Putative evolutionary scenario for the AluYb lineage. A schematic diagram of the hominid primates is shown with the approximate time scale shown on the bottom in million years. The blue lines indicate the expansion of the AluYb lineage, and the thickness of the lines represents its relative retrotransposition activity. The estimated copy number of AluYb elements in various primates is shown after their names. The blue triangle represents the estimated integration time period of AluYb founder gene, and the star represents the estimated integration time period of the oldest known AluYb8 element (Pan4).