In the era of raw meat and blood, people survived by hunting, gathering, and other activities. During these activities, people might kill animals and carry various bacteria on them. However, at that time, people's immune system might have developed immunity to certain bacteria. In addition, the living environment of people in the era of raw meat and blood may be worse than that of modern society. They may live in a natural environment and face various kinds of pathogen infection. Therefore, people's immune system may also be stronger and better able to resist infection by pathogenic organisms. How did people survive in the era of raw meat containing bacteria? Through hunting, gathering, and other activities to obtain food, they developed the immunity to certain bacteria and a strong immune system, so that they could better resist the infection of the pathogen and survive.