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Chemists Concoct Part of Life's Recipe

For decades, scientists have argued about and pondered over whether biology began on our planet or arrived from above. If it started here, it presumably took millions of years for Earth to cook up life's essential molecules from scratch.

Now a team of chemists has computed a possible real-world recipe for one of these biomolecules, in research that suggests life started in a local pond rather than raining down from space.

Living cells are like tiny chemical factories, assembling long molecular chains such as DNA and proteins. But prior to life's emergence on Earth, these complex molecules must have come together by themselves, without the help of living cells.

"Just where these biomolecules originated isn’t known," said Paul von Rague Schleyer from the University of Georgia. "They could have formed from smaller molecules present on primitive Earth, either very slowly over millions of years or rapidly before the Earth cooled down."

A number of biomolecule ingredients have been detected in space and in meteorites. Recently some researchers postulated that adenine—one of the four nucleic bases of DNA—formed in interstellar clouds and later rained down on Earth, reminiscent of an earlier comet-seeding idea.

Adenine is abundant on our planet and has even been found in meteorites. It is vital to life as part of the four-letter alphabet that encodes genetic information.

In 1960, scientists showed that a small fraction of adenine could be made from a mixture of poisonous hydrogen cyanide (HCN) and ammonia. Over the years, other researchers have made adenine from HCN, but the exact mechanism has never been explained.

Now Schleyer and his colleagues have theoretically calculated all of the intricate reaction steps that transform simple HCN molecules into adenine, as described in the Oct. 30 issue of the journal Proceedings of the National Academy of Sciences.

Their model does not pinpoint where this adenine formation could have occurred, but the reactions are unlikely to proceed outside of a liquid solution, which may argue against a purely space-based origin. The authors are aware, however, that much work remains to explain how the other pieces of DNA came to be.

"Our investigation should trigger similar investigations of the abiotic formation of the remaining nucleic acid bases as well as other biologically relevant molecules,” the authors wrote. 

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Does Turkey Make You Sleepy?

Stop blaming the bird for your turkey daze.

roast-turkey 
TURKEY DAZE: Gluttony is more to blame for post-Thanksgiving tiredness than anything in the turkey itself.

Let us give thanks on Thanksgiving for its cornucopia of foods: mashed potatoes, gravy, stuffing, creamed corn, cranberry sauce and, of course, turkey, among other delights. Every fourth Thursday of November, friends and family in the U.S. travel thousands of miles to gather and gorge in a celebration tracing back to 1621 when Plymouth Pilgrims and Native Americans spent three days breaking bread in gratitude for the year's plentiful harvest.

Those early revelers were probably knocked out by their marathon feast, and most people today are familiar with the post-Thanksgiving food coma. But often the blame falls on the bird. Turkey allegedly causes drowsiness because it is packed with a nutrient called tryptophan.

Tryptophan is one of 20 naturally occurring amino acids—the building blocks of proteins. Because the body is unable to manufacture tryptophan on its own, it must be obtained from food protein. Turkey is a great source of this essential acid, but it is not unique: many meats and other protein products pack comparable amounts.

Tryptophan is used by the human body to make serotonin, a neurotransmitter. It has a somnolent effect on fruit flies, whose sleep is most likely equivalent to our slow-wave (non-REM) sleep, says neuroscientist Amita Sehgal of the University of Pennsylvania School of Medicine in Philadelphia. Other studies show that one function of serotonin is the promotion of slow-wave sleep in nonhuman mammals, she adds, and it may do the same for humans.

Thus, it is no wonder that turkey, which provides the raw material for the synthesis of sleep-related serotonin, is purported to have soporific power.

But eating turkey does not translate to amplified serotonin production in the brain, says neuropharmacologist Richard Wurtman of the Massachusetts Institute of Technology's Department of Brain and Cognitive Sciences in Cambridge, Mass.

Turkey and other protein-rich foods contain many amino acids, and tryptophan is the scarcest among them, Wurtman says. After a turkey dinner, several amino acids circulate through the bloodstream. To get into the brain they must be shuttled across the blood–brain barrier by specialized transport proteins. Like passengers trying to board a crowded bus, amino acids compete for rides on these transporters. Not only does tryptophan have paltry representation among the passengers; it also competes with five other amino acids for the same transporter. Aced out by other amino acids, tryptophan thereby has a tough time hitching a ride to the brain.

