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Why Don't Valentine Hearts Look Like Real Hearts?

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Love is in the air this month, and images of two-lobed hearts are all over everything: candy, cards, decorations, you name it. That the heart is symbolic of love and passion isn't surprising—ancient Greek and Roman thinkers, including Aristotle, thought the organ was the center of all emotions. Why the heart symbol you see everywhere in February doesn't look anything like an actual human heart, though, is a little less clear.

The symbol goes at least as far back as the 1400s, when it appeared on European playing cards to mark one of the red suits, though it may even be older than that. The shape is pretty much a mystery, though. There are a few different hypotheses to explain it, but none of them have been confirmed.

One suggested origin for the symbol is that it comes from the ancient African city-state of Cyrene, whose merchants traded in the rare, and now extinct, plant silphium. The plant was used to season food, but doubled as a contraceptive. A silphium seedpod looks like a valentine's heart, so the shape became associated with sex, and then with love.

Another possibility is that the shape is a crude representation of a pubic mound, the vulva, a pair of breasts, buttocks, or a pair of testicles. It may even have come from a poor attempt at drawing an actual heart. A lousy artist, an inaccurate description of the subject, or a malformed model all could have led to that shape.

The Catholic church explains the symbol as coming from a vision that Saint Margaret Mary Alacoque had, where the "Sacred Heart of Jesus"—associated with love and devotion by Catholics—appeared in this shape surrounded by thorns. But Alacoque didn't have this vision until the late 1600s, well after the symbol was already documented. This makes it the unlikeliest of origin stories, but the church's frequent use of the shape was probably a driving factor in popularizing it as a symbol of love.

This story originally appeared in 2012.

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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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Big Questions
Why Do Cats 'Blep'?
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As pet owners are well aware, cats are inscrutable creatures. They hiss at bare walls. They invite petting and then answer with scratching ingratitude. Their eyes are wandering globes of murky motivations.

Sometimes, you may catch your cat staring off into the abyss with his or her tongue lolling out of their mouth. This cartoonish expression, which is atypical of a cat’s normally regal air, has been identified as a “blep” by internet cat photo connoisseurs. An example:

Cunning as they are, cats probably don’t have the self-awareness to realize how charming this is. So why do cats really blep?

In a piece for Inverse, cat consultant Amy Shojai expressed the belief that a blep could be associated with the Flehmen response, which describes the act of a cat “smelling” their environment with their tongue. As a cat pants with his or her mouth open, pheromones are collected and passed along to the vomeronasal organ on the roof of their mouth. This typically happens when cats want to learn more about other cats or intriguing scents, like your dirty socks.

While the Flehmen response might precede a blep, it is not precisely a blep. That involves the cat’s mouth being closed while the tongue hangs out listlessly.

Ingrid Johnson, a certified cat behavior consultant through the International Association of Animal Behavior Consultants and the owner of Fundamentally Feline, tells Mental Floss that cat bleps may have several other plausible explanations. “It’s likely they don’t feel it or even realize they’re doing it,” she says. “One reason for that might be that they’re on medication that causes relaxation. Something for anxiety or stress or a muscle relaxer would do it.”

A photo of a cat sticking its tongue out
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If the cat isn’t sedated and unfurling their tongue because they’re high, then it’s possible that an anatomic cause is behind a blep: Johnson says she’s seen several cats display their tongues after having teeth extracted for health reasons. “Canine teeth help keep the tongue in place, so this would be a more common behavior for cats missing teeth, particularly on the bottom.”

A blep might even be breed-specific. Persians, which have been bred to have flat faces, might dangle their tongues because they lack the real estate to store it. “I see it a lot with Persians because there’s just no room to tuck it back in,” Johnson says. A cat may also simply have a Gene Simmons-sized tongue that gets caught on their incisors during a grooming session, leading to repeated bleps.

Whatever the origin, bleps are generally no cause for concern unless they’re doing it on a regular basis. That could be sign of an oral problem with their gums or teeth, prompting an evaluation by a veterinarian. Otherwise, a blep can either be admired—or retracted with a gentle prod of the tongue (provided your cat puts up with that kind of nonsense). “They might put up with touching their tongue, or they may bite or swipe at you,” Johnson says. “It depends on the temperament of the cat.” Considering the possible wrath involved, it may be best to let them blep in peace.

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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