Hello Nature readers, would you like to get this Briefing in your inbox free every day? Sign up here.

The second X chromosome in female cells — previously thought to be ‘silent’ — might explain why women tend to live longer and be more resilient to cognitive decline than men. In mice, researchers found that ageing activates expression of the ‘silent’ X chromosome in cells in the hippocampus, a brain region crucial to learning and memory. When they boosted the expression of one of these genes in mature mice of both sexes, it improved the mice’s cognition, as measured by how well they explored a maze.

Nature | 5 min read

Reference: Science Advances paper

Bone tools discovered in Tanzania reveal that ancient humans consistently used such tools at least one million years earlier than we thought. The previous estimate put the earliest use of bone tools at around 400,000 years ago. The new findings smash that record, dating the implements to around 1.5 million years ago. The utensils were crafted from elephant, hippopotamus and bovine bones, and were probably used for tasks such as butchering and digging out tubers, says palaeoanthropologist Jackson Njau.

Nature | 4 min read

Reference: Nature paper

In mice, the activity of three types of neurons is involved in the decision to persist with a task, explore new options, or give up. Researchers genetically engineered the neurons — which release the neurotransmitters GABA, glutamate and serotonin — so they could be switched on and off with light and placed the mice in a box with 20 unfamiliar objects. If researchers suppressed GABA-releasing neurons, the mice spent more time investigating one object. Turning off glutamate-related neurons made the mice shop around between objects more often, and if serotonin-producing neurons were inhibited, the mice lost interest altogether.

Nature | 5 min read

Reference: Nature paper

A machine-learning algorithm could alert researchers to the impending collision of two neutron stars, which would allow researchers to observe the crash in real time. The algorithm was trained on simulations of the data that a gravitational-wave observatory collects in the minutes before a rarely observed event called a kilonova — a merger of two neutron stars. The algorithm would enable observatories to tell astronomers that a collision is about to happen at a given time and location in the sky, with 30% more accuracy than existing rapid-response techniques.

Nature | 4 min read

Reference: Nature paper

Infographic of the week

Areas of deforestation in Amazonia affect rainfall patterns in both wet and dry seasons. In wet seasons heat from patches of cleared land pushes air upward to create an area of low pressure (top). This draws moisture from neighbouring areas, increasing rainfall over the cleared land and reducing it elsewhere. During a dry season, less moisture enters the atmosphere, which reduces rainfall over a wide region (bottom). (Nature News & Views | 7 min read)

Reference: Nature paper

Today I’m appreciating the unicorn of the seas — the mighty narwhal (Monodon monoceros). A narwhal’s distinctive ‘horn’ (actually a very long, protruding tooth) might look threatening, but they don’t use them to fight. Instead, scientists think they use them to assess potential mates, sense changes in their environment and, as new research has revealed, play. Using a drone, researchers captured the elusive animals chasing fish and using their tusks to nudge them in a particular direction. It isn’t my idea of fun, but I’m sure those narwhals were having a ball.

Help us nudge this newsletter in the right direction by sending your feedback to briefing@nature.com.

Thanks for reading,

Jacob Smith, associate editor, Nature Briefing

With contributions by Flora Graham

Want more? Sign up to our other free Nature Briefing newsletters:

• Nature Briefing: Careers — insights, advice and award-winning journalism to help you optimize your working life

• Nature Briefing: Microbiology — the most abundant living entities on our planet — microorganisms — and the role they play in health, the environment and food systems

• Nature Briefing: Anthropocene — climate change, biodiversity, sustainability and geoengineering

• Nature Briefing: AI & Robotics — 100% written by humans, of course

• Nature Briefing: Cancer — a weekly newsletter written with cancer researchers in mind

• Nature Briefing: Translational Research — covers biotechnology, drug discovery and pharma