Biologists Say They Cracked One of Life's Biggest Mysteries

ELI5/TLDR

Most of the molecules inside you have a handedness — they come in left and right versions, like gloves, and life on Earth only uses one of each. Nobody really knows why. A new paper claims it found the reason: one version is just better at moving electrons around, and since chemistry is basically electrons hopping between atoms, that version wins every reaction. Sabine thinks the experiment is probably wrong, because the result would quietly break some rules of physics she takes very seriously.

The Full Story

The handedness problem

Some molecules can be built in two versions that contain the exact same atoms and the exact same connections, but are still not the same shape — like your two hands. Chemists call this property handedness, or in technical language, chirality. (Sabine says “chyro,” which is the same word.)

Life on Earth picked a side. DNA and RNA only use right-handed sugars. Proteins only use left-handed amino acids. The mirror-image version of life would work chemically — it just doesn’t exist here.

The mirror image version of life is chemically as possible as ours, but it’s not the version we see.

This matters beyond Earth. If the reason we ended up one-handed is some deep fact about the universe, then alien life will share our handedness and we could, in principle, eat each other. If it’s a fluke, alien proteins would slide past ours like a left shoe on a right foot.

The old explanation, and why it doesn’t really explain

For a while the leading guess involved magnetic rocks. Iron-bearing minerals can act as scaffolds where complex molecules assemble, and the handedness of what assembles depends on which way the rock is magnetised. The effect is small but measurable, and a small head start in a self-copying system can snowball.

The trouble, as Sabine points out, is that this just moves the question. Now you have to explain why the rocks were magnetised one way rather than the other. Blaming the Earth’s magnetic field doesn’t work — it’s too weak, it varies across the planet, and it flips over geological time.

The new claim

A new paper says the bias is much more basic: one handedness is simply better at moving electrons through it.

To test this, the authors made gold films with a built-in twist. Gold isn’t normally handed, but they grew it in a solution of tartaric acid — a small handed molecule — using either the left or right version. The handed solution nudges the growing metal into a microscopic spiral.

They then ran a current through the film and measured a sideways voltage — a standard way to see how electrons move through a material. The left- and right-handed films pushed current in opposite directions, which is expected. What’s surprising is that the two pushes were not the same strength. One handedness conducted better than the other, period.

One-handed version was not simply the mirror image of the other. One was better period.

Why does a curl of gold tell us anything about life? Because every chemical reaction is, at heart, electrons looking for somewhere to go. If one handedness moves electrons more easily, it will tend to win at chemistry, and life will get built out of the winning side.

Sabine’s skepticism

She isn’t buying it. As a physicist, she expects the mirror-image of any experiment to give a mirror-image result — same size, opposite sign. The standard model of particle physics does break this symmetry, but only at energies far above anything happening in a tabletop electronics experiment. Her guess is that the gold films weren’t actually mirror images of each other — a sample prep problem, not a discovery.

If this result is correct, it could change our understanding of life in the universe. If it’s wrong, it’ll change our understanding of how carefully one should prepare a sample.

Key Takeaways

Biological molecules come in left- and right-handed versions; life on Earth uses only one of each
DNA/RNA: right-handed sugars. Proteins: left-handed amino acids
The “magnetic rocks” explanation just pushes the question back one step
New paper: handed gold films conduct electrons unequally, suggesting one handedness wins at chemistry generally
Sabine’s objection: equal-and-opposite currents are what basic physics predicts, so an inequality is more likely a sample artefact than new physics
If true, alien life would likely share our handedness — which has implications for whether we’d be biochemically compatible

Claude’s Take

Sabine is doing what she does well here — explaining a real and interesting result, then immediately playing skeptic. The video is honest about the limits of her expertise (this isn’t her field) and she flags the standard-model angle correctly: parity violation exists but is far too weak to matter at the energies of a benchtop experiment.

Her instinct that the experiment probably reflects sample asymmetry rather than new physics is reasonable. Two films grown in left- versus right-tartaric-acid solutions are not guaranteed to be perfect mirror images of each other in every other respect — film thickness, defects, contamination — and any of those could produce a current asymmetry. That said, “I don’t see how this is possible” is not the same as “this is wrong,” and chiral-induced spin selectivity (CISS) is an established area where handed molecules really do behave asymmetrically with electron transport. So the finding may be less heretical than she suggests; she leans into the skeptical framing a bit.

Score: 7. Useful and well-paced introduction to the chirality problem and a fresh result, with a fair caveat. Knocked down because she doesn’t name the paper or the CISS literature it sits inside, which would help anyone who actually wants to evaluate it.