The number of twins born each year in the United States has more than doubled since 1980, federal health officials reported Wednesday [pdf].

For most of the last century the rate at which American women gave birth to twins remained steady at about 2 percent of all births.

But the rate increased steadily between 1980 and 2009, according to the latest data from the National Center for Health Statistics. And by 2009, more than 3 percent of all births produced twins.

As a result, the number of twins born in the U.S. soared from about 68,000 in 1980 to more than 137,000 in 2009.

What's going on? More women started waiting until they were older to have children, and older women are more likely to have twins, the report states. ...

But the government researchers figure that the rise in age of moms alone accounts for about a third of the increase. The other two-thirds is probably due to the increase in the number of women getting pregnant using fertility treatments, including in-vitro fertilization, the researchers say.

Labels: children, culture, fertility, fertility treatment

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The 21-year-old woman was carefully trained not to flirt with anyone who came into the laboratory over the course of several months. She kept eye contact and conversation to a minimum. She never used makeup or perfume, kept her hair in a simple ponytail, and always wore jeans and a plain T-shirt.

Each of the young men thought she was simply a fellow student at Florida State University participating in the experiment, which ostensibly consisted of her and the man assembling a puzzle of Lego blocks. But the real experiment came later, when each man rated her attractiveness. Previous research had shown that a woman at the fertile stage of her menstrual cycle seems more attractive, and that same effect was observed here — but only when this woman was rated by a man who wasn’t already involved with someone else.

The other guys, the ones in romantic relationships, rated her as significantly less attractive when she was at the peak stage of fertility, presumably because at some level they sensed she then posed the greatest threat to their long-term relationships. To avoid being enticed to stray, they apparently told themselves she wasn’t all that hot anyway.

This experiment was part of a new trend in evolutionary psychology to study “relationship maintenance.” Earlier research emphasized how evolution primed us to meet and mate: how men and women choose partners by looking for cues like facial symmetry, body shape, social status and resources. ...

“It seems the men were truly trying to ward off any temptation they felt toward the ovulating woman,” said Dr. Maner, who did the work with Saul Miller, a fellow psychologist at Florida State. “They were trying to convince themselves that she was undesirable. I suspect some men really came to believe what they said. Others might still have felt the undercurrent of their forbidden desire, but I bet just voicing their lack of attraction helped them suppress it.”

It may seem hard to believe that men could distinguish a woman who’s at peak fertility simply by sitting next to her for a few minutes. Scientists long assumed that ovulation in humans was concealed from both sexes.

But recent studies have found large changes in cues and behavior when a woman is at this stage of peak fertility. Lap dancers get much higher tips (unless they’re taking birth-control pills that suppress ovulation, in which case their tips remain lower). The pitch of a woman’s voice rises. Men rate her body odor as more attractive and respond with higher levels of testosterone. ...

This is good news for fans of fidelity, but there’s one caveat from a subsequent study by Dr. Maner along with C. Nathan DeWall of the University of Kentucky and others. This time, the researchers subtly made it difficult to pay attention to the attractive faces. Both men and women responded by trying harder to look at the forbidden fruit. Afterward, they expressed less satisfaction with their partners and more interest in infidelity.

The lesson here seems to be that too much “mate-guarding” can get in the way of “relationship maintenance.

Labels: adultery, committed relationships, fertility, heterosexual couples, men, women

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Labels: cohabitation, culture, fertility, Marriage

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Is having more than two children selfish? The future of the planet rarely plays a part when planning a family, but that's got to change, say environmental campaigners.

Parents who have more than two children are "irresponsible" for placing an intolerable burden on resources and increasing damage to eco-systems, says a leading green campaigner.

Curbing population growth through contraception must play a role in fighting global warming, argues Jonathon Porritt.

This week, the Optimum Population Trust (OPT), of which Mr Porrit is a patron, launched its "Stop at Two" online pledge to encourage couples to limit their family's size. ...

Each extra person in the UK emits around 11 tonnes of carbon dioxide per annum, he argues, but he warns population is a subject even some environmentalists think too controversial to discuss.

The Total Fertility Rate (TFR) in the UK reached 1.90 children per woman in 2007. UK fertility has not been this high since 1980, according to the Office for National Statistics.

The UK population alone is expected to increase from 61 million to 77 million by 2051 but the OPT believes the UK's long-term sustainable population level may be lower than 30 million.

Labels: demographics, fertility

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In recent years, American conservatism has morphed from a smoke-filled room of martini-swilling adults into nothing short of a nursery. The Right, once known for its emphasis on individual accomplishment and personal responsibility, once a haven for those keen on adults making their own decisions, has linked arms with the stroller moms of Park Slope and put babies at the center of its universe.

The most sensational recent case of this may have been Sarah Palin’s “Seventh Heaven”-esque family, which pitted those inspired by such fruitfulness against those repulsed by it. But even before the Palin brood hit the national scene, conservative intellectuals far from Wasilla had been celebrating babies at all costs. City Journal contributing editor Kay Hymowitz argues that the fight against teen pregnancy is based on a middle-class bias that misapprehends “adolescent baby lust.” Traditionally, conservatives discussing teen birthrates do not accept any lust as worth reckoning with, so this makes for a change. Ross Douthat and Reihan Salam’s recent book, Grand New Party: How Republicans Can Win the Working Class and Save the American Dream (2008), proposes family-friendly policies, a two-step approach intended first to gain the support of parents with many children (a traditionalist-leaning bloc), and, in turn, to see those same policies encourage all Americans to have larger families, and thus to shift, for the sake of the children, towards social conservatism.

What ties these authors together is the belief that social ills come not from unwanted pregnancy, but from the fact that we think a pregnancy could possibly be undesirable. In other words, for Hymowitz, the problem is not that very young women want children, but that our society frowns on early marriage. For Douthat and Salam, the concern is not that those who can’t afford to have babies have them anyway, but that the state fails to make childrearing affordable. These writers, along with columnist David Brooks, do not merely want to correct what they see as a stigma surrounding procreation. The purpose of the movement is to encourage Americans—even arugula-eating sophisticates—to have more babies.

Labels: babies, demographics, fertility, natalism, tax policy

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