The study of longevity genes is a developing science. Longer life spans tend to run in families, which suggests that shared genetics, lifestyle, or both play an important role in determining longevity. The brothers and sisters of centenarians typically have long lives, and if they develop age-related diseases (such as high blood pressure, heart disease, cancer, or type 2 diabetes), these diseases appear later than they do in the general population. People with centenarian parents are less likely at age 70 to have the age-related diseases that are common among older adults. The siblings and children (collectively called first-degree relatives) of long-lived individuals are more likely to remain healthy longer and to live to an older age than their peers. Because of their healthy habits, these older adults are less likely to develop age-related chronic diseases, such as high blood pressure, heart disease, cancer, and diabetes, than their same-age peers. The similarities they do share, however, reflect their lifestyles-many are nonsmokers, do not have obesity, and cope well with stress. They have found that long-lived individuals have little in common with one another in education, income, or profession. Scientists are studying people in their nineties (called nonagenarians) and hundreds (called centenarians, including semi-supercentenarians of ages 105-109 years and supercentenarians, ages 110+) to determine what contributes to their long lives. Now people in the United States live about 80 years on average, but some individuals survive for much longer. Most significant were public health advances that reduced premature death by decreasing the risk of infant mortality, increasing the chances of surviving childhood, and avoiding infection and communicable disease. Environmental improvements beginning in the 1900s extended the average life span dramatically with significant improvements in the availability of food and clean water, better housing and living conditions, reduced exposure to infectious diseases, and access to medical care. The duration of human life (longevity) is influenced by genetics, the environment, and lifestyle.