Most male mammals wield a penis covered with spines made of keratin, the same material that forms fingernails, to sweep out competitors' sperm and irritate a female into ovulating. You can add humans' lack of penile spines to the list of ways we are misfits among primates, along with our absence of tails and fur. Even chimpanzees, our closest relatives, have penile spines. A new study suggests that this feature disappeared due to a chunk of DNA that went missing after our evolutionary divergence from chimps. The researchers have identified another DNA deletion that may have contributed to humans' bigger brains...

One group of women was told that these four men were those who liked them the most, a second group heard that these men rated them as average and a third group was left in the unsettling position of thinking that the men might like them either the most or an average amount.

Not surprisingly, women were more attracted to men who found them attractive than men who rated them average. This is called the “reciprocity principle,” which holds that a woman should like a man less if he doesn’t like her much, and reflects earlier research. The shocker was that the women who found the men most attractive of all were those who weren’t sure just how much the men liked them...

Sexual practices don't really leave much of an imprint in the fossil record. And dinosaurs, themselves, are not, shall we say, the most nubile-looking creatures. According to paleo-blogger Brian Switek, you aren't alone in your confusion. He says scientists have been pondering dino-sex for more than 100 years. (Like you do.) In fact, until recently, paleontologists weren't even totally clear which dinosaurs were girls and which were boys.

And, once that mystery was solved, there were still a lot of other obvious questions. Such as: How did pointy, heavily-armored Stegosaurs get amorous?...

There is already evidence from animal research that males increase the amount of sperm in their ejaculate when there is more competition around. In 2005, Kilgallon and Simmons conducted an experiment to see whether human males viewing “images depicting sperm competition” also had a higher percentage of motile sperm in their ejaculates...

they compared ejaculate in 52 heterosexual men looking at pornography with two men and one woman, against pornography with three women, whereas I think it would have been better to use comparison images with one man and one woman, but there you go. They found that men viewing the “two men one woman” pornography had a higher percentage of motile sperm...

Yamamoto and colleagues in 2000 studied 19 men masturbating into a jar, either alone in a room, or with “sexually stimulating videotaped visual images” at hand. Sperm volume, total sperm count, sperm motility, and percentage of morphologically normal sperm were all higher when the men had pornography...

Brain injuries caused by strokes, tumors or head trauma can, on occasion, result in Unusual Changes in Sexuality, as discussed in an earlier blog post. A new case report by Bianchi-Demicheli et al. (2010) describes a unique paraphilia in a married 34 year old man. The authors called it Sleeping Beauty paraphilia:

This [man] felt sexually aroused from seeing sleeping women as well as from taking care of their hands and nails while they were asleep.

The patient came to the attention of the authors when he was brought to the emergency psychiatric unit after assaulting his wife with pepper spray while wearing a latex mask...

The ability to judge another individual's romantic interest level—both toward oneself and toward others—is an adaptively important skill when choosing a suitable mate to pursue. We tested this ability using videos of individuals on speed dates as stimuli. Male and female observers were equally good at predicting interest levels, but they were more accurate when predicting male interest: Predictions of female interest were just above chance. Observers predicted interest successfully using stimuli as short as 10 s, and they performed best when watching clips of the middle or end of the speed date. There was considerable variability between daters, with some being very easy to read and others apparently masking their true intentions...

Stomach fat is considered more metabolically active than lower body fat. While that may sound good, as this fat breaks down easily, the result is a release of substances called cytokines, which have been linked to cardiovascular disease, insulin resistance and diabetes. In fact, research on mice reported in 2008 revealed that belly fat boosts inflammation and is linked with hardening of the arteries – known to increase the risk of heart attacks.

But scientists think lower body fat, like that around the hips and thighs, produces beneficial hormones that protect against these diseases, though more research is needed to firm up this expectation.

In addition, this lower body fat also traps fatty acids. While this long-term storage can make it tricky to slim down your butt and thighs, it's healthier for you if some fat stays put...

[A]n academic analysis of 1.4 million chess-tournament game records (pdf) by Christer Gerdes and Patrik Gränsmark shows that not only do men players tend to be less risk-averse than women but (emphasis mine)

A novel finding is that males choose more aggressive strategies when playing against female opponents even though such strategies reduce their winning probability...

