Reptilian Origins of the Placenta
By Danell Swim
April 23, 2008
Someone seeing for the first time a placenta spill out of a woman’s body after childbirth is likely surprised at how large it is and might wonder where it really came from. Scientists have no clue, either, at least insofar as evolution is concerned.
The gooey thing, which looks like a big, red kidney, is rather reptilian in its ancestry, new research suggests.
The placenta develops inside the womb and supplies a fetus with oxygen and nutrients and ensure a mother’s body does not reject the fetus, just as it might normally attack a germ, parasite or transplanted organ.
“The placenta is this amazing, complex structure and it’s unique to mammals, but we’ve had no idea what its evolutionary origins are,” said researcher Julie Baker, a molecular biologist at Stanford University in California.
Now Baker and her colleague have discovered that the inner lining of eggs laid by the distant ancestors of all mammals could be the origin of the placenta, and the whole setup evolved as mammals employed leftover reptilian-like genes. A better understanding of all this could shed light on pregnancy and disorders linked to it, the researchers say.
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