On the study of naked mole-rats.

On the study of naked mole-rats.

This is a riff on an essay from several years ago.

In 1974, evolutionary biologist Richard Alexander gave a lecture describing the conditions that might spawn eusocial vertebrates. 

Alexander was a bug guy – “eusocial” refers to extremely cooperative animals like bees, ants, and termites. Individuals sacrifice themselves for others.  Non-breeders help with childcare.  The colony seems more intelligent than its members.

Alexander proposed that a eusocial mammal could evolve if the animals were small compared to their food sources, and if they lived in underground burrows that could be expanded easily and defended by a small percentage of the colony.

After the lecture, an audience member mentioned that this “hypothetical eusocial mammal” sounded a lot like the naked mole-rat.  Alexander was introduced to Jennifer Jarvis, who had studied individual naked mole-rats but not their social lives.  Alexander and Jarvis collaborated to write The Biology of the Naked Mole-Rat.

Eliot Weinberger condensed this 500-page textbook into his 3-page essay, “Naked Mole-Rats.”

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Like us, naked mole-rats are both good and bad.  They are cooperative.  They are affectionate.  They are always touching.  When they meet strangers, they fight to the death.  When a breeding female dies, many other females regain fertility and the colony erupts into civil war.

Weinberger wrote that naked mole-rats “are continually cruel in small ways.”  But they are outdone by naked apes. 

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For a research paper published in 2008, Thomas Park and colleagues found that being pinched by tweezers causes naked mole-rats pain, but injection with caustic acid does not.

“We tested naked mole-rats in standard behavioral models of acute pain including tests for mechanical, thermal, and chemical pain.  We found that after noxious pinch or heat, the mole-rats responded similarly to mice.”

“In contrast to the results using mechanical and thermal stimuli, there was a striking difference in responses to strong chemical irritants.  Two chemicals were used – capsaicin from hot peppers and hydrochloric acid – which normally evoke very intense pain in humans and other animals.  Injection of either rapidly evoked intense licking and guarding behaviors in mice.”

“In contrast, naked mole-rats showed virtually no response.”

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Perhaps you worry that acid-resistant naked mole-rats could conquer the world.  Fear not.  A form of kryptonite exists.  Injection of an 11-amino-acid signaling peptide allows acid to hurt naked mole-rats just as much as it hurts mice.  Or us.

Half a dozen animals were subjected to each treatment.

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Naked mole-rats don’t die from cancer. 

They should.  Their cells, like ours, are copied from copies of copies.  Errors compound.

Some errors are particularly deadly.  Our cells are supposed to stop growing when they touch.  They are supposed to commit suicide when old.  But the instructions telling a cell when and how to kill itself can be lost, just like any other information.

This is cancer.

In cancer, a single cell proliferates at the expense of others.  A cancer cell claims more than its fair share of space.  It commandeers nutrients.  This cell, and its progeny, and its progeny’s progeny, will flourish. 

Then the scaffolding creature dies.  Then the cancer cells die, too. 

But every cell that isn’t an egg or sperm is terminal anyway.  In the colony of our body, most cells are non-breeding members.  From a cancer cell’s perspective, it has nothing to lose.

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We develop cancer often.  With each passing day, we produce about 100 billion new cells.  Each time we produce a new cell, all 3 billion letters of our genome must be copied. 

The enzymes that copy our genome make one mistake every billion letters.  Each cell division: three new mutations.  Each day: three hundred billion new mutations.

Some mutants are trouble. 

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Our bodies kill cancer.  Your immune system – the same mess of mucous, inflammation, and goo that goes haywire during the flu – seeks and destroys renegade cells.  Your body is a fascist enterprise; white blood cells, its militarized police.

Chemotherapy does not kill cancer.  Chemotherapy means flooding the body with poisons that stop all cells from reproducing.  With luck, if the spread of cancer is slowed, your immune system can kill it before it kills you.

In naked mole-rats, cancers always grow as slowly as if the rodents were receiving chemo, allowing their immune systems to squelch cancers at a leisurely pace.  Their cancers are slowed by a heavy sugar called “hyaluronan,” which is packed so tightly into the space between cells that there is no room to grow.

In 2013, biologist Xiao Tian and colleagues wrote that “naked mole-rats may have evolved a higher concentration of hyaluronan to provide the skin elasticity needed for life in underground tunnels.  This trait may have then been co-opted to provide cancer resistance and longevity.”

They became impervious to cancer almost by mistake.

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The record lifespan for a naked mole-rat in captivity is 28 years, 4 months.  The record-holder was nicknamed James Bond.  He was senior consort to his queen and continued rutting – and siring pups – up until the day he died.

Bond was dissected.  His cells showed extensive oxidative damage in their lipids, proteins, and DNA.  Bond should have been hobbled by age.  But time did not slow him down.

Science writer David Stipp described him as “a little buck-toothed burrower who ages like a demigod.”

