I also want to write on this topic:
The life-expectancy of every country has increased considerably compared with the past. This positive tendency is due to two main reasons: the improvement in both physical and mental life.
First, nowadays, people live longer because of their high nutritional meals and the availability of medical service. In the past, the fact that people died for starvation was something more commonplace; Humans needed to struggle with the wild nature to subsist. Now that, modern technology has allowed the production of all kinds of food with much higher quantity and quality, we can not only eat larger amount but also more delicious food. Good meals undoubtedly have made people taller, stronger and more intelligent than their forefathers. Besides, the tremendous development of medical service in the past centuries has protected us from the threat of many diseases once considered incurable. Of course, when we have more medicine and trained doctors, we have more solutions to prolong our life.
Second, the fact that the mental life of humans has been improved by better education, recreation and social activities also contributes to longer life. No one can deny that nowadays we have more schools than ever; therefore, people have more chances to gain knowledge. And, researchers have shown that people with higher education can probably live longer. In addition, the economic development gives rise to recreation and social activities which help people achieve their satisfaction. And of course, that happiness makes people live longer.
In short, people now live longer because every aspect of their life is better than it used to be. We need to keep the balance between working, relaxing and resting to have a healthy life.