Junk DNA Gave Us the Modern Uterus, in a Giant Genetic Cut-and-Paste Operation

By Veronique Greenwood | September 27, 2011 8:00 am

What’s the News: A new analysis finds that many of the genes behind the development of modern mammalian pregnancy are controlled by mysterious genetic elements called transposons, long referred to as “junk DNA.” The results suggest that the placental uterus did not evolve gradually but instead arose from a massive, transposon-driven genetic rewiring.

How the Heck:

  • The research team looked at the DNA of uterine cells from the possum, a marsupial that gives birth two weeks after conception and shelters its developing young in a pouch, and compared them with cells from armadillos and humans, which both carry their children to term in a womb lined with a nutrient-rich placenta. The uterine cells of armadillos and humans shared more than 1,500 active genes that possums lacked.
  • Looking closer, the team saw that a number of these genes—about 13%—were very near on the genome to a particular kind of transposon specific to placental mammals. The origins of transposons, jumping genetic elements that copy and insert themselves in their host genomes seemingly at random, are still unclear, and their purpose has long been so opaque that they were called “junk DNA” until relatively recently. We now know that they play an important role in activating and disrupting the expression of genes.
  • The particular transposons the researchers observed turned out to make uterine cells sensitive to the hormone progesterone, encouraged the cells’ development into the placenta, kept the genes from being turned off, and influenced a variety of other changes central to modern placental pregnancy.

The Future Holds: The fact that genes so crucial to modern mammalian pregnancy are controlled at so many levels by these mysterious jumping elements, which likely cut-and-pasted themselves into the genome years ago, is a new revelation, and the primary message the researchers take from this is that gradual modification of existing genes isn’t the only way evolution can happen. Future work will likely investigate the different levels at which transposons control pregnancy, as well as further work on other areas where transposons have been involved in evolution.

Reference: Lynch, et al. Transposon-mediated rewiring of gene regulatory networks contributed to the evolution of pregnancy in mammals. Nature Genetics (2011) doi:10.1038/ng.917 Published online 25 September 2011.

  • tall blue ape

    err – hold your horses. this saltationist ‘breakthrough’ is funded by Templeton. color me very skeptical about the conclusions reached in this paper.

  • Chrysoprace

    I recall reading an interview recently with a woman whos name I cant recall. She explained a theory that genes are transplanted causing much of evolution, and that natural selection removes but rarely creates. She also said that this theory and those who support it are a shunned minority, but this seems to support that theory.

  • Gil

    @2 From your description, it sounds like you were reading something by an ID Creationist, which isn’t really what this is about. This article is about a specific sort of genetic recombination having played a stronger role in the evolution of the mammalian reproductive system than previously thought. These sorts of mutations are already incorporated in our current understanding of evolutionary biology and the sources of novelty.

  • http://DiscoverMagazine Templar 7

    Well, Gil, they are not already incorporated, and the evidence of that is this article. Give an example please when you make statements like “These sorts of mutations are already incorperated in our current understanding of evolutionary biolog and the sources of novelty.”

    True science should be built on facts, should it not?? So please include specific examples in the future to support your comments. This goes for all of you.!!

    Good Day!

  • Johannes


    They obviously are incorporated or this research wouldn’t have been done. Transposons wouldn’t be named transposons if their properties weren’t at least partially understood.

    True science should be built on facts, so please include specific examples in the future to support your comments. If you are claiming this property of transposons is not accepted by scientists you will have to back that up with proper citations. I wouldn’t be surprised if you are just a creationist trying to misrepresent the facts and spread doubt.

  • Jennifer


    The article you were referring to is from this site, an interview of Lynn Margulis.

  • amphiox

    Margulis tends to overstate that “shunned minority” thing. And she uses a peculiarly restricted definition of natural selection when she makes these arguments. A lot of these mechanisms that she argues to be “non-Darwinian”, or “non-Evolutionary” (whereby evolutionary one means standard current evolutionary theory) really aren’t – they’re just somewhat more extreme examples of the spectrum of mechanisms we already know about.

    This example, for instance, is simply one kind of mutation – a variation of a duplication mutation. It just happens to be a particularly big mutation.

    And everything that happens afterwards, to optimize the further development and evolution of the organ, is mostly natural selection. ie Mutation + Selection, standard evolutionary theory.

  • John Kwok

    @ tall blue ape –

    I wouldn’t dismiss this work because it was funded by Templeton. If the work should be dismissed, then it would be due to its quality, and, judging from the comments I have seen so far (especially amphiox’s), then it shouldn’t.


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