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Humans typically cease breeding long before we die.  From an evolutionary perspective, as soon as we stop having children, our fitness drops to zero.

And yet, we have long lifespans.  The dominant theory is an offshoot of “the grandmother hypothesis” – because we often care for grandchildren, there may have been evolutionary pressure to maintain good health until our grandchildren also reach reproductive age. 

With twenty-year generations, there’d be an incentive to survive until our sixties.

After that, perhaps our ancestors were no longer helpful.  And so we’ve inherited a propensity to decay.  Expensive medical interventions can preserve us longer, but once we pass our natural lifespans, brains and bodies weaken.

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When scientists starve animals in the lab, it’s called “caloric restriction.”  This protocol extends lifespan in a wide variety of species.  Monkeys, mice, flies, and worms.  Ten-fold increases in lifespan have been observed.

Caloric restriction should extend the lives of humans, too.

There are unpleasant side effects.  Caloric-restricted mice spend their time staring at empty food bowls.  They are listless: barely moving, barely sleeping.  They live longer, but worse – and if they are fed slightly less, they die of malnutrition.

Frequent starvation in the wild may have caused naked mole-rats to evolve their prodigious longevity.

Naked mole-rats expand their colonies outward, searching for edible roots.  When they find a good root, they gnaw it carefully, attempting to keep the plant alive as long as possible.  But a colony of naked mole-rats eats faster than any plant can grow.  When the plant dies, the colony plunges into famine. 

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Most eusocial animals carefully ventilate their homes.  Termites build giant pylons in the desert.  Although temperatures outside careen from 35 degrees at night to over 100 during the day, the interior of the mound remains a constant 87 degrees.  And the termites do not asphyxiate.  Their exhalations are swept away by circulating air.

Naked mole-rats burrow with less care.  They sleep in piles, hundreds of bodies lumped together underground.  Those near the center soon run out of oxygen.

We would die.

Most animals, deprived of oxygen, can’t fuel their brains.  Thoughts are expensive.  Even at rest, our brains demand a constant influx of energy or else the neurons “depolarize” – we fall apart.

Since the death penalty was reintroduced in the United States in 1976, we have killed eleven prisoners in gas chambers.  During the 1983 execution of Jimmy Lee Gray in Mississippi, officials cleared the observation room after eight minutes.  Gray was still alive, gasping for breath.  His attorney said, “Jimmy Lee Gray died banging his head against a steel pole in the gas chamber while reporters counted his moans.”

Gas chambers are pumped full of cyanide gas, carbon monoxide, or carbon dioxide.  Carbon dioxide is cheapest. 

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With each breath, we inhale oxygen, burn sugar, and exhale carbon dioxide.  When we drive, our cars intake oxygen, burn gasoline, and exhaust carbon dioxide. 

In small amounts, carbon dioxide is beneficial.  Carbon dioxide allows plants to grow.  But when you put too much inside a chamber, somebody dies.  Put too much in the air worldwide and we all die.

The planet Venus was habitable, once.  Humans could have lived there.  Venus had a deep ocean and mild weather.

Through some fluke, Venus experienced a temporary bump in the amount of carbon dioxide in the air.  Carbon dioxide traps heat, which caused water to evaporate.  Clouds formed, which trapped more heat.  The cycle continued. 

Venus is now a fiery inferno.  The ground is bare rock.  Sulfuric acid rains from the sky.

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Lab mice die in gas chambers.  Sometimes one mouse is set inside the plexiglass box; sometimes several mice inside a Chinese-food takeout container are gassed together.  A valve for carbon dioxide is opened; the mice lose consciousness; they shit; they die.

A naked mole-rat would live.  Unless a very determined researcher left the gas flowing for half an hour.  Or so found Thomas Park and colleagues – the same team that discovered that naked mole-rats dislike being pinched.  As they reported in 2017:

Human brains drink sugar.  We are like hummingbirds that way.  And our brains are very fussy eaters.  We are fueled exclusively by glucose.

Naked mole-rats are less particular.  Their minds slurp fructose to keep from dying.

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Naked mole-rats are the most cooperative of mammals.  They are resistant to cancer.  Unperturbed by acid.  They age with the libidinous gracelessness of Hugh Hefner. 

They are able to withstand the horrors of a gas chamber.

And yet, for all these talents, naked mole-rats are easily tormented by human scientists.

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Featured image from Wikimedia Commons.

On violence and gratitude.

On violence and gratitude.

Although I consider myself a benevolent tyrant, some of my cells have turned against me.  Mutinous, they were swayed by the propaganda of a virus and started churning out capsids rather than helping me type this essay.  Which leaves me sitting at a YMCA snack room table snerking, goo leaking down my throat and out my nose.

Unconsciously, I take violent reprisal against the traitors.  I send my enforcers to put down the revolt – they cannibalize the still-living rebels, first gnawing the skin, then devouring the organs that come spilling out.  Then the defector dies.

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CD8+ T cell destruction of infected cells by Dananguyen on Wikimedia.

