There are many factors that come into play when it comes to how long they will live for. According to a study done by Nicholette Zeliadt, "A person's life span is thought to be largely determined by the combined effects of genetic and environmental effects. Twin studies suggests genetics only accounts for approximately 20 to 30 of an individual's chance of surviving to age 85." Poor habits like a bad diet, drinking, or smoking make someone's fitness worse. The theory of exceptional longevity (EL) being common in family tree's makes it seem that life expectancy can be inherited amongst genetics. EL is when someone lives a decade past the average life expectancy of their generation, that tends to be common in families rather than sporadic. Where as genetics can become beneficial to a person's longevity, they can also lower someone's chance of a long life. Inheriting an unfavorable disease is just as possible as a favorable one is.