Volume 650

From sticky hinges to bicycle brakes, squeaks are part of everyday life. Although the way sound is generated when two rigid bodies slide over each other is relatively clear, what happens when a soft material slides on a rigid body is much less well understood. In this week’s issue, Katia Bertoldi and colleagues reveal what generates the squeak in such a situation. Using high-speed imaging and acoustic analysis, the researchers examined basket-ball shoes sliding on a smooth glass plate (as imaged on the cover). They found that friction effects at the interface between the shoe and the floor cause wave-like deformations of the sole, resulting in pulses. These pulses travel across the sole in bursts, and the pitch of the squeak matches the repetition rate of the bursts. Using silicone rubber blocks instead of shoes, the team found that ridges cause the block to lock into a specific natural frequency set by the height of the block — to such an extent that the researchers could use tuned blocks to play a song.

The cover shows examples of early rock art found in limestone caves on the Indonesian island of Sulawesi. As Adhi Agus Oktaviana and colleagues report in this week’s issue, a hand stencil dated to at least 67,800 years ago at Liang Metanduno could be the oldest rock art yet discovered. Indonesia is already well known for its ancient cave art, but Sulawesi’s southeast region had remained largely unexplored. To rectify this, the researchers surveyed caves across the area and recorded 44 sites, including 14 previously unknown locations. Their dating of the hand stencil makes this image a minimum of 1,100 years older than the previously known oldest art — a hand stencil attributed to Neanderthals in Spain. The team notes that the Sulawesi art adds strong support to the idea that early humans migrated to Sahul (the ancient landmass that formed Australia and New Guinea) via a northern route through Sulawesi.

The use of synthetic pesticides is widespread, and their potentially harmful effects on wildlife — from bees to fish— and human health are well documented. Somewhat less clear are their effects on soil biodiversity. In this week’s issue, Marcel van der Heijden and colleagues address this issue with a report on how pesticide residues affect soils across Europe. The researchers assessed 63 pesticides across 373 sites in 26 European countries. Pesticide residues were present at 70% of the sites and showed the second biggest effect on soil biodiversity patterns after soil properties. The team also saw specific patterns, with pesticides altering microbial functions and suppressing beneficial organisms, suggesting that functional and taxonomic characteristics need to be part of risk assessments for preserving soil biodiversity.

The cover shows members of a local community in the Western Province of the Solomon Islands taking part in a traditional fish drive, in which multiple members of a community work together to make the catch. The world’s oceans and their resources are crucial to humanity, but there is increasing inequity when it comes to accessing these resources. The benefits tend to be accrued by the powerful, whereas the burdens — from pollution to biodiversity loss — are more often shouldered by the most vulnerable. Many of these vulnerable groups, such as Indigenous peoples and small-scale fishers, are also excluded from the decision-making processes and a fair share in ocean benefits. In this week’s issue, Jessica Blythe, Joachim Claudet, David Gill and colleagues present the Ocean Equity Index — a framework for advancing equity. Consisting of 12 criteria, the index offers a transparent and standardized way to assess and monitor equity in ocean initiatives, projects and policies. The researchers hope that the index will improve the way equity is incorporated into ocean initiatives and so pave the way to better outcomes for coastal people and marine ecosystems.