A New America of Mutts?

8687286808_ce53c853e7_oI recently wrote about my biracial daughter and public assumptions about inheritance for the blog DoubleXScience. Nearly the same day, columnist David Brooks’ op-ed piece, “A Nation of Mutts,” appeared in The New York Times. As you might imagine, I read it with interest.

In his column, Brooks writes about how the long-European roots of America are becoming outnumbered by those of immigrants from elsewhere in the world.  Add to that racial intermarriage and mixed-race offspring and you’re left with what Brooks calls the coming New America. What will this New America look like? Brooks is happy to venture guesses, predicting how the complex forces of socioeconomics, education, ethnicity and heritage may play out in coming generations. Among these predictions: that America will become “a nation of mutts, a nation with hundreds of fluid ethnicities from around the world, intermarrying and intermingling.” The piece sparked an outcry from readers and an online conversation via social media, much of it over his use of the term mutt. While it was obviously an unwise and insensitive word for him to use, I think this was the lesser of the problems with his piece.

According to New York Times public editor Margaret Sullivan, columnists are supposed to stir things up. But in “A Nation of Mutts,” Brooks merely takes a centuries-old argument, injects it with Botox, squeezes it into skinny jeans, and calls it something new.

He begins by telling us that “American society has been transformed” as increasing numbers of immigrants have come to the U.S. in recent decades. He adds that, “up until now, America was primarily an outpost of European civilization” with immigrants who came from Northern, Western, Southern, or Central Europe (depending on the era) but all “with European ideas and European heritage.” That is now changing. Brooks tells us that European-American five-year-olds are already a minority. We have thirty years, tops, before Caucasians will be the minority in America overall.

What strikes me is Brooks’ simplistic picture of racial and cultural differences. He portrays America’s past immigrants from Europe as a monolithic, homogeneous bunch (against which he will compare the diverse immigrants of today) when of course this is a straw man. Ask anyone at a European soccer championship match or at the Eurozone bailout negotiations whether Europeans all have the same “European ideas and European heritage.” On second thought, probably better you don’t.

Americans haven’t historically thought of all Europeans as similar or even equal. Take the 19th century Nativists, or Know-Nothings, who thought that immigrants were ruining America. What exotic nation supplied these immigrants? The Tropics of Ireland.

Our country’s long history of interracial children aside, Caucasians from all over Europe have been intermarrying in America for centuries. I have American ancestors dating back to colonial times and am part German and part British with at least one Frenchman and one Scot thrown in for good measure. Why does David Brooks consider my daughter a mutt yet doesn’t consider me one? Because my ancestors all had more or less the same skin color while my husband is several shades darker than me.

So what is David Brooks really recounting when he writes about the coming nation of mutts? What’s so different about the immigrants of today? Mostly superficial details of appearance. Brooks’ New America is based on the preponderance of pigments in skin, the shape and slope of eyes, the texture of hair. His seemingly profound comment is about the spread of a handful of genes that create innocuous (but visible) proteins like melanin. Big frickin’ deal.

Ultimately, David Brooks is guilty of recycling the same tired old tune: immigrants are changing America and who knows what it might become when they’re done with it? Of course immigrants change our national demographics and  cultural melange. Each generation has wrestled with this self-evident fact for different reasons and in different ways. But if there is anything constant about America’s history, it is the presence of immigration and continuous change. Which means that Brooks was wrong when he said that a New America is coming. It has been here all along.

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Photo credit: Steve Baker on Flickr

Plastic and the Developing Brain

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When I was pregnant with my daughter, I had enough on my mind. I didn’t have much time to think much about plastic. I knew vaguely that plastics can release estrogen-mimicking substances like bisphenol A (BPA) into our food and I’d heard that they might cause genital defects in male fetuses. But once my husband and I had the 20-week ultrasound and knew we were having a girl, I thought I could stop searching for products in cardboard or glass. It was just too hard. Everything is packaged in plastic these days.

Apparently I jumped the gun.

Scientific papers warning about the hazards of prenatal exposure to BPA have been coming out in a steady stream, with a string of particularly damning ones appearing over the last 18 months in the Proceedings of the National Academy of Sciences. Last month one in particular caught my eye: a study of how prenatal BPA exposure changes the brain. The results were enough to make this neuroscientist pause.

While we tend to think of estrogens as the sex hormones that manage ovulation and pregnancy, these molecules also have powerful and direct effects on the brain. Many types of neurons have estrogen receptors on their outer surface. While there are several kinds of estrogen receptors in the brain, all bind to estrogens (and other molecules that resemble estrogens) and all trigger changes within their neurons as a result. These small changes can potentially add up to alter how entire neural circuits function. In fact, estrogens influence a wide range of skills and behaviors – from cognitive function to mood regulation and even fine motor control. While we don’t yet know why estrogens have such a broad and powerful influence on the brain, it does appear that we should think twice before mucking around with estrogen levels, particularly in the developing brain.

