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Some people may think that the spread of herpes is a modern problem.

But scientists have found that Herpes Simplex Virus-1, which manifests itself as cold sores, infected hominids before the evolutionary split from chimpanzees, six million years ago.

While genital herpes, or HSV-2, jumped from ancient chimpanzees to ancestors of modern humans - Homo erectus - approximately 1.6 million years ago, they claim.

Scientists studied the cross-species transmission, from chimps (stock image pictured) to human ancestors using advanced models of molecular evolution. They found the HSV-1, which manifests itself as cold sores, infected hominids before the evolutionary split from chimpanzees six million years ago

This jump occurred long before the rise of early modern humans about 200,000 years ago.

'Before we were human, there was still cross-species transmission into our evolutionary lineage,' said Joel Wertheim, assistant research scientist at the University of California San Diego.

Modern versions viruses are spread by intimate contact and HSV-1 can also be spread by sharing drinks.

'The results help us to better understand how these viruses evolved and found their way into humans,' Dr Wertheim explained.

'Animal disease reservoirs are extremely important for global public health.

'Understanding where our viruses come from will help guide us in preventing future viruses from making the jump into humans.'

It is thought that two thirds of the human population is infected with at least one form of the virus, which shows itself as cold sores on the mouth or blisters on the genitals.

Dr Wertheim said: 'Humans are the only primates we know of that have two herpes simplex viruses. We wanted to determine why.'

Genital herpes or HSV-2 (pictured) jumped from ancient chimpanzees to ancestors of modern humans - Homo erectus - approximately 1.6 million years ago, experts claim

The researchers compared the HSV-1 and HSV-2 gene sequences to the family tree of simplex viruses from eight monkey and ape host species.

Using advanced models of molecular evolution, they were able to estimate ancient viral divergence times more accurately than before.

This allowed the experts to determine when HSV-1 and HSV-2 were introduced into humans with far more precision than previous models, which do not account for natural selection over the course of viral evolution.

The genetics of human and primate herpes viruses were examined to assess their similarity.

Scientists found that HSV-1 has been present in humans far longer than HSV-2, prompting the researchers to further investigate the origins of HSV-2 in humans.

The viral family tree showed that HSV-2 was far more genetically similar to the herpes virus found in chimpanzees.

This level of divergence indicates that humans must have acquired HSV-2 from an ancestor of modern chimpanzees about 1.6 million years ago, prior to the rise of modern humans roughly 200,000 years ago.

'Comparing virus gene sequences gives us insight into viral pathogens that have been infecting us since before we were humans,' Dr Wertheim said.

It is thought that two thirds of the human population is infected with at least one form of the virus, which shows itself as cold sores on the mouth (pictured) or blisters on the genitals