After I wrote about research showing that women have less appetite for competition than men do, a number of women wrote to inform me that they're just as competitive as any guy. If the tone of their letters is any indication, I have no doubt they are.

Nor do researchers doubt that such women exist. As Danica Patrick showed in the Indianapolis 500, some women can successfully compete with men at the highest level. But why aren't there more of them?

Discrimination is one big reason, because men have traditionally made the rules to suit themselves and keep out women. But if you think that leveling the playing field would eliminate gender disparities, consider an unintentional experiment conducted in the Scrabble world, which is hardly a hostile environment for women.

For a quarter-century, women have outnumbered men at Scrabble clubs and tournaments in America, but a woman has won the national championship only once, and all the world champions have been men. Among the top-ranked 50 players, typically about 45 are men.

How the functioning of X chromosomes differs in women and men may help to explain biological differences between the sexes, according to a new study by researchers from Duke and Pennsylvania State Universities.

The researchers, writing today in the journal Nature, said the results implied that women make higher doses of certain proteins than men, which could result in differences in both normal life and disease. A second paper presented an analysis of the X chromosome's DNA, in which an international team of scientists found 1,098 genes.

Together, the two papers may explain some of the behavioral and biological differences among women, and perhaps between women and men, according to an article in Nature about the study.

Men are from Mars and women from Venus - except when they are in love. During this intense period, men and women become more like each other than at any other time.

We already know that falling in love is a bit like going crazy. Donatella Marazziti of the University of Pisa in Italy showed in 1999 that levels of the neurotransmitter serotonin, which has a calming effect, dip below normal in those who say they are in love as well as in people with obsessive compulsive disorder. Both groups spend inordinate amounts of time obsessing about something or someone (New Scientist print edition, 31 July 1999).

Now Marazziti has looked at the hormonal changes that occur in people who are in love. Her team measured the blood levels of several key hormones in 12 men and 12 women who said they had fallen in love within the past six months. The researchers compared these hormone levels to those in 24 other volunteers who were either single or in stable long-term relationships.

The first finding was that both men and women in love have considerably higher levels of the stress hormone cortisol, indicating that courtship can be somewhat stressful. "But the most intriguing finding is related to testosterone," says Marazziti.

Split the difference

Men who were in love had lower levels of the male sex hormone testosterone - linked to aggression and sex drive - than the other men. Love-struck women, in contrast, had higher levels of testosterone than their counterparts, the team will report in Psychoneuroendocrinology.

"Men, in some way, had become more like women, and women had become like men," says Marazziti. "It's as if nature wants to eliminate what can be different in men and women, because it's more important to survive and mate at this stage."

But is falling in love really responsible for these changes? Andreas Bartels of University College London points out that the hormonal changes could just be a result of increased sexual activity. "There's a high degree of affection, but there's also, without any doubt, extremely high sexual activity," he says.

Marazziti thinks that this explanation is unlikely, however, because in her study those in the control group were having sex just as often as those in the "in love" group.

Love is blind

What is more, other studies suggest that testosterone levels in men rise as sexual activity increases (New Scientist, 27 November 1999). So if the hormonal changes were just the result of sex, testosterone levels would be expected to increase in men, rather than fall.

Converging levels of testosterone may not be the only thing that helps a man and woman overcome their differences. Other research has shown that falling in love really does make us blind to our partner's faults.

Bartels's team has found that when people look at their lovers, the neural circuits that are normally associated with critical social assessment of other people are suppressed (Neuroimage, vol 21, p 1155).

But the blissful state that is romantic love does not last. When Marazziti retested the same people one or two years later, when they said they were no longer madly in love, their hormone levels had returned to normal.

Sure, they're only machines. But the more they interact with us humans, the more important their apparent gender becomes.

Is your Roomba a boy or a girl?

The Roomba, of course, is that clever little house-cleaning robot. I reviewed Roomba in October 2002, then bought my own a few months later. Since then it’s been happily sweeping my living room and dining room every week or so. It also terrifies my cats and my three-year-old twin boys. All well and good—but what’s the Roomba’s gender?

“It’s a girl,” says my wife. “It’s round. It’s close to the floor. It ends with an ‘a’. I always think of it as a ‘wom-ba.’”

But if the Roomba is a girl, then Asimo is definitely a boy. Developed by Honda Motor, Asimo is a humanoid robot that walks around like a short astronaut in a white space suit. Four-foot tall Asimo is the latest in a long line of the company’s bipedal robots. These days Asimo spends his time as Honda’s goodwill ambassador to the world’s science museums, auto shows, and other venues. Last month he was spotted in Hanoi, Vietnam.

Asimo doesn’t look especially boy-like—there’s no slingshot in his back pocket, there’s no telltale bulge under his belt, and there’s no hint of facial hair. In fact, you can’t even see his face: the robot’s head is covered with a visor that has just two big holes for its video-camera eyes. But Honda repeatedly refers to the robot with the pronoun “he” on the Asimo website.

Indeed, Honda has taken great pains to make its walking robots more lifelike, and part of that realism appears to include giving the robot a friendly sounding name (the previous generation was called simply “P3”). The company’s earliest attempts at walkers were really nothing more than a pair of legs and feet with a big box on top of them. But over the years the robot forms have become decidedly more human—and more male.

