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Jennifer Dickert, Wikimedia Commons /  CC by 2.0 
Jennifer Dickert, Wikimedia Commons /  CC by 2.0 

Why Are Wedding Rings Worn on the Left Hand?

Jennifer Dickert, Wikimedia Commons /  CC by 2.0 
Jennifer Dickert, Wikimedia Commons /  CC by 2.0 

For years, couples have dedicated a single "ring" finger to romance when any other digit would do. A case of left side, strong side? Not according to history.

In medieval times, getting caught scribbling with one's left hand could earn accusations of being possessed and, during the Spanish Inquisition, lefties were more likely to be tortured or killed. In fact, the aversion touched many cultures, from the long-standing taboo in Islamic countries against eating and drinking with one’s left hand, to the expectation in ancient Japan that any wife who didn’t favor her right could be legally divorced on the spot, no questions asked. So why do we favor a finger on a cursed hand to symbolize lasting love?

Past perception wasn't all bad. The union between marriage and the now-standard ring placement can be traced back to second-century Egyptians who falsely believed that “a certain most delicate nerve” began in the fourth left finger and stretched directly to the heart, according to the Greek scholar Appian. Centuries later, the Romans came to a similar conclusion. In place of a nerve, they were convinced that a vena amoris—or “lover’s vein”—connected this digit with the blood-pumping organ.

During the Roman engagement process, a well-off suitor who could afford a ring would slip it over his bride-to-be’s fourth finger. Thus, he’d always have a symbolic grip around her lover’s vein. The modern world may have adopted that practice from the Romans. 

Still, others argue that reverence for the fourth finger begun as an early Christian ritual. While crossing themselves in an Orthodox Church, worshipers are expected to join the thumb with the index and middle fingers. Historians contend that the group represented the father, son, and Holy Ghost when placed together, while the “ring” finger signified earthly love, making it the perfect location for a spouse’s wedding ring.

Until the seventeenth century, Orthodox couples normally wore their rings on the right hand (an extremity that’s associated with strength) and most Europeans of all faiths followed suit. But during the Reformation in 1549, an English Bishop and Protestant reformer named Thomas Cranmer used wedding rings as a way to break from tradition. That year, he published The Book of Common Prayer, which instructs couples to ditch a centuries-old practice in favor of slipping their wedding rings over the left fourth finger. Before long, husbands and wives throughout the continent were doing so.

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Big Questions
How Are Speed Limits Set?
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When driving down a road where speed limits are oppressively low, or high enough to let drivers get away with reckless behavior, it's easy to blame the government for getting it wrong. But you and your fellow drivers play a bigger a role in determining speed limits than you might think.

Before cities can come up with speed limit figures, they first need to look at how fast motorists drive down certain roads when there are no limitations. According to The Sacramento Bee, officials conduct speed surveys on two types of roads: arterial roads (typically four-lane highways) and collector streets (two-lane roads connecting residential areas to arterials). Once the data has been collected, they toss out the fastest 15 percent of drivers. The thinking is that this group is probably going faster than what's safe and isn't representative of the average driver. The sweet spot, according to the state, is the 85th percentile: Drivers in this group are thought to occupy the Goldilocks zone of safety and efficiency.

Officials use whatever speed falls in the 85th percentile to set limits for that street, but they do have some wiggle room. If the average speed is 33 mph, for example, they’d normally round up to 35 or down to 30 to reach the nearest 5-mph increment. Whether they decide to make the number higher or lower depends on other information they know about that area. If there’s a risky turn, they might decide to round down and keep drivers on the slow side.

A road’s crash rate also comes into play: If the number of collisions per million miles traveled for that stretch of road is higher than average, officials might lower the speed limit regardless of the 85th percentile rule. Roads that have a history of accidents might also warrant a special signal or sign to reinforce the new speed limit.

For other types of roads, setting speed limits is more of a cut-and-dry process. Streets that run through school zones, business districts, and residential areas are all assigned standard speed limits that are much lower than what drivers might hit if given free rein.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
Do Bacteria Have Bacteria?
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Drew Smith:

Do bacteria have bacteria? Yes.

We know that bacteria range in size from 0.2 micrometers to nearly one millimeter. That’s more than a thousand-fold difference, easily enough to accommodate a small bacterium inside a larger one.

Nothing forbids bacteria from invading other bacteria, and in biology, that which is not forbidden is inevitable.

We have at least one example: Like many mealybugs, Planococcus citri has a bacterial endosymbiont, in this case the β-proteobacterium Tremblaya princeps. And this endosymbiont in turn has the γ-proteobacterium Moranella endobia living inside it. See for yourself:

Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)
Fluorescent In-Situ Hybridization confirming that intrabacterial symbionts reside inside Tremblaya cells in (A) M. hirsutus and (B) P. marginatus mealybugs. Tremblaya cells are in green, and γ-proteobacterial symbionts are in red. (Scale bar: 10 μm.)

I don’t know of examples of free-living bacteria hosting other bacteria within them, but that reflects either my ignorance or the likelihood that we haven’t looked hard enough for them. I’m sure they are out there.

Most (not all) scientists studying the origin of eukaryotic cells believe that they are descended from Archaea.

All scientists accept that the mitochondria which live inside eukaryotic cells are descendants of invasive alpha-proteobacteria. What’s not clear is whether archeal cells became eukaryotic in nature—that is, acquired internal membranes and transport systems—before or after acquiring mitochondria. The two scenarios can be sketched out like this:


The two hypotheses on the origin of eukaryotes:

(A) Archaezoan hypothesis.

(B) Symbiotic hypothesis.

The shapes within the eukaryotic cell denote the nucleus, the endomembrane system, and the cytoskeleton. The irregular gray shape denotes a putative wall-less archaeon that could have been the host of the alpha-proteobacterial endosymbiont, whereas the oblong red shape denotes a typical archaeon with a cell wall. A: archaea; B: bacteria; E: eukaryote; LUCA: last universal common ancestor of cellular life forms; LECA: last eukaryotic common ancestor; E-arch: putative archaezoan (primitive amitochondrial eukaryote); E-mit: primitive mitochondrial eukaryote; alpha:alpha-proteobacterium, ancestor of the mitochondrion.

The Archaezoan hypothesis has been given a bit of a boost by the discovery of Lokiarcheota. This complex Archaean has genes for phagocytosis, intracellular membrane formation and intracellular transport and signaling—hallmark activities of eukaryotic cells. The Lokiarcheotan genes are clearly related to eukaryotic genes, indicating a common origin.

Bacteria-within-bacteria is not only not a crazy idea, it probably accounts for the origin of Eucarya, and thus our own species.

We don’t know how common this arrangement is—we mostly study bacteria these days by sequencing their DNA. This is great for detecting uncultivatable species (which are 99 percent of them), but doesn’t tell us whether they are free-living or are some kind of symbiont. For that, someone would have to spend a lot of time prepping environmental samples for close examination by microscopic methods, a tedious project indeed. But one well worth doing, as it may shed more light on the history of life—which is often a history of conflict turned to cooperation. That’s a story which never gets old or stale.

This post originally appeared on Quora. Click here to view.

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