Great question. Lots of people would like to
know that. Humans live a long time compared with
most animals, but lots of people would like to
live longer and to avoid some of the problems of
So let’s start off by looking at what old age is.
Our cells divide to make new cells. Some of our
cells are dividing fast all the time. The cells of
our skin and the cells of our digestive tract
divide a lot. Other cells divide slowly, like our
liver cells. Some cells, like our brain and muscle
cells, do little or no dividing after we’re
Almost every cell in your body has a nucleus
with DNA in it. The DNA tells the cell how to do
its job. Every time a cell divides, the DNA
has to be copied and divided so that the new cells
each get a full set of DNA. When the DNA
divides, a part of it at the end called the
telomere gets shorter. When a cell’s telomere
gets too short, it will no longer divide. This
puts a limit on cell division. So after a
while, the cells stop dividing.
Another thing that causes aging is damage to
cells from sunlight, radiation, chemicals,
disease, use, and just random events. When we’re
young, damaged cells (except for muscle and brain
cells) can be replaced. With fewer and fewer cells
dividing, replacement takes longer, then finally
The powerhouses of our cells, the
mitochondria, may also stop working as well as
we age, so less of the energy we take in as food
winds up as energy we can actually use.
So what do tortoises have that we don’t?
Like us, they have cells with DNA and telomeres.
Unlike us, have a VERY slow metabolism.
Metabolism refers to all the chemical reactions
that our bodies do. Everything is slower in a
tortoise. This means that all of the wastes that
metabolism makes are going to be made very slowly,
reducing damage to the cells.
If we look at the other end of metabolic rate for
vertebrates (animals with skulls and backbones),
we have the shrew. It looks a lot like a tiny
mouse, but it’s an insectivore. It has a
super-fast metabolism. Its heart beats so fast
that it may be impossible for the heart muscle to
work faster. They can starve to death in few
hours. They are also dead of old age in about 2
years. Maybe their cells don’t divide any more or
less than a tortoise’s cells, but they do it a
whole lot faster. Their wastes from metabolism
would also be produced a lot faster.
There’s probably a lot more to learn before we
understand the whole picture, but it looks like
if you live fast you die young.
A lot of animals that live a long time are big
(elephants, whales, us). A lot of animals that
live a short time are small. Why do you think
If you are interested in questions like this,
you may want to study animal physiology.
Thanks for asking,
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