While studying last night, I came across an interesting animal. I was studying the circulatory systems of various animals and came across cnidarians, specifically hydra. They look like this:
They are teenie-tiny water creatures (meaning only a few millimeters long) and they can do some pretty amazing things. For one thing, they can regenerate any appendages that are lost. It would be as if someone cut off your arm and then you could grow it back. How awesome would that be? Not that I have ever lost an arm or anything...
However, the most amazing thing about them is that they appear to be biologically immortal. Meaning that they don't age. If left on their own, they could live basically forever ... or so some scientists believe. Being biologically immortal isn't the same as never dieing; they can still die if you squish them or if they get eaten.
Cells tend to die off because they are either programmed to die (called apoptosis) or the DNA becomes riddled with too many mistakes through either faulty copying or outside influences. These things can be prevented by having the right "stuff" in the cell to go back through the DNA and correct the mistakes, which hydra and other things (like cancer cells) apparently have.
I read that a biologically immortal human being would statistically only live to be around 1200 years old before he/she would die from some sort of accident, like being hit by a car. Perhaps this can explain the long lives of Adam and Methuselah? Maybe our cell make-up changed way-back-when so that the repair system didn't work as efficiently, thus reducing our life span.
Can you imagine what life would be like if everyone lived to be over 1000 years old? Henry IV of the Holy Roman Empire, Genghis Khan, and Christopher Columbus would probably be still alive. Well, probably not Genghis Khan. I'm pretty sure he didn't die of natural causes.