Most people would count getting married as one of the most romantic steps a couple can take.

A wedding day marks the special bond between two people, marking a promise to share their lives together.

But the root of marriage can be traced back to nothing more romantic than avoiding sexually transmitted diseases, a new study has revealed.

Most people would count getting married as one of the most romantic steps a couple can take but the root of marriage can be traced back to nothing more romantic than avoiding sexually transmitted diseases, a new study has revealed (stock image)

Monogamy is a trait present in just three per cent of mammal species, and for a long time scientists have wondered why it evolved in humans.

Now a study shows monogamy emerged in early farmers after 'sleeping around', which had been the norm among hunter gatherers, became too risky because of genital herpes and other diseases.

Scientists have long thought our ancestors did not start raising crops until 12,000 years ago, although a study earlier this year suggested it dawned much earlier with the first cultivation beginning 23,000 years ago on the shores of the Sea of Galilee in Israel.

Monogamy is a trait present in just three per cent of mammal species, and for a long time scientists have wondered why it evolved in humans. Now a study shows monogamy emerged in early farmers after 'sleeping around' became too risky because of genital herpes, gonorrhea (pictured) and other diseases

Scientists have long thought our ancestors did not start raising crops until 12,000 years ago, although a study earlier this year suggested it dawned much earlier with the first cultivation beginning 23,000 years ago. Whenever it was, as hunter gatherers began living in bigger groups the spread of STIs became a risk

But, whenever this was, as hunter gatherers began living in bigger farming groups the spread of STIs may explain a shift towards the emergence of preferring one sexual partner over many.

Computer simulations found larger populations fuelled by agriculture meant outbreaks of sexually transmitted infections (STIs) would be more prolonged, harming women's fertility and giving monogamy an evolutionary advantage over the previous polygamous lifestyle.

Mathematician Professor Chris Bauch and colleagues from the University of Waterloo, Canada, believe this led to prehistoric humans remaining in stable, faithful relationships, leading to the institution of marriage.

WHY ANCIENT HUMANS STOPPED SLEEPING AROUND The results follow a paper published earlier this week that claimed Neanderthals (shown) were killed off by catching STIs from humans In early hunter-gatherer populations, it was common for a few men to monopolise many women in order to increase their number of offspring. In these small societies with a maximum of 30 sexually mature individuals, STI outbreaks were short lived and tended not to have as significant an effect on the population. But as societies evolved around agriculture and the size grew to a maximum of 300 the prevalence of STIs became endemic in the population, reducing fertility rates and favouring the emergence of monogamists. These would have punished both members of their own community, and other groups, that did not conform. With the absence of modern medicines infertility from syphilis, chlamydia and gonorrhea would have been high among those refusing to adopt the new social norm. Males were better off mating monogamously and, more importantly, punishing other males who did not. Groups that enforced monogamous social norms could therefore out-compete those lacking them. Advertisement

The researchers added STIs may be one factor among many, including female choice, pathogen stress and technological impacts, which altered human behaviour from polygamy to monogamy (wedding bells pictured)

Polygamists would have been punished and made social outcasts thanks to the presence of STIs and peer pressure not to spread them.

'This research shows how events in natural systems, such as the spread of contagious diseases, can strongly influence the development of social norms and in particular our group oriented judgements,' said Professor Bauch.

'Our research illustrates how mathematical models are not only used to predict the future, but also to understand the past.'

Historically, most human societies have been polygynous, a form of polygamy where males are allowed to mate with multiple female partners.

THE HISTORY OF SEXUALLY TRANSMITTED DISEASES Syphilis is caused by the bacterium treponema pallidum (pictured) The researchers think the presence of syphilis, chlamydia and gonorrhea would have been high among those refusing to adopt the new social norm. This means STIs will have been present much earlier than any recorded cases known today. The first well-recorded European outbreak of what is now known as syphilis occurred in 1494. It broke out among French troops besieging Naples in the Italian War of 1494 and 1498. Gonorrhoea is recorded at least 700 years ago and associated with a district in Paris formerly known as 'Le Clapiers'. This is where the prostitutes were found at that time and is why the disease is informally referred to as the 'clap.' Prior to the invention of modern medicines, sexually transmitted diseases were generally incurable, and treatment was limited to treating the symptoms of the disease. In the 1980s, first genital herpes and then Aids emerged into the public consciousness as sexually transmitted diseases that could not be cured by modern medicine. Advertisement

As hunter gatherers began living in bigger groups the spread of STIs explains a shift towards the emergence of preferring one sexual partner. Infertility from syphilis, chlamydia and gonorrhea would've been high among those refusing to adopt the social norm. These days, STIs are treated by modern medicine (pictured)

HOW THE STUDY WORKED The study used computer modelling to simulate the evolution of different social mating behaviours in populations based on demographic and disease. They conducted 2,000 simulation runs, each lasting 30,000 years of simulated time. Historically, most human societies have been polygynous, a form of polygamy where males are allowed to mate with multiple female partners. But the researchers found when population sizes become large the presence of STIs decreases fertility rates more among males with multiple partners. This changes which mating behaviour proves to be most beneficial to individuals and groups. It was published in the journal Nature Communications. Advertisement

But the researchers found when population sizes become large the presence of STIs decreases fertility rates more among males with multiple partners.

This changes which mating behaviour proves to be most beneficial to individuals and groups.

'Our social norms did not develop in complete isolation from what was happening in our natural environment. On the contrary, we cannot understand social norms without understanding their origins in our natural environment,' said Professor Bauch.

'Our social norms were shaped by our natural environment. In turn, the environment is shaped by our social norms, as we are increasingly recognising.'

The researchers note that STIs may be one factor among many, including female choice, pathogen stress and technological impacts, which altered human behaviour from polygamy to monogamy.

The results follow a paper published earlier this week that claimed Neanderthals were killed off by catching STIs from humans with whom they mated.