Harnessing the power of fire may have unwittingly led to the evolution of tuberculosis, according to a new study out this week.
One third of the world's population are infected with Mycobacterium tuberculosis (MTB), which causes lung and bone infections and can also spread to the brain other tissues in some cases.
Humans are the only natural hosts of TB and although animals have their own strains of the disease, genetic tests have shown that these are all descended from the human form of the disease.
So the question is, how did mankind come by this widespread infection in the first place? The theory being advanced by a team in Sydney this week is that early human adoption of fire was responsible.
Writing in PNAS, UNSW scientist Rebecca Chisholm and her colleagues make the case that, alongside the obvious advantages that fire brings: improved food quality and storage, defence against predators and biting insects, the ability to clear vegetation, benefits to tool manufacture and the provision of light and warmth, there is nevertheless a downside and smoke inhalation might have led to significant lung damage among our ancient ancestors.
This, the team propose, would have impaired normal chest defences and made it much easier for weakly pathogenic forms of mycobacteria, which are common in the environment, to gain a toe-hold in man and begin the process of adaptation to a human host.
They cite as evidence the demonstration by palaeontologists of small charcoal particles in dental plaque characteristic of smoke inhalation recovered from Homo remains dating back 400,000 years.
A mathematical model compiled by the team also shows that the likelihood of a bug like TB adapting to a human host is made orders of magnitude more likely under the influence of fire conditions, along the lines they suggest.
At the moment there is only a sparse fossil record charting the time span reported, and fossil remains bearing signs of disease are rarer still. But the theory is an interesting one and suggests that smoke might well have made early man cough for more reasons than just lungfuls of smoke...