Hello Nature readers,
Today, we look at clues that suggest human ancestors ate each other and learn how the Paris climate-finance summit unlocked loans for poorer countries.

Ancient humans probably ate each other

A carved-up leg bone might be the earliest evidence that ancient humans butchered and ate each other's flesh. The 1.45-million-year-old hominin bone features cuts similar to the butchery marks made by stone tools found on fossilized animal bones. The scrapes are located at an opportune spot for removing muscle, suggesting that they were made with the intention of carving up the carcass for food. It isn't possible to say whether this is an example of cannibalism, because the bone belongs to an unidentified hominin species. The discovery was "shocking, honestly, and very surprising, but very exciting", says palaeoanthropologist Briana Pobiner.

New obesity drugs are cheap and effective

Two new obesity medications could offer advantages beyond those of the blockbuster drugs trizepatide and semaglutide. The first, orforglipron, will probably be available as a pill — current drugs require weekly injections — and it will probably be cheaper than other treatments. In a trial of the second drug, retatrutide, participants lost an average of 24% of their body weight over 11 months. Other drugs lead to a body-weight reduction of about 15–20%. Both of the new drugs mimic appetite-lowering hormones produced by the gut lining.

Summit unlocks loans for poor countries

Low- and middle-income countries facing crushing debt burdens have been thrown a climate-finance lifeline at a summit last week in Paris. Global leaders, the International Monetary Fund and the World Bank agreed — in principal — to share access to low-cost loans and pause some debt repayments. The group also proposed a tax on marine shipping emissions to raise cash. The moves are separate from pledges (as yet unmet) to provide US$100 billion annually to mitigate the effects of climate change and a promised 'loss and damage' fund to help recover from disasters, which spawned from last year's United Nations climate conference. "My plea simply now is to step up the pace, and let's get going," said Barbadian Prime Minister Mia Mottley, a leading voice for sustainable finance in the form of a suite of proposals known as the Bridgetown Initiative.

How to collaborate with mathematicians

"When you ask questions that are to do with somebody else's expertise, they shouldn't simply say, 'Just believe me'," says Ingrid Daubechies, one of the mathematicians who shares insights on how to forge and maintain collaborations. It's important that everybody is listened to — and that people understand each other's lingo. "Translation was the biggest challenge," says Jamie Foster, who worked with a chemist to understand espresso extraction. "Go to other researchers' seminars and laboratory meetings so that you can understand what's important and start speaking the language of their discipline," suggests Yun Kang, who modelled honeybee populations in a joint project with an entomologist.

'Impact bonds' could transform funding

A funding model akin to social impact bonds could shift risk from governments to private investors while increasing accountability and impact, says Michael Hill who heads the Swiss National Science Foundation's grant management. With research impact bonds, private investors would cover a project's cost and be repaid by a public funder only if agreed goals are achieved. "Scientists might be leery of committing to specific research outcomes," says Hill. "But many researchers already preregister their projects, which commits them to a methodology."

Stop policing women's leadership styles

Women in senior positions walk a tightrope as scientific leaders: behaviour that seems acceptable for men is perceived as overconfident, difficult and unlikeable in women, argue crop scientist Alison Bentley and geographer Rachael Garrett. "We have lost count of the number of times we have been encouraged to 'relax' by our male colleagues when debating a point." To end this subtle but relentless misogyny, institutions should do more to cultivate all leadership styles — from assertive to cautious, they argue. One immediate action could be to move away from a single, all-powerful leader to a broader management committee that gives everyone an opportunity to lead.