Taken in isolation, tryptophan would increase brain serotonin, Wurtman says, but no food source contains tryptophan in the absence of other amino acids.

"Paradoxically, what probably makes people sleepy after Thanksgiving dinner is…dessert," he adds. "Eating carbohydrates increases brain serotonin in spite of the fact that there is no tryptophan in carbohydrates."

Gobbling a slice of sweet pumpkin pie, for instance, causes beta cells in the pancreas to secrete insulin, a hormone that allows the uptake of glucose and most amino acids into the tissues. But insulin has little effect on tryptophan, a large percentage of which travels the bloodstream bound to the protein albumin and therefore is unavailable to the tissues, the notable exception being the brain. By sopping up other amino acids from the blood, however, insulin reduces the tryptophan's competition; the transport system is no longer tied up and more tryptophan can cross the blood–brain barrier. As Wurtman and others have shown, when more tryptophan arrives in the brain, serotonin synthesis steps up and serotonin-mediated transmission is amplified among neurons.

There is another reason turkey has been accused of causing drowsiness: Tryptophan is also a precursor to melatonin, a sleep-associated hormone manufactured in the brain's pineal gland. "Melatonin secretion is increased during sleep," and some studies have suggested that melatonin helps people fall asleep as well as adjust their body clocks to new time zones, says psychiatrist Jerry Siegel of the Center for Sleep Research at the University of California, Los Angeles.

Those early revelers were probably knocked out by their marathon feast, and most people today are familiar with the post-Thanksgiving food coma. But often the blame falls on the bird. Turkey allegedly causes drowsiness because it is packed with a nutrient called tryptophan.

Tryptophan is one of 20 naturally occurring amino acids—the building blocks of proteins. Because the body is unable to manufacture tryptophan on its own, it must be obtained from food protein. Turkey is a great source of this essential acid, but it is not unique: many meats and other protein products pack comparable amounts.

Tryptophan is used by the human body to make serotonin, a neurotransmitter. It has a somnolent effect on fruit flies, whose sleep is most likely equivalent to our slow-wave (non-REM) sleep, says neuroscientist Amita Sehgal of the University of Pennsylvania School of Medicine in Philadelphia. Other studies show that one function of serotonin is the promotion of slow-wave sleep in nonhuman mammals, she adds, and it may do the same for humans.

Thus, it is no wonder that turkey, which provides the raw material for the synthesis of sleep-related serotonin, is purported to have soporific power.

But eating turkey does not translate to amplified serotonin production in the brain, says neuropharmacologist Richard Wurtman of the Massachusetts Institute of Technology's Department of Brain and Cognitive Sciences in Cambridge, Mass.

Turkey and other protein-rich foods contain many amino acids, and tryptophan is the scarcest among them, Wurtman says. After a turkey dinner, several amino acids circulate through the bloodstream. To get into the brain they must be shuttled across the blood–brain barrier by specialized transport proteins. Like passengers trying to board a crowded bus, amino acids compete for rides on these transporters. Not only does tryptophan have paltry representation among the passengers; it also competes with five other amino acids for the same transporter. Aced out by other amino acids, tryptophan thereby has a tough time hitching a ride to the brain.

Taken in isolation, tryptophan would increase brain serotonin, Wurtman says, but no food source contains tryptophan in the absence of other amino acids.

"Paradoxically, what probably makes people sleepy after Thanksgiving dinner is…dessert," he adds. "Eating carbohydrates increases brain serotonin in spite of the fact that there is no tryptophan in carbohydrates."

Gobbling a slice of sweet pumpkin pie, for instance, causes beta cells in the pancreas to secrete insulin, a hormone that allows the uptake of glucose and most amino acids into the tissues. But insulin has little effect on tryptophan, a large percentage of which travels the bloodstream bound to the protein albumin and therefore is unavailable to the tissues, the notable exception being the brain. By sopping up other amino acids from the blood, however, insulin reduces the tryptophan's competition; the transport system is no longer tied up and more tryptophan can cross the blood–brain barrier. As Wurtman and others have shown, when more tryptophan arrives in the brain, serotonin synthesis steps up and serotonin-mediated transmission is amplified among neurons.

There is another reason turkey has been accused of causing drowsiness: Tryptophan is also a precursor to melatonin, a sleep-associated hormone manufactured in the brain's pineal gland. "Melatonin secretion is increased during sleep," and some studies have suggested that melatonin helps people fall asleep as well as adjust their body clocks to new time zones, says psychiatrist Jerry Siegel of the Center for Sleep Research at the University of California, Los Angeles.

