Hello Nature readers,
Today we look at the outcomes of a pivotal gathering to protect the ocean, learn that researchers have grown hearts containing human cells in pig embryos for the first time and ponder a mysterious connection between magnetism and oxygen on Earth.

From biologist to photojournalist

Although he has pivoted to conservation photojournalism, former marine biologist Sirachai (Shin) Arunrugstichai still considers the ocean as his office. “I want to share new findings about the sea with other people,” he says. “I can reach more people with my photography than I can with my papers.”

The first pig embryos with human hearts

Researchers have grown hearts containing human cells in pig embryos for the first time. The embryos survived for 21 days, and during that time their tiny hearts started beating. Growing animal embryos that contain some human cells — called human-animal chimaeras — takes scientists a step closer to generating animals with human organs that can be used for transplantation into people. Pigs are a good candidate because the size and anatomy of their organs are comparable to those of humans, says developmental biologist Lai Liangxue.

Earth’s magnetism and oxygen correlate

The abundance of oxygen in Earth’s atmosphere seems to be linked with the strength of the planet’s magnetic field. Over the past 540 million years, the two appear to have risen and fallen in tandem, though it is unclear whether they directly influence one another, or are both controlled by a third factor. Explaining the link could help to reveal fundamental trends in the evolution of life on Earth — and could show astronomers the most promising places to look for signs of complex life on other planets.

One bark if by land

Long-billed curlews (Numenius americanus), a North American bird species, eavesdrop on the barks of prairie dogs (Cynomys ludovicianus) for intel on the approach of predators. Prairie dogs have specific calls that alert their neighbours if a predator is closing in by land or by air. When nesting curlews hear these barks, they press their bodies to the ground, which makes them “essentially invisible on the Plains,” says ornithologist and study co-author Andrew Dreelin. Without the cues, researchers were able to get a remote-controlled ‘predator’ within 16 metres of the birds before they sensed danger.

‘Glimmer of hope’ at UN Ocean Conference

“Never before have so many heads of state and governments met to discuss the seas,” said French President Emmanuel Macron at the UN Ocean Conference in Nice, which ended on Friday. The event resulted in a political declaration and a slew of voluntary commitments, including efforts to remove underwater munitions, tackle undersea noise and create more marine protected areas. Fifty counties have now ratified the UN High Seas Treaty, with dozens more promising to do so. (Sixty are needed for the agreement to come into force). Only patchwork progress was made on efforts to reduce marine plastic pollution and to regulate destructive deep-sea mining and bottom trawling.

The ideal recyclable solar cell

Some of the features that make solar cells affordable, durable and efficient are at odds with the goal of making them recyclable: materials that work well together are not usually easy to pull apart. Solar-cell scientists Ian Peters and Christoph Brabec probe the trade-offs required to build the perfect panel.

What protests work best to change minds

Mass demonstrations against the administration of US President Donald Trump took place across the United States on Saturday — but are protests effective at driving change? “The honest answer is ‘sometimes’,” said Lisa Mueller, who studies social movements, in our June 2024 feature. Large protests seem more effective than small ones; non-violent protests appear to be more potent than violent ones; unified goals might achieve more than diffuse demands do. Repression — by police, for instance — can win more support for protesters. “It’s a vibrant time to be studying protests,” Mueller says.