A team at Stanford has revealed the effort to mix brain tissues of distant species this week. They previously showed that human brain organoids could survive, and even function, after being injected into the heads of baby rodents. Now, they’ve taken things a step further by genetically modifying mice so their brains don’t fully develop in the first place.

The work could help scientists study brain injuries, but it also raises questions about how far these experiments should go.

Here’s what the researchers discovered—and where they draw the line.

—Antonio Regalado

These innovators under 35 are shaping climate tech

Each year, the editorial team at MIT Technology Review puts together a list of 35 Innovators Under 35—a group of researchers, inventors, and other young minds worth following. The final slate includes nine people tackling some of the biggest challenges in climate and energy, from critical materials to cleaner industry.

Their innovations include new ways to extract lithium, a furnace built to make steel cleaner and cheaper, and solid refrigerants that could cut energy consumption. There are also efforts to make AI more energy-efficient, track pollution more effectively, and turn invasive weeds and food waste into useful materials.

Taken together, they tell us something about where climate tech is at this moment—and where it’s heading.

Get to know the innovators and their breakthroughs.