In the mountain forests of China grows a tree that remembers the dinosaurs. Cathaya argyrophylla is a living fossil; its lineage split from pines over a hundred million years ago. But instead of a mighty long-liver, we have a vulnerable species: it grows slowly and often falls ill. Why — was long a mystery.

The answer was found in 22 billion letters of DNA. The genome of this tree resembles a bloated encyclopedia where useful articles drown in endless repeats. Nearly three-quarters of the genome consists of repetitive regions that code for nothing. But the main discovery is not the size. The genes responsible for defense against fungi and bacteria turned out to be compressed to a minimum. The plant seems to have unlearned how to defend itself on its own.

Instead, the genes that control the transport of substances across cell membranes are expanded. This is like a house with a leaky roof but a huge staff of couriers. The tree, it seems, survives thanks to symbiosis: it lets in needed molecules from fungi and helper bacteria through its roots. Without them, it is like a defenseless child in the forest.

Now biologists know the species' weak points at the molecular level. They can select the right microbial partners for seedlings or boost the fallen defense genes. The genome has become a treasure map for conservation programs.