Stripping Down Science (10 page)

But if Curie's light was blue, where does the idea that radioactive chemicals glow green come from? The most likely source was the 1902 invention, by the American engineer William J. Hammer, of a radiation-powered glow-in-the-dark paint. Researchers found that the substance zinc sulphide would glow bright green when it was excited, including when it was exposed to radioactivity. The glow could also be made brighter if a small amount of copper was added. So Hammer put two and two together and mixed in some glue and a small amount of radium, producing a paint that was kept permanently illuminated. Overnight, quite literally, reliable glow-in-the-dark products were born.

Scientists subsequently tinkered with the chemicals to produce a range of different colours, but the greens were the easiest for the eye to see, so those were the ones that stuck, together with the myth that radiation glows in the dark. Radium-powered watch and instrument dials continued to be produced into the 1960s. Today, safer alternatives to radium have been found,
together with better materials that can soak up the energy in natural light and release it very slowly to produce glow-in-the-dark products that shine for much longer without the need to resort to radioactivity. That said, radiation-powered fluorescence still has its place, mainly on the hands of certain expensive watches and in military equipment, although these tend to use the safer substance tritium to achieve what radium once did.

FACT BOX

Radium Girls

The First World War created a huge surge in demand for glow-in-the-dark instrument panels, watch dials and other devices. An American company called the US Radium Corporation launched a radium-powered paint which they called ‘Undark'. This was used chiefly to treat military equipment, so soldiers could read their instruments under blackout conditions, but the company also made a version of the product for the domestic market
so users could illuminate their house numbers, light switches, or even, according to a company promotional leaflet, the backs of their slippers to make them easy to locate in the dark.

To keep up with demand, especially during the war, the company employed a large female workforce at their New Jersey factory. These women worked as dial-painters, each delicately applying radium-based paint to the hands and
numbers of about 250 watch faces per day. The intricacy of the work meant that the camel-hair paintbrushes they were using required regular re-pointing, which the women, not recognising the danger, did with their lips and tongues. Consequently, they were inadvertently exposed to huge doses of radiation.

In an official report commissioned to investigate conditions at the factory, Harvard professor Cecil Drinker
³⁰
wrote, ‘Dust samples collected in the workroom from various locations and from chairs not used by the workers were all luminous in the dark room. Their hair, faces, hands, arms, necks, the dresses, the underclothes, even the corsets of the dial painters, were luminous. One of the girls showed luminous spots on her legs and thighs. The back of another was luminous almost to the waist.'

Not surprisingly, large numbers of these women subsequently developed horrific symptoms, including the loss of all of their teeth, jaw bones that crumbled like sponge
and disfiguring cancerous growths arising from the facial bones. The bones were the major manifestation of the radiation exposure, because radium behaves chemically a bit like calcium in the body, meaning that it tends to build up in bony tissue, which is why the teeth and jaws of the women were most affected.

It's not clear how many workers died as a result, but US Radium employed thousands. They were eventually taken to court on occupational health grounds and some of the women received small amounts of compensation, although most didn't live long enough to spend it. Their graves, however, remain radioactive to this day.

As anyone who has ever kept a female dog knows, at certain times of the year she becomes the focus of affection for any male canine within sniffing distance. It's because she is ‘on heat', which is another name for the mammalian oestrus, a time when animals advertise their fertility and attractiveness to the opposite sex. So does this happen to us? Prevailing wisdom says not and that evolution has abandoned the process in humans. After all, we're far too civilised to be obsessed with women's rear ends, aren't we? Apparently not, because thanks to a team of lap dancers in Albuquerque, it looks like the human oestrus is a myth no more.

Geoffrey Miller and his colleagues at the University of New Mexico
³¹
hypothesised that if women do subconsciously advertise their peak fertility in some subtle way, then men ought to find them most attractive at this time. If that's the case, then in a setting where men have to buy a
lady's attention, such as in a lap-dancing club, the woman's earnings from tips ought to peak in line with her fertility during her menstrual cycle. This fertile time is at ovulation, midway through their 28-day cycles between days 13 and 15. Critically, this is when, if a woman has sex, her prospects of pregnancy peak.

To test their theory, the New Mexico team recruited 18 local lap dancers and asked them to keep a daily tally of their earnings over a 60-day period. At the same time, the women recorded the stages of their menstrual cycles and whether or not they were using the oral contraceptive pill. The pill works by fooling a woman's body into believing that she is pregnant, which prevents ovulation and the other hormone changes that accompany the process, so it could have an effect on how attractive men find women to be.

