Sunday SciKu | Overkill

For 20+ years, I’ve found the nonsense of the overkill hypothesis maddening. The idea is that humans are such efficient, warlike creatures that we arrive on new continents and murder everything we come across. The Neanderthals in Europe and the Diprotodons in Australia 42,000 years ago. The North American mammoths and mastodons 12,500 years ago. It’s the most obvious scientific farce I’ve ever heard, and yet for decades it’s remained the mainstream explanation for these recent extinction events. Really, this is nothing but the projection of our contemporary fears and guilts into the past, based on flimsy circumstantial evidence, turning science into a morality play for kindergarteners.

The obvious problem is this: Neanderthals and Diprotodons went extinct at the exact same time on opposite sides of the world. And during the Younger Dryas event 12,500 years ago, it wasn’t just mammoths that died out—it was 70% of North American megafauna, including sabretooth tigers, the American lion, 12-foot-tall short-faced bears, dire wolves, American camels, ground sloths the size of elephants, armadillos the size of Volkswagen Beetles—including even the Clovis people who were supposedly killing them. Stone age humans with spears didn’t hunt out all these massive species in a few hundred years and then kill themselves. How absurd is that? And yet most textbooks still say that’s what happened.

What actually did happen, though, is one of the deepest and most important mysteries in history. These weren’t just extinction events—big changes to the global environment were going on at the same time. There are really only two plausible explanations. There might have been a series of comet or asteroid impacts into the ice sheets and ocean, and we just haven’t found the craters. But more and more it’s looking like the real story is in the magnetic fields of the Earth and Sun, and researchers added more to the pile of evidence this week, looking at prehistoric kauri trees preserved in the bog swamps of New Zealand.

What they found was a huge increase in Carbon-14 right at the Laschamps Magnetic Excursion, 42,000 years ago. Just as the Neanderthals and Australian megafauna were going extinct, the Earth’s magnetic field was in the middle of a potential pole flip, and dropped as low as 6% of its normal strength. Carbon-14 is made in the atmosphere when cosmic rays (particles ejected from supernovae traveling near the speed of light) slam into nitrogen atoms, knocking off a proton and turning N-14 into radioactive C-14. With the Earth’s magnetic field so weak, there were way more cosmic rays reaching the atmosphere and way more C-14.

More and more we’re learning that cosmic ray penetration has a large influence on the climate. Increased cosmic rays cause a thinning of the ozone layer. They excite the silica-rich magma in volcanos, leading to increased stratospheric ash injections. They play a crucial role in cloud formation. All of these things result in rapid drops in the global temperature.

With the Earth’s magnetic field so weak, we had little shielding against solar storms and coronal mass ejections. Auroras during this time would have been global, sometimes coming close enough to the ground to create arc discharges—continent-wide lightning storms, lighting the forests on fire, creating black mat layers and nanodiamonds in the soil. They’d have seemed like fluorescent snakes spitting electricity and setting the entire world ablaze. With the ozone depleted, we had little protection from the sun’s UV light even in calm conditions. Cancer rates increased, pathogens mutated more rapidly.

This happened at the Laschamp Excursion 42,000 years ago, and it happened again during the Gothenburg Excursion 12,500 years ago. During the latter, a CME likely struck while North America was sun-facing in summer.

The picture is becoming clear: our ancestors weren’t butchers; they were survivors of a world we can’t even imagine, a Biblical apocalypse with fire in the sky, massive floods and continent-wide fires. They fled to caves to survive. They made red ochre—the pigment used in cave paintings—as primitive sunscreen, protecting them from the intense radiation. They found food and adapted as all these other animals were dying out. They lived through a catastrophe that the Neanderthals couldn’t. And that’s the only reason we’re here today, blaming them for it.

