A little PSAN (Public Service Announcement of Niftiness):

We talked a little in class last week about chimeras - not the Greek monster, though that would merit a PSAN as well, but creatures that manage to get more than one strand of DNA in their cells. It can happen in non-human animals (as seen with this fine "shoat" (I obey the disclaimer)), which produces some neat fur patterns and such.

But apparently it can also happen with humans. There are boring examples, based on things like blood transfusion or organ donation, when we just put someone else's DNA right into you. But niftier are the tetragametic chimeras. "Four gametes" - sort of gives it away. If, say, two fertilized eggs decide to merge, the adult human ends up with two sets of DNA, which may be distributed unevenly throughout the body. Your liver and heart, for example, may look like they come from different people. Or you can get two different colored eyes. Or Blaschko's lines, which I think look a lot like racing stripes. Zoom! Theoretically your two halves couldn't be that different from each other - you can only be as far apart genetically as two siblings could be, at the very most. (People sometimes like to say that chimeras are their own twin.) I imagine you're also limited by immunological issues - no embryo is going to make it too far if its two DNA lines view the other one as a foreign invader and attack it.

So that is neat for biological reasons. Nerds rejoice. But there's some nice potential for legal fallout as well. Take the case of Lydia Fairchild, an unknown tetragametic chimera who was told by social workers that she wasn't the mother of her own children - their DNA didn't match. Since "DNA is 100 percent foolproof and it doesn't lie," Fairchild actually was in the process of losing custody of her children before someone figured it out. I wonder if there's any potential for chimeric criminals out there, though that does seem like something of a comic book supervillian power. Quadruple Helix, they'd call him.

So just more evidence that human development is surprisingly durable - so many things can go wrong, and do, but somehow all of us are here. Amazing.