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Did you hear? The genome of the banana has been sequenced, an important development in scientist's efforts to produce better bananas. 

A look at that genome has revealed curious things, said Pat Heslop-Harrison, a plant geneticist at the University of Leicester in England who was a coauthor of the report published this week in the journal Nature. 

For example, there are regions of the banana genome that don't seem to be involved in making proteins but are shared by many different species of plants, far beyond bananas. What, he wonders, are they doing? 

There are remnants of bits of banana streak virus spliced into the banana genome (too broken-up to cause disease, however). 

There are whole sets of DNA repeats that plants normally have but bananas do not. And, intriguingly, three times since this genus of giant herbs took an evolutionary turn away from its relatives -- the grasses -- it has duplicated its entire set of chromosomes. 

Two of the doublings took place at the Cretaceous-Tertiary boundary 65 million years ago, back when the dinosaurs and lots of other species went extinct, Heslop-Harrison noted. 

Duplications like this are known to have happened in other plant groups at this same time but haven't occurred since, Heslop-Harrison said. Scientists don't know why, but they believe having extra copies of genes may have imparted some stability to plants during a time of rapid climate change after an asteroid hit Earth.

Having more than one gene of each type means that if one gene of a set loses function, the plant still has another one that works. And there's more room for adaptability to new circumstances, because one gene could be altered and co-opted for new purposes and there would still be the other one left to perform the original job. 

"Perhaps it's the reason [bananas have] done so well in the subsequent millions of years," Heslop-Harrison said. "One can ask, will changes occurring in the world's climate now mean there's going to be a whole set of new genome duplications that will enable plants to survive? We don't know that, but it's interesting to consider." 

The banana genome sequenced by the French scientists was from the Pahang, a wild Malaysian banana of the species Musa acuminata. It's a key species in the complicated evolution of the bananas and plantains people eat around the world, including the Cavendish banana that we buy at the supermarket. 

The sterile Cavendish is a so-called triploid: It has three sets of chromosomes instead of the normal two. One of those genomes came from Pahang. The others came from other subspecies of Musa acuminata. 

The changes occurred stepwise, and went something like this:
  • Thousands of years ago, two wild banana species from different parts of the islands of Southeast Asia were brought into the same range by people. They formed hybrids. A bit like mules, the hybrids were vigorous but fairly sterile.
  • The hybrids were kept going without through propagation of their shoots.
  • At some point, the hybrids developed the ability to set fruit without being fertilized.
  • Then (for most bananas, including the Cavendish) came another chance event that caused the hybrids to end up with three sets of chromosomes. Every now and again, the few viable eggs and pollen that they made would mistakenly contain two sets of chromosomes instead of just one.



When a double-chromosome pollen combined with a single-chromosome egg (or vice versa), the result was a hopelessly sterile plant with even more vigorous fruit.

Events like this happened more than once and sometimes included other types of ancestral banana species. 

Some scientists, in fact, have made a whole study of banana domestication and movement around the world. They've pieced the story together using quite different strands of information, including the genomes of wild and cultivated bananas, the microscopic relics of banana leaf material found at archaeological sites, and even the word for "banana" in different languages. 
ادامه مطلب


Map of Eurasia

Pastoralism is a lifestyle in which economic activity is based primarily on livestock. Archaeological evidence suggests that by 3,000 B.C., and perhaps even earlier, there had emerged on the steppes of Inner Eurasia the distinctive types of pastoralism that were to dominate the region’s history for several millennia. Here, the horse was already becoming the animal of prestige in many regions, though sheep, goats, and cattle could also play a vital role. It is the use of horses for transportation and warfare that explains why Inner Eurasian pastoral-ism proved the most mobile and the most militaristic of all major forms of pastoral-ism. The emergence and spread of pastoral-ism had a profound impact on the history of Inner Eurasia, and also, indirectly, on the parts of Asia and Europe just outside this area. In particular, pastoral-ism favors a mobile lifestyle, and this mobility helps to explain the impact of pastoralist societies on this part of the world.

