I contain multitudes

One of the things that even folks conversant in the evolutionary model sometimes don't know is the extent to which we are composite organisms.

On the gross level (and I mean that in both senses of the word), there is the sheer number of cells in us that are not human.  The adult human body has about 10 trillion human cells, and (depending on who you talk to) between 1 and 3 times more bacterial cells -- intestinal flora, bacteria hitching a ride on our skin, in our mouths, in our respiratory mucosa.  Most of these are commensals at the very worst -- neither harmful nor helpful -- but a significant number are in a mutualistic arrangement with us, which is one of several reasons why the overuse of antibiotics is a bad idea.

Then there are the little invaders we can't live without -- namely the mitochondria, those tiny organelles that every high school biology student knows are the "powerhouses of the cell."  What fewer people know is that they are actually separate organisms, descended from aerobic prokaryotes that colonized our cells 2.5 billion years ago (give or take a day or two).  They have their own DNA, and reproduce inside our cells by binary fission the same way they did when they were free-living proto-bacteria.

Mitochondria [Image is in the Public Domain courtesy of photographer Louisa Howard]

But that's not all. If you're a plant (I'm assuming you're not, but you never know), you have three separate ancestral lines -- your ordinary plant cells, the mitochondria, and the chloroplasts, which are also little single-celled invaders that now plants can't live without.  But even that's not the most extreme example.  The microorganism Mixotricha paradoxa is a composite being made up of five completely separate ancestral genomes that have fused together into one organism.

It's amazing how much these relationships alter behavior, sometimes in ways that blur the definition of the word "organism."  Is Mixotricha one organism or five?  Unsurprisingly, given their history of anticipating scientific discoveries, Star Trek gave a hard look at this question with the character of Jadzia Dax.  Dax is a Trill -- an individual produced by the fusion of a humanoid host and a long-lived symbiont.  Although the symbiont can survive after the death of the host, and go on to fuse with another one, the personalities remain blended, and the symbiont brings to its new host all the memories, skills, and traits it accessed from previous ones.

Weird stuff, but not so far off from what we see down here on Earth.

But back to humans, if you're not already so skeeved out that you've stopped reading.  Because it's even more complicated than what I've already told you -- check out a paper by geneticists Cedric Feschotte , Edward Chuong and Nels Elde of the University of Utah, in which we find out that even our nuclear DNA isn't entirely human.  Feschotte et al. have shown that ten percent of our thirty-thousand-odd genes and three-billion-odd base pairs...

... came from viruses.

We usually think of viruses as pesky little parasites that cause colds, flu, measles, mumps, and so on, but they're more than that.  Some of them -- the retroviruses (HIV being the best-known example) -- are capable of inserting genetic material into the host's DNA, thus altering what the host does.  Certainly, sometimes this is bad; both AIDS and feline leukemia are outcomes of this process.  But now Feschotte, Chuong, and Elde have shown that some of our viral hangers-on have had their genes repurposed to work in our benefit.

These stowaway bits of DNA are called endogenous retroviruses (ERVs), and some of them seem to be associated with cancer.  Others have been implicated in multiple sclerosis and schizophrenia.  But what the researchers found is that not all of them are deleterious; the gene that allows us to digest starch, and (even more importantly) the gene that triggers the fusion of the developing embryo to the placenta, seem to have viral origins.

"We think we’ve only scratched the surface here on the regulatory potential of ERVs," Feschotte said.

All of which is pretty amazing.  And it definitely gives one pause when you stop to think of how we define the word "organism."  Am I a single organism?  Well, not really.  Besides my regular human cells, I've got trillions of mitochondria, each with their separate bacterially-derived genome; and ten percent of what I think of as "my DNA" came from viruses, at least some of which has then been modified into genes that I depend on to survive.  So humans -- and all living things -- are looking more and more like composite colonies of symbiotic life forms, representing a web of interrelationships that is so complex that it's mind-boggling.

So, to hell with the weird, exotic life forms from Star Trek.  I'm too busy being blown away by how bizarre and cool the life here on Earth turns out to be.

