If not for genetic parasites, mammals — and thus humans — would never have existed, a new Yale study shows.
According to a new study by researchers in the Ecology and Evolutionary Biology department, alien DNA from other organisms is the reason that mammals developed the ability to give birth instead of laying eggs. The research, published in the journal Nature Genetics Sunday, found that the foreign genetic material, called transposons, lodged itself into humans’ DNA and created unique characteristics in our biological makeup, including placental pregnancy. The study confirms what evolutionary scientists have suspected for a long time, EEB department chair Paul Turner said, but the Yale team took this theory a step further by locating the precise genes involved.
“What excites me about this study is that it shows that what’s often seen as an antagonistic relationship can actually be a beneficial one,” Turner said. “These conflicts of interest [between host and parasite] can open up huge leaps in evolution and synergy.”
The study — whose senior author is EEB professor Gunter Wagner — investigated specific cells found in the uteri of three different mammals: armadillos, opossums (who give birth after only two weeks of pregnancy), and humans.
All told, Wagner and his team discovered over 1500 separate genes that are unique to mammals and all of which were traceable to known genetic parasites. And while these DNA strands used to be considered “junk” in our genetic coding, researchers were able to find a correlation between these genes and mammalian pregnancy.
“In the last two decades there have been dramatic changes in our understanding of how evolution works,” Wagner said in an Office of Public Affairs press release last week. “We used to believe that changes only took place through small mutations in our DNA that accumulated over time. But in this case we found a huge cut-and-paste operation that altered wide areas of the genome to create large-scale morphological change.”
Wagner did not respond to requests for comment Thursday.
The foreign DNA spreads in mammals like parasitic organisms that have invaded the body, Vincent J. Lynch, a research scientist in EEB and lead author of the paper, said in the press release. As a result, these genes copy themselves within their host and sometimes push out other indigenous genetic material.
Although any theory of humans’ deep genetic past may be difficult to confirm with absoulte certainty, Turner called the team’s research “rigorous and elegant” in its comparison of multiple mammals.
The research was funded by the John Templeton Foundation, a philanthropic organization based in Philadelphia.