When ancient Polynesians first reached the Pacific archipelagos of Samoa and Tonga, they presumably liked what they found. For the next 1,700 or so years, they rarely ventured further. Then, within a century or two, they suddenly settled almost every remaining habitable island in the Pacific.

What changed? That question is central to both Disney’s new Moana movie and decades of archaeological research.

Now, a team led by David Sear of the University of Southampton presents new evidence that a prolonged drought may have triggered this spectacular feat of exploration. Combined with growing populations and new canoe technology, this environmental change may help explain why Polynesian expansion began when it did.

Meanwhile, some AIs are autonomously rewriting their own code. Researchers at the University of Galway say this “recursive self-improvement” could represent the dawn of superintelligence and must be regulated urgently.

And Ruth Ellis, the last woman to be hanged in Britain, has been granted a posthumous conditional pardon. The decision is long overdue, says criminologist Lizzie Seal of the University of Sussex, who says the legal system has evolved to better account for violence aimed at domestic abusers.