Stress isn’t always a bad thing; it can be handy for a burst of extra energy and focus, like when you’re playing a competitive sport or have to speak in public. But when it’s continuous, it actually begins to change your brain. Madhumita Murgia shows how chronic stress can affect brain size, its structure, and how it functions, right down to the level of your genes.

Invented in 1793, the cotton gin changed history for good and bad. By allowing one field hand to do the work of 10, it powered a new industry that brought wealth and power to the American South -- but, tragically, it also multiplied and prolonged the use of slave labor.