Sunday, February 10, 2008

Are girls wired not to win?

Most women in the West are now in the workplace and young women are doing exceptionally well at school and university in comparison with their male peers. But gifted, talented women with the most choices and freedoms don’t seem to be choosing the same paths, in the same numbers, as the men around them. Even with barriers stripped away, they don’t behave like male clones.

As a developmental psychologist, I began to wonder about the science. We have come to expect that there should be no real differences between the sexes. But the science that’s emerging upends the notion that male and female are interchangeable, symmetrical or the same. The psychology, neuro-science and economics of people’s choices and behaviour have exploded with amazing findings in the past 10 years alone.

In particular, an opiate-like hormone, oxytocin, which one anthropologist calls “the elixir of contentment” (it surges during breastfeeding, childbirth, sex, cuddling and nurturing), has emerged as a key to understanding ….

There are distinctive design elements in female brains that evolved to promote the survival of infants. An avalanche of hormones at childbirth and during nursing trigger behaviour and emotions that don’t vanish simply because the new mothers have to go to work.

Breastfeeding releases hormones and neurotransmitters that induce euphoria in mothers. Prolactin turns on breastfeeding in females and circulates any time feeding, nurturing or protecting is on the agenda. And oxytocin, “the elixir of contentment”, is evolution’s way of making proximity to infants and feeding them so attractive.

Regular intimate contact becomes a physiological imperative. After infusing her brain with the analgesic and pleasure-inducing effects of oxytocin every few hours when she nurses her baby, a mother is suddenly cut off from her supply when not breastfeeding. That’s why nursing mothers newly returned to full-time work can’t wait to get home to feed the baby again. HORMONES are the catalysts that set dynamic sex differences in motion. Based on studies in animals, scientists expect that certain regions of the brain are not just transformed by hormones early on but are also endowed with receptors that enable the hormones to continue to play a role throughout life.

Rats help us to get a deeper understanding. The behavioural geneticist Michael Meaney has found that a mother rat’s style of nurturing can switch on genetic functions in the pups that skew their emotions and ability to deal with stress.

“Under normal circumstances, high-licking mothers are less anxious and their female offspring are less anxious,” he explained.

Anxious mothers lick and groom their pups less. But when Meaney matched high-licking mothers with foster pups, he found that a stress regulating capacity in the newborns’ genes was switched on. Providing all is well in the environment around them, these more relaxed pups then pass on the attentive mothering they received to their own pups, whose brain circuits are altered in the same way – via their mother’s nurturing.

This clever study shows how maternal behaviour, hormones, empathy, stress and genes interact. But they’re rats and we’re humans, you might say. Rats don’t know much about the Mummy Wars – whether to consider children’s needs first or take a much-vaunted promotion.

While it’s hard to infer empathy in rats, there are hormonal and neural pathways that are common to all mammals. A mechanism that allows a human mother and infant to transmit their emotional states to each other would have survival benefits and Meaney’s work, among others, shows that just such a system exists.

We see the evidence in the pleasure pathways lit up by holding and feeding babies – a phenomenon I noticed whenever a newborn was in my own clinic. I could hear from the chorus of high-pitched cooing that the female family doctors and office staff had gathered yet again around a new mother, admiring her baby and waiting for their “fix” – the opportunity to hold it close.

All these women had already chosen work that would bring them into contact with children, but babies under four months continued to exert a magnetic pull that never wore off. In animals, the nurturing relationship is so inherently rewarding to mothers that when given the choice, new mother rats choose newborn pups over cocaine.

The same pathways may allow Barbary macaques, the monkeys found in Gibraltar, to get stress-reduction benefits from grooming other monkeys. It has long been thought that, just as at the hair salon, the monkey being groomed gets the stress reduction. But Kathryn Shutt of Roehampton University has found that the longer a female macaque spends grooming others, the less stressed she is. For female macaques, anyway, it is better to give than to receive.

Shelley Taylor, a psychologist at UCLA, was the first to theorise that nurturing and stress reactions are tightly bound together in humans. Having interviewed women with cancer about how they dealt with their stresses, she was struck by how many chalked up their resilience to their social connections. Could something biochemical be triggered by reaching out to others?

