Interesting, if novel, story. But how does it contradict the theory
that there are continuants and occurents, and that a human body, say, is
a continuant, I can't see. A continuant is not (not necessarily) a
structure which, at any time of its existence, has exactly the same
parts (the notion of sameness a topic for a separate discussion). (01)
You replace a battery in your laptop; is it a new laptop? Does the
change of the battery make the laptop a process rather than an object? (02)
vQ (03)
Azamat wrote:
> BS: Perhaps someone can even look at Fritz's body and see it as a life,
> though I find it hard to do so.
>
> Don't remember the URL. Below some interesting empirical findings made
> by a stem cell biologist shedding light on the issue: what is a human
> body, a process or a substance. Enjoy and surpise.
> Your Body Is Younger Than You Think
>
> Top of Form
>
> By NICHOLAS WADE
>
> Published: August 2, 2005
>
> Whatever your age, your body is many years younger. In fact, even if
> you're middle aged, most of you may be just 10 years old or less.
>
> This heartening truth, which arises from the fact that most of the
> body's tissues are under constant renewal, has been underlined by a
> novel method of estimating the age of human cells. Its inventor, Jonas
> Frisen, believes the average age of all the cells in an adult's body may
> turn out to be as young as 7 to 10 years.
>
>
>
>
>
> An Eye is Forever, but Is a Liver?
>
> But Dr. Frisen, a stem cell biologist at the Karolinska Institute in
> Stockholm, has also discovered a fact that explains why people behave
> their birth age, not the physical age of their cells: a few of the
> body's cell types endure from birth to death without renewal, and this
> special minority includes some or all of the cells of the cerebral cortex.
>
> It was a dispute over whether the cortex ever makes any new cells that
> got Dr. Frisen looking for a new way of figuring out how old human cells
> really are. Existing techniques depend on tagging DNA with chemicals but
> are far from perfect. Wondering if some natural tag might already be in
> place, Dr. Frisen recalled that the nuclear weapons tested above ground
> until 1963 had injected a pulse of radioactive carbon 14 into the
> atmosphere.
>
> Breathed in by plants worldwide and eaten by animals and people, the
> carbon 14 gets incorporated into the DNA of cells each time the cell
> divides and the DNA is duplicated.
>
> Most molecules in a cell are constantly being replaced but the DNA is
> not. All the carbon 14 in a cell's DNA is acquired on the cell's birth
> date, the day its parent cell divided. Hence the extent of carbon 14
> enrichment could be used to figure out the cell's age, Dr. Frisen
> surmised. In practice, the method has to be performed on tissues, not
> individual cells, because not enough carbon 14 gets into any single cell
> to signal its age. Dr. Frisen then worked out a scale for converting
> carbon 14 enrichment into calendar dates by measuring the carbon 14
> incorporated into individual tree rings in Swedish pine trees.
>
> Having validated the method with various tests, he and his colleagues
> have reported in the July 15 issue of Cell the results of their first
> tests with a few body tissues. Cells from the muscles of the ribs, taken
> from people in their late 30's, have an average age of 15.1 years, they
> say.
>
> The epithelial cells that line the surface of the gut have a rough life
> and are known by other methods to last only five days. Ignoring these
> surface cells, the average age of those in the main body of the gut is
> 15.9 years, Dr. Frisen found.
>
> The Karolinska team then turned to the brain, the renewal of whose cells
> has been a matter of much contention. Prevailing belief, by and large,
> is that the brain does not generate new neurons after its structure is
> complete, except in two specific regions, the olfactory bulb that
> mediates the sense of smell, and the hippocampus, where initial memories
> of faces and places are laid down.
>
> This consensus view was challenged a few years ago by Elizabeth Gould of
> Princeton, who reported finding new neurons in the cerebral cortex,
> along with the elegant idea that each day's memories might be recorded
> in the neurons generated that day.
>
> Dr. Frisen's method will enable all regions of the brain to be dated to
> see if any new neurons are generated. So far he has tested only cells
> from the visual cortex. He finds these are exactly the same age as the
> individual, showing that new neurons are not generated after birth in
> this region of the cerebral cortex, or at least not in significant
> numbers. Cells of the cerebellum are slightly younger than those of the
> cortex, which fits with the idea that the cerebellum continues
> developing after birth.
>
> Another contentious issue is whether the heart generates new muscle
> cells after birth. The conventional view that it does not has recently
> been challenged by Dr. Piero Anversa of the New York Medical College in
> Valhalla. Dr. Frisen has found the heart as a whole is generating new
> cells, but he has not yet measured the turnover rate of the heart's
> muscle cells.
>
> Although people may think of their body as a fairly permanent structure,
> most of it is in a state of constant flux as old cells are discarded and
> new ones generated in their place. Each kind of tissue has its own
> turnover time, depending in part on the workload endured by its cells.
> The cells lining the stomach, as mentioned, last only five days. The red
> blood cells, bruised and battered after traveling nearly 1,000 miles
> through the maze of the body's circulatory system, last only 120 days or
> so on average before being dispatched to their graveyard in the spleen.
>
> The epidermis, or surface layer of the skin, is recycled every two weeks
> or so. The reason for the quick replacement is that "this is the body's
> saran wrap, and it can be easily damaged by scratching, solvents, wear
> and tear," said Elaine Fuchs, an expert on the skin's stem cells at the
> Rockefeller University.
>
> As for the liver, the detoxifier of all the natural plant poisons and
> drugs that pass a person's lips, its life on the chemical-warfare front
> is quite short. An adult human liver probably has a turnover time of 300
> to 500 days, said Markus Grompe, an expert on the liver's stem cells at
> the Oregon Health & Science University.
>
> Other tissues have lifetimes measured in years, not days, but are still
> far from permanent. Even the bones endure nonstop makeover. The entire
> human skeleton is thought to be replaced every 10 years or so in adults,
> as twin construction crews of bone-dissolving and bone-rebuilding cells
> combine to remodel it.
>
> About the only pieces of the body that last a lifetime, on present
> evidence, seem to be the neurons of the cerebral cortex, the inner lens
> cells of the eye and perhaps the muscle cells of the heart. The inner
> lens cells form in the embryo and then lapse into such inertness for the
> rest of their owner's lifetime that they dispense altogether with their
> nucleus and other cellular organelles.
>
> But if the body remains so perpetually youthful and vigorous, and so
> eminently capable of renewing its tissues, why doesn't the regeneration
> continue forever?
>
> Some experts believe the root cause is that the DNA accumulates
> mutations and its information is gradually degraded. Others blame the
> DNA of the mitochondria, which lack the repair mechanisms available for
> the chromosomes. A third theory is that the stem cells that are the
> source of new cells in each tissue eventually grow feeble with age.
>
> "The notion that stem cells themselves age and become less capable of
> generating progeny is gaining increasing support," Dr. Frisen said. He
> hopes to see if the rate of a tissue's regeneration slows as a person
> ages, which might point to the stem cells as being what one unwetted
> heel was to Achilles, the single impediment to immortality.
>
>
> As reality is in the state of constant flux, so our body is in constant
> change, renewal. It appears that there is no permanent structure in the
> world barring ontological truths: fundamental principles, essential
> invariants, objective patterns, underlying laws of unvarying validity.
>
> Azamat
>
>
>
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Wacek Kusnierczyk (05)
------------------------------------------------------
Department of Information and Computer Science (IDI)
Norwegian University of Science and Technology (NTNU)
Sem Saelandsv. 7-9
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Norway (06)
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