For most of human history, human longevity stood at around 40 years, give or take a few. And the lifespan for most humans followed the same type of pattern, for many, a brutal ending at birth or within a couple years after, for the rest, a relatively safe run through adolescence and young adulthood. They progressed through adulthood, enduring the injuries and ailments that accompanied a mostly adverse environment, and if they were lucky, they facilitated the advancement of several offspring through childhood and into adulthood themselves. While most of our ancient ancestors had the physiology to make it into old age, their environment had other ideas.
Ironically, as we “evolved” from hunter-gatherer, to farmer, to factory worker, we seemed to actually be creating an environment that fostered more things that could kill us than things that could help us live longer. The air we were breathing got worse, the food we ingested got less natural as well as the liquids we started drinking, and the products we were inhaling. For a while we were experiencing the worst of both worlds, the high infant mortality rate of our hunter gatherer ancestors as well as the lifestyle causes of death of the modern era.
Then, around the turn of the 20th century, we began cleaning up our urban environment through improved hygiene and sanitation, as well as developing antibacterial medicines. This was the one-two punch that has drastically reduced infant mortality throughout the world. These changes vastly improved our expected lifespan (life expectancy at birth), but did little for the maximum age that humans could expect to live. In fact, even today, our life expectancy, at the age of 75, has gone up very little (see graphic below).