****************************************

Golden years gold medal

You've probably heard the old joke about a man going in for major surgery.  "Doc," he says, right before the anesthetic is administered, "I gotta ask... after this surgery, will I be able to play the piano?"

The surgeon smiles reassuringly and says, "Of course you will."

"Awesome!" the man says.  "I've always wanted to play the piano!"

That's what came to mind when I read an article in Science called, "Will You Keep Winning Races Into Old Age?  Your Cells Hold Clues," by Tess Joosse.  I'm hoping that like the aspiring pianist, old age will put me into the winner's bracket, because since I started running semi-competitively forty years ago, I've yet to win a race.  I train, I run regularly, but I'm still (and probably always will be) a solid middle-of-the-packer.  The closest I've ever come was about three years ago, when I came in third in my age group.

To be scrupulously honest, there were only six people in my age group.  But I'll take my little victories wherever I can get them.

Me last year, about to not cross the finish line first

Be that as it may, I'm still in there trying.  I'm 61, and I know that regular exercise is essential not only for continuing physical health but mental wellbeing.  In fact, on June 8 I'm running in the Ithaca Twilight 5K, a wonderful race down the footpaths along Cayuga Lake, and because I'm recovering from a series of health setbacks I've lowered my sights to simply getting across the finish line without having to be carted over it in a wheelbarrow.

Even though the "will you keep winning?" part of the headline of the article struck me as funny, the research itself is pretty cool.  Russell Hepple, a biologist at the University of Florida, wondered what was going on with people who are still competitive racers even into old age -- such as his father-in-law, who holds the record time for an eighty-year-old in the Boston Marathon.  Hepple and his colleagues did an assay on the muscle tissue of world-class senior athletes and a group of non-athletes, and found no fewer than eight hundred proteins that were produced in amounts that were significantly different between the two groups.  Some were higher in the athletes; others were lower.  But one obvious patterns was that over half of the proteins the study found were ones that are expressed by, or otherwise affect, the mitochondria.

For some reason, the factoid "the mitochondria are the powerhouses of the cell" is one that sticks in the minds of just about everyone who has taken high school biology, but the way they work is actually pretty amazing.  Your mitochondria are actually symbiotic single-celled life-forms living inside your cells -- they even have their own DNA -- and they have evolved a complex series of chemical reactions (collectively known as aerobic cellular respiration) to break down glucose and store its energy in a molecule called ATP, which is the direct driver of damn near every process living things do.  The amount of ATP created and the rate at which it's used are in an incredibly tight balance; it's estimated that you produce (and consume/recycle) your body weight in ATP every day, which amounts to ten million ATP molecules per second, per cell.

So it's no surprise that octogenarian racers have better mitochondrial function than the rest of us slobs.  In fact, the study found that 176 of the proteins studied were unique to elite senior athletes; how much of that is because of a lucky combination of genes, and how much is because their continuous training has triggered protein production that in non-athletes tapers off or stops entirely, isn't known.

Also an open question is whether administering one or more of these proteins would boost aerobic exercise capacity in older people who aren't athletes (but would like to be).  Luigi Ferrucci of the National Institute on Aging, who co-authored the study, has proposed trying this in mice and seeing if it does increase endurance and stamina, without any untoward side effects.

In any case, I suspect that no matter what I do, I'll never be a gold medalist.  That's okay with me.  I love running for running's sake, and the race community (at least around here) is super supportive of everyone regardless of their level.  (At a race I was in a while back, a twelve-year-old boy had posted himself just past the finish line, and was high-fiving each runner as they crossed.  When I stumbled my way across, he grinned at me and said, "Well done, Shirtless Tattoo Guy!"  That, to me, encapsulates the spirit of racing in my area.)

But I'll be interested to see where this research leads.  Anything I can do to stave off decline (physical or mental) as I get older is a good thing.  Until then, though, I'll keep running, and keep being okay with finishing in the middle of the pack.

**************************************

I contain multitudes

One of the things that even folks conversant in the evolutionary model sometimes don't know is the extent to which we are composite organisms.

