.1038/534152a

News

News Features

News & Views

Rules of the game for microbiota p.182

Are the dynamics of our microbial communities unique to us or does everyone's microbiota follow the same rules? The emerging insights into this question could be of relevance to health and disease. See Letter p.259

doi: 10.1038/534182a

Hydrogen and oxygen in the deep Earth p.183

The finding that an unusual iron oxide forms at extremely high pressures suggests that hydrogen and oxygen — two elements that strongly influence Earth's evolution — are generated in the mantle. See Letter p.241

doi: 10.1038/534183a

To mimicry and back again p.184

Deadly coral snakes warn predators through striking red-black banding. New data confirm that many harmless snakes have evolved to resemble coral snakes, and suggest that the evolution of this Batesian mimicry is not always a one-way street.

doi: 10.1038/nature18441

Microbial signals to the brain control weight p.185

The bacteria that inhabit the rodent gut promote insulin secretion and food intake by activating the parasympathetic nervous system — a hitherto unknown mode of action for this multifaceted microbiota. See Article p.213

doi: 10.1038/534185a

No turning back for motorized molecules p.187

Two molecular motors have been developed that use chemical energy to drive rotational motion in a single direction. The findings bring the prospect of devices powered by such motors a tantalizing step closer. See Letter p.235

doi: 10.1038/534187a

The dawn of Homo floresiensis p.188

New fossil findings demonstrate that the diminutive hominin Homo floresiensis lived on the Indonesian island of Flores at least 700,000 years ago, and may point to its rapid dwarfism from the larger Homo erectus. See Letters p.245 & p.249

doi: 10.1038/534188a

Perspective

Articles

The genetic history of Ice Age Europe p.200

Analysis of ancient genomic data of 51 humans from Eurasia dating from 45,000 to 7,000 years ago provides insight into the population history of pre-Neolithic Europe and support for recurring migration and population turnover in Europe during this period.

doi: 10.1038/nature17993

Letters

Cold, clumpy accretion onto an active supermassive black hole p.218

The so-called accretion flow that powers the growth of supermassive black holes in galaxy centres is assumed to be dominated by a smooth, steady flow of very hot plasma, but now observations instead reveal a clumpy accretion of very cold molecular clouds onto a supermassive black hole in the nucleus of a nearby giant elliptical galaxy.

doi: 10.1038/nature17969

Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off p.227

Metals have been mankind’s most essential materials for thousands of years; however, their use is affected by ecological and economical concerns. Alloys with higher strength and ductility could alleviate some of these concerns by reducing weight and improving energy efficiency. However, most metallurgical mechanisms for increasing strength lead to ductility loss, an effect referred to as the strength–ductility trade-off. Here we present a metastability-engineering strategy in which we design nanostructured, bulk high-entropy alloys with multiple compositionally equivalent high-entropy phases. High-entropy alloys were originally proposed to benefit from phase stabilization through entropy maximization. Yet here, motivated by recent work that relaxes the strict restrictions on high-entropy alloy compositions by demonstrating the weakness of this connection, the concept is overturned. We decrease phase stability to achieve two key benefits: interface hardening due to a dual-phase microstructure (resulting from reduced thermal stability of the high-temperature phase); and transformation-induced hardening (resulting from the reduced mechanical stability of the room-temperature phase). This combines the best of two worlds: extensive hardening due to the decreased phase stability known from advanced steels and massive solid-solution strengthening of high-entropy alloys. In our transformation-induced plasticity-assisted, dual-phase high-entropy alloy (TRIP-DP-HEA), these two contributions lead respectively to enhanced trans-grain and inter-grain slip resistance, and hence, increased strength. Moreover, the increased strain hardening capacity that is enabled by dislocation hardening of the stable phase and transformation-induced hardening of the metastable phase produces increased ductility. This combined increase in strength and ductility distinguishes the TRIP-DP-HEA alloy from other recently developed structural materials. This metastability-engineering strategy should thus usefully guide design in the near-infinite compositional space of high-entropy alloys.

doi: 10.1038/nature17981

Strongly correlated perovskite fuel cells p.231

A fundamentally different approach to designing solid oxide electrolytes is presented, using a phase transition to suppress electronic conduction in a correlated perovskite nickelate; this yields ionic conductivity comparable to the best-performing solid electrolytes in the same temperature range.

doi: 10.1038/nature17653

An autonomous chemically fuelled small-molecule motor p.235

A system is described in which a small macrocycle is continuously transported directionally around a cyclic molecular track when powered by irreversible reactions of a chemical fuel; such autonomous chemically fuelled molecular motors should find application as engines in molecular nanotechnology.

doi: 10.1038/nature18013

FeO2 and FeOOH under deep lower-mantle conditions and Earth’s oxygen–hydrogen cycles p.241

