An evolutionary tree of transposons (IMAGE) University of California - Berkeley Caption Viral elements called transposons have invaded mammalian genomes for millions of years and currently make up nearly half the DNA in the genomes of all living mammals. The image depicts species-specific transposon integrations as unique events in the evolutionary history of each species. Credit UC Berkeley image by Kerry Lin Usage Restrictions none License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.