Are We Too Promiscuous for Own Good?

If you were a zoologist, or an animal behaviourist, you could probably go to Africa and observe a couple of wildebeest mating, and you’d probably be observing the very same thing that you would have witnessed their wildebeestian ancestors doing a couple of million years ago.

Humans aren’t like that – our sexual behaviour isn’t static; it’s constantly changing. It changes because social structures and marital systems change. It changes because we develop contraceptives to thwart nature’s reproductive end-game. It changes because we learn about new ways of having fun and enjoying ourselves in the bedroom.

And it also changes because of the sexually transmitted infections that so frequently want to share in any fun that we might be having.

The Kinsey Reports, two books titled Sexual Behaviour in the Human Male and Sexual Behaviour in the Human Female, were published in 1948 and 1953, respectively, and they probably mark the beginning of our modern quest to document, and catalogue and understand the breadth of human sexual behaviour. Even in the few short decades since these books were published, there have been dramatic changes to sexual practices.

Interestingly, some of the changes in our sexual behaviour not written in any report, but are instead written in the sexually transmitted infections that have co-evolved with us.

How herpes has evolved along with our sexual behaviour

My favourite example is herpes.

Genital herpes is that awful STI that causes bouts of tingling blisters that rupture into unsightly sores in sites usually unseen by all but the most intimate of companions. As far as STIs go, genital herpes isn’t actually that bad. Up to 80% of people who have been infected remain completely asymptomatic, and most others will have only one or perhaps a few outbreaks, despite the virus establishing a lifelong residence inside the sensory nerve cells that lie under the skin.

There are in fact two different types of herpes simplex virus that infect humans – herpes simplex virus 1 (HSV-1) and herpes simplex virus 2 (HSV-2). Most cases of genital herpes in humans are caused by the HSV-2, and in Australia, HSV-2 affects around 12% of adults. Its cousin, HSV-1, usually stays above the belt, causing facial cold sores.

Humans and herpes viruses have been evolving together for millennia. In the late 1960s, researchers made the observation that the two herpes simplex viruses in humans clearly occupied different territories on the human body – HSV-1 on the mouth, HSV-2 on the genitals.

Humans are actually quite unique in having two very closely related viruses that have evolved to occupy very distinct ecological niches on our bodies. In our primate relatives, a single virus infects both mouth and genitals. This is more than likely due to their sexual and social behaviour, and also their anatomy. In chimpanzees and other non-human primates, there is frequent genital inspection – of their own and others’ in their troop; there’s oral sex between males and females; and they also have a more compact body shape, which means that self-grooming and auto-fellatio are literally within reach.

It’s quite likely that these behaviours were also common for our own distant ancestors – which, depending on your views of auto-fellatio, is perhaps another reminder that evolution doesn’t breed perfection. But I guess that’s the price you pay for being able to walk upright.

But over evolutionary time, through changes in behaviour and changes to our anatomy, our genitals and mouths became isolated, allowing HSV-1 and HSV-2 to become the genetically distinct viruses that they are today. Not only did our flexibility change as we began to walk upright, but our ancestors sexual and social behaviour also changed. A proclivity for oral sex was replaced with a preference for face-to-face sex and kissing, so that mouths were kept with mouths and genitals with genitals.

Just as we can learn something of our ancestors’ behaviours by looking at how we came to have two herpes simplex viruses, we can now also learn about current sexual norms by looking at where these two viruses reside. The 1960s observation that HSV-1 occurred in the mouth and HSV-2 in the genitals is still largely true, but the two viruses are increasingly squatting on each other’s turf. Two decades ago, in 1994, less than 30% of Australian genital herpes cases were caused by facial HSV-1 – the virus that usually causes cold sores. But by 2006, the number had increased to over 40%. We are apparently having more oral sex than we did in the 1960s, and probably more than we did even 20 years ago.

But that’s not really a big deal, and it doesn’t mean that we’re more promiscuous.

Chlamydia: Australia’s most common STI

So, what other aspects of sexual behaviour have changed? Here, again, I’d like to introduce you to one of our evolutionary fellow travellers – another sexually transmitted infection that takes up residence in our nether regions if we give it half the chance: chlamydia.

In Australia, chlamydia is our most common bacterial STI, as it is in many Western countries. Every diagnosis of chlamydia is notified to the Department of Health, and the numbers of notifications have been steadily increasing. In 1994, there were 7,500 notifications of chlamydia infection across Australia. In 2014, we can fairly safely assume it will be more than 10 times that number; last year, there were over 82,000 cases of chlamydia diagnoses. Surveys suggest that around 5% of young people below the age of 30 have chlamydia – that’s one in 20. If you were all between the ages of 15 and 30, there’d be a handful of people in here with chlamydia.

Chlamydia is incredibly easy to test for, really easy to treat, but also extremely easy to pass on from one person to another. This is particularly so, because around 4 out of 5 men and women who have chlamydia are completely unaware of the infection. And while it hangs around in its unsuspecting host, not only can it be transmitted unwittingly to their sexual partners, but it can also do some pretty serious damage, particularly in women. It can cause internal scarring of women’s reproductive tracts – especially the fallopian tubes – that leave some women infertile, or at higher risk of having an ectopic pregnancy if they fall pregnant. Other women develop painful infections that leave them with chronic pelvic pain, even after the infection has subsided.