But eating loads of turkey, or any tryptophan-rich food for that matter, does not boost melatonin production, Wurtman says. Situated outside the blood–brain barrier, the pineal gland has ready access to blood tryptophan, which it uses to make serotonin. In contrast to Different from how this neurotransmitter functions in the brain, however, pineal serotonin is just a chemical precursor of melatonin; subsequent biochemical reactions in this gland are necessary to convert it to melatonin.

After a turkey meal, blood levels of tryptophan rise, which may amplify the pineal's production of such serotonin, but not melatonin, whose synthesis rate depends on the amount of enzymes available for the subsequent biochemical reactions to occur, Wurtman says.

If turkey is not the culprit, then what besides dessert causes post-Thanksgiving torpidity? It may simply be a function of scarfing down enormous quantities of food.

"Studies have indicated that stretching of the small intestine induces sleepiness and a protein–fat loading of the stomach induces sleepiness," says biologist H. Craig Heller at Stanford University in Palo Alto, Calif., "and, more blood going to the gastrointestinal tract means less going elsewhere,"—for example, the brain or skeletal muscle.

"Also, there is the general phenomenon of parasympathetic tone—rest and digest—that is conducive to sleep," Heller says. Working in opposition to the sympathetic "fight or flight" stress response, the parasympathetic nervous system restores and conserves energy by reducing heart rate and blood pressure while increasing salivation and gastric action for digestion.

Don't forget the beverages either. Thanksgiving feasts are often washed down with bubbling champagne, beer, wine or other spirits. Despite the latter's name, all have a lulling affect on the mind and body. So don't blame the turkey for your postprandial lethargy, instead give thanks for the abundance of drink and carbohydrate-rich, albeit slumber-inducing fare.

The Profound History of Coins

More than 100 million $1 coins featuring the likeness of Thomas Jefferson were put into circulation in September, but few people plan to use them, or even know they exist.

Only a quarter of U.S. residents have actually seen a Jefferson coin, or either of the other two Presidential $1 coins that are part of a series the United States Mint started to released earlier this year, according to a USA Today/Gallup Poll. Americans are also attached to their paper bills, another poll found, and prefer using them instead even if it costs the government more money.

It's a far cry from the social and political upheaval caused by the introduction of the first coins more than 2,500 years ago, said Tom Figueira, professor of Classics at Rutgers University in New Jersey.

"Mental changes with the introduction of coins were profound," Figueira said. "It was a whole new way of thinking about value."

The first coins

The world's first coins appeared around 600 B.C., jingling around in the pockets of the Lydians, a kingdom tied to ancient Greece and located in modern-day Turkey. They featured the stylized head of a lion and were made of electrum, an alloy of gold and silver.

The concept of money had been around awhile. Shells were used as currency in ancient China and, about 5,000 years ago, Mesopotamians had even developed a banking system where people could "deposit" grains, livestock and other valuables for safekeeping or trade.

But it wasn't until the actual coins appeared—money for money's sake—that the social effects of having a currency really started to take hold, Figueira explains. Keeping things tidy in a society that had gradually become very complex was the catalyst for minting those first pieces, he thinks.

"Coins allowed the processes of city-states to be organized in a way that was elegant and just," Figueira told LiveScience. "They made people feel that things like war subsidies were orderly and transparent."

Greek labs

Shiny new coins began sprouting up throughout the Mediterranean just a few decades later, as the Lydian experiment appeared to be going well.

"It's pretty clear that it worked," Figueira said, "and Greek city-states were a laboratory for all kinds of social experiments like this."

Athens, Aegina and Corinth and Persia all developed their own coins by the 6th-century B.C, expanding trade networks with a newfound ease. Gold and silver replaced electrum as the material of choice, with coin values reflecting the actual value of the metal and not an arbitrary amount imposed on the coin, as in the case with modern currencies. Roman and then Celtic coins later followed the same traditions.

Coins provided social mobility to those who didn't have it, everywhere they appeared. People could move around with something to show for it, aside from just the clothes on their backs, Figueira said.

There were some early kinks to iron out, said Figueira, mostly to do with the sheer variety of coins around Europe. The majority of cities had their own design to reflect local pride.

"The pictures were a way to communicate social solidarity," he said, "letting people know who we are, who our heroes are." Romans commemorated their emperors, while the Celts engraved their money with runes, animals and important kings.

