(left to right): ARINA HABICH/ALAMY STOCK PHOTO; WANG CHI LAU/ EMBRYOLOGY COURSE AT THE MARINE BIOLOGICAL LABORATORY; istock.com/martinedoucet

Top stories: Chocolate money, the rise of multicellularity, and pet rabbit brains

The Maya civilization used chocolate as money

Your Hershey bar may have been worth its weight in gold in Mayan times. A new study reveals that chocolate became its own form of money at the height of Mayan opulence—and that the loss of this delicacy may have played a role in the downfall of the famed civilization.

The momentous transition to multicellular life may not have been so hard after all

Billions of years ago, life crossed a threshold. Single cells started to band together, and a world of formless, unicellular life was on course to evolve into the riot of shapes and functions of multicellular life today, from ants to pear trees to people. It's a transition as momentous as any in the history of life, and until recently we had no idea how it happened.

Why your pet rabbit is more docile than its wild relative

Why does a wild rabbit flee when a person approaches, but a domestic rabbit sticks around for a treat? A new study finds that domestication may have triggered changes in the brains of these—and perhaps other—animals that have helped them adapt to their new, human-dominated environment.

U.S. judge tosses climate lawsuits by California cities, but says science is sound

A federal judge this week threw out lawsuits from two California cities seeking to make oil companies pay for worsening sea-level rise and other climate change impacts. San Francisco and Oakland, California, sued Chevron Corp., BP PLC, ConocoPhillips, Exxon Mobil Corp., and Royal Dutch Shell PLC, arguing the companies make and sell products that, when combusted, create a public nuisance. The cities also contended that the companies knew the global dangers for decades and hid that information while protecting their assets.

Hundreds of new genes may underlie intelligence—but also autism and depression

Being smart is a double-edged sword. Intelligent people appear to live longer, but many of the genes behind brilliance can also lead to autism, anxiety, and depression, according to two new massive genetic studies. The work is also one of the first to identify the specific cell types and genetic pathways tied to intelligence and mental health, potentially paving the way for new ways to improve education, or therapies to treat neurotic behavior.