Whether or not you think that gender belongs in our mechanical creations has a lot to do with your vision of how these creatures will fit into our future. It certainly takes more effort to make a robot that’s gendered than one that’s asexual. But engineers just want to have fun. Building gender into robots might be a way for the robots’ designers to express their own playfulness and creativity.

Dig a little deeper, though, and you’ll discover another reason why gender might be a good thing for our robot servants: gender will make robots more compatible with their human masters.

Young female chimpanzees are better students than males, at least when it comes to catching termites, according to a study of wild chimps in Tanzania's Gombe National Park. While daughters watch their mothers closely, the boys spend more time monkeying around.

The discovery mirrors differences in the learning abilities of human children, says the research team behind the study. Girls tend to catch on faster than boys when learning skills such as writing and drawing, they say.

A male baboon named Sherlock sat on a cliff, unable to take his eyes off his favorite female, Cybelle, as she foraged far below. Each time Cybelle approached another adult male, Sherlock froze with tension, only to relax again when she ignored a potential rival. Finally, Cybelle glanced up and met his gaze. Instantly Sherlock flattened his ears and narrowed his eyes in what baboon researchers call the come-hither face. It worked; seconds later Cybelle sat by her guy, grooming him with gusto.

After observing many similar scenarios, I realized that baboons, like humans, develop intense attractions to particular members of the opposite sex. Baboon heterosexual partnerships bear an intriguing resemblance to ours, but they also differ in important ways. For instance, baboons can simultaneously be "in love" with more than one individual, a capacity that, according to anthropologist Helen Fisher, most humans lack.

Fisher is well known for her three previous books (The Sex Contract, Anatomy of Love and The First Sex), which bring an evolutionary perspective to myriad aspects of sex, love, and sex differences. This book is the best, in my view, because it goes beyond observable behaviors to consider their underlying brain mechanisms. Most people think of romantic love as a feeling. Fisher, however, views it as a drive so powerful that it can override other drives, such as hunger and thirst, render the most dignified person a fool, or bring rapture to an unassuming wallflower.

For almost a decade, researchers at Pfizer struggled to show that Viagra, the male impotence drug, could enhance sexual function in women.

Last month, they gave up.

Countless tests on thousands of women made it clear that the little blue pill, though able to stir arousal, did not always evoke sexual desire.

Viagra's failure underscored the obvious: when it comes to sexuality, men and women to some extent are differently tuned. For men, arousal and desire are often intertwined, while for women, the two are frequently distinct.

Scientists have recently begun to map out how this difference shows up in the brain.

For example, male arousal, studies find, is strongly visual, and when men engage in sexual activity or even anticipate it, brain structures once thought to have little connection to sex spring into action. The same brain regions, however, remain relatively quiet when women are aroused.

The emotion control center of the brain, the amygdala, shows significantly higher levels of activation in males viewing sexual visual stimuli than females viewing the same images, according to a Center for Behavioral Neuroscience study led by Emory University psychologists Stephan Hamann and Kim Wallen. The finding, which appears in the April edition of "Nature Neuroscience," demonstrates how men and women process visual sexual stimuli differently, and it may explain gender variations in reproductive behavior.

Male babies surgically turned into girls at birth because of a rare birth defect frequently continue to feel like boys and may eventually switch their gender back to male, even with no knowledge of their history, according to a new study.

Behavior and biology both suggest that females respond to environmental stress by redoubling efforts to care for offspring and creating social support networks, said psychologist Shelley E. Taylor, PhD, at a Nov. 13 lecture, presented as part of the National Institutes of Health (NIH) behavioral and social sciences research lecture series. The talk was given to NIH staff to inform them about a potential paradigm shift in stress research. According to Taylor, who published her "tend and befriend" theory in the July 2000 issue of Psychological Review (Vol. 107, No. 3), this pattern of behavior makes for a significant contrast to the "fight or flight" paradigm that has dominated stress response theory for the last 50 years.

Psychologists in Canada have finally proved what women have long suspected - men really are irrational enough to risk entire kingdoms to catch sight of a beautiful face.

Biologists have long known that animals prefer immediate rewards to greater ones in the future. This process, known as "discounting the future", is found in humans too and is fundamental to many economic models.

Resources have a value to individuals that changes through time. For example, immediately available cash is generally worth more than the same amount would be in the future. But greater amounts of money in the future would be worth waiting for under so-called 'rational' discounting.

It's the chromosome that has for years been relegated to the sidelines of science. But now this tiny cell particle is providing the answers to some very big cultural questions - and putting a match to political time bombs.

It's the runt of the genome. A comma of a chromosome that might be called in evidence to show that the Creator has a feminist sense of humour. It has to be a joke. To design the one chromosome that appears only in male bodies, that sets the developing embryo off on the path of bigger muscles and more aggression, and then to make it such a weedy and insignificant thing.

Women and cats will do as they please, and men and dogs should relax and get used to the idea.
- Robert Heinlein

The great question -- which I have not been able to answer -- is, "What does a woman want?"
- Sigmund Freud