The results of the study were ‘sit up and take notice'-ably amazing. The earnings of the normally cycling (non-pill-using) lap dancers nearly doubled to US$350 per shift around the times when they ovulated and were therefore at their most fertile. Then, as they approached menstruation and their fertility fell, their earnings declined to a baseline of about US$200 per shift.
The pill users, by comparison, fared less well. They earned a flat average of US$200 per shift throughout their cycles. Why? Were the pill-using women just less attractive than their non-contraceptively compromised counterparts?

‘No,' say the researchers, because both groups earned approximately the same amounts at the beginnings and ends of their cycles, indicating that the effect was not due to an overall difference in attractiveness. Instead, the results suggest that men can subconsciously detect when women are at their most fertile and judge them to be more attractive, valuable and, it would seem, worthy of more attention and larger tips at this time. As Miller points out, ‘This is the first time that anyone has shown direct economic evidence for the existence and importance of oestrus in human females.'

It's not known what triggers the effect. It could be down to altered behaviour on the part of the fertile woman, such as chatting engagingly or wearing more provocative clothing and make-up, or it might be that chemical cues, like pheromones, are responsible. A strong possibility is that the sound of the woman's voice plays a part too. Indeed, the appropriately named Nathan Pipitone
and his colleague Gordon Gallup, two researchers from the State University of New York at Albany,
³²
have recently discovered that the menstrual cycle affects how attractive a woman sounds.

Evidence for this fertile form of conversation emerged when the scientists made recordings every week for one month of the voices of 30 female students counting to 10. About half of the students they studied were contraceptive pill users, the other half reported regular, natural menstrual cycles. The four recordings from each of the women were played back, in a random order, to a large panel of ‘raters' consisting of equal numbers of male and female students who were asked to judge the attractiveness of the voices they were hearing.

When Pipitone and Gallup matched up the scores given to each woman with where she was in her menstrual cycle when each of the recordings was made, a pattern just like the lap dancers' tips emerged. The voices of non-pill-using females were rated as significantly more attractive at the times when the women were ovulating, and therefore most fertile, compared with other times
of the month. Amongst the pill users, on the other hand, the voice ratings barely changed across the month. There were also no differences between the verdicts of the male and female raters.

So how does this happen? It's probably down to the levels of the sex hormones oestrogen and progesterone. Scientists have found that lower levels of oestrogen and higher levels of progesterone, which occur towards the end of each monthly cycle, can cause the vocal cords to swell slightly, reducing voice pitch. And as lower-pitched voices, studies have shown, tend to be rated as less attractive than higher voices, this could explain the effect.

Regardless of how women broadcast their fertility – and researchers suspect that a combination of different signals is involved as a form of ‘multiple messaging' – the effect does appear to be real. The bottom line would seem to be, ladies, if you want that new car at a knockdown price, consider ditching the pill, time your approach to coincide with day 14 and always head for the male sales assistant …

It's well known that women can influence each other's menstrual cycles using just the power of smell: ladies living together can synchronise their periods and, experimentally, women sniffing pads worn in the underarms of other females can alter their menstrual timings by up to two weeks. But if you still thought men were immune to the effect, then you've been myth-led – because males too, it now turns out, are equally sensitive to ladies' smells. In fact, research has shown that men exposed to the whiff of a woman experience a testosterone surge, although only on certain days of the month.

This came to light recently when two scientists at Florida State University, Saul Miller and Jon Maner,
³³
asked a group of 37 heterosexual (and possibly ‘metrosexual') young men to lend their noses in the name of science and sniff some ladies'
t-shirts. The men, who did not know the purpose of the study, were asked to smell t-shirts that had been worn by four non-pill-using women for three nights at points straddling the time when ovulation occurs in the middle of their cycles.

The men were also asked to smell a second set of t-shirts that had been worn by the same women, also for three nights, but this time towards the ends of their cycles (days 20 to 22), when fertility is low. A set of unworn t-shirts were also included as controls, and the women were asked, for the duration of the study, to use only neutral-smelling soaps and to avoid wearing perfumes or consuming foods with strong odours, like garlic or onions.

Before and after the men smelled the shirts, saliva samples were collected from each of them to measure their testosterone levels. They were also asked how ‘pleasant' they found the shirt odour to be in each case. The results revealed that the men were rating the smells of the shirts worn around the time of ovulation (days 13 to 15) as much more pleasant. Moreover, the average post-sniff testosterone level was also significantly higher than when the men smelled control shirts or shirts worn by the women towards the ends
of their cycles. So something in the shirts was peaking the men's sexual interests and provoking a libido-boosting burst of testosterone when the women were ovulating and most likely to conceive. Women, it seems, chemically augment their allure at certain times of the month.