My cells are also expected to commit suicide whenever they cease to be useful for my grand designs.  Any time a revolutionary loses the resolve to commit suicide, my enforcers put it down.  Unless my internal surveillance state fails to notice in time – the other name for a cell that doesn’t want to commit suicide is “cancer,” and even the most robust immune system might be stymied by cancer when the traitor’s family grows too large.

Worse is when the rebels “metastasize,” like contemporary terrorists.  This word signifies that the family has sent sleeper agents to infiltrate the world at large, attempting to develop new pockets of resistance in other areas.  Even if my enforcers crush one cluster of rebellion, others could flourish unchecked.

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How metastasis occurs. Image by the National Cancer Institute on Wikimedia.

I know something that perhaps they don’t – if their rebellion succeeds, they will die.  A flourishing cancer sequesters so many resources that the rest of my body would soon prove too weak to seek food and water, causing every cell inside of me to die.

But perhaps they’ve learned my kingdom’s vile secret – rebel or not, they will die.  As with any hereditary monarchy, a select few of my cells are privileged above all others.  And it’s not the cells in my brain that rule.

Every “somatic cell” is doomed.  These cells compose my brain and body.  Each has slight variations from “my” genome – every round of cell division introduces random mutations, making every cell’s DNA slightly different from its neighbors’.

The basic idea behind Richard Dawkins’s The Selfish Gene is that each of these cells “wants” for its genome to pass down through the ages.  Dawkins argued that familial altruism is rational because any sacrifice bolsters the chances for a very similar genome to propagate.  Similarly, each somatic cell is expected to sacrifice itself to boost the odds for a very similar genome carried by the gametes.

Only gametes – the heralded population of germ cells in our genitalia – can possibly see their lineage continue.  All others are like the commoners who (perhaps foolishly) chant their king or kingdom’s name as they rush into battle to die.  I expect them to show absolute fealty to me, their tyrant.  Apoptosis – uncomplaining suicide – was required of many before I was even born, like when cells forming the webbing between my fingers slit their own bellies in dramatic synchronized hara-kiri.

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Human gametes by Karl-Ludwig Poggemann on Flickr.

Any evolutionary biologist could explain that each such act of sacrifice was in a cell’s mathematical best interest.  But if I were a conscious somatic cell, would I submit so easily?  Or do I owe some sliver of respect to the traitors inside me?

The world is a violent place.  I’m an extremely liberal vegan environmentalist – yet it takes a lot of violence to keep me going.

From Suzana Herculano-Houzel’s The Human Advantage:

image (1)Animals that we are, we must face, every single day of our lives, the consequences of our most basic predicament: we don’t do photosynthesis.  For lack of the necessary genes, we don’t just absorb carbon from the air around us and fix it as new bodily matter with a little help from sunlight.  To survive, we animals have to eat other living organisms, whether animal, vegetable, or fungus, and transform their matter into ours.

And yet the violence doesn’t begin with animals.  Photosynthesis seems benign by comparison – all you’d need is light from the sun! – unless you watch a time-lapsed video of plant growth in any forest or jungle.

The sun casts off electromagnetic radiation without a care in the world, but the amount of useful light reaching any particular spot on earth is limited.  And plants will fight for it.  They race upwards, a sprint that we sometimes fail to notice only because they’ve adapted a timescale of days, years, and centuries rather than our seconds, hours, and years.  They reach over competitors’ heads, attempting to grab any extra smidgen of light … and starving those below.  Many vines physically strangle their foes.  Several trees excrete poison from their roots.  Why win fair if you don’t have to?  A banquet of warm sunlight awaits the tallest plant left standing.

And so why, in such a violent world, would it be worthwhile to be vegan?  After all, nothing wants to be eaten.  Sure, a plant wants for animals to eat its fruit – fruits and animals co-evolved in a system of gift exchange.  The plant freely offers fruit, with no way of guaranteeing recompense, in hope that the animal might plant its seeds in a useful location.

But actual pieces of fruit – the individual cells composing an apple – probably don’t want to be eaten, no more than cancers or my own virus-infected cells want to be put down for the greater good.

A kale plant doesn’t want for me to tear off its leaves and dice them for my morning ramen.

But by acknowledging how much sacrifice it takes to allow for us to be typing or reading or otherwise reaping the pleasures of existence, I think it’s easier to maintain awe.  A sense of gratitude toward all that we’ve been given.  Most humans appreciate things more when we think they cost more.

We should appreciate the chance to be alive.  It costs an absurd amount for us to be here.

But, in the modern world, it’s possible to have a wonderful, rampantly hedonistic life as a vegan.  Why make our existence cost more when we don’t have to?  A bottle of wine tastes better when we’re told that it’s $45-dollar and not $5-dollar wine, but it won’t taste any better if you tell somebody “It’s $45-dollar wine, but you’ll have to pay $90 for it.”

Personally, I’d think it tasted worse, each sip with the savor of squander.