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.