Longevity

Longevity refers to the length of time an individual or a population lives. Scientists often distinguish this from life expectancy, which is a statistical average. Life expectancy represents the average number of years remaining at a specific age. For example, life expectancy at birth is the average age at death for everyone born in a single year.

Understanding these concepts helps researchers study how to extend human life. This subject has fascinated people for centuries, appearing in science fiction and ancient legends.

Biological longevity is driven by two primary factors: genetics and lifestyle. Genetics provide the internal blueprint for how a body ages. Studies using twins suggest that genetics account for about 20% to 30% of the variation in human lifespan. The remaining portion is determined by environmental factors and individual behaviors.

These environmental factors are often called "plastic" because they can be changed through different choices and conditions.

Research into human genetics has revealed specific mechanisms that support long life. For instance, centenarians—people who live to be 100 or older—show higher activity in a protein called PARP. This protein, known as Poly ADP ribose polymerase, helps repair DNA damage. By repairing this damage, the cells can maintain functions similar to those of younger people. Furthermore, scientists have identified genomic loci, or specific locations on a genome, that influence healthspan. Some research suggests that genes involved in metabolizing iron may also increase healthy years of life.

Lifestyle choices play a massive role in determining how long a person lives. Physical exercise is a powerful tool for increasing life expectancy. One 2012 study suggested that even modest leisure-time exercise could extend life by up to 4.5 years. Diet is another major factor, though the evidence is complex. While certain foods affect health, there is no clinical evidence that specific dietary practices or fasting promote longevity in humans. Researchers have studied caloric restriction, which is a sustained reduction in energy intake. While this helped some animals like rhesus monkeys, preliminary human research shows little evidence of a lifespan effect.

Historical data shows that human life expectancy has increased significantly over time. In preindustrial eras, many people died young due to disease, accidents, or malnutrition. Before the 20th century, many medical issues were untreatable. For example, an 1871 UK census showed a male life expectancy of only 44 years. However, if you remove infant mortality from that number, males who reached adulthood averaged 75 years.

Today, life expectancy in developed nations is much higher, often ranging from 77 to 90 years.

There are several documented individuals who have set records for the longest human lifespan. Jeanne Calment is the oldest person in history whose age has been verified by modern documentation. She lived to be 122 years and 164 days old.

Jiroemon Kimura holds the record for the oldest verified man, living to 116 years and 54 days. Other notable figures include Kane Tanaka, who lived to 119 years, and Sarah Knauss, the oldest American at 119 years. These individuals help scientists define the modern limits of the human life span.

Demographic differences also exist in how long different groups of people live. Women generally outlive men in most populations. This may be due to biological factors, such as women having smaller bodies that place less strain on the heart. Additionally, the X chromosome contains more genes related to the immune system, which helps women fight pathogens.

Economic and social factors also matter. In the United States, life expectancy varies by group; for example, Asian-American females average the longest lifespans, while Black American males average 69 years. This variation often reflects differences in access to healthcare, diet, and the prevalence of diseases like diabetes.