Al Stahler: Repelling invaders |

Al Stahler: Repelling invaders

Life evolved, from rock and water and air, roughly four billion years ago. Around the same time – just before, or just after – lifeless viruses also evolved: Rogue genes, genes without bodies.

No one knows what the earliest life looked like, but it soon evolved into similar-but-different bacteria and archaea (“ar-KEE-uh”). Evolving to eat almost anything – rocks, gases, each other – bacteria and archaea colonized the world (archaea went especially for extreme environments, like hot springs).

To avoid being eaten themselves, bacteria evolved ways to fight off other bacteria, and to fight off viruses.

Animals and plants came later: We showed up roughly half-a million years ago. With a three-and-a-half billion year head-start, bacteria and viruses saw us coming … colonized our bodies. Bacteria saw us as food; viruses would hijack our bodies, force us to make more viruses.

But we were not defenseless. One or two billion years before animals and plants appeared, our ancestors had themselves evolved from bacteria, and inherited many of their defenses.

But then, sometime around four hundred million years ago, animals evolved a new defense system, all their own. The most-evolved animals on the planet then were fish; we – their descendants – have inherited their invention.

Touch your tongue to the side of your mouth and you’re touching living cells. Cells are tiny – five hundred, side-by-side, measure an inch. Yet each and every one of those tiny cells holds the instruction manual for your whole body … instructions for keeping cells and bodies alive, instructions for making new cells and bodies. The instructions are written in threads of DNA – a couple-dozen threads, measuring a total of six feet long, all packaged into each tiny cell.

When a body is growing … when a body is wounded … when a mom makes a baby … all these tasks require cells to reproduce themselves, to make new “daughter” cells. Each daughter cell needs a copy of the DNA instruction book, so the instructions must be copied, time and again.

Internal “machinery” – enzymes – replicate the instructions. But anytime you make copies, you’ve got to expect mistakes.

So we have proofreading machinery, to looks for mistakes, to correct them. The proof-reading system is pretty darn good, typically allowing just one mistake in a billion “words.”

But such accuracy creates a problem. To fight invaders, we deploy 3D jig-saw puzzle-pieces. When one of these puzzle-pieces fits into another puzzle-piece – a puzzle-piece that our own bodies would never make – we know we’ve been invaded. But bacteria and viruses carry puzzle-piece of gazillions of different shapes. How can the body make so many different puzzle-pieces? It would require gazillions of genes – gazillions more than we could fit into six feet of DNA.

That’s the problem our fishy ancestors solved some four hundred million years ago. They learned to shut down the genetic proofreading system … in just a few genes. Those few genes would mutate like mad, to guide the creation of nearly a trillion (a million million) different-shape puzzle-pieces – enough to recognize nearly anything that bacteria and viruses might throw at us.

Once an invader is recognized by an appropriately-shaped puzzle-piece, the immune system makes more of that particular puzzle-piece … makes them by the gazillions, to fight off the invader.

The system works well … but churning out gazillions of puzzle-pieces takes time.

A vaccine does not fight bacteria and viruses. A vaccine simply gives the immune system a heads-up – a warning – of what an invader looks like, before the invader arrives. The vaccine gives the immune system a head-start in ramping up production of the specific puzzle-pieces it will need to fight the invader … should the invader show up.

A vaccine is not a magic bullet – it doesn’t fight off an infection that’s already begun. And, even when vaccinated, it’s the immune system that does the work.

A strong immune system depends on eating well … exercise … sleep … and, it’s been found recently … minimizing stress.


If skies are clear, local astronomers will set up scopes at the intersection of the old Downieville Highway and SR49, this Saturday night, 6PM. The star party is free, and all ages are welcome. Dress for a January night.

Al Stahler enjoys sharing science and nature with friends and neighbors in The Union and on KVMR-FM. He teaches classes for both kids and grown-ups, and can be reached at

In this cartoon, blue puzzle-pieces (antibodies) are about to fit onto green puzzle pieces on the virus.
Courtesy Nation Institute of Health
Electron micrograph of the COVID-19 virus — notice the spikes.
Courtesy National Institute of Allergy and Infectious Diseases

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Family Focus

Al Stahler: Living chemistry


We are – all of us – master chemists. By us, I mean you, me, our pets, the bacteria turning cabbage into sauerkraut … and the cabbage, too … we are all master chemists.

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