Final answer:
Fatal illnesses are less common in developed nations until later in life primarily due to medical prevention, lifestyle choices, and advancements in public health and sanitation.
Step-by-step explanation:
In developed nations, fatal illnesses are rare until late adulthood because of medical prevention. Many chronic noninfectious diseases, such as heart disease, stroke, diabetes, and cancer, are largely preventable despite having some genetic components. Lifestyle choices play a significant role in these illnesses, and mitigation strategies include regular screening, adopting healthy eating habits, and maintaining regular exercise routines. Additionally, the rise in life expectancy can be attributed to improved sanitation, public behavior changes like reduced tobacco use, and medical advancements including immunizations and antibiotics.