Living things convert the relatively simple squalene molecule to lanosterol, which is the precursor to all steroids, and hopenes in the plant world.

This much has been known for some time, but the discovery of the animal steroid progesterone in the vascular plant, Juglans regia, in 2010, threw up striking evidence of just how old is this biochemistry, suggesting that hopenes, triterpenes and steroids are linked by the common ancestor of plants and animals. Now, density functional theory has shed new light on the biochemistry and how it proceeds towards these different end products.

• Compelling Computational Evidence for the Concerted Cyclization of the ABC Rings of Hopene from Protonated Squalene,
  Lidia Smentek, B. Andes Hess, Jr.,
  J. Am. Chem. Soc. 2010.
  DOI: 10.1021/ja1039133