Here is a heart-shaped piece of cactus I found on yesterday’s walk. I’ve just finished Iain Gately’s excellent essay on the iconography of love, “A Heart-Shaped History,” all about how the ♥ became the near-universal symbol for love:

The ♥ in geometric terms a cardioid, is common in nature. It appears in the leaves and flowers of various plants, it is formed by swans when they touch beaks, by doves as they unfold their wings, by strawberries, cherries and beet-roots in cross section, and is suggested by various portions of the human anatomy.

Lots of tasty historical tidbits follow — the Egyptians, for example, left hearts inside of the corpse so the Goddess could weigh them in the afterlife, the Greeks’ Eros shot his arrows at people’s eyeballs instead of their chests, the ♥ replaced the grails in the first decks of cards, etc.

As far as accuracy goes, Leonardo da Vinci produced the first well-rendered depiction of the heart in 1498. (Scientists wouldn’t figure out what the heart actually did until a century later.) Leonardo drew a seed next to one of the drawings in his notebooks, and wrote, “The heart is the nut which generates the tree of the veins.” (Isaacson devotes a whole section to Leonardo’s heart studies in his biography.)

Isaacson points out this page, where Leonardo draws a heart inside of his longtime companion, Salaì:

At the top is a drawing of the heart’s papillary muscle and a description of how it shortens and elongates when the heart beats. Then, as if he were being too clinical, he let his mind wander and pen begin to doodle. And there, in loving profile, is a drawing of Salai, his beautiful curls flowing down his long neck, his signature receding chin and fleshy throat softly modeled with Leonardo’s left-handed hatching. In his chest is a section of a heart, with its muscles sketched in. An analysis of the drawing shows that the heart was sketched first. It seems as if Leonardo drew it, then sketched Salai around it.

Happy Valentine’s Day.