So when I see the handprints in the caves they sheltered in tens of thousands of years ago, they seem to me gestures of love and perseverance though an impossible barrier of time and trauma.


my brother’s palm
on the prison glass
red ochre


Sunday SciKu | Lovely Lemurs

Science folks save their love-related press releases for the week of Valentine’s Day, and this Sunday sciku is no exception. Monogamy is rare in mammals, with only around 4 percent of our animal class exhibiting long-term pair-bonding. Thirty years ago, researchers looked inside the brains of committed voles to see what makes love tick, and came to the conclusion that it seemed to be extra oxytocin receptors creating a kind of love circuit.

This year, researchers at Duke tried to find the same thing in a romantic species of lemurs, which are more closely related to humans—but it just plain wasn’t there. It turns out that there is no common program for love—it’s complicated, and likely arises in various species independently, as convergent evolution. So there’s not much hope of inventing Love Potion #9. We just have to keep working at it every Valentine’s Day.


great love
in the red-bellied lemurs


Sunday SciKu | Pruning

Researchers at the University of Pittsburgh have been exploring the ways SARS-CoV-2 mutates at the spike protein to evade antibodies. Coronaviruses have an error-checking system that keeps them more stable from mutation than other RNA viruses, but it turns out the proofreader doesn’t notice deletions. So there are certain segments in the spike protein sequence that can be removed without eliminating binding and replication, and we can see these same deletions again and again as we look through the genomic databases, with the virus slowly evolving to avoid our immune response. This is one of the selective pressures that makes a virus less deadly over time, as it sacrifices some of its binding affinity for immune evasion.

Last summer, our plum tree was overburdened with fruit, to the point where I had to prop up limbs to keep them from breaking, so a few weeks ago I was out there figuring out where to prune it, like some big spike protein sticking out of the earth. The combination became this week’s SciKu.


the plum tree
for lines to cut


Sunday SciKu | Fungi

This week’s sciku is inspired by Virginia Tech researchers who discovered the oldest known terrestrial fossil. The fungal filaments found deep within dolostone rocks in Southern China might help explain an ancient mystery. They date to 635 million years ago, as the climate was exiting a “snowball earth” phase. For 10 million years, an abledo/H2O feedback loop triggered runaway cooling, locking more and more water vapor as ice, until glaciers covered every continent and oceans were frozen solid over a kilometer deep.

An era of volcanism seems to have saved the planet, but how exactly the biosphere recovered relatively swiftly from such harsh conditions has always been a bit of a puzzle. One hypothesis is that fungi hidden within caves and crevices played a crucial role in life’s return to land, with their enzymes breaking up rock and tough organic matter, basically restoring a soil where plants could grow. It’s far from proven, but these fossils support that hypothesis, and if true, we really have these fungi to thank for being alive today.

I was tempted to write a bad joking senryu about how these microscopic heroes were also fun guys. But then for some reason it reminded me of the way early friends in pre-school disappear from our lives completely, yet play a major role in the development of our psyches. I remember my first crush was a girl name Sarah, and my best friend was some kid named John. I don’t remember anything else about them. In a weird way, though, those are the foundational archetypes that we build many of our relationships from for the rest of our lives. That’s even weirder to think about than a 635 million year-old fungus.


old friends
still alive in the layers
of who we are


Sunday SciKu | Butterfly Wings

In science news this week, researchers at the University of Lund put a butterfly in a wind tunnel for the first time to study the aerodynamics of their flight. It’s often been assumed that their flat floppy wings were an inefficient way to fly, but nature is often more than what it seems.

It turns out that the clapping action of their wings shoots a jet of air backward, propelling them 28% faster than they’d be able to fly otherwise. Yes, like jetpacks!

These short bursts of irregular motion make them much more difficult to catch as prey for swooping birds. Predicting where the butterfly will be as they strike is like a batter trying to hit a knuckleball. Which should be no surprise—baseball players like Willie Stargell have long compared hitting the pitch to catching a butterfly with tweezers.
It’s another great lesson from nature about the quality of our assumptions.


bobbing butterfly—
answers to the question
of one hand clapping