 

The mobility of pastoralist societies reflects their dependence on animal-based foods. While agriculturalists rely on domesticated plants, pastoralists rely on domesticated animals. As a result, pastoralists, like carnivores in general, occupy a higher position on the food chain. All else being equal, this means they must exploit larger areas of land than do agriculturalists to secure the same amount of food, clothing, and other necessities. So pastoralism is a more extensive lifeway than farming is. However, the larger the terrain used to support a group, the harder it is to exploit that terrain while remaining in one place. So, basic ecological principles imply a strong tendency within pastoralist lifeways toward nomadism (a mobile lifestyle). As the archaeologist Roger Cribb puts it, The greater the degree of pastoralism, the stronger the tendency toward nomadism.” A modern Turkic nomad interviewed by Cribb commented: The more animals you have, the farther you have to move.”

 

Nomadism has further consequences. It means that pastoralist societies occupy and can influence very large territories. This is particularly true of the horse pastoralism that emerged in the Inner Eurasian steppes, for this was the most mobile of all major forms of pastoralism. So, it is no accident that with the appearance of pastoralist societies there appear large areas that share similar cultural, ecological, and even linguistic features. By the late fourth millennium B.C., there is already evidence of large culture zones reaching from Eastern Europe to the western borders of Mongolia. Perhaps the most striking sign of mobility is the fact that by the third millennium B.C., most pastoralists in this huge region spoke related languages ancestral to the modern Indo-European languages. The remarkable mobility and range of pastoral societies explain, in part, why so many linguists have argued that the Indo-European languages began their astonishing expansionist career not among farmers in Anatolia (present-day Turkey), but among early pastoralists from Inner Eurasia. Such theories imply that the Indo-European languages evolved not in Neolithic (10,000 to 3,000 B.C.Anatolia, but among the foraging communities of the cultures in the region of the Don and Dnieper rivers, which took up stock breeding and began to exploit the neighboring steppes. 

Nomadism also subjects pastoralist communities to strict rules of portability. If you are constantly on the move, you cannot afford to accumulate large material surpluses. Such rules limit variations in accumulated material goods between pastoralist households (though they may also encourage a taste for portable goods of high value such as silks or jewelry). So, by and large, nomadism implies a high degree of self-sufficiency and inhibits the appearance of an extensive division of labor. Inequalities of wealth and rank certainly exist, and have probably existed in most pastoralist societies, but except in periods of military conquest, they are normally too slight to generate the stable, hereditary hierarchies that are usually implied by the use of the term class. Inequalities of gender have also existed in pastoralist societies, but they seem to have been softened by the absence of steep hierarchies of wealth in most communities, and also by the requirement that women acquire most of the skills of men, including, often, their military skills.


Humans are uniquely smart among all the other species on the planet.  We are capable of outstanding feats of technology and engineering.  Then why are we so prone to making mistakes?  And why do we tend to make the same ones time and time again?  When Primate Psychologist Laurie Santos from the Comparative Cognition Lab at Yale University posed this question to her team, they were thinking in particular of the errors of judgement which led to the recent collapse of the financial markets.   Santos came to two possible answers to this question.  Either humans have designed environments which are too complex for us to fully understand, or we are biologically prone to making bad decisions.

In order to test these theories, the team selected a group of Brown Capuchin monkeys.  Monkeys were selected for the test because, as distant relatives of humans, they are intelligent and have the capacity to learn.  However, they are not influenced by any of the technological or cultural environments which affect human decision-making.  The team wanted to test whether the Capuchin monkeys, when put into similar situations as humans, would make the same mistakes.

[A] Of particular interest to the scientists was whether monkeys would make the same mistakes when making financial decisions.  [B] In order to find out, they had to introduce the monkeys to money.  [C] The team distributed metal discs to the monkeys, and taught them that the discs could be exchanged with team-members for food. The monkeys soon cottoned on, and as well as learning simple exchange techniques, were soon able to distinguish 'bargains' – If one team-member offered two grapes in exchange for a metal disc and another team-member offered one grape, the monkeys chose the two-grape option.  [D] Interestingly, when the data about the monkey's purchasing strategies was compared with economist's data on human behavior, there was a perfect match.

