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[poplar petiolegall aphid, a gall cut open with aphids of the Pemphigus genus visible. Photo courtesy of forestryimages.org and the Texas Forest Service]
List and his coauthors, Jeffrey Flory, a graduate student in economics at the University of Maryland, and Andreas Leibbrandt, a postdoctoral fellow at Chicago, were intrigued by a number of recent laboratory studies showing that men are, by nature, more competitive than women. Most of us probably don't need scholarly studies to tell us that, because we see it all around us.
Women are raised to be understanding and conciliatory; men are raised to slay wild beasts and triumph over their male friends.
- The Neanderthal Nose Enigma: Why So Big? (2011) (MSNBC; click the link for the picture alone--beatific-looking Neanderthal in contemplation, hilarious)
- Proboscis Monkey (2006) (Afarensis, Scienceblogs)
- How a Bat Got Its Big Nose (2009) (Physicsworld.com)
- Acoustic Effects Accurately Predict an Extreme Case of Biological Morphology (Zhang et al., 2009) (Physical Review Letters)
- Why Is a Moose's Nose so Big? (2004) (Alaska Science Forum)
- DNA Clue to How Neanderthal Man Got His Big Nose (2006; misleading headline; The Telegraph)
- The Human Lineage, Cartman et al. (2009; book) (Google books)
- Why Did Neanderthals Have Such Big Noses (2008) (New Scientist)
- The Paradox of a Wide Nasal Aperture in Cold-adapted Neandertals: a Causal Assessment (Holton and Franciscus, 2008, Journal of Human Evolution)
- Neanderthals Ugly Faces Weren't Adaptations to Cold (2011) (New Scientist)
- The Neanderthal Face Is not Cold Adapted (Rae et al., 2011, Journal of Human Evolution)
- Cave Speak: Did Neanderthals Talk? (Scientific American)
A study coming out in Pediatrics reports that second children born soon after their older siblings are at a higher risk of developing autism, a developmental difference or disorder characterized in general by social and communication deficits. Note that even with the increased risk, the overall risk of autism even for these second siblings is still quite small.
The study is based on a large group derived from data maintained by the California Department of Developmental Services. Findings based on this database must include the caveat that anyone included in the database purposely sought and received services, so there can be a bias against and exclusion of people who sought services elsewhere or are living undiagnosed. It may represent about 75% to 80% of people in
The authors assessed the rates of autism in second-born children relative to how long after the birth of their older sibling they arrived. They counted the inter-pregnancy interval (IPI) as time between the births of each sibling minus the gestational age of the second sib. Their analysis indicated that those second-borns who were conceived within a year of the older sibling’s birth were more than three times more likely to have autism (OR 3.39; 3.00-3.82). For IPIs of 12 to 23 months, the OR was 1.86 (1.65-2.10), while OR for those with an IPI of 24 to 25 months was 1.26 (1.10-1.45). Thus, they identified an inverse linear relationship between time and autism—the longer the time between the first birth and the conception of the second born, the lower the autism rate.
Is the sex of the second sibling involved?
When they looked at other factors, such as preterm birth or sex of the second sibling, they didn’t find much. In fact, across all time periods, ORs for girls as second siblings were higher than ORs for boys, although none of the differences were significant.
There was no assessment of what might cause this mathematical relationship, but the authors offered that the first pregnancy and birth might have depleted nutrients in the uterus, depriving the second-born of them. The authors comment that these findings are becoming increasingly relevant as the number of closely spaced births has grown from 11% of all births in 1995 to 18% in 2002.
The complexity of the womb
The idea of nutrient depletion may be a plausible one, but another one comes to mind that the paper does not appear to address: the relationship between the sex of the previous occupant of the uterus and effects on the next occupant. A well-known hypothesis is that autism develops because of an excess of exposure to androgens in the womb, and research has shown that androgenization can occur in siblings that follow a male older sib in the womb. There’s also the “fraternal birth order effect,” in which the more older brothers a man has, the more likely that man is to be homosexual. This hypothesis, coupled with the idea that homosexual men are hyperandrogenized, has led to some speculation about the influence of an androgenized womb on those who experience that environment.
The DES story
The womb is a changeable place, and the changes that happen there can effect changes in its occupants. This connection may have first come into the spotlight with the studies of DES, or diethylstilbestrol, a powerful synthetic estrogen given to women in the 1940s through the 1960s as a miscarriage preventive. Researchers later discovered that the children of these women—specifically the daughters—were developing rare reproductive tumors. The women who initially received it had an increased risk of breast cancer, not surprising given the 100-fold affinity of this estrogen for one of the estrogen receptors compared to our native prevalent estrogen, estradiol. Sons of DES-treated mothers may also have experienced effects on the reproductive system.
And then there are the grandchildren, the offspring of mothers who themselves were exposed to DES in utero. In an almost biblical expansion of the effects of this synthetic hormone, there is concern based on studies with animal models that grandchildren of the women originally treated with DES during pregnancy may experience higher rates of various reproductive abnormalities, thanks to epigenetic influences of DES their parent experienced in the womb.