BPA and other compounds found in plastics resemble estrogens. The similarity is close enough to fool estrogen receptors, which bind to these foreign molecules and interpret them as additional estrogen. Although BPA has been used commercially as a dental sealant and liner for food containers (among many other uses) since the 1960s, the health consequences of this case of mistaken identity are just beginning to be understood.

In the PNAS paper published last month, a group of scientists headed by Dr. Frances Champagne at Columbia report the effect of prenatal BPA exposure on mice. They fed pregnant laboratory mice one of three daily doses of BPA (2, 20, or 200 μg/kg) or a control product without BPA. These are not high doses of BPA. Based on the amount of BPA found in humans, scientists estimate that we are exposed to about 400 μg/kg per day. The U.S. Food and Drug Administration reached their own estimate by testing the amount of BPA in various foods and then approximating how much of these people consume daily. Their calculations put the figure at around 0.19 μg/kg daily for adults. This discrepancy (400 versus 0.19) is one of many points of contention between the FDA, the packaging industry, and the scientific community on the subject of BPA.

Champagne and her colleagues fed their mice BPA on each of the twenty days of mouse gestation. (That’s right, ladies: mouse pregnancies last less than three weeks.) After each mouse pup was born, the scientists either studied its behavior or sacrificed it and examined its brain.

What did they find? Prenatal BPA exposure had a noticeable impact on mouse brains, even at the lowest dose. They found BPA-induced changes in the number of new estrogen receptors being made in all three brain areas they examined: the prefrontal cortex, hypothalamus, and hippocampus. These effects were complex and differed depending on the gender of the animal, the brain area, the BPA dose, and the type of estrogen receptor. Still, in several cases the researchers found a surprising pattern. Without BPA-exposure, female mice typically made more new estrogen receptors than their male counterparts. The same was true for mice given the highest BPA dose. But among pups exposed to the two lowest BPA doses, male mice made more estrogen receptors than females! This sex-difference reversal stemmed from changes in both genders; male mice made more estrogen receptors than normal at these doses while female mice made fewer than their norm.

Champagne and colleagues also observed and recorded several behaviors of the mice in different circumstances. For most behaviors, males and females were naturally different from one another.  Just as human boys tend to chase each other more than girls do, male mouse pups chased more than females. Unexposed male mice sniffed a new mouse more than unexposed females did. They showed more anxiety-like behavior in an open space and were less active in their home cages. Prenatal BPA treatment reversed these natural sex differences. Exposed female mice did more sniffing, acted more anxious, and ran around less than their exposed male counterparts. And at the highest prenatal BPA dose, the male mice chased each other as rarely as the females did. In one case, BPA treatment affected the two genders similarly; both sexes were less aggressive than normal at the two lower doses and more aggressive than normal at the highest dose.

Overall, the results of the study are complex and it might be easy to ignore them because they don’t seem to tell a straightforward tale. Yet their findings can be summed up in a single sentence: BPA exposure in utero has diverse effects on the mouse brain and later behavior. Not only does the BPA ingested by the mom manage to affect the growing fetus, but those effects persist beyond the womb and past the end of the exposure to BPA.

Some will dismiss these results because they come from mice. After all, how much do we really resemble mice? Yet studies in monkeys have also found that BPA affects fetal development. And while mice and monkeys excrete BPA differently, they clear it at a similar rate — to each other and to human women. Results from correlational studies in humans also suggest that BPA exposure during development affects mood, anxiety and aggressiveness to varying degrees (depending on the child’s gender).

Still, there’s a lot we don’t know about the relevance of this study for humans. At the end of the day, mice aren’t humans and no one has agreed on how much BPA pregnant women ingest. Moreover, Champagne and colleagues examined only a small subset of the neural markers and behaviors that BPA might affect in mice. Perhaps the changes they describe are the worst of BPA’s effects, or perhaps they are only the tip of the iceberg. We don’t yet know.

What’s the upshot of all this? You may want to err on the side of caution, particularly if you’re pregnant. Avoid plastics when possible. Be aware of other sources of BPA like canned foods (which have plastic liners) and thermal receipts. Do what you can do and then try not to let it stress you out. If you’re pregnant, you already have enough on your mind.

As for my daughter, she seems to be fine despite her plasticized third trimester. While she doesn’t do much sniffing, she does occasionally slap my husband or me in the face. It could be the BPA making her aggressive. I choose to blame it on her sassy genes instead.

