Daily briefing: ‘Overweight’ BMI might be set too low

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Daily briefing: ‘Overweight’ BMI might be set too low


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Sea squirts belong to a group of spineless animals called tunicates, which are vertebrates’ closest living relatives, despite their many differences. (K. Nanglu et al./Nat Commun (CC-BY-4.0))

An exquisitely preserved 500-million-year-old fossilized sea squirt offers new insight into the evolution of tunicates, the sister group to vertebrates and a key to unravelling our own evolutionary origins. “It looks like a tunicate that died yesterday and just happened to fall down on some rock,” says developmental biologist Nicholas Treen. The fossil resembles living tunicates that have two life stages: free-swimming larvae and adults that live rooted to the sea floor. This suggests that a crucial evolutionary moment — when sessile tunicates diverged from free-floating ones — happened 50 million years earlier than currently estimated on the basis of molecular clocks.

Science | 4 min read

Read more: An ancient link between heart and head — as seen in the blobby, headless sea squirt (Nature | 10 min read, Nature paywall)

Reference: Nature Communications paper

A slab of light brown rock bears the fossilised imprint of a sea squirt as an upright, vase-like structure.

The specimen of Megasiphon thylakos preserves in glorious detail the soft sea squirt’s barrel-shaped body, with two long siphons and prominent longitudinal muscles. (K. Nanglu et al./Nat Commun (CC-BY-4.0))

People with an ‘overweight’ body mass index (BMI) have a slightly lower rate of death than people with a supposedly ideal BMI, suggesting that the threshold at which higher weight might be a health risk is not accurate. The BMI was developed as a population-level measure but is often used to give health advice to individuals. Researchers tracked the survival of an ethnically diverse group of around 500,000 US adults for up to 20 years and found that having a BMI between 25 and 29.9 — classified as ‘overweight’ — is associated with an 5–7% lower risk of death within the study period than having one in the ‘healthy’ range. Lead researcher Aayush Visaria says this shows that “BMI overall is just not a good indicator of mortality risk — other factors such as body fat distribution also play an important role”.

New Scientist | 4 min read (free registration required)

Reference: PLoS ONE paper

Researchers who study conspiracy theories say that they are now being drawn into one: allegations that they are helping to suppress conservative opinions in the United States. There are at least three House of Representatives judiciary committees that are investigating the alleged ‘censorship regime’ involving academic researchers, government programmes designed to counter disinformation and social-media platforms, such as Twitter and Facebook. In parallel, some researchers are facing lawsuits or being blocked from working with federal agencies. The moves contribute to a worrying trend in which climate scientists, for instance, are targeted by conservative activists and leaders. “This is a practice that is going to touch more and more researchers’ lives,” says political scientist Rebekah Tromble.

Nature | 6 min read

Features & opinion

More than 150 companies around the world are working on growing meat without the animal. Cells from an animal biopsy are grown in a laboratory, nurtured and coaxed into multiplying to create muscle or fat. Advocates say that such cultured meat will almost certainly use less land and water than rearing livestock, which accounts for about 15% of global greenhouse-gas emissions. Critics argue that cultured meat will be too unaffordable and energy-intensive. Using renewable energy could shrink the carbon footprint of lab-grown meat to below that of conventional farming — or even lower than that of plant and insect protein, according to one analysis.

Nature | 11 min read

Demographic-prediction algorithms can infer gender, race and ethnicity from people’s names on scientific papers, on social media or in political-donor databases. Comparisons with self-identification surveys reveal how flawed these tools can be: in one example, they misgender women 3.5 times more often than men, and racially misclassify 80% of Black people with highly educated parents. Sometimes, accuracy can be increased with tools hand-crafted with a particular population in mind. Often, researchers need to ask themselves whether it’s effective, justified and ethical to use algorithms at all. The good news is that imputation algorithms present new research opportunities. Because society’s biases are reflected in the way algorithms classify names, they could help with understanding name-based discrimination.

Nature | 7 min read

The world’s largest economies need to enshrine equity in their climate action to ensure that responsibility doesn’t fall to those who have contributed least to the problem, argues climate-policy researcher Navroz Dubash. A summit for leaders of the G20 group this September is a chance to frame a declaration around low- and middle-income countries’ specific needs and to redouble efforts by industrialized nations to support shifts to low-carbon development. Importantly, Dubash says, the few fossil fuels that fall in the remaining global carbon budget should be used where they contribute the most to human welfare: in poorer countries.

Nature | 5 min read

Infographic of the week

Temperature records broken: A host of climate markers reached their highest-ever figures for the month of June.

Source: ClimateReanalyzer.org, Climate Change Institute, University of Maine

Last month was a record-breaking one for Earth. Key climate markers, including global air and sea surface temperatures, both surpassed previous records for June, and global sea ice was at an all-time low for the month. Records for individual climate phenomena have been broken in previous years, but this June felt different, says environmental geographer Thomas Smith. “At the moment everything is record-breaking and I don’t think any of us have seen that.” (Nature | 4 min read)

See more of the week’s key infographics, selected by Nature’s news and art teams.

Quote of the day

Former Google chief executive Eric Schmidt explores how he thinks artificial intelligence will transform the practice of science. (MIT Technology Review | 10 min read)

Today I’m surprised to hear that one of the best ways to handle not being able to fall asleep is just to get up. “I would recommend getting out of bed and sitting somewhere quietly with dim light and just relaxing, doing something boring,” says sleep-medicine specialist Kim Hutchison.

Thanks to all who wrote to tell our reporters about your experiences with sleep-deprived science, from drowsy lab work to overnight responsibilities. If you haven’t had a chance to share your story, it’s still very welcome at naturecareerseditor@nature.com.

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Thanks for reading,

Flora Graham, senior editor, Nature Briefing

With contributions by Gemma Conroy and Katrina Krämer

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