Could Earth have a 'shadow' biosphere?
Some scientists think there may be a hidden, second form of life living right under our noses.
- All life on Earth shares some basic characteristics, such as being carbon-based; using DNA, RNA, and proteins to function; and so on.
- Many of these characteristics are simply the only ones that could work in Earth's environment, but there are also a surprising number of seemingly arbitrary features of life.
- Under the shadow biosphere theory, some scientists argue that alternative forms of life exist right here on Earth, undetected simply because we don't know to look for them.
In 2009, a NASA researcher isolated a peculiar bacteria from Mono Lake in California. Mono Lake is hypersaline and rich in arsenic, making it a difficult place for life to eke out an existence with the exception of some hard-scrabbling brine shrimp, the migratory birds that feed upon them, and some very interesting extremophile bacteria.
The researcher believed that this particular bacteria, dubbed GFAJ-1, was capable of an incredible trick. All life on Earth — and consequentially, all life that humans know of — uses phosphorus in its DNA. But when GFAJ-1 had no phosphorus, it seemed able to grow using just arsenic. The closest analogy would be to say that the researchers had just discovered alien life right on Earth.
There was a flurry of excitement and activity amongst the scientific community, but it was unfortunately short-lived; further research failed to replicate the experiment, and it appeared that GFAJ-1 was simply remarkably resistant to arsenic and had been surviving on trace amounts of phosphorus that had contaminated the culture.
This episode raises a question that bothers molecular biologists and astrobiologists alike; why is life the way it is? Why couldn't GFAJ-1 have used that arsenic molecule in place of the standard phosphorus molecule? There are plenty of hypothetical forms of life that simply couldn't exist under the conditions on Earth, such as silicon-based life rather than our carbon-based one, but there are also many, many variations on Earth's carbon-based life that should do fine.
These questions lead to another: What if there are indeed other forms of microbial life on Earth, unnoticed but existing in parallel with our own? This hypothetical scenario is referred to as the shadow biosphere.
Mysterious co-inhabitants of Earth
Mono Lake and GFAJ-1 (inset).
If Earth hosted not one, but two fundamentally different forms of life, it would substantially increase the odds of alien life existing out in the universe. If a shadow biosphere existed, then it would stand to reason that when a planet exists under the right conditions, life doesn't just have a shot at emerging, it's practically guaranteed.
But then again, this idea also seems extremely far-fetched. If a second form of life existed in parallel alongside our own, one would expect that we would have detected it by now. To that point, proponents argue that our techniques for detecting life are based on our current understanding of it. Hypothetical, alternate microbial life forms could go undetected.
It is important to note that the majority of biologists do not endorse the idea of a shadow biosphere. There is little evidence to suggest that such a biosphere exists, and it is extremely difficult to prove a negative, so we are left with assuming that ours is the only format that life takes. Still, contemplating the shadow biosphere is a useful exercise, as it may help us understand alien life. Not to mention that the shadow biosphere may in fact be real.
What would the shadow biosphere look like?
All life relies on DNA, RNA, and proteins to function. DNA and RNA are composed of 5 nucleobases in total, and proteins are composed of 20 amino acids. The problem is that these 5 nucleobases and 20 amino acids seem arbitrary — there are plenty of other nucleobases and hundreds of naturally occurring and abundant amino acids. Meteorites have even landed on Earth loaded with these apparently extraneous amino acids and nucleobases. It's plausible that alternate forms of life could use different combinations of these building blocks.
Another possible candidate for the shadow biosphere would be RNA-based life. Both DNA and RNA carry genetic information, and life on Earth uses both to function. Unlike DNA, RNA only has a single strand, uses the nucleobase uracil rather than thymine, and directly codes for amino acids.
Because RNA is structurally simpler than DNA, some scientists argue that predominantly RNA-based life evolved first on Earth, often referred to as the "RNA World." Under a shadow biosphere, such life would have persisted, branching off from what would eventually become DNA-based life.
There could also be organisms with the opposite chirality to ours. Perhaps one of the most arbitrary characteristics that life on Earth exhibits is its chirality, or handedness. In molecular biology, the shape of a molecule plays a large part in its function, but some shapes are simply mirror images of the other, like our left hand is a mirror image of our right.
These molecules are functionally the same, they just need the right kind of molecular machinery to work. Life on Earth has somehow decided that left-handed amino acids make up proteins and right-handed sugars make up our DNA and RNA, but there's no reason why this couldn't be flipped. We may be exposed to molecular life with the opposite chirality to ours and not even know it; none of our cells could interact with a molecule using the "wrong" hand to ours.
Unfortunately, we will likely only be able to shut the book on the shadow biosphere if we find life that deviates from the formula that seems to work so well on Earth. Proving the absence of all other varieties of life on Earth is an impossible task, so we will likely be left to speculate. If, however, we do discover evidence of a shadow biosphere in some of Earth's stranger nooks and crannies, we will have to look at life in the universe from an entirely new point of view.
