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The Club of Rome’s population estimates come from a model created to explore which policies would deliver the most good for the majority of people. (Richard Ellis/Alamy)

Fairer world could cool population growth

The number of people living on Earth could peak at 8.5 billion in 2040 and decline to 6 billion by the end of the century — if there’s an unprecedented push to eliminate poverty and inequality. The projection takes into account environmental, economic and social factors that aren’t considered in the United Nations’ estimate that we will exceed 10 billion by 2050. By itself, a fall in the world’s population won’t stop us from destabilizing Earth’s life-support systems, says human-development researcher David Collste. “It’s what people do, how they do it and how much they do it.”

New Scientist | 4 min read (free registration required)

Reference: Club of Rome report

Fish can sense each other’s fear

Zebrafish (Danio rerio) become afraid when they see other members of their species in distress. This fear mirroring is regulated by oxytocin: fish that lack the genes to produce and absorb the hormone fail to detect others’ anxiety but regain the ability when they receive an oxytocin injection. Oxytocin has the same effect in mice, and is known to affect humans’ social responses, meaning it’s likely that this empathy mechanism evolved many millions of years ago, before fish and mammals diverged on the tree of life.

Associated Press | 4 min read

Reference: Science paper

Brain prosthesis improves memory

A ‘memory prosthesis’ seems to boost people’s ability to remember new information. It consists of a deep-brain electrode that records and then mimics the electrical activity pattern of the hippocampus, a brain region that has a crucial role in memory. Twenty-four people, who had already had electrodes implanted to study their epilepsy, volunteered to try the device: it improved their performance in short- and long-term memory tests by up to 54%. “It’s a glimpse into the future of what we might be able to do to restore memory,” says neuroscientist Kim Shapiro.

MIT Technology Reviews | 6 min read

Reference: Frontiers in Human Neuroscience paper

Features & opinion

Why water must be central to climate action

Last week, a long-awaited United Nations water conference resulted in hundreds of non-binding pledges from governments, non-profit organizations and businesses. Not everyone came away satisfied: in an open letter, 100 water experts called for more accountability, rigour and ambition.

A group of water and climate specialists write that “the gap between articulation and action urgently needs to be bridged”. Water management and climate mitigation measures need to work in tandem, they argue.

Clean water must become a global common good, suggests a team of sustainability scientists. Research is badly needed to understand water flows’ connectivity: for example, deforestation in the Congo Basin lowers rainfall in neighbouring countries, and heavy crop irrigation in India can boost the streamflow of the Yangtze River in China.

The Guardian | 5 min read, Nature | 11 min read & Nature | 12 min read

How Nancy Hopkins measured sexism in science

One night in 1993, frustration prompted molecular biologist Nancy Hopkins to measure the dimensions of every room in her building at the Massachusetts Institute of Technology (MIT). Her work revealed that women were given less space than men, forcing MIT to admit to having discriminated against female researchers for decades and leading to a US-wide reckoning about sexism in science. In The Exceptions, journalist Kate Zernike details Hopkins’s journey and provides a deeply researched dive into the history of gender discrimination in US higher education. Even though the main events transpired decades ago, they remain remarkably relevant today, writes reviewer and Nature correspondent Alexandra Witze.

Nature | 5 min read

Video: A stress-test for autonomous cars

Researchers have created a fiendishly difficult test to help self-driving cars learn how to deal with rare but dangerous situations. On a test track, a real car steered by an artificial-intelligence (AI) system was pitted against virtual AIs that were terrible drivers. “I was one of the test drivers,” says transport researcher Henry Liu, recalling how he sometimes felt a little nervous when the AI slammed on the brakes of his car to avoid a virtual obstacle that he couldn’t see.

Nature | 5 min video

Reference: Nature paper

Quote of the day

“All I was trying to do was get that message across, that by putting more and more stuff on a chip we were going to make all electronics cheaper.”

Semiconductor pioneer Gordon Moore has died aged 94. As well as co-founding Intel, he coined ‘Moore’s Law’, which predicted that every year, engineers would manage to double the number of transistors crammed onto a computer chip. (BBC | 4 min read)