First-principles calculations and experiments are used to identify a stable, pyrite-structured iron oxide at 76 gigapascals and 1,800 kelvin that holds an excessive amount of oxygen and to show that goethite (rust) decomposes under these deep lower-mantle conditions to form an iron oxide and release hydrogen; this process provides another way to interpret the origin of seismic and geochemical anomalies in the deep lower mantle of Earth.

doi: 10.1038/nature18018

Homofloresiensis-like fossils from the early Middle Pleistocene of Flores p.245

The evolutionary origin of Homo floresiensis, a diminutive hominin species previously known only by skeletal remains from Liang Bua in western Flores, Indonesia, has been intensively debated. It is a matter of controversy whether this primitive form, dated to the Late Pleistocene, evolved from early Asian Homo erectus and represents a unique and striking case of evolutionary reversal in hominin body and brain size within an insular environment. The alternative hypothesis is that H. floresiensis derived from an older, smaller-brained member of our genus, such as Homo habilis, or perhaps even late Australopithecus, signalling a hitherto undocumented dispersal of hominins from Africa into eastern Asia by two million years ago (2 Ma). Here we describe hominin fossils excavated in 2014 from an early Middle Pleistocene site (Mata Menge) in the So’a Basin of central Flores. These specimens comprise a mandible fragment and six isolated teeth belonging to at least three small-jawed and small-toothed individuals. Dating to ~0.7 Ma, these fossils now constitute the oldest hominin remains from Flores. The Mata Menge mandible and teeth are similar in dimensions and morphological characteristics to those of H. floresiensis from Liang Bua. The exception is the mandibular first molar, which retains a more primitive condition. Notably, the Mata Menge mandible and molar are even smaller in size than those of the two existing H. floresiensis individuals from Liang Bua. The Mata Menge fossils are derived compared with Australopithecus and H. habilis, and so tend to support the view that H. floresiensis is a dwarfed descendent of early Asian H. erectus. Our findings suggest that hominins on Flores had acquired extremely small body size and other morphological traits specific to H. floresiensis at an unexpectedly early time.

doi: 10.1038/nature17999

Age and context of the oldest known hominin fossils from Flores p.249

Stratigraphic, chronological, environmental and faunal context are provided to the newly discovered fossils of hominins that lived in the So’a Basin in Flores, Indonesia, 700,000 years ago; the stone tools recovered with the fossils are similar to those associated with the much younger Homo floresiensis from Flores, discovered in Liang Bua to the west.

doi: 10.1038/nature17663

Universality of human microbial dynamics p.259

A new computational method to characterize the dynamics of human-associated microbial communities is applied to data from two large-scale metagenomic studies, and suggests that gut and mouth microbiomes of healthy individuals are subjected to universal (that is, host-independent) dynamics, whereas skin microbiomes are shaped by the host environment; the method paves the way to designing general microbiome-based therapies.

doi: 10.1038/nature18301

Ribosome-dependent activation of stringent control p.277

The structure of a bacterial ribosome–RelA complex reveals that RelA, a protein recruited to the ribosome in the case of scarce amino acids, binds in a different location to translation factors, and that this binding event suppresses auto-inhibition to activate synthesis of the (p)ppGpp secondary messenger, thus initiating stringent control.

doi: 10.1038/nature17675

Charge-density analysis of an iron–sulfur protein at an ultra-high resolution of 0.48 Å p.281

The fine structures of proteins, such as the positions of hydrogen atoms, distributions of valence electrons and orientations of bound waters, are critical factors for determining the dynamic and chemical properties of proteins. Such information cannot be obtained by conventional protein X-ray analyses at 3.0–1.5 Å resolution, in which amino acids are fitted into atomically unresolved electron-density maps and refinement calculations are performed under strong restraints. Therefore, we usually supplement the information on hydrogen atoms and valence electrons in proteins with pre-existing common knowledge obtained by chemistry in small molecules. However, even now, computational calculation of such information with quantum chemistry also tends to be difficult, especially for polynuclear metalloproteins. Here we report a charge-density analysis of the high-potential iron–sulfur protein from the thermophilic purple bacterium Thermochromatium tepidum using X-ray data at an ultra-high resolution of 0.48 Å. Residual electron densities in the conventional refinement are assigned as valence electrons in the multipolar refinement. Iron 3d and sulfur 3p electron densities of the Fe4S4 cluster are visualized around the atoms. Such information provides the most detailed view of the valence electrons of the metal complex in the protein. The asymmetry of the iron–sulfur cluster and the protein environment suggests the structural basis of charge storing on electron transfer. Our charge-density analysis reveals many fine features around the metal complex for the first time, and will enable further theoretical and experimental studies of metalloproteins.

doi: 10.1038/nature18001