A call for another analysis
As the data are presented in the Pediatrics paper, we have no way of knowing if there was a relationship between having a male older sibling and risk of autism in this cohort. Based on my review of the paper, the authors provide autism risk broken down by sex for the second siblings, but do not provide information about the sex of the first sibling or about the rate of autism in second siblings who followed a male older sibling. They likely have these data in hand and may be able to perform this analysis; they may have done so and simply not reported it because there was nothing to report. But in my mind, in the context of the prevailing androgen hypothesis of autism, this analysis would be worth pursuing.
And a call for accurate headlines
I posted an article about this over at BlogHer, and the immediate responses—two of them—were from parents who focused more on feeling blamed and feeling guilt, yet again, over yet another potential factor in a child’s autism. This feeling is essentially battle fatigue, as a headline every other day or so seems to pinpoint something a parent coulda-shoulda-woulda done to head off their child’s autism. The burden remains on the news media who report these stories to make the difference between correlation and causation clear. That clarity must begin with the headlines. A sampling of headlines for this story:
Closely spaced pregnancies might up autism risk (Business Week)
Autism study: Timing is everything (Local television station)
Closely spaced pregnancies increase autism risk (CNN)
Age difference between siblings, not parental age, may indicate higher risk for autism (NY Daily News)
Autism Risk: Is timing everything? (Yahoo News)
Another thing to worry about? Closely spaced second sibs at greater autism risk (My piece at BlogHer)
Of these, the ones that use “might” (get that equivocation across right away) and talk about “risk” come closest to reflecting the paper. But the ones that say “Timing is everything” or assert that parental age is not associated with risk are off base. I’m not thrilled with the headline on the piece I wrote for BlogHer, and I’m afraid that in including it, I unconsciously fell into the “catching clicks and eyeballs” trap, imitating what I’ve seen all over the Web. The answer, of course, to the question the headline poses is, in my opinion, “no,” and I indicate that in the piece. But what I’ve just discovered in this foray into women’s health is that reading to the end doesn’t always happen, and my readers—at least the first two—simply came away feeling like crap about it all. Not the point, not my intention.
The best way to write this headline would be to use words like “associated” or “linked” and “risk” and if you could, work in “correlation, not causation.” I know that latter is unlikely, as it makes eyes roll back and elicits drooling, but could we just develop some quick shorthand so readers can immediately identify a correlation study? I think the subhead I used at the top of this piece sufficiently captures the needed accuracy, but...how clickable is that thing, really?
What’s the take-home?
Back to interpretation: The going wisdom on child bearing is that a mother should wait at least two—if not three—years between conceptions. Of course, some of us are older and don’t have the luxury of spacing our children that way. I, for instance, conceived our second son when his older brother was 8 months old and I was 33. They’re just over 16 months apart in age. Based on the risk categorization in this Pediatrics paper, our second son’s risk of autism from this factor alone would have been 3.3. The thing is, his older brother is the one who’s diagnosed with autism. I’ve spoken with other autism parents whose experience better fits the observations from the Pediatrics paper.
But these are all just anecdotes, not data. The best we can do is—the best we can do. We can follow the going medical wisdom to space our children by two years at least—or, we may be older and not have that luxury. At the very least, it’s not time to add sibling spacing to our list of autism causes. This paper simply showed a mathematical association, which does not mean a confirmed physiological connection, and their findings require considerable further study.
These findings call into question the view of oxytocin as an indiscriminate “love drug” or “cuddle chemical” and suggest that oxytocin has a role in the emergence of intergroup conflict and violence.
for openphoto.net CC:PublicDomain
Religion is about helping us to deal with the sorrow that we see in life, helping us to find meaning in life, and helping us to live in relation to that transcendence that I was speaking about earlier. Religious people are ambitious. They want to feel enhanced. They want to feel at peace within themselves.
This post has been submitted to NESCent for their "Best Evolution-Themed Blog Post" contest. The winner receives a travel award to attend Science Online 2012. I think there would be a delicious irony if the winning post for a evolution-themed contest were about prayer.
Biological models of violence have identified distinct neural patterns that characterize each type of violence. For example, the "low-arousal" aggressor more likely to commit instrumental violence is underreactive and responds sluggishly to stressors. In contrast, the "high-arousal" aggressor who is more prone to hostile violence tends to be hypervigiliant and easily frustrated
In humans, instrumental aggression is roughly analogous to predatory aggression although it is limited to intraspecies behavior....Similarly, emotional or hostile aggression in humans could be considered the analogue of defensive aggression in response to a threat or perceived threat.
"Much is made of the epidemiological studies that have failed to show an association between MMR and autism. However, these studies are open to serious criticism."
I examined the original cohort of children, and they had no physical neurological abnormalities. I have recently seen one of them again. His behaviour is much worse, at times being uncontrollable. He has developed epilepsy and bilateral extensor plantar responses. [From EW: I do not have any idea what a bilateral Babinksi's--an upper motor neuron sign--would have to do with autism]
Another author, Dr Peter Harvey, a board member of Visceral, a registered charity set up to support Wakefield, spoke out in his defence. Harvey said he did not think the funding was relevant and he would have still have put his name to the study if he had known. "I don't think there was any conflict of interest," he said.
Elevated urinary methylmalonic acid and early reports of response to oral B12 from John Linnell, research director at The Children's Medical Charity, U.K. Some reports of response to B12 shots.