On the gross level (and I mean that in both senses of the word), there is the sheer number of cells in us that are not human.  The adult human body has about 10 trillion human cells, and (depending on who you talk to) between 1 and 3 times more bacterial cells -- intestinal flora, bacteria hitching a ride on our skin, in our mouths, in our respiratory mucosa.  Most of these are commensals at the very worst -- neither harmful nor helpful -- but a significant number are in a mutualistic arrangement with us, which is one of several reasons why the overuse of antibiotics is a bad idea.

Then there are the little invaders we can't live without -- namely the mitochondria, those tiny organelles that every high school biology student knows are the "powerhouses of the cell."  What fewer people know is that they are actually separate organisms, descended from aerobic prokaryotes that colonized our cells 2.5 billion years ago (give or take a day or two).  They have their own DNA, and reproduce inside our cells by binary fission the same way they did when they were free-living proto-bacteria.

Mitochondria [Image is in the Public Domain courtesy of microscopist/photographer Louisa Howard]

And that's not all.  If you're a plant (I'm assuming you're not, but you never know), you have three separate ancestral lines -- your ordinary plant cells, the mitochondria, and the chloroplasts, which are also little single-celled invaders that now plants can't live without.  But even that's not the most extreme example.  The microorganism Mixotricha paradoxa is a composite being made up of five completely separate ancestral genomes that have fused together into one organism.

But back to humans, if you're not already so skeeved out that you've stopped reading.  Because it's even more complicated than what I've already told you, as you'll learn from geneticists Cedric Feschotte, Edward Chuong and Nels Elde of the University of Utah in a paper in which we find out that even our nuclear DNA isn't entirely human.  10% of our 30,000-odd genes and three-billion-odd base pairs...

... came from viruses.

We usually think of viruses as little parasites, some of which are killers like COVID-19, rabies, and ebola fever, but also include nuisances like colds, flu, warts and chickenpox.  Turns out, though, that they're more than that.  Some of them -- the retroviruses (HIV being the best-known example) -- are capable of inserting genetic material into the host's DNA, thus altering what the host does.  Certainly, sometimes this is bad; both AIDS and feline leukemia are outcomes of this process.  But now Feschotte, Chuong, and Elde have shown that some of our viral hangers-on have had their genes repurposed to work in our benefit.

These stowaway bits of DNA are called endogenous retroviruses (ERVs), and some of them seem to be associated with cancer.  Others have been implicated in multiple sclerosis and schizophrenia.  But what the researchers found is that not all of them are deleterious; the gene that allows us to digest starch, and (even more importantly) the gene that triggers the fusion of the developing embryo to the placenta, seem to have viral origins.

"We think we’ve only scratched the surface here on the regulatory potential of ERVs," Feschotte said.

All of which is pretty amazing.  And it definitely gives one pause when you stop to think of how we define the word "organism."  Am I a single organism?  Well, not really.  Besides my regular human cells, I've got trillions of prokaryotic hangers-on and trillions of mitochondria, each with their separate bacterially-derived genome; and 10% of what I think of as "my DNA" came from viruses, at least some of which has then been modified into genes that I depend on to survive.  So humans -- and all living things -- are looking more and more like composite colonies of symbiotic life forms, representing a web of interrelationships that is so complex that it's mind-boggling.

Remember the Trill from Star Trek:Deep Space Nine?  A lot of us were kind of creeped out to find out that Jadzia Dax's personality and intelligence didn't come from her humanoid brain, but from a weird, crustacean-like symbiotic life form that was wired into her nervous system.  Turns out that once again, Star Trek hit close to the target of the reality we've now uncovered with science -- only the reality is even more bizarre than the fiction.

So step aside, Star Trek aliens.  I'm too busy being blown away by how weird and cool the life here on Earth turns out to be.

*********************************

Back when I taught Environmental Science, I used to spend at least one period addressing something that I saw as a gigantic hole in students' knowledge of their own world: where the common stuff in their lives came from.  Take an everyday object -- like a sink.  What metals are the faucet, handles, and fittings made of?  Where did those metals come from, and how are they refined?  What about the ceramic of the bowl, the pigments in the enamel on the surface, the flexible plastic of the washers?  All of those substances came from somewhere -- and took a long road to get where they ended up.