Pornography. Most people have seen it, and have a strong opinion about it. Many of those opinions are negative—some people argue that ready access to pornography disrupts social order, encouraging people to commit rape, sexual assault, and other sex-related crimes. And even if pornography doesn’t trigger a crime, they say, it contributes to the degradation of women. It harms the women who are depicted by pornography, and harms those who do not participate but are encouraged to perform the acts depicted in it by men who are acculturated by it. Many even adamantly believe that pornography should become illegal.

Alternatively, others argue that pornography is an expression of fantasies that can actually inhibit sexual activity, and act as a positive displacement for sexual aggression. Pornography offers a readily available means of satisfying sexual arousal (masturbation), they say, which serves as a substitute for dangerous, harmful, and illegal activities.

Some feminists even claim that pornography can empower women by loosening them from the shackles of social prudery and restrictions.

But what do the data say? Over the years, many scientists have investigated the link between pornography (considered legal under the First Amendment in the United States unless judged “obscene”) and sex crimes and attitudes towards women. And in every region investigated, researchers have found that as pornography has increased in availability, sex crimes have either decreased or not increased....

As reviewed in Komisaruk et al..., there are published reports of orgasms elicited by stimulation also of lips, hand, knee and anus occurring during dreaming sleep, of phantom limbs, from electrical or chemical stimulation of the septum, amygdala or thalamus of the brain and of the spinal cord.

Orgasms have also been described by men and women when they suffer epileptic seizures that are triggered by specific activity (e.g. brushing the teeth...), or that occur spontaneously. While these epileptic orgasms are in some cases described as ‘unwelcome’..., others describe them as pleasurable, one woman refusing anti-epileptic medication for that reason ...

We have measured autonomic and brain activity during orgasms that women have produced by thought alone. During the thought orgasms, the magnitude of the increases in heart rate, blood pressure, pain threshold, pupil diameter, and brain regions are similar to those that we observe during vaginal or cervical self-stimulation-induced orgasms... It is not surprising that in those cases of thought-induced orgasms, the specific genital sensory thalamic and cortical, and specific limb-motoric regions, are not activated....

Fantasizing about sex gets more than just your juices flowing—it also boosts your analytical thinking skills. Daydreaming about love, on the other hand, makes you more creative, according to a study published in the November 2009 Personality and Social Psychology Bulletin.

Previous research suggests that our problem-solving abilities change depending on our states of mind and that love—a broad, long-term emotion—triggers global brain pro cessing, a state in which we see the big picture, make broad asso­ciations and connect disparate ideas. Sex, on the other hand—more specific and here and now—initiates more local processing, in which the brain zooms in and focuses on details...

Women looking for that special someone might want to think twice before spritzing Chanel No. 5. A new study suggests that a woman's natural scent may be all she needs.

Recent research shows that a man's testosterone levels, which are linked with sexual interest, are significantly higher when they smell the shirt of a woman who is ovulating. These findings could lead to the development of new fragrances that mimic this effect, and answer basic questions about human biology...

An economics graduate student in the UK has used the well-known Drake Equation - used to figure out how many advanced civilizations might reside in our galaxy - to determine why he hasn't had a girlfriend in three years.

The Drake Equation was created by astronomer Frank Drake at the first SETI conference in the 1960s, and was used to determine how many civilizations in our galaxy might be capable of communicating with ours.

To investigate his girlfriend problem, researcher Peter Backus wrote a brief paper in which he modified the parameters of the Drake Equation to discover the number of women in the UK who could be his girlfriend...

Lovatt and his team observed the dance floor closely and took certain dancers aside for a solo performance. Those selected groovers were then filmed for 30 seconds on a separate dance floor which was, according to Lovatt, "just as lively and noisy as the main dance floor." Then the team headed back to the lab with their videos.

Lovatt then applied a filter to the footage so that the dancers could only be seen in silhouette, which meant that any viewer had to focus solely on their movements. He showed these films to students, who had to rate the dancers on a five-point scale from "very attractive" to "very unattractive."

The results showed that women gave the highest attractiveness ratings to men with the highest levels of prenatal testosterone. The men with the lowest testosterone in turn got the lowest attractiveness ratings. "Men can communicate their testosterone levels through the way they dance"...

Men who have sex at least twice a week can almost halve their risk of heart disease, according to new research.

It shows men who indulge in regular lovemaking are up to 45 per cent less likely to develop life-threatening heart conditions than men who have sex once a month or less.
The study, of over 1,000 men, shows sex appears to have a protective effect on the male heart but did not examine whether women benefit too.

Now the American researchers who carried out the investigation are calling for doctors to screen men for sexual activity when assessing their risk of heart disease...