The human lifespan seems to cap out at about 120.
Though there have been improvements in the human lifespan made in the last century or so due to the advent of modern medicine, these have tended to shift only the average lifespan upwards–not the maximum lifespan.
Much of the shift is due to improving the chance that infants will not die soon after birth. Even two hundred years ago, people who made it out of infancy tended to live almost as long as the average person does today, so the average lifespan of post-infants hasn’t shifted that much.
The maximum lifespan hasn’t really changed: Humans just don’t tend to live past 120.
That fact has caused many to speculate that there is a "death gene" that prevents us from living longer. If our deaths were simply caused by minor problems building up over time ("wear & tear") then we’d expect to see modern medicine extending not only the average lifespan but also the maximum lifespan.
It hasn’t.
This raises the possibility that we may one day find and be able to switch off the "death gene"–if there is one–in which case we may be able to break the 120 barrier.
But one woman may have already done so.
Reports are that Maria Olivia da Silva, a native of Brazil, is 125 years old.
I don’t know if this is accurate or not, but if so, maybe she has a defective death gene.
(Cowboy hat tip to the reader who e-mailed.)
Death gene search? I’m sure Arnold and his Planet Hollywood buddies are right on it.
Neat idea about the death gene concept though. I wonder how each of our cells “knows” how old it is so that it can activate the death gene.
Whatever it is that indicates age to a cell doesn’t seem to get passed on to the new cell at conception when sperm and egg meet.
Also, isn’t there a disease that rapidly accelerates aging, so that 12 year olds look like 100 year olds? Have they identified the gene that causes that?
If we ever figure that death gene out, warp drive better not be far behind. Will need lots more planets!
Chromosomes lose a little bit of their DNA when they replicate, so each round of cell division reduces their size. Some cells in the human body that replicate over and over again have extra sequences on the ends of their chromosomes called telomeres, that solve this problem. For example the stem cells that regenerate the various blood cells, or germ line cells that produce sperm cells.
Not all human cells do, however (e.g. neurons or muscle cells). So after a certain period of time, the DNA in these cell lines just wears down too much.
Interesting fact about telomeres #1: cells that become cancerous due to some mutation often develop the ability to add telomeres to their chromosomes, giving them an indefinite growth potential.
Interesting fact #2: Humans with a defect in telomerase, the enzyme responsible for telomeres, have some problems due to tissues aging very fast, and cancer development. (The disease is called dyskeratosis congenita, DKC). Mouse telomeres are much much longer. So if a mouse happens to get a mutation in its gene for telomerase, this problem will only be seen three to four generations later, when it’s descendant will develop problems.
#3: Human fetuses all have telomerase activity, since they are growing so rapidly and doing so much cell division. It’s only later that they shut off the telomerase in most of their genes.
Billy HW: there are several diseases that cause premature aging, usually due to defects in the processes that repair DNA.
Sorry this comment was so long, I just love love love genetics.
Didn’t Abraham live to be 180 or thereabouts? And didn’t his forefathers live even longer? I read an interesting article that postulated that it may be because Noah’s descendents did not have the ability to manufacture vitamin C.
http://www.lewrockwell.com/orig/sardi9.html
Blast! Dev beat me to it! I know that there is a lot of work right now trying to delay that breakdown. I used to work at a genetics company and these caused quite a stir.