人類壽命是否有一自然極限，或因醫療衛生條件而有技術的上限，至今仍是一個具高度爭議性的問題。本文使用台灣與日本自1920至1995年的人口資料 計算生命表，並以邏輯成長函數從事長期趨勢之比較，結果顯示台灣與日本之 人口出生時平均餘命皆有明顯而穩定的上限；年齡別死亡率的下降也將因等待生命科學的重要突破，與面臨投資報酬遞減的困境，而有其顯然的限制。因此 ，就邏輯函數檢討平均餘命的長期趨勢，我們取得相當可靠穩定的參數估計， 而這些參數之一正是平均餘命長期趨勢的上限值。對於平均餘命的上限，我們 傾向於認同Olshansky等人所主張的物種進化理論，相信人口平均壽命的極限約莫落在生殖期後段四十歲以後，與已知最高齡（約一百三十歲）的分佈區間中 點，也就是八十五歲上下。

　　　　　Many demographers believe that, given the state of medical knowledge and technology, there is a limit to the growth of the life expectancy. But it is also well-known that this limit to the human life expectancy can shift upwards with the technological progress. Using data from Taiwan and Japan from 1920-1995, our simulations show that the upper limits of life expectancy for both countries are quite stable; the mortality decline will face an inevitable barrier shortly due to the diminishing return of investments in the vital sciences and the limitations on bio-medical technology. Therefore, we tend to believe that the evolutionary theory proposed by Olshansky et al. is close to the developments in both Taiwan and Japan. It is found that the upper limit of life expectancy should be around 85.