The potato that reached Europe in the late 1500s was the andigena (page 97). But how it became the modern potato is a matter of debate. When grown in Europe today, andigena's stolons are very slow to swell to form tubers, and it produces little or no yield. Differences in daylength between the short days of the central Andes and the long days of a northern European summer are the cause.

It is probably accidental that the andigena was transformed into a useful crop for Europe. In the 1600s and 1700s, some people propagated potatoes by planting botanical seeds. The resulting seedlings were highly variable; virtually every plant differed from all the others. This allowed a vast number of genes to be combined and expressed, and among the types that arose were some that could tuberize during long days.

This is the explanation believed by most potato geneticists. There is, however, a possible alternative: that an unrecorded ship introduced “long-day potatoes” from southern Chile. Chilean potatoes are almost certainly also derived from andigena, but for centuries they have been adapted to long-day production.

Whichever method transformed andigena, it was one of the most valuable genetic developments of all time; it gave the world what is now its fourth largest food crop: the modern potato.