A bit of DNA that has the ability, heretofore unseen in humans, to “jump” from one organism to another may have given rise to the human immune system, according to Yale researchers. A team led by David G. Schatz, Ph.D., associate professor of immunobiology and an HHMI investigator, has found evidence that tiny gene particles vital to the task of producing millions of different kinds of antibodies in humans act like a gene segment that can “jump” into foreign DNA. Their findings were published in the Aug. 20 issue of the journal Nature. Although such genes abound in lower organisms, the “jumping DNA” is the first cut-and-paste “transposase” ever found in humans. Dr. Schatz theorizes that such a jump may have happened within the mammalian genome some 450 million years ago. “This helps explain why the jawed vertebrates—including humans—are the only species that have a second, adaptive immune system in addition to the innate immune system that all other species have,” says Dr. Schatz. Any clinical applications of this knowledge are speculative, he says, although there may be implications for the diagnosis or prevention of lymphoma.