I have a beautiful word for you: senescence.
It’s the word for how, as multicellular organisms age, they die more, and reproduce
less. It’s the deterioration that comes from getting older.
But there are a few exceptions to this get-older-and-die thing -- including, it turns out, tiny sea
creatures called hydras.
We humans, like a lot of other animals, experience a peak period of fertility during the first
third of our lifespans -- the period of our lives when we’re least likely to die from
most things. Your body is working as well as it’s ever going to, and you’re as good
as you’re gonna get at firing out babies.
Then, senescence kicks in. All of those things get less and less true, until eventually,
you die.
For a long time, senescence was thought to be universal -- that all multicellular organisms
capable of breeding more than once will get worse at it over time, and the older they
get, the more likely it is that they’ll die.
Until researchers found that a certain kind of jellyfish can make itself young again,
a power I would like to have.
According to a study that came out this week from the Max Planck Institute in Germany,
there’s another exception to this rule: the hydra.
Not the mythical beast with all the heads.
This hydra is a freshwater polyp that’s a centimeter long, and reproduces both asexually
and sexually, can regenerate after it’s been cut into pieces, including being able
to regenerate its ENTIRE HEAD, and, as it turns out, is pretty much immortal.
Not bad, being immortal and stuff, but I would like to see it try to host youtube show.
The hydra has fascinated scientists for centuries, and when they sequenced its genome back in
2010, they discovered that it had the same number of genes as humans.
We also have a surprising number of genes in common: including certain genes associated
with Alzheimer’s and Huntington’s disease. So we’ve been studying these tentacular
little guys ever since.
Because, like, maybe they can magically repair the neurodegeneration that leads to Alzheimer’s,
that would pretty much be exactly what we would expect from hydras at this point. Like,
why not?
Because we’ve been watching hydras for so long, scientists have suspected for a long
time that they don’t senesce. But this was the first large-scale study that focused on
finding out for sure.
The team followed more than two thousand individual hydras for a combination of 3.9 million days.The
hydras they studied were between zero and 41 years old, and they observed them over
a period of 8 years.
The result? No decline in fertility, or increase in mortality, was observed at any point in
the hydra life cycle. Although if they don’t age, it’s not really a cycle, is it? It’s
more of a life...line. That gets cut off when they get eaten by something.
And THAT is what I have been able to do that most hydras can’t. Avoid getting eaten.
So far, at least.
These Hydras reproduced, or “budded,” about once a month, and they died at a rate
of about one of 167 per year, no matter how old or young they were.
If the mortality rates observed in this study continued, that means that in 3000 years,
5% of those hydras would still be alive, if they were kept safe in the lab. That’d be
a really long experiment.
So how do hydras not decline with age? Well, there are a lot of factors that might contribute.
They have a relatively simple body plan, and relatively few different types of cells, which
probably helps.
But the most important factor is most likely that hydras constantly produce new stem cells.
Every cell in a hydra’s body is replaced every three to four weeks, by fresh cells
produced by brand new stem cells.
It’s essentially regenerating once a month -- and in a completely different way from
the jellyfish we talked about earlier, which reverts to an earlier stage of its life cycle
when it’s stressed.
There’s a lot we might be able learn from this. What we now know about hydras suggests
that they could hold the keys to big breakthroughs in research on stem cells, aging, and diseases
like Alzheimer’s.
And while we’re at it, maybe we should leave little notes in the hydra’s genetic code,
for any future aliens who might one day find our planet. Maybe they’d sequence the genome
of our immortal little buddies, and it would say, “WE WERE HERE. -Signed, Humanity.”
And then we could leave a link they could follow to the last working internet server,
which would just be… Rick Astley’s “Never Going to Give You Up”.
Thanks for watching this episode of SciShow News, and thanks especially to all of our
patrons on Patreon like Emily Burrows and Mike Boyle who make this show possible. We
just picked a couple to say thanks to them specifically. If you want to help us keep
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