What Makes Us Different

Image courtesy of University of North Texas Dept of Biological Sciences

As I have mentioned before, Birdie and Princess are identical twins.  Recently, Birdie has really been fixated on and fascinated by the fact that her sister is called her "identical twin", and yet there are many differences between them.  Being very literal in speech, every time this comes up, Birdie is really bugged by the discrepancy.  The fact that she and Princess have the same genetic material-- which is supposed to define you-- and yet they are so very different really drives Birdie's need to understand how DNA works.  I have not wanted to get into a huge amount of detail with her about the mechanics of genetics-- mainly because I am pretty sure I would run out of info before she was satisfied.  We have, however, talked a tiny bit about how a baby's womb environment can change its DNA expression.  She was not impressed by this explanation, and has apparently given the whole identical DNA thing a lot of thought.

Last week, Birdie and I had the following conversation:


Birdie:  So Sissy and I are identical twins, huh?

Me:  Yup.  (I'm thinking this conversation again?!  Maybe I should get her some reading material from the library, or (*cringe*) show her the NatGeo article on twins?  Something-- anything-- to stop this broken record!)  

B:  And you agree that we are really different, not identical, right?

M:  Of course, honey.  You have the same DNA but you two are completely different people.  You have several physical similarities, but totally different personalities!  I've told you all this before.  Identical just means you have the same genetic make up, not the same everything. *hint, hint*

B:  I know, Moooommm.  Gah-- I'm just thinking here.

M:  (In my head, my brain is moaning oh no, where is this going this time?  I don't know if I can ever answer this question the way she wants.) *reluctantly* What are you thinking, Birdie?

B:  DNA is just your body's instruction manual, basically.  At least that's what I think.

M:  I'd say that's a pretty good description.

B:  It tells you how to make each part of your body and then how to put them all together, I bet.

M:  Sounds good.  Lots of scientists agree with your idea.  What they don't agree on is why people with the same DNA end up different.

B:  Well, I'm pretty sure I know why.

M:  Really.  Okay then-- wow me, Birdie.

B:  If DNA is instructions on how to build you, but they are being read by two separate people, then there's no way what they make will ever be exactly the same.  Believe me, I've seen it with my own eyes!  We did this craft at school one time, where we were all given the exact same materials and the exact same written directions, and NOBODY'S bear looked like anyone else's!  We all had brown bears, and googly eyes, and the same nose and decorations, but we all glued them together in different ways!  Even with the exact same instructions!  Now, probably some kids didn't read the directions at all... but you see what I mean.

M:  Okay, Birdie, I'm officially wowed.  (Advanced genetics in a nutshell, maybe?  She won't be writing any scientific papers anytime soon, but that's a damn good theory for an eight year-old!)

B:  Maybe when Sissy was putting herself together, she paid more attention to different parts of the directions then I did.  We both have the same hair and skin and voice, but we put our faces together a little different because the directions meant different things to us!  I think that is so COOL!

M:  I think that is really cool, too, Birdie!  You've thought really hard about all this, haven't you?  (At this point, I am a little flabbergasted by the whole conversation, and I am feeling proud mommy-tears rising to the rims of my eyes.)

B:  Some.  I just wanted it to make sense to me.  You think it could work like that, Mom?

M:  I don't think I have ever heard a better explanation.

And for that, I got the biggest hug and grin you could possibly imagine.  :)


I thought later about referring Birdie to the recent article on twins in NatGeo, if the topic ever came up again.   (Shocker, I know, considering our NatGeo drama.)  So far it hasn't.  After reading the fascinating article A Thing or Two About Twins once more, though, I'm not sure she'll feel like it changes her theory a whole lot-- but she'd probably dig it, anyway.