Oxytocin, the underlying driver in tending children, is also the hormone of befriending. Besides being triggered by childbirth, breastfeeding, nurturing and orgasm, it is also released at critical moments in women’s relationships and menstrual cycles, damping down other stress responses. It helps to keep mothers going, providing sedative and analgesic effects, calming and immediately rewarding the women who instinctively reach out to others when they are in trouble.

Oxytocin is not just a feel-good, nurturing drug. It helps people to read emotions in other’s faces and increases their trust, according to two studies at the University of Zurich. These showed that oxytocin in nasal spray even has a positive effect on men’s usual behavioural limitations: it boosts their trust in social situations and their ability to read facial expressions.

Both studies bolster the idea that this hormone secreted in greater quantities in females – when they have babies, when they nurture them, when they cuddle or have sex with their partners, or when they reach out to others – facilitates females’ capacity for empathy and their trust in others.

Here is evidence, then, that biochemical drivers underlie some of the most obvious behavioural differences we see between the sexes.

Testosterone, secreted in greater quantities in males, may alter some neural connections related to reading others’ emotional states. And oxytocin seems to do the reverse. It seems to help women guess what’s going on inside the heads of other people, enabling them to trust them enough to seek them out, especially when they’re stressed, and to feel pleasure and relief when they do.

Studies have also shown that women on average perceive, experience and remember emotional events more intensely than men do and that these experiences are encoded in more areas of their brains than in men’s. From this, it makes sense that their emotional attachments will figure more strongly in their career decisions.

In the context of male-dominated “extreme” jobs, being aware of others’ needs can be a liability if promotion is the yardstick of success.

The science showing that many women feel empathy more acutely than many men doesn’t mean they must or should make trade-offs over their work. It simply explains why some women might want to, as the British sociologist Catherine Hakim understands.

For years she has pricked the ire of the European feminist establishment by asserting that persisting gender gaps in pay are the result of women’s deep-seated preferences.

Her worst sin, according to her critics, was asserting that social policy could never allow the majority of women to have it all, since a measurable slice of the population – 10% to 30% – never wanted it all, anyway, and another 60% adapt their ambitions to their family’s needs.

“If you are seriously interested in a career you don’t have time for children and if you are seriously interested in bringing up more than one child, you don’t have the time, effort and imagination for getting to the top of a career,” she told me.

Half of all women in the top professional and managerial grades are childless, Hakim reports, which is similar to women in academic science and engineering. Reliable contraception has allowed them to choose how they want to direct their energies and to plan their ascent.

In Hakim’s case, over the past eight years she has written six books and “there’s no way I could have done that if I had had children. The fact is that children are a 20-year project and a career is a 20 to 40-year project and there is an incompatibility there”.

And she added mildly: “If someone tested me, I’m sure I’d have the highest level of testosterone.”

Full article:

© Susan Pinker 2008

Extracted from The Sexual Paradox by Susan Pinker, to be published by Atlantic Books on March 1

Saturday, February 09, 2008

Team Uncovers New Evidence of Recent Human Evolution

Amber waves.

Dependence on cereal grains such as barley influenced recent human evolution.
Credit: USDA/Doug Wilson

By Ann Gibbons
ScienceNOW Daily News
4 February 2008

In the past 100,000 years, modern humans have colonized the far corners of the globe, adapting to new environments as they migrated. Researchers have long assumed that these dramatic transitions resulted in a sort of accelerated evolution in which genes for traits such as skin color and stature changed rapidly to allow humans to survive in their new habitats. Now, a team of French and Spanish researchers has found powerful new evidence to support this idea, identifying 582 genes that have evolved differently in different populations in the past 60,000 years, including a dozen that protect people from obesity, diabetes, hypertension, and other diseases.

The team, led by population geneticist Lluis Quintana-Murci of the Pasteur Institute and Centre National de le Recherche Scientifique in Paris, analyzed DNA of 210 individuals from the database of Phase II of the International HapMap Project, an effort to identify variations in human genes that cause disease. The researchers analyzed 2.8 million single nucleotide polymorphisms (SNPs)--mutations in a single nucleotide in a genome that varies between individuals or populations--from Europeans, Africans, and Asians. Then they sorted the mutations by type, focusing on 15,259 nonsynonymous mutations, which alter amino acids and thus a gene's function.