When we look at who gets chlamydia, there is a pretty clear picture that emerges about who’s at risk of infections. And it’s a picture that is mirrored in most sexually transmitted infections that are studied – from gonorrhoea to HIV to genital herpes.

Reluctance to use condoms

Perhaps surprisingly, the picture that emerges is not all about condoms. For a start, condoms won’t protect you from everything. They won’t protect you from our friend herpes simplex, and they are probably not great at protecting you from genital warts, either.

The other thing is that people are reluctant to use condoms, which does put them at risk of contracting an STI. In 2008, researchers at La Trobe University’s Australian Research Centre in Sex, Health & Society conducted a survey of Australian school students to ask them about their sexual practices and what they knew about sex. Of those who were having sex – which was over a quarter of Year 10 students, and over half of Year 12 students – only half were consistently using condoms.

So apart from not using a condom, what behaviours put you at risk of contracting an STI?

A survey of chlamydia infection in young people attending general practices was recently conducted by former colleagues at the University of Melbourne. When they looked at what factors were associated with infection, they found that the number of partners that someone had in the 12 months before being tested was more strongly associated with chlamydia infection than whether or not they had consistently used condoms. So, around 5% of young people overall were infected with chlamydia, but for people who had 3 or more partners, 11% were infected. Women with multiple partners were 4 times as likely to have an infection than the women who only had one partner, and men were 5 times as likely to have a chlamydia infection than if they were less promiscuous.

Photo courtesy of Quinn Dombrowski

More sexual partners than ever before

And we are more promiscuous than we used to be. At the time of the Kinsey reports – the late 1940s and early 1950s — women aged 30-44 years reported an average of just 4 male partners in their lifetime. Men reported a slightly higher, but still rather modest, 6-8 female partners. Those high school kids that I mentioned earlier – 30% reported 3 or more partners just in the year leading up to the survey. If we take a slightly older crowd – young people attending a Big Day Out music festival in 2006, where participants were between 16 and 29 years old, the average number of lifetime sexual partners was reported as 5 for both men and women. So, women in 2006 had exceeded the number of lifetime partners that their grandmothers in the middle of the 20th century did, when they were still several years younger on average. Men in 2006 were also well on their way to surpassing the number of lifetime partners of their older male counterparts 75 years ago. But, most of you probably know all this from your own personal experience.

Does promiscuity matter? Does this mean that we’re too promiscuous for our own good?

No, I don’t think so. But that’s not to say that promiscuity comes without consequences. Our sexual behaviour has changed, and as a consequence, our sexual health behaviour must also change.

Normalising preventative health

Knowing that we are at risk, so that we can minimise the risk to ourselves and to others, is probably the first hurdle. And it’s by no means a small hurdle. Thirty per cent of the music festival revellers that I mentioned before said they didn’t bother to use condoms all (or even most of) the time, and yet only a quarter of these people thought they were at any risk of catching an STI. Proper sexual health education in school, followed by ongoing public health campaigns, need to keep the message coming loud and clear: STIs are everywhere, and you need to protect yourself and your partners by staying safe – and of course wearing condoms is a big part of that.

But sexual health check-ups also need to become a normal part of preventive health care, alongside things like exercise and good diet and getting your moles checked out for skin cancer. Doctors can certainly play an important role in encouraging young people to get tested – not because having an STI means you are leading a wild and debauched existence, but because STIs are a fact of life, and getting the right treatment as early as possible helps to keep you and your partners, and the community, safe.

But it’s not just about individual attitudes and choices and behaviours. Policy can also play a important role in improving sexual health for Australians.

HPV vaccine: How good policy can reduce STIs

Let’s take the example of the HPV vaccine. Australia was the first country to introduce a school-based HPV vaccination program for girls in 2007. HPV is probably best known for its capacity to cause cervical cancer. But there is now clear evidence that it can also cause anal cancer, penile cancer, vaginal and vulval cancers, and cancers of the oropharynx, or throat.

People are probably more aware of this last one thanks to Michael Douglas’s famous ‘cunnilingus gave me throat cancer’ remarks that he made last year at the Cannes film festival. Gardisil, the vaccine used in the school vaccination program, protects against two of the main HPV types that cause cancer, as well as two types that don’t cause cancer, but instead cause the majority of cauliflower-shaped genital warts.

When the HPV vaccine was introduced into Australia in 2007, there were the usual outcries from fringe groups in the community claiming that vaccinating 12- and 13-year-olds would somehow make them more promiscuous. But sense prevailed and research has already shown that the vaccination program is working. At the Melbourne Sexual Health Centre, clinicians have already seen a dramatic decrease in genital warts in young women since the vaccination program was introduced; between 2004 – before the vaccine was introduced – and 2010-11, the rate of genital warts in female patients plummeted from 9.6% to less than 2%.

It is likely that a similar decline in cervical and other genital cancers, as well as head and neck cancers, will be observed over the coming decades, especially now that boys are also included in the immunisation program.

This is a clear example of sensible policy that has listened to science, and it’s now minimising the harm that a sexually transmitted infection can cause.

So, are we too promiscuous for our own good? I don’t think so. But we do need to remain vigilant if we are going to reduce the spread of sexually transmitted infections and reduce the harm that they can cause. Humans and sexually transmitted infections have been bedfellows for millennia. But with the right knowledge, evidence-based policies, and an openness to discuss and address sexual health as a community, we can certainly make a difference.