Monday, September 24, 2012

Designer Babies, Probabilities, and Problem Abilities. (Part 1 of 3)

As is tradition in the blogging world, I'd like to note that yesterday marked the start of my fourth year writing here at The Mermaid's Tale and I couldn't be more grateful for all of the wonderful things this experience has brought to me over the past three years. Thank you Ken and Anne and thank you readers.

After that preamble, today's post requires its own preamble as well.

I'm writing a popular science book about subjects that are so far afield that I will most certainly embarass myself. But it's for good cause. It's subject matter that anyone who's interested in human evolution (and sex) needs to cover and no one has. Enter my dumbass. Enter my concept of "reproductive consciousness."

Anyway, in further preparation (as if 35 years hasn't been enough) for the droplets of flopsweat sure to pour when my book is published, here's a peek at Yours Truly wrapping my head around a fundamental concept that I take for granted every day and thought I'd gotten a grip on back in high school, if not before:

Very simple probabilities.

It's as simple as flipping a coin.
Oh really?! Please enlighten me, world. 
 
Intro, context, yadda
I had just asked if anyone at our lunch table knew of a decent TV news program to watch while exercising in the mornings, since I was--hours later--still traumatized from watching the hosts of Good Morning America read Hannah Montana's existential tweets with their journo-sylLAHbles.

Needless to say, we all decided that the newspaper and NPR are the only morning news options.

Naturally this lead me to remember a quality story and discussion I'd heard from the BBC on NPR about the latest in "designer babies," which is to say the latest methods for controlling the genotypes of offspring and the ethical issues and debates over it all. This particular story was about taking healthy mitochondria from one female to replace harmfully mutated mitochondria in a mother who wants to have healthy babies but with her own nuclear DNA. Or, alternatively, taking a donor embryo from a woman with healthy mitochondria and replacing the nuclear DNA with the parents' who are trying to conceive a healthy baby.

And the controversy about that led me to share what I'd learned in another story recently on Slate--a practice that seems more deserving of the criticisms described in the BBC story. In this instance, the harmful mutation is an entire chromosome: the unwanted Y or X, depending on parental desire. And biotech has advanced far past separating the heavy slow swimmers (X sperm) from the fast nimble ones (Y) and only allowing the one type to enter the race to the egg. For those who are desperate to control the outcome, you can now test the embryos directly and implant only the ones with the desired pair of sex chromosomes.


Now if you're one of those people like in that Slate story who's just dying to have a girl so you can do makeup and hair with her, I hope it's obvious that although you may be closer to your dreams with this sort of genetic control, you're still not guaranteed to hit the baby jackpot simply by getting one with an XX.  There are lots of XX humans who would rather curl up and die than curl their eyelashes or dye their hair.  And, on the other hand, there are lots of XY who fancy it. There is nothing on the X or Y chromosome that anyone has linked definitively to the proclivity for behaving in these sorts of gendered and cultured ways. [Except indirectly of course, by priming an individual to be gendered and cultured according to whether they have boy or girl anatomy.]

Further, even if there is a genetic component involved in affinity for doing hair and makeup, this method for choosing baby sex isn't typing or sequencing any genes! It's just dealing with the whole chromosomes, and even if it was typing or sequencing the genes on the chromosomes for such behaviors (if there are any such genes), those genes would still only indicate a probabilistic phenotypic outcome, not a determined, certain one. Other parts of the genome as well as the epigenome, microbiome, environment in utero and beyond, including interactions with humans and their behaviors... these factors and more contribute to these sorts of complex behavioral phenotypes.

So I hope that parents who are putting $18,000 dollars towards making sure that their child has XX chromosomes know that the genotype is only probabilistically linked to certain parentally-desired phenotypes. That's not just a large financial gamble (well, for most Americans), but it's also a huge gamble with someone's life, someone who's sitting completely vulnerably and literally in your hands for the earliest years. That gamble piles on top of the risks (to parents and the new human) already inherent in making a new life in the first place. No matter how much money you throw at biology, you can never contain all the probability. But I guess if you have 18,000 bucks you can get the probability to lean towards your dreams.

If you sensed a bit of prickliness here, it's for two reasons: The biological complexities to be sure, but also my lack of empathy for these sex-obsessed parents. It's hard for me to imagine creating and clinging to such specific dreams about uncertain biological and cultural outcomes rather than simply being hopeful that you'll be pleasantly surprised and then mostly happy with whatever uncertainly happens and unfolds in life.

But that's not even what got me to write this post, if you can believe it
While on the topic of choosing your baby's sex, a colleague who's one of five girls shared a good question: Within couples, is there a biological basis for a sex bias? She wondered if there could be some reason that a child from a particular couple might not have a 50/50 shot at being a boy or a girl. She wondered if something about a couple’s chemistry skewed the odds towards one sex and that this could explain why some families have a biased sex ratio, like hers with five girls.

That’s a good question and the first thing you'd have to do before you start investigating is you'd have to calculate the probability of having five girls, particularly five kids who are all girls. That way you could test your estimated, expected frequency against the frequency that you later go out and observe in nature.

Okay, easy.

Easy... Ha. Ha. Ha. If you could listen inside my skull, you'd hear me telling my younger math-savvier self two little words that rhyme with Chekhov.

