根据以下材料，回答题 Factors to Influence the Life Span Being sociable looks like a good way to add years to your life. Relationships with family， friends，neighbours， even pets， will all do the trick， but the biggest longevity （长寿） boost seems to come from marriage or an equivalent relationship. The effect was first noted in 1858 by William Farr， who wrote that widows and widowers （鳏夫） were at a much higher risk of dying than their married peers. Studies since then suggest that marriage could add as much as seven years to a man' s life and two to a woman's. The effect holds for all causes of death， whether illness， accident or self-harm. Even if the odds are stacked against you， marriage can more than compensate. Linda Waite of the University of Chicago has found that a married older man with heart disease can expect to live nearly four years longer than an unmarried man with a healthy heart. Likewise， a married man who smokes more than a pack a day is likely to live as long as a divorced man who doesn't smoke. There's aflip side， however， as partners are more likely to become ill or die in the couple of years following their spouse's death， and caring for a spouse with mental disorder can leave you with some of the same severe problems. Even so， the odds favour marriage. In a 30-year study of more than 10，000 people， Nicholas Christakis of Harvard Medical School describes how all kinds of social networks have similar effects. So how does it work? The effects are complex， affected by socio-economic factors，health-service provision， emotional support and other more physiological （ 生理的 ） mechanisms. For example， social contact can boost development of the brain and immune system， leading to better health and less chance of depression later in life. People in supportive relationships may handle stress better. Then there are the psychological benefits of a supportive partner. A life partner， children and good friends are all recommended if you aim to live to 100. The ultimate social network is still being mapped out， but Christakis says: 'People are interconnected，so their health is interconnected.' William Farr‘s study and other studies show that 查看材料