Professor Gagneux says TB left Africa when humans did, about 65 to 70 thousand years ago. Then, about 10 thousand years ago, came the Neolithic Demographic Transition. That is the period when people started to develop agriculture and to domesticate, or train, animals. But, it was also a time when diseases jumped from domesticated animals to humans for the first time.

Professor Gagneux says for many years people thought that TB took the same path – from animals to humans. But, the research shows that TB first appeared in humans before the domestication of animals. In fact, the bacteria learned to live inside people and now cannot survive by itself in the environment.There was another important development during the Neolithic Demographic Transition. Humans started to form communities with lots and lots of people. That would have been ideal for the spread of tuberculosis through the air from person to person.

Professor Gagneux says before settlements, in the hunter-gatherer days, TB may not have been as deadly.

“Overly deadly would be a bad strategy for any pathogen because you might just kill off all susceptible hosts and you might end up with nobody else to infect.”

After humans left Africa, they started to change in appearance as they reacted to new environments in other parts of the world. TB also changed and now there are many different forms of bacteria that cause the disease. The one found in South Africa differs from that found in China, but Africa still has the greatest number of TB strains. Researchers hope that knowing the history of TB will help in the development of new drug treatments and vaccines. Now, the number of drug-resistant TB cases is growing. The knowledge may also help predict what the scientists are calling “future patterns of the disease.”