A new analysis published in the journal Science reveals that overfishing has caused populations of chondrichthyan fishes – sharks, rays, and chimaeras – to decline by more than 50 per cent since 1970. To determine the consequences, a team of researchers developed an aquatic Red List Index (RLI) which shows that the risk of extinction for chondrichthyan has increased by 19 per cent. The study also highlights that the overfishing of the largest species in nearshore and pelagic habitats could eliminate up to 22 per cent of ecological functions.

Chondrichthyans are an ancient and ecologically diverse group of over 1,199 fishes that are increasingly threatened by human activities. Overexploitation by target fisheries and incidental capture (bycatch), compounded by habitat degradation, climate change and pollution, has resulted in over one-third of chondrichthyans facing extinction. Here, the RLI was used to track the status of these species over the past 50-years.

In a Policy Forum, scientists discuss lifeforms composed of mirror-image biological molecules – also known as “mirror life” – and say creation of such lifeforms, which could evade immune mechanisms and predators, warrants careful consideration. The hallmark of mirror organisms is reversed chirality – a feature that would render them resistant to normal forms of biological degradation, making them useful for applications like long-lasting therapies. While these organisms haven’t yet been observed in nature, and the capability to create them is likely at least a decade away, requiring large investments and major technical advances, now is the moment, say the authors, to consider and preempt risks. The authors – an interdisciplinary researcher group, including researchers who have held the creation of mirror life as a long-term aspirational goal – call for broader discussion amongst the global research community, policymakers, research funders, industry, civil society, and the public, to chart an appropriate path forward. The detailed analysis on mirror life they present is perhaps the most comprehensive assessment to date. It qualitatively assesses the feasibility and risks of creating mirror bacteria, considering factors including the nature, magnitude, and likelihood of potential harms, the ease of accidental or deliberate misuse, and the effectiveness of potential countermeasures. The authors focus on mirror bacteria in this analysis but note that many of the considerations might also apply to other forms of mirror life. Among concerns, the authors say their analysis suggests that mirror bacteria would likely evade many immune mechanisms, potentially causing lethal infection in humans, animals, and plants. Such bacteria are likely to evade predation from phages and many other predators, facilitating spread in the environment. The authors explain that though they were initially skeptical that mirror bacteria could pose such major risks, they have since become deeply concerned. They call for additional scrutiny of their findings and further research to improve understanding of these risks. However, they note, in the absence of compelling evidence for reassurance, their view is that mirror bacteria and other mirror organisms should not be created. They believe that this can be ensured with minimal impact on beneficial research.

The findings of these researchers – summarized in the Policy Forum – are available in more detailed form in a separate, in-depth technical report that can be accessed at a link in the related press release (https://www.eurekalert.org/news-releases/1067465/).

A genomic study encompassing more than 300 genomes spanning the last 50,000 years has revealed how a single wave of Neandertal gene flow into early modern humans left an indelible mark on human evolution. Among other findings, the study reports that modern humans acquired several Neanderthal genes that ended up being advantageous to our lineage, including those involved in skin pigmentation, immune response, and metabolism. To date, sequencing of Neanderthal and Denisovan genomes has revealed substantial gene flow between these archaic hominins and modern human ancestors, even as scientists have also reported that Neanderthal ancestry is unevenly distributed across the genome. Moreover, certain regions of the genome – known as archaic deserts – completely lack Neandertal ancestry, while others exhibit high frequencies of Neanderthal variants, potentially due to beneficial adaptive mutations. However, much about the nature of this ancient admixture, including the role evolutionary forces like genetic drift or natural selection played in shaping these patterns, remains unclear. Using genomic data from 334 modern humans, including 59 ancient individuals ranging from 45,000 to 2,200 years old, and 275 present-day individuals from diverse global populations, Leonardo Iasi et al. performed a comprehensive evaluation of Neanderthal ancestry variation in modern humans over the last ~50,000 years. Iasi et al. discovered that the vast majority of Neanderthal gene flow is attributable to a single, shared extended period of gene flow that likely occurred 50,500 to 43,500 years ago, which is consistent with archeological evidence for the overlap of modern humans and Neandertals in Europe. Additionally, the findings demonstrate that Neanderthal ancestry underwent rapid natural selection – both positive and negative – within 100 generations after gene flow, especially on the X chromosome.

Nature is publishing a related paper, “Earliest modern human genomes constrain timing of Neanderthal admixture,” embargoed for the same time (Thursday, 12 December at 2pm US ET). To obtain a copy of this paper, please email press@nature.com or visit the Springer Nature press site (https://press.springernature.com/). An online press briefing for the two papers will take place UNDER STRICT EMBARGO on Wednesday at 3pm London time (GMT) / 10 am US Eastern Time. To attend this briefing please pre-register here (https://register.gotowebinar.com/register/2888900175525652313).