Another key difference between those first coins and the latest ones issued? Only 7 percent of Americans can name the four presidents being honored on the 2007 dollar coins in the order they served, according to a poll by the U.S. Mint, conducted in "celebration" of the launch of the Jefferson coin

Denial Makes the World Go Round 

 
Varieties of denial include inattention, passive acknowledgement, reframing and willful blindness.

Friends at first dropped hints to go easy or rechannel her creative instincts. Her mother grew concerned enough to ask pointed questions. But sales clerks kept calling with early tips on the coming season’s fashions, and the seasons kept changing.

“It got so bad I would sit up suddenly at night and wonder if I was going to slip up and this whole thing would explode,” said the secretive shopper, Katharine Farrington, 46, a freelance film writer living in Washington, who is now free of debt. “I don’t know how I could have been in denial about it for so long. I guess I was optimistic I could pay, and that I wasn’t hurting anyone.

“Well, of course that wasn’t true.”

Everyone is in denial about something; just try denying it and watch friends make a list. For Freud, denial was a defense against external realities that threaten the ego, and many psychologists today would argue that it can be a protective defense in the face of unbearable news, like a cancer diagnosis.

In the modern vernacular, to say someone is “in denial” is to deliver a savage combination punch: one shot to the belly for the cheating or drinking or bad behavior, and another slap to the head for the cowardly self-deception of pretending it’s not a problem.

Yet recent studies from fields as diverse as psychology and anthropology suggest that the ability to look the other way, while potentially destructive, is also critically important to forming and nourishing close relationships. The psychological tricks that people use to ignore a festering problem in their own households are the same ones that they need to live with everyday human dishonesty and betrayal, their own and others’. And it is these highly evolved abilities, research suggests, that provide the foundation for that most disarming of all human invitations, forgiveness.

In this emerging view, social scientists see denial on a broader spectrum — from benign inattention to passive acknowledgment to full-blown, willful blindness — on the part of couples, social groups and organizations, as well as individuals. Seeing denial in this way, some scientists argue, helps clarify when it is wise to manage a difficult person or personal situation, and when it threatens to become a kind of infectious silent trance that can make hypocrites of otherwise forthright people.

“The closer you look, the more clearly you see that denial is part of the uneasy bargain we strike to be social creatures,” said Michael McCullough, a psychologist at the University of Miami and the author of the coming book “Beyond Revenge: The Evolution of the Forgiveness Instinct.” “We really do want to be moral people, but the fact is that we cut corners to get individual advantage, and we rely on the room that denial gives us to get by, to wiggle out of speeding tickets, and to forgive others for doing the same.”

The capacity for denial appears to have evolved in part to offset early humans’ hypersensitivity to violations of trust. In small kin groups, identifying liars and two-faced cheats was a matter of survival. A few bad rumors could mean a loss of status or even expulsion from the group, a death sentence.

In a series of recent studies, a team of researchers led by Peter H. Kim of the University of Southern California and Donald L. Ferrin of the University of Buffalo, now at Singapore Management University, had groups of business students rate the trustworthiness of a job applicant after learning that the person had committed an infraction at a previous job. Participants watched a film of a job interview in which the applicant was confronted with the problem and either denied or apologized for it.

If the infraction was described as a mistake and the applicant apologized, viewers gave him the benefit of the doubt and said they would trust him with job responsibilities. But if the infraction was described as fraud and the person apologized, viewers’ trust evaporated — and even having evidence that he had been cleared of misconduct did not entirely restore that trust.

“We concluded there is this skewed incentive system,” Dr. Kim said. “If you are guilty of an integrity-based violation and you apologize, that hurts you more than if you are dishonest and deny it.”

The system is skewed precisely because the people we rely on and value are imperfect, like everyone else, and not nearly as moral or trustworthy as they expect others to be. If evidence of this weren’t abundant enough in everyday life, it came through sharply in a recent study led by Dan Ariely, a behavioral economist at the Massachusetts Institute of Technology.

Dr. Ariely and two colleagues, Nina Mazar and On Amir, had 326 students take a multiple-choice general knowledge test, promising them payment for every correct answer. The students were instructed to transfer their answers, for the official tally, onto a form with color-in bubbles for each numbered question. But some of the students had the opportunity to cheat: they received bubble sheets with the correct answers seemingly inadvertently shaded in gray. Compared with the others, they changed about 20 percent of their answers, and a follow-up study demonstrated that they were unaware of the magnitude of their dishonesty.

