點解我們會死？點解我們會有不同的壽命？

世界上所有生物都是由細胞組成，細胞是十分重要的，因為細胞內儲存了很多種作資料。有些細胞如果受到損害，它們會復原，但另一些細胞是不會復原的，例如腦細胞；當細胞不能復原，細胞所屬的器官便漸漸會失去功能。在這情況下，身體便不能正常地運作，功能會慢慢衰退而死亡。

人類死亡有兩大原因：疾病和退化。外來因素如細菌會損害人類體內的細胞，如果細胞不能復原，那部分器官便開始失去它的功用（身體內每個器官都有它獨特的功能），這樣便會影響整個身體的正常運作。如果身體不能正常運作，我們便會死亡。

另外一個因素是細胞退化，每個細胞都知道它們的壽命，這個現象稱為program death，當細胞運作一段時間後，細胞便開始疲勞、衰退以至死亡。這時候器官慢慢失去功能，這樣我們便會退化而死。

其實世界上任何一種生物都會死，不過有不同的壽命，有些是短短的一兩天，有些可長達數百年，但是最終都會死亡。

this is a basic concept of evolution, only the success can survive.
and most of which.. depend on our genetic composition.
e.g. why many african has sickle cell anemia? because malaria is common in africa, but they cannot infect the sickled cell! so, those genetically carring this abnormal gene will be free from malaria.. and those are normal may die from the disease.

because of our medical advance, we have already prolonging some life e.g.beta thalaseamia major.

so, other than the physical damage, we are mostly killed by our own genetic composition (many cancer is caused by individual mutation or mutation from familty) and also pathogen. but how our body react to different pathogen, it is depends on our immunity (which differ by nutrition, life style, pressure.. etc)

lastly, every cell division shorten the length of telomere of each chromosome. some scientist estimate that, the telomere can only provide the cell divisions upto around 200 years. if no cell division, there is no cell regeneration. so we die anyway.

因為如果我地唔死...地球就會月黎月多人....會唔夠位住

因為我們是生物