5 Most Incredible Discoveries of the Week

Why our knuckles crack and bad news for pot smokers' GPAs make the list:

• Archaeologists May Have Found World's First Tools: Stone tools found at a site in Kenya may date back 3.3 million years, shattering the previous record by about 700,000 years. The new date is significant because the first modern humans didn't arrive until 2.8 million years ago, meaning these tools would have been used by our ancient predecessors. This discovery may fill in the blanks to a fascinating 2010 find.

• Where Did Chins Come From?: Most people probably haven't thought too hard about this question, but scientists at the University of Iowa have. A previous theory suggested that chins are shock absorbers of sorts, offering support as we chew, but this new research has come up with an entirely different postulation. Hint: Neanderthals had really big heads.
• Scientists Answer Age-Old Question About Knuckles: "Pull my finger" isn't just a dumb gag. It's also how University of Alberta scientists say they've figured out why our knuckles make that popping sound when cracked. To solve this mystery, they used an MRI scanner, a finger-pulling device, and a man they call the "Wayne Gretzky of knuckle-cracking." If the theory pans out, it could help doctors fend off joint pain before it starts.
• Pot-Smoking Students Fail More Courses: Researchers compared more than 54,000 grades of undergraduates in the Dutch city of Maastricht, where some of the students were banned from the city's cannabis coffee shops. Those who who weren't banned apparently had a somewhat hazier understanding of all things school than their toke-free classmates—especially in one important subject.
• What Changed Caesar's Personality: One leading theory about Julius Caesar is that his health problems later in life were caused by epilepsy. A new idea, however, suggests something else entirely: mini-strokes. Researchers say it can explain why Caesar's personality became the way it did as he aged.

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