What would happen if you tripled the US population? Join Matthew Yglesias and Charles Duhigg at 1pm ET on Monday, September 28.
Whether or not women think beards are sexy has to do with "moral disgust"
- A new study found that women perceive men with facial hair to be more attractive as well as physically and socially dominant.
- Women tend to associate more masculine faces with physical strength, social assertiveness, and formidability.
- Women who display higher levels of "moral disgust," or feelings of repugnance toward taboo behaviors, are more likely to prefer hairy faces.
Beards and perceptions of masculinity<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjU5OTg0MC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0NzkxMjM3N30.cH-GqNwP5GVqvstgJWAhBPn1B_lYpVEAI0I7iax7EQw/img.jpg?width=1245&coordinates=0%2C1900%2C0%2C849&height=700" id="caae6" class="rm-shortcode" data-rm-shortcode-id="cb0a355a4e8e1899789bc45f3f7aef56" data-rm-shortcode-name="rebelmouse-image" />
Photo Credit: Wikimedia<p>The study used 919 American (mostly white) women ages 18-70 who rated 30 pictures of men they were shown with various stages of facial hair growth. The photographs depicted men with faces that had been digitally altered to look more feminine or more masculine, with a beard and without a beard. The women rated the men according to perceived attractiveness for long-term and short-term relationships. The study found that the more facial hair the men had, the higher the men were rated on their attractiveness, particularly for their suitability for a long-term relationship.</p><p>Part of this might be attributed to facial masculinity — i.e. protruding brow ridge, wide cheekbones, thick jawline, and deeply set narrow eyes — which conveys information to a woman about a man's underlying health and formidability. Women tend to associate more masculine faces with physical strength and social assertiveness. It can also indicate a man with a superior immune response. The researchers suggested that their findings favoring bearded men could be due to the fact that facial hair enhances the masculine facial features on a man's face, like creating the illusion of a thicker jaw line. This could communicate direct benefits to women like resources and protection that would enhance survival among mothers and their infants. In other words, while a beard doesn't mean superior genetics in and of itself, it might be a primitive, ornamental way of saying, "Hey girl, I'm a testosterone-fueled lean, mean, pathogen fighting machine." <br></p><p>It could also be that a beard becomes its own destiny. The researchers in this study cite prior research that found that by growing a beard, men felt more masculine and had higher levels of serum testosterone, which was linked to a higher level of social dominance. They also tended to subscribe to more old-school beliefs about gender roles in their relationships with women as compared to men with clean-shaven faces.<span></span><br></p>
What does disgust have to do with beard preference?<p>Obviously, not all women dig beards. The researchers were particularly interested in what traits make a women prefer bearded men over clean-shaven faces. They looked into several factors including a woman's disgust levels on various concepts, her desire to become pregnant, and her exposure to facial hair in her personal life. </p><p>According to the study, women who were not into facial hair were turned-off by potential parasites or other critters they imagined could be in the hair or skin. Women ranking high on this "ectoparasite disgust" scale might have viewed beards as a sign of poor grooming habits. However, women who ranked higher in levels of "pathogen" did find the bearded men to be desirable, possibly because they perceived beards as a signal of good health and immune function. An intriguing discovery in the study was links to morality. Women who displayed higher levels of "moral disgust," or feelings of repugnance toward taboo behaviors, were more likely to prefer hairy faces. The authors opined that this could reflect a link between beardedness, politically conservative outlooks, and traditional views regarding performances of masculinity in heterosexual relationships.</p>
Additional findings<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjU5OTg1My9vcmlnaW4uZ2lmIiwiZXhwaXJlc19hdCI6MTYyNDI1NjUyOX0.P9B8WbmJR0q4nfzYZKbuNSA-2SAigVWJgrQE-_Gxlds/img.gif?width=980" id="49143" class="rm-shortcode" data-rm-shortcode-id="2ed3b1d6f20fc170bf2974646e565e8d" data-rm-shortcode-name="rebelmouse-image" />Giphy<p>The correlations that existed between married and single women's rating on the attractiveness of beards were not particularly clear, although the researchers noted that single and married women who wanted children tended to find beards more attractive than the women who didn't want children. They also found that women with bearded husbands found beards to be more attractive, which might indicate that social exposure to beards influences how desirable they are perceived of as being. Or it could be that men with wives who like beards grow beards.</p><p>It's important to note that culture plays a huge role in how attractive women perceive certain male characteristics as being. This study looked at a small, culturally specific group of American women, so no big, universal claims should be made about masculinity, facial hair, and male desirability to women. However, research like this is important in highlighting how human grooming decisions are driven by much more than fashion trends. Sociobiological, economic, and ecological factors all play a part in the way we choose to present ourselves.</p>
Dominique Crenn, the only female chef in America with three Michelin stars, joins Big Think Live.
Having been exposed to mavericks in the French culinary world at a young age, three-star Michelin chef Dominique Crenn made it her mission to cook in a way that is not only delicious and elegant, but also expressive, memorable, and true to her experience.
New experiments find weird quantum activity in supercold gas.
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