Climate niche history of humans
In the current climate, MATs above 29 °C are restricted to small, dark areas in the Sahara region. In 2070, such conditions are projected throughout the shaded area in the worst-case scenario. Background colors represent current MATs.
As Earth’s climate continues to warm, some regions may become unsuitable for human life while conditions in other regions improve. Chi Xu et al. (pp. 11350–11355) examined data from several sources that included global temperature, human population, and land-use estimates dating from the mid-Holocene, 6,000 years ago, to 2015 CE. The authors also estimated future human populations and global climate conditions by 2070 CE to determine where optimal climate conditions may occur. Humans, crops, and livestock are currently concentrated in a narrow subset of suitable climate space, which exhibits a mean annual temperature (MAT) of approximately 11–15 °C. The authors report that such conditions suitable for human life have remained largely the same since the mid-Holocene. The authors predicted that by 2070 approximately 1–3 billion people are likely to live under climate conditions that are warmer than conditions deemed suitable for human life to flourish. The findings suggest the need to enhance human development in areas where adaption to climate change is low. Furthermore, future migration from regions undergoing degradation from climate change to regions with ideal climates may be necessary, according to the authors. — M.S.
Vocalizations and body movement
Researchers examine links between movement and speech. Image credit: Pixabay/mcmurryjulie.
Human vocal abilities are the most advanced among those of hominins. Hand movements often occur during verbal communication, even when gestures cannot visually enrich speech, such as during phone conversations. To determine whether humans can perceive upper limb movements made in conjunction with vocalizations, Wim Pouw et al. (pp. 11364–11367) recruited three men and three women to phonate a vowel with one breath while moving the arm or wrist at different tempos. Thirty participants listened to 36 of the vocalizations. Although they were unable to see the vocalizer, listeners synchronized their own arm and wrist movements with those of the vocalizer. This phenomenon also occurred with subtle movements that were hard to detect as well as across slow, medium, and fast tempos. However, listeners had slightly more difficulty synchronizing with a vocalizer’s wrist movements than hand movements. The findings suggest that musculoskeletal tensioning of the body constrains speech, which affects the respiratory–vocal system. Communication cues, such as excitement, may be perceived through gesture-induced acoustics, given that the human voice provides information about an individual’s dynamic physical state. — M.S.
Self-replication of Alzheimer-associated amyloid
Cryoelectron microscopy reveals various stages (1–4; Arrows) of secondary nucleation events along Aβ42 fibril sides.
In Alzheimer’s disease (AD), preexisting amyloid fibrils catalyze a self-sustaining feedback loop, whereby normally soluble and inert Aβ peptide monomers aggregate into neurotoxic oligomers. Although researchers have determined that this process occurs at the surface of fibrils via secondary nucleation, the precise molecular interactions remain unknown. Focusing on Aβ42, a predominant Aβ peptide in AD plaques, Mattias Törnquist et al. (pp. 11265–11273) used nuclear magnetic resonance and optical spectroscopy to track free monomer concentrations in solution and examine the aggregation reaction and its products during secondary nucleation at the surface of Aβ fibrils. The authors found that, under specific solution conditions, new aggregates form on the sides of fibrils and along the fibrils’ length, growing into large structures that are morphologically distinct from fully formed fibrils. Furthermore, the appearance of the intermediate structures along the sides delineates them from growth sites at fibril ends, where growth occurs via elongation. The authors suggest that monomers may initially attach to the fibril surface and form oligomers, which grow into a mature fibrillar structure that eventually detaches. — T.J.
Ancestor of salamanders
Fossilized skeleton of T. sixtelae with interpretive drawing.
Little fossil evidence exists to connect the features of tetrapods in the Paleozoic Era with lissamphibians, a group that contains all living amphibians, in the Mesozoic Era. This fossil gap renders the origins of modern amphibians unclear. Rainer Schoch et al. (pp. 11584–11588) report a specimen of Triassurus sixtelae, a tetrapod from the middle to late Triassic discovered in Kyrgyzstan. The fossil is better preserved, larger, and more mature than a previously identified larval specimen and contains features suggesting that it may be an ancestor of salamanders. Geological context suggests that T. sixtelae may have lived in a shallow lake environment. Salamander-like characteristics of the skull, vertebrae, and trunk show evolution of the salamander body plan. The fossil specimen also contains features similar to an order of tetrapods called temnospondyls, but with differences that place it in an evolutionary relationship above the temnospondyls and within the batrachians, a group that includes modern frogs and salamanders. According to the authors, the specimen extends the fossil record of salamanders by around 60–74 million years and suggests that Eurasia may be the point of origin for salamanders, which may have dispersed via landbridges in the Triassic Period. — P.G.