“What we concluded is that good people can be dishonest up to the level where conscience kicks in,” said Dr. Ariely, author of the book “Predictably Irrational: The Hidden Forced that Shape Our Decisions,” due out next year. “That essentially you can fool the conscience a little bit and make small transgressions without waking it up. It all goes under the radar because you are not paying that much attention.”

It is a mistake to underestimate the power of simple attention. People can be acutely aware of what they pay attention to and remarkably blind to what they do not, psychologists have found. In real life, to be sure, casual denials of bad behavior require more than simple mental gymnastics, but inattention is a basic first ingredient.

The second ingredient, or second level, is passive acknowledgment, when infractions are too persistent to go unnoticed. People have adapted a multitude of ways to handle such problems indirectly. A raised eyebrow, a half smile or a nod can signal both “I saw that” and “I’ll let this one pass.”

The acknowledgment is passive for good reasons: an open confrontation, with a loved one or oneself, risks a major rupture or life change that could be more dire than the offense. And more often than is assumed, a subtle gesture can be enough of a warning to trigger a change in behavior, even one’s own.

In an effort to calculate exactly how often people overlook or punish infractions within their peer groups, a team of anthropologists from New Mexico and Vancouver ran a simulation of a game to measure levels of cooperation. In this one-on-one game, players decide whether to contribute to a shared investment pool, and they can cut off their partner if they believe that player’s contributions are too meager. The researchers found that once players had an established relationship of trust based on many interactions — once, in effect, the two joined the same clique — they were willing to overlook four or five selfish violations in a row without cutting a friend off. They cut strangers off after a single violation.

Using a computer program, the anthropologists ran out the simulation over many generations, in effect speeding up the tape of evolution for this society of players. And the rate of overlooking trust violations held up; that is, this pattern of forgiving behavior defined stable groups that maximized the survival and evolutionary fitness of the individuals.

“There are lots of way to think about this,” said the lead author, Daniel J. Hruschka of the Santa Fe Institute, a research group that focuses on complex systems. “One is that you’re moving and you really need help, but your friend doesn’t return your call. Well, maybe he’s out of town, and it’s not a defection at all. The ability to overlook or forgive is a way to overcome these vicissitudes of everyday life.”

Nowhere do people use denial skills to greater effect than with a spouse or partner. In a series of studies, Sandra Murray of the University of Buffalo and John Holmes of the University of Waterloo in Ontario have shown that people often idealize their partners, overestimating their strengths and playing down their flaws.

This typically involves a blend of denial and touch-up work — seeing jealousy as passion, for instance, or stubbornness as a strong sense of right and wrong. But the studies have found that partners who idealize each other in this way are more likely to stay together and to report being satisfied in the relationship than those who do not.

“The evidence suggests that if you see the other person in this idealized way, and treat them accordingly, they begin to see themselves that way, too,” Dr. Murray said. “It draws out these more positive behaviors.”

Faced with the high odor of real perfidy, people unwilling to risk a break skew their perception of reality much more purposefully. One common way to do this is to recast clear moral breaches as foul-ups, stumbles or lapses in competence — because those are more tolerable, said Dr. Kim, of U.S.C. In effect, Dr. Kim said, people “reframe the ethical violation as a competence violation.”

She wasn’t cheating on him — she strayed. He didn’t hide the losses in the subprime mortgage unit for years — he miscalculated.

This active recasting of events, built on the same smaller-bore psychological tools of inattention and passive acknowledgment, is the point at which relationship repair can begin to shade into willful self-deception of the kind that takes on a life of its own. Everyone knows what this looks like: You can’t talk about the affair, and you can’t talk about not talking about it. Soon, you can’t talk about any subject that’s remotely related to it.

And the unstated social expectations out in the world often reinforce the conspiracy, no matter its source, said Eviatar Zerubavel, a sociologist at Rutgers and the author of “The Elephant in the Room: Silence and Denial in Everyday Life.”

“Tact, decorum, politeness, taboo — they all limit what can be said in social domains,” he said. “I have never seen tact and taboo discussed in the same context, but one is just a hard version of the other, and it’s not clear where people draw the line between their private concerns and these social limits.”

In short, social mores often work to shrink the space in which a conspiracy of silence can be broken: not at work, not out here in public, not around the dinner table, not here. It takes an outside crisis to break the denial, and no one needs a psychological study to know how that ends.