Using statistical analysis, the researchers found that some mutations occurred at such high frequencies compared to other SNPs in the same populations that they must have improved survival and reproductive success and been the result of strong positive selection pressure. These mutations varied tremendously between populations, which counters a popular view that many of the differences between populations arose by chance or were genetic variants that hitchhiked along with other genes that improved reproductive success, says biological anthropologist Henry Harpending of the University of Utah, Salt Lake City, and co-author of another study of accelerated evolution.

Although the researchers don't know the function of most of the 582 genes that were under such intense positive natural selection, they have identified about 50 that appear to be responses to diseases or changes in diet or environment. Some examples include mutations that alter how adults regulate insulin, digest sugars and starches, metabolize ethanol and zinc, transport fats, regulate the immune response to pathogens, and repair and replicate DNA. "New mutations that 'protect' people from diabetes and obesity have been selected probably because they significantly improved peoples' ability to handle agricultural diets," says biological anthropologist John Hawks of the University of Wisconsin, Madison, who collaborates with Harpending. For example, he says, new dependence on a few cereal grains required efficient digestion of starches.

The study, reported online 3 February in Nature Genetics, is the latest in a series of recent reports to identify genes that are still evolving or have evolved recently in different human populations (ScienceNOW, 10 December 2007). "I think it is clear there's quite a bit of recent selection going on," says population geneticist Jonathan Pritchard of the University of Chicago in Illinois.

Source: Science

Genes and environment interact in first graders to predict physical but not social aggression

Physical aggression in children comes from their genes and the environment in which they grow up. Social aggression, such as spreading rumors or ignoring other children, has less to do with genetic factors and more with environmental factors.

One important environmental influence on children is friends. But while past studies have shown an association between physically aggressive friends and increased physical aggression in children and teens, few studies have looked at how socially aggressive friends affect children's social aggression, nor have they considered possible gene-environment transactions in these behaviors.

A new study by researchers at the University of Quebec at Montreal, Laval University, Concordia University, and the University of Montreal sought to determine whether the interaction between nature and nurture, that is, between children's genetic disposition to aggression and friends' aggression (social or physical), could help explain differences in children's own aggression. The study appears in the January/February 2008 issue of Child Development.

The researchers assessed approximately 400 pairs of 7-year-old twins, each of whom was asked to list up to three friends in their classroom. Teachers and peers evaluated the twins' and their friends' levels of social and physical aggression.

The researchers found that friends' physical aggression interacts with genetic liability to predict children's own physical aggression. Specifically, the genetic disposition to physical aggression is more likely to express itself when children are exposed to physically aggressive friends. No gene-environment interaction was found with respect to children's social aggression. Instead, friends' social aggression seems to be directly associated with children's own social aggression, independent of children's genetic disposition to this behavior.

The results also revealed that the effect of friends' aggression on children's aggression only seems to occur in the context of the same type of aggression. In other words, friends' physical aggression predicts children's physical but not their social aggression, whereas friends' social aggression predicts children's social but not their physical aggression.

Source: Society for Research in Child Development

Is political orientation transmitted genetically?

As reported in this week's issue of New Scientist magazine, research by Rice University professor of political science John Alford indicates that what is on one's mind about politics may be influenced by how people are wired genetically.

Alford, who has researched this topic for a number of years, and his team analyzed data from political opinions of more than 12,000 twins in the United States and supplemented it with findings from twins in Australia. Alford found that identical twins were more likely to agree on political issues than were fraternal twins. On the issue of property taxes, for example, an astounding four-fifths of identical twins shared the same opinion, while only two-thirds of fraternal twins agreed.

"What we found was that it probably is going to take more than a persuasive television ad to change someone's mind on a certain political position or attitude," said Alford. "Individual genes for behaviors do not exist and no one denies that humans have the capacity to act against genetic predispositions. But predictably dissimilar correlations of social and political attitudes among people with greater and lesser shared genotypes suggest that behaviors are often shaped by forces of which the person themselves are not consciously aware."

Alford believes that political scientists are too quick to dismiss genetics; rather, he believes genetics should be studied and taught along with social-environment influences.

"It has been proven that genetics plays a role in a myriad of different human interaction and makeup," said Alford. "Why should we exclude political beliefs and attitudes?"

Source: Rice University