As we began down this thought-experiment rabbit hole--mentioning first, of course, how there’s 50/50 odds at each birth--a colleague quickly mentally calculated that the odds are 1 in 32 for having five girls and no boys.

Yes: (1/2)^5  (i.e. 50% times itself five times) gives you a 1 in 32 chance (roughly 3%) of having five girls.

But this sounds way too rare. If odds are 50/50 each time you make a baby and if events are independent, that is the odds do not change based on prior events, then how could the odds of having five girls be so small? How could it be any smaller than having any other kind of family? The odds for all families should be the same.*

I was simultaneously reminded of so many correct answers I’d rotely written in math and stats courses, while also feeling completely repulsed by the theory. What kind of meaning does 1/32 contain? It seems like nothing! Each birth is a discrete event. No outcome of prior births have anything to do with the odds that each birth will be 50/50 odds a girl. So how does multiplying their odds together in a string tell you anything meaningful except that we're so clever we can multiply fractions together and come up with a smaller chance for a series of events than for a single event? Isn’t this basically biological meaningless information? Whenever I feel this vehemently frustrated I should probably figure out why, and I may as well drag you all along for the ride in case you can empathize or in case anything I uncover helps you too.

To be continued tomorrow...(linked here)

And it's already written, so don't nobody go and post any answers below in the comments, okay?

(And as we'll see, they are. Sort of.)

11 comments:

JKW said...

It's important for us all to keep in mind, however, that there are many reasons other than curling hair or playing with makeup that influence a woman or couple's interest in selecting the sex (not gender) of a future child. One reason is avoidance of particular congenital diseases that are sex-linked when there is known or suspected family history. Another reason is that a woman or couple may have multiple sons and really, really want a daughter (or, contrastingly, have multiple daughters and really, really want a son). Still other reasons require us to think outside our US-centric perspective to consider restrictions on the number of children a couple is permitted by government to have (e.g. China) or cultural norms that influence interest in having male heirs (e.g. India). For further reading check out Bumgarner, "A right to choose? Sex selection in the International Context" Duke Journal of Gender, Law & Policy 2007; 14: 1289.

The fact is that not everyone who attempts ART (assisted reproductive technology) is motivated by the potential behavior (including gender identity) of the future child.

Holly Dunsworth said...

Thanks for your comment JKW.

However, I don't agree with your use of "however" considering I never claimed to be describing the whole issue or all the details and circumstances under the umbrella.

Holly Dunsworth said...

I believe that people have a right to choose and to pay for technology that allows it.

I wonder with concern if expecting a son and getting a son (XY) who does not embody expectations is worse than just letting biology take its course.

Holly Dunsworth said...

And one more because I'm feeling very defensive by your comment, whether or not you intended dear friend...

The BBC link I provided is a great example of your second paragraph.

EllenQ said...

Holly, I had the same reaction to the Slate article. It isn't something I understand doing, but whatever people want to put a second mortgage on their house for is mostly their business.

JW, you might enjoy tracking down the Slate article. What was interesting about it was precisely the focus on predominately white, North American families without pre-existing medical conditions, as opposed to international perspectives more common in discussing sex-selection. It isn't a perspective that many of us think about.

JKW said...

Holly, I didn't mean to imply an attack on anything you wrote - merely intended to provide some supplemental information. I knew this was a one of three-part series (and I look forward to reading the next two).

I wanted to just mention some of the other issues because I teach ART in my Culture and Genomics course. I asked my students to consider ethical/philosophical differences between ART used for medically necessary vs. elective purposes; considerations surrounding use of ART to avoid a condition vs. use to increase the likelihood of a condition; legal implications of multiple "biological" parenthood; and a whole bunch of other issues related to sex equality and family rights in the US. I didn't mean to suggest that you weren't aware of these things, but I have no idea of all of the readers of MT are aware of these things and felt like it was important to at least put out there... Again, sorry to offend. Definitely didn't mean to do that.

Ellen, I read the Slate article. I agree it is a really interesting perspective. I'm definitely adding it to my list of readings in that section of the course (assuming I'll ever have the opportunity to teach it again).

Holly Dunsworth said...

The next two parts are about probabilities, hence my focus on probabilistic phenotypes in the post.

Holly Dunsworth said...

And Jen that sounds like a course all humans should have to take! Here's hoping you get to teach it like crazy for years to come

Holly Dunsworth said...

As I've already said to Jen (JKW)... I need to stop getting defensive about comments and I need to allow people to see the purpose of the blog differently than I do.

Holly Dunsworth said...

My post is so timely!
Headline:
Fertility Clinic Offers Gender Selection, Draws Women From Abroad

Except how do you choose gender? :)

Patrick Clarkin said...

Holly, I just read this today, and already feel behind. The idea of conscious reproduction is a fascinating one. I recall that when the movie Gattaca came out, they did some guerilla marketing by putting fake ads in newspapers about a new technology available making 'designer babies' a reality. Supposedly, they got a lot of interest and phone calls from prospective parents. The desire is out there, even if the ethics are debatable.

Another idea that I find mind-boggling is that we can choose NOT to reproduce. Evolutionarily, how did we get to that point? It seems to defy what evo is about. I have some guesses, but they aren't much more than that.

BTW, love the way you write... great combo of fun and insight. One phrase I'll take away from this is:

"No matter how much money you throw at biology, you can never contain all the probability."

Looking forward to the book.