Hi,
Why is there no simple biological test for determining the exact age of a human being? I get the concept that due to environment/genetics each body part ages at a different rate, but how then does the brain know to start growing hair out of my ears or turning the hair on top of my head grey?
To clarify; you’re asking why is there no way of testing for age apart from calender years, not a biological test to determine how many calender years someone is, correct?
That’s right. On news programs and CSI-type shows, they can only estimate the age of the ‘specimen’ as “between 18 and 24, judging by the size of the femur”. Surely there should be some more exacting test that can be done.
Okay, now I’m more confused.
Basically, everyone enters puberty at a different age, and exists puberty at a different age. And, of course, peoples environmental factors change the rate at which they age.
What I am asking is this - why is there no simple biological test that can answer a question of how old an individual is? Does puberty wipe out all (internal/biological) records of when you were born? Are there no indicators within the human body that exist from birth to death?
Like when those Chinese gymnasts claimed to be old enough to compete in the Olympics, why couldn’t a biological test be conducted to determine their exact age?
Why would anyone expect that there could be such a test?
Humans are not identical machines who operate in a controlled environment where their wear could be measured precisely.
Animals are individual. No two are the same. Each grows differently, ages differently, encounters its different environment differently.
Even identical twins, who start out truly identical when they are each only a few cells, are a few percent different before they emerge from the womb. They get more different each day for the rest of their lives.
What could one possibly measure on an animal which would be guaranteed to change over time in exactly the same way for absolutely everyone whether tall or short, male or female, Chinese or Icelandic, well-fed or starving, etc.?
So bottomline, there is no “test” (measurement really) because any of the things we’d be trying to measure differ more between individuals of a single age than they do between a given individual over different ages. The noise of variation between individuals greatly exceeds the signal of differences caused by one individual’s changing age.
So even things like exposure to elements (like mercury or carbon) varies so greatly among individuals (both in terms of individual response and in terms of environmental exposure) that even such a measurement is relatively useless? The best we can do is estimate based on the size of the femur?
On top of things like Stress, nutrition, exposure to germs and virus’, etc.
hmmm - okay - it would be nice if one could simply slice across the femur and count the rings - unless the person was still alive, of course.
thanks for the responses
well, not really but close.
It’s good for estimation, but I don’t know if it gives you the precision you are looking for
Keep in mind that “counting the rings” is a rare exception. It only occurs in trees because they are exposed annually to extreme temperature changes and because they essentially keep their old cells around forever. Most organisms don’t have to make physical adjustments of that degree on an annual basis and those that due generally just lose the changes with each spring so there’s no permanent evidence.
Note that no extreme temperature change is required. There are, for example, locations in places like Hawaii that have annual temperature variations comparable to or less than diurnal variations. Yet the trees there typically show annual growth rings.
There is one possible technique to estimate age by the length of the telomeres in a person’s DNA. There is mention of a study in regards to using it in forensics on the wiki page for telomeres, but the link to the actual paper timed out for me.
Edit: I was looking at the wrong footnote. The study can be found here but you need an account.
I was thinking about that nitpick too.
In many parts of the tropics the year is divided into rainy season and dry season with no variance in temperature. Could the difference in rainfall account for tree rings? I’m looking at the bottoms of my Balinese wood carvings, and they all have variences in the thickness of the rings. I’m no master woodcarver but I did work in construction and cabinet mills for a few years. One of the things I learned is that dryer years will produce thinner annular rings and denser wood than the wetter years, which will produce wider annular rings and softer wood.
http://www3.interscience.wiley.com/journal/110523206/abstract?CRETRY=1&SRETRY=0
http://www.ispub.com/ostia/index.php?xmlFilePath=journals/ijfs/vol3n1/osteon.xml
http://www.ncbi.nlm.nih.gov/pubmed/6642346?dopt=Abstract
http://cat.inist.fr/?aModele=afficheN&cpsidt=1668383
http://www3.interscience.wiley.com/journal/110486822/abstract
We’ve discussed this at least a couple of times. Read this:
AFAIK, the only way to do it is the method I described.
ETA: Here.
Because when we were intelligently designed, somebody forgot to install an odometer. 