Achille the bull and Patrocolo the male donkey could have chosen partners of the same species and opposite sex. But don’t. Image: Martina Francesconi, UNIPI

Sex between two animals of the same sex is widespread. Over 1,000 animal species from nematode worms to penguins to cattle all dabble in same-sex interactions. But a relationship between a bull named Achille and a male donkey named Patrocolo is raising eyebrows. The pair lives on a plateau in Ethiopia, and both could have chosen partners of the opposite sex and same species on numerous occasions. However, they continued to choose each other, despite belonging to different owners and only seeing one another when spending time in a pasture.…