The lipidomes of cell membranes, cells, organs, and the human body are immense, reflecting that many different lipids are involved in a wide range of important and diverse biochemical and physiological functions. However, one specific type of lipid, cholesterol, stands out as a unique case being the single most abundant type of molecule in all animal plasma membranes which typically contain about 20% to 30% cholesterol. Even if derivatives of cholesterol are engaged in a host of biochemical processes, the simple cholesterol molecule itself seems by evolution to have been selected for its unique ability to modulate the physical state of membranes. Other higher sterols, such as sitosterol, ergosterol, and fucosterol, appear to have been evolved to serve a similar function in the kingdoms of plants, fungi, and algae, respectively.