"Alu" elements in primates form a fossil record that is relatively easy to decipher because "Alu" element insertion events have a characteristic signature that is both easy to read and faithfully recorded in the genome from generation to generation. The study of "Alu Y" elements (the more recently evolved) thus reveals details of ancestry because individuals will most likely only share a particular "Alu" element insertion if they have a common ancestor. This is because insertion of an Alu element occurs only 100 - 200 times per million years, and no known mechanism of deletion of one has been found. Therefore, individuals with an element likely descended from an ancestor with one—and vice versa, for those without. In genetics, the presence or lack thereof of a recently inserted "Alu" element may be a good property to consider when studying human evolution.