In Ms. Farrington’s case, the event was a move out of the country for her husband’s job. Unable to earn much money from her own work, she kept buying but had no way to cover the credit card payments.

“Basically,” she said, “I had to fess up. It was terrible, but I fessed up to my husband, I fessed up to my mother and to another friend who was getting the bills while I was away. This whole web of intrigue, and in the end it just had to crash.” She now hunts for better bargains on eBay.

Use It or Lose It: Why Language Changes over Time

More commonly used words are the least likely to evolve

dictionary

CONSTANTLY EVOLVING: Two new studies show the words in a language that are used infrequently are subject to change rapidly over time.

The words used the most in everyday language are the ones evolving at the slowest rate, say two new studies published in Nature.

In one paper, researchers at Harvard University focused on the evolution of English verb conjugations over a 1,200-year period. In a separate study, a team at the University of Reading in England reviewed cognates (similar sounding words in different languages for the same object or meaning, such as "water" and the German "wasser") to determine how all Indo-European tongues progressed from a common ancestor that existed between 6,000 and 10,000 years ago.

"What our frequency effect allows us to do is identify…ultraconserved linguistic elements," says Mark Pagel, an evolutionary biology professor at Reading, about his research. "Namely, they're the words we use all the time."

In their search for cognates, Pagel and his team examined some 200 words in 87 Indo-European languages, including those for "water," "two," "to die" and "where." The number of distinct classes of cognates for each word ranged from one (indicating all the words sound similar) for frequently used concepts such as numbers to as many as 46 different basic sounds to describe a single entity such as a bird. The word for the number three in all Indo-European languages, for instance, is similar to the English version: from tres in Spanish to drei in German to the Hindi theen. In contrast, the word for bird has several different sounds associated with it like pajaro in Spanish and oiseau in French.

The researchers then narrowed their focus to the frequency of use of each of the words in just four Indo-European languages—English, Spanish, Greek and Russian. Pagel says the team found that they were used at similar rates across the board even if the words with the same meaning were not cognates. "The high frequency words in Spanish are the same as the high frequency English," he says. "That [indicated] that we could come up with a kind of Indo-European frequency of use."

By combining their data, the researchers determined that it would take as little as 750 years to replace less-used words and up to 10,000 years for new words to evolve in place of the most frequently used ones.

The Harvard researchers specifically studied the roots of English, tracing verb conjugations in the language from the time of Beowulf 1,200 years ago through Shakespeare in the 16th century to its current form. Over the years, several past tense forms of verbs have died out in English and now only one persists as a rule: adding "-ed" to the end of verbs. (Verbs that end in "-ed" in their past tense form "regular verbs" in modern English.)

Researchers scoured grammatical texts dating back to the days of Old English, cataloguing all the irregular verbs they came across. Among them: the still irregular "sing" / "sang," "go" / "went" as well as the since-regularized "smite" which once was "smote" in Old English but since has become "smited," and "slink," which is now "slinked" but 1,200 years ago was "slunk." They located 177 verbs that were irregular in Old English and 145 that were still irregular in Middle English; today, only 98 of the 177 verbs have not been "regularized.'"

After calculating the frequency of use of each of the 177 irregular Old English verbs, researchers determined that the words that evolved most quickly into regular conjugational forms were used significantly less than those that went unchanged over time. In fact, their statistical analysis determined that given two verbs, if one was used 100 times less frequently than the other, it would evolve 10 times faster than the verb employed more often. They predict the next verb to fall into line will be wed, the past tense of which will regularize from wed to wedded.

By being more frequent, a verb is more stable," says study co-author Erez Lieberman, a graduate student in applied mathematics at Harvard University. He adds that both the Harvard and Reading papers lay out a case for a version of natural selection that acts on linguistic evolution and mirrors biological evolution. "Both studies," he says, "illustrate this profound effect that frequency has in the survival of a word."

Partha Niyogi, author of the book The Computational Nature of Language Learning and Evolution and a professor of computer science and statistics at the University of Chicago, says these empirical findings are consistent with theoretical models on the lexical evolution. "Languages are constantly changing," he notes. "In biological evolution that fact has been given a lot of attention, but the fact is that in languages this is happening all the time, [as well]. Darwin in [The Descent of Man] commented that languages were evolving over time, and it was just like speciation." 

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