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Photo credit: .imelda on Flickr

ResearchBlogging.org

Kundakovic M, Gudsnuk K, Franks B, Madrid J, Miller RL, Perera FP, & Champagne FA (2013). Sex-specific epigenetic disruption and behavioral changes following low-dose in utero bisphenol A exposure. Proceedings of the National Academy of Sciences of the United States of America, 110 (24), 9956-61 PMID: 23716699

Genetics Post on DoubleXscience

I recently contributed a post to DoubleXScience, a site dedicated to all things women and science. The piece is called Armchair Genetics from Jamestown to Scott Brown and can be found here. It touches on children and race, assumptions, celebrities, a Cheerios ad, and the history of anti-miscegenation laws in the US (particularly relevant in light of the recent rulings on gay marriage). Please feel free to comment and share your own experiences or just let me know what you think!

Memory: Up in Smoke?

002578cd_scan199_0199I recently joined a memory lab at Wayne State University. The timing seems fitting, as I’ve been doing a little memory experiment of my own of late. My father died ten years ago today and I’ve found myself wondering how my memory of him has fared over the decade. Which parts of him do I remember and which have I lost? They say we live on after we die, if nowhere else than in the memories of those we leave behind. Is it true, or does my father die a little each day as my brain cells age and adjust the strengths of their tiny connections?

I do, at least, remember how my father looked. Certain small details stick out in my memory – the wart beside his nose, his dulled gold wedding band beside a broad, flat knuckle, the remarkable definition of his calf muscles (thanks to his marathon bike rides). I can still see how he brushed his hair back from his face and how he crossed his legs – ankle to knee – and mopped up his sweat with a paper towel after a long ride. But are those the memories that matter? Do I remember how it felt to hug him? Do I remember all of the stories from his youth or any particular instance (of the many) when he said that he loved me? Not really. Not well enough to save him from oblivion.

I imagine I’m not the first person to experience the guilt of forgetting.

Unfortunately, memory loss picks up speed with the passage of time and the brain changes associated with old age. We will only ever have more to feel guilty about. But sometimes, on rare and bittersweet occasions, a chance encounter can trigger a memory we didn’t know we had. It is the psychological equivalent to finding coins wedged between the cushions of the couch and it happened to me a couple years back.

I was walking home from work when I smelled something. It was an odor I couldn’t identify, one that didn’t seem familiar, and yet it filled me with a sense of well-being. I stopped walking and inhaled deeply through my nose. What on earth was this compound? I spotted a man walking half a block ahead of me. He was a professor type with long white hair, a briefcase, and a trail of smoke fanning out behind him. The smell had to be coming from him, yet it was nothing like cigarette smoke.

I started walking again and then picked up the pace to get closer to the man. I’m not proud to say it, but I started to follow him, inhaling as I went. When he turned a corner I caught him in profile and saw that he was smoking a pipe. The intriguing smell was that of pipe smoke. For a moment I was confused. I didn’t recall having ever smelled someone smoking a pipe before and I find both cigar and cigarette smoke aversive.

Then I remembered hearing stories about my dad’s pipe. A professor type himself, my father smoked a pipe for many years and only gave up the habit after a triple bypass surgery. I was three years old at the time. Thanks to childhood amnesia, I don’t remember seeing or smelling my father with his pipe. Yet the memory of that smell, and the comfort I once associated it with, have been buried in my brain all these years like lost coins.

In theory, the memory isn’t a positive one. The secondhand smoke my brother and I inhaled early in life may have had something to do with the asthma we developed later in childhood. Still, my reaction to that stranger’s pipe smoke feels positive.  Precious, even. I’d like to think it reflects how I felt in those early years when I sat in my father’s lap or wrapped my fingers around those broad, flat knuckles. Contented and safe. And as a mother, I’d like to think that I’m planting the same warm feelings in my young daughter. Maybe someday after I’m gone an association will unearth them and she can revisit that innocent comfort all over again.

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Even after I solved the mystery of the scent I followed the smoking stranger for a couple more blocks, inhaling and even closing my eyes as I experienced something of my father that I never knew I knew. It was hard to turn back for home. I didn’t want to lose him quite yet. I wasn’t ready. But then again no one ever is.

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Photo credits: Sally Frye Schwarzlose

Flipping the Baby Switch

img_2348-1Rewind to last night. It was bedtime. My infant daughter was screaming and struggling in my lap while I tried to rock her to sleep. She pulled and twisted the skin on my face. She sunk her tiny teeth into my shoulder and chest. Exasperated, I rose from the rocker and started pacing around the nursery. Her tense little body instantly relaxed. Within ten seconds she was quiet and still. Within two minutes she was asleep.

The scene was not unusual for our household. Even as a newborn, my daughter was easy to upset and hard to soothe. When nothing else worked and I was about to lose my mind I’d get up and walk with her. Often the results were nothing short of miraculous. Imagine going from 100 miles per hour to zero in a snap. For those who recall the child android Vicki on the ‘80s TV show Small Wonder, think of the times someone flipped the off-switch on her back. That’s what it’s like when I walk with my daughter. Our aimless walking flips a switch somewhere inside of her. But how does the switch work? And why does she have one in the first place? A study published in Current Biology last month helps to explain this curious facet of infant behavior.

