Answer by Tirumalai Kamala:
In other words, since we evolved without vaccines, why do we need them now? Pre-vaccines, how many humans, including babies, died from vaccine-preventable infections? The data suggests many. Here’s some morbidity (not mortality) data from the CDC.
Why did we have so many vaccine-preventable deaths? A restless species, in recent centuries we evolved to gather in ever closer proximity in ever larger groups, and with ever increasing mobility. By doing so, we created conditions for rapid spread of vaccine-preventable diseases, conditions such as rapid and tremendous migrations from rural and isolated communities to chaotic, densely populated and unsanitary cities with unsanitary working conditions, inadequate nutrition and unsafe food supplies. Thus, we were an active agent in increasing deaths from vaccine-preventable infections. How? We evolved on a microbial planet. Microbes existed long before us and will probably outlast us. To our disadvantage, microbes mutate exponentially faster. This microbe-human difference is a difference in kind, and when we disturb human-microbe status quo through our agency, we bear the disproportionate cost of increase in human mortality, usually child mortality. This is how we arrive at our time and its need for mass vaccinations. Had we stayed in small, isolated hunter-gatherer communities that interacted rarely with each other, we may not have such a need for vaccines.
How did the need for vaccination to newborn babies arise when humans evolved facing a lot of health problems over generations?