It’s August in Australia, and a small, mouse-like creature called an antechinus is busy killing himself through sex. He was a virgin until now, but for two to three weeks, this little lothario goes at it non-stop. He mates with as many females as he can, in violent, frenetic encounters that can each last up to 14 hours. He does little else.

A month ago, he irreversibly stopped making sperm, so he’s got all that he will ever have. This burst of speed-mating is his one chance to pass his genes on to the next generation, and he will die trying. He exhausts himself so thoroughly that his body starts to fall apart. His blood courses with testosterone and stress