Along those same lines, there are a lot of questions about those same substances that never occur to us.  Why is the elastic of a rubber band stretchy?  Why is glass transparent?  Why is a polished metal surface reflective, but a polished wooden surface isn't?  Why does the rubber on the soles of your running shoes grip -- but the grip worsens when they're wet, and vanishes entirely when you step on ice?

If you're interested in these and other questions, this week's Skeptophilia book-of-the-week is for you.  In Stuff Matters: Exploring the Marvelous Materials that Shape Our Man-Made World, materials scientist Mark Miodownik takes a close look at the stuff that makes up our everyday lives, and explains why each substance we encounter has the characteristics it has.  So if you've ever wondered why duct tape makes things stick together and WD-40 makes them come apart, you've got to read Miodownik's book.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

I contain multitudes

One of the things that even folks conversant in the evolutionary model sometimes don't know is the extent to which we are composite organisms.

On the gross level (and I mean that in both senses of the word), there is the sheer number of cells in us that are not human.  The adult human body has about 10 trillion human cells, and (depending on who you talk to) between 1 and 3 times more bacterial cells -- intestinal flora, bacteria hitching a ride on our skin, in our mouths, in our respiratory mucosa.  Most of these are commensals at the very worst -- neither harmful nor helpful -- but a significant number are in a mutualistic arrangement with us, which is one of several reasons why the overuse of antibiotics is a bad idea.

Then there are the little invaders we can't live without -- namely the mitochondria, those tiny organelles that every high school biology student knows are the "powerhouses of the cell."  What fewer people know is that they are actually separate organisms, descended from aerobic prokaryotes that colonized our cells 2.5 billion years ago (give or take a day or two).  They have their own DNA, and reproduce inside our cells by binary fission the same way they did when they were free-living proto-bacteria.

Mitochondria [image courtesy of Louisa Howard and the Wikimedia Commons]

But that's not all.  If you're a plant (I'm assuming you're not, but you never know), you have three separate ancestral lines -- your ordinary plant cells, the mitochondria, and the chloroplasts, which are also little single-celled invaders that now plants can't live without.  But even that's not the most extreme example -- the microorganism Mixotricha paradoxa is a composite being made up of five completely separate ancestral genomes that have fused together into one organism.

But back to humans, if you're not already so skeeved out that you've stopped reading.  Because it's even more complicated than what I've already told you -- geneticists Cedric Feschotte , Edward Chuong and Nels Elde of the University of Utah have just published a paper in which we find out that even our nuclear DNA isn't entirely human.  10% of our 30,000-odd genes and three-billion-odd base pairs...

... came from viruses.

We usually think of viruses as pesky little parasites that cause colds, flu, measles, mumps, and so on, but they're more than that.  Some of them -- the retroviruses (HIV being the best-known example) -- are capable of inserting genetic material into the host's DNA, thus altering what the host does.  Certainly, sometimes this is bad; both AIDS and feline leukemia are outcomes of this process.  But now Feschotte, Chuong, and Elde have shown that some of our viral hangers-on have had their genes repurposed to work in our benefit.

These stowaway bits of DNA are called "endogenous retroviruses" (ERVs), and some of them seem to be associated with cancer.  Others have been implicated in multiple sclerosis and schizophrenia.  But what the researchers found is that not all of them are deleterious; the gene that allows us to digest starch, and (even more importantly) the gene that triggers the fusion of the developing embryo to the placenta, seem to have viral origins.

"We think we’ve only scratched the surface here on the regulatory potential of ERVs," Feschotte said.

All of which is pretty amazing.  And it definitely gives one pause when you stop to think of how we define the word "organism."  Am I a single organism?  Well, not really.  Besides my regular human cells, I've got trillions of mitochondria, each with their separate bacterially-derived genome; and 10% of what I think of as "my DNA" came from viruses, at least some of which has then been modified into genes that I depend on to survive.  So humans -- and all living things -- are looking more and more like composite colonies of symbiotic life forms, representing a web of interrelationships that is so complex that it's mind-boggling.

So, to hell with the weird, exotic life forms from Star Trek.  I'm too busy being blown away by how bizarre and cool the life here on Earth turns out to be.