I, Charlemagne Darwinius, am a great scientist who has devoted his life to the study of the evolution of different species. Priests speak of man being created by a supernatural being called God, who became increasingly angry with them due to their descent into wickedness. To punish man, he sent a great flood to wipe all life from the earth, sparing only a few humans and animals who took shelter in a great ark. For 40 days and nights, the flood drowned all living things on the planet, until the waters receded. The survivors on the ark were able to carry on their existence, and today's humans are the descendants of those survivors. However, as a way to humble humanity, God decreased their lifespans going forward. When once humans would live hundreds of years in good health, now they would be lucky to live a few decades. As they aged, their bodies would grow old and decrepit until dying, as a way to remind humanity of who was really in charge.
Recent archeological evidence has revealed that their actually had been a great flood at one point which encompassed the entire world, leading to an extinction level event. Other evidence has emerged which suggests that human civilizations existed before this flood, with numerous empires and cultures inhabiting the earth. This gives credence to the stories told in these parables, which has forced me to update my theories. If the evidence is true, then humans had lived much longer, healthier lives in the past, and were far more able than we are today. For reasons left unexplained, our lifespans had shortened over millennia, to the point where those who get past a century is incredibly rare. This is despite the fact that we are much more technologically advanced than our ancestors, with access to better medicine and care.
My phrase "Survival of the fittest" is a way of describing the mechanism of natural selection. The biological concept of fitness is defined as reproductive success. It is best understood as survival of the form that will leave the most copies of itself in successive generations. Shorter lived humans have outcompeted those with longer lifespans, appearing to make us less fit. What explanation could be given for this occurrence?