The head scientist behind the study was Dr. Kumi Kuroda at the RIKEN Brain Science Institute in Japan. As she described in an interview with ScienceNOW, she became interested in the topic when she noticed that she could calm her own newborn son by carrying him. She later tested 12 other newborns with their mothers and found that they behaved like her son. Overall, the effect was rapid and dramatic. Some babies stopped crying as soon as their mothers began to walk with them. The rest cried less and were less shrill when they did cry. The babies also moved less and had lower heart rates while they were being carried.

To study the biological mechanisms behind this remarkable calming response, Dr. Kuroda and her colleagues turned to mice. They showed that mouse pups have a similar response when carried by their mothers. Mouse moms carry their pups by the scruff of their necks. When carried, mouse pups less than 20 days old stop wriggling. Their heart rate slows and they stop crying out. (Like most mouse vocalizations, baby mouse cries are ultrasonic). They also draw their legs in when carried, making their bodies more compact for toting around.

Kuroda and colleagues investigated several physiological aspects of the calming response in mice. Only a few of these experiments are probably relevant for infants, since human babies don’t assume a compact position like carried mouse pups do. One looked for the triggers that make carried pups stop squirming. The scientists anesthetized the neck skin of baby mice and found that these animals wriggled more than untreated mouse pups when carried. They got the same result when they overdosed pups with vitamin B6 before testing. (Vitamin B6 overdose causes animals and humans to lose the sense of their body position and movement.) The upshot? For a mouse pup to stop wriggling when carried it must 1) sense that it’s being lifted and 2) sense that something is pulling on its neck skin. Take either sense away and the calming response disappears. My daughter may draw on similar senses to trigger her miraculous stillness while carried. (Only if you replace neck pulling with the pressure of my arms around her, of course. I don’t carry her by her neck skin, I swear.)

The scientists also wondered why a baby’s heart rate drops when it’s picked up and carried. To test this in mice, they gave pups a drug that turns down the parasympathetic nervous system (the set of nerves that return the body to a calm state after arousal). Pups treated with the drug still stopped wriggling when lifted, but their heart rates didn’t drop as they do in untreated pups. So while the parasympathetic nervous system slows down the carried pup’s (and possibly infant’s) heartbeat, it can’t take credit for other features of the calming response.

Clearly this calming response is more complicated than it seems. Many of my daughter’s brain areas, neural pathways, and sensory mechanisms were working in concert to soothe her last night as I walked her in circles. But why does she have this complex reaction to carrying in the first place? Grateful parents might imagine that the calming response evolved to keep us from going crazy, but unless going crazy involves committing infanticide, this explanation doesn’t hold water. Evolution doesn’t care whether parents are happy or well rested or have time to watch Game of Thrones. It only cares whether our offspring survive.

Dr. Kuroda and her colleagues propose that the calming response helped parents escape dangerous situations while protecting their young. According to this logic, calmer carried babies meant faster escapes and higher rates of survival. Certainly if you were running from a wild beast or a member of a rival village, holding a struggling infant might slow you down. Of course holding any infant would slow you down and it’s not clear that sprinting with a struggling newborn is much harder than lugging one that’s asleep.  The paper’s authors present little evidence to support their proposal, particularly in the context of human evolution. They point to a minor result with their mice that doesn’t easily translate to human behavior. In effect, the jury’s still out.

There are other possible explanations for the calming response, ones that don’t involve predators outrunning parents. Shushing can calm crying babies too, probably because it simulates an aspect of their environment in the womb (in this case,  physiological noise). The same could be true of walking with infants. The mothers in the Kuroda study held their babies against their chest and abdomen, which is also how I hold my daughter when I walk to soothe her. The type of movement she feels in that position is probably similar to the rocking and jostling she felt as a fetus in utero whenever I walked. If so, the calming response might be a result of early learning and comfort by association – a nice thought when you consider the gory alternative.

Each year at the end of May we find ourselves as far as possible from Thanksgiving Day. It can be something of a thankfulness drought. This May I am thankful for women in science and maternity leaves, computer-generated dragons and ’80s sitcom androids. And like Vicki’s parents, I am profoundly thankful that my daughter came furnished with an off-switch. Whatever the reason why.

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Photo credit: Sabin Dang

Esposito G, Yoshida S, Ohnishi R, Tsuneoka Y, Rostagno Mdel C, Yokota S, Okabe S, Kamiya K, Hoshino M, Shimizu M, Venuti P, Kikusui T, Kato T, & Kuroda KO (2013). Infant Calming Responses during Maternal Carrying in Humans and Mice. Current biology : CB, 23 (9), 739-45 PMID: 23602481

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