So, after establishing that the monkey market was operating effectively, the team decided to introduce some problems which humans generally get wrong.  One of these issues is risk-taking.   Imagine that someone gave you $1000.  In addition to this $1000, you can receive either A) an additional $500 or B) someone tosses a coin and if it lands 'heads' you receive an additional $1000, but if it lands 'tails' you receive no more money.  Of these options, most people tend to choose option A.  They prefer guaranteed earnings, rather than running the risk of receiving nothing.  Now imagine a second situation in which you are given $2000.  Now, you can choose to either A) lose $500, leaving you with a total of $1500, or B) toss a coin; if it lands 'heads' you lose nothing, but if it lands 'tails' you lose $1000, leaving you with only $1000.  Interestingly, when we stand to lose money, we tend to choose the more risky choice, option B.  And as we know from the experience of financial investors and gamblers, it is unwise to take risks when we are on a losing streak.

So would the monkeys make the same basic error of judgement?  The team put them to the test by giving them similar options.  In the first test, monkeys had the option of exchanging their disc for one grape and receiving one bonus grape, or exchanging the grape for one grape and sometimes receiving two bonus grapes and sometimes receiving no bonus.  It turned out that monkeys, like humans, chose the less risky option in times of plenty.  Then the experiment was reversed.  Monkeys were offered three grapes, but in option A were only actually given two grapes.  In option B, they had a fifty-fifty chance of receiving all three grapes or one grape only.  The results were that monkeys, like humans, take more risks in times of loss.

The implications of this experiment are that because monkeys make the same irrational judgement that humans do, maybe human error is not a result of the complexity of our financial institutions, but is embedded in our evolutionary history.  If this is the case, our errors of judgement will be very difficult to overcome.  On a more optimistic note however, humans are fully capable of overcoming limitations once we have identified them.  By recognizing them, we can design technologies which will help us to make better choices in future.


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نتیجه من: 26 دقیقه، 8/9، 4/4

ادامه مطلب

No student of a foreign language needs to be told that grammar is complex.  By changing word sequences and by adding a range of auxiliary verbs and suffixes, we are able to communicate tiny variations in meaning.  We can turn a statement into a question, state whether an action has taken place or is soon to take place, and perform many other word tricks to convey subtle differences in meaning.  Nor is this complexity inherent to the English language.  All languages, even those of so-called 'primitive' tribes have clever grammatical components.  The Cherokee pronoun system, for example, can distinguish between 'you and I', 'several other people and I' and 'you, another person and I'.  In English, all these meanings are summed up in the one, crude pronoun 'we'.  Grammar is universal and plays a part in every language, no matter how widespread it is.  So the question which has baffled many linguists is - who created grammar?

At first, it would appear that this question is impossible to answer.  To find out how grammar is created, someone needs to be present at the time of a language's creation, documenting its emergence.  Many historical linguists are able to trace modern complex languages back to earlier languages, but in order to answer the question of how complex languages are actually formed, the researcher needs to observe how languages are started from scratch.  Amazingly, however, this is possible.

Some of the most recent languages evolved due to the Atlantic slave trade.  At that time, slaves from a number of different ethnicities were forced to work together under colonizer's rule.  Since they had no opportunity to learn each other's languages, they developed a make-shift language called a pidgin.  Pidgins are strings of words copied from the language of the landowner.  They have little in the way of grammar, and in many cases it is difficult for a listener to deduce when an event happened, and who did what to whom.  [A] Speakers need to use circumlocution in order to make their meaning understood.  [B] Interestingly, however, all it takes for a pidgin to become a complex language is for a group of children to be exposed to it at the time when they learn their mother tongue.  [C] Slave children did not simply copy the strings of words uttered by their elders, they adapted their words to create a new, expressive language.  [D] Complex grammar systems which emerge from pidgins are termed creoles, and they are invented by children.

Further evidence of this can be seen in studying sign languages for the deaf.  Sign languages are not simply a series of gestures; they utilize the same grammatical machinery that is found in spoken languages.  Moreover, there are many different languages used worldwide. The creation of one such language was documented quite recently in Nicaragua. Previously, all deaf people were isolated from each other, but in 1979 a new government introduced schools for the deaf.  Although children were taught speech and lip reading in the classroom, in the playgrounds they began to invent their own sign system, using the gestures that they used at home.  It was basically a pidgin.  Each child used the signs differently, and there was no consistent grammar.  However, children who joined the school later, when this inventive sign system was already around, developed a quite different sign language.  Although it was based on the signs of the older children, the younger children's language was more fluid and compact, and it utilized a large range of grammatical devices to clarify meaning.  What is more, all the children used the signs in the same way.  A new creole was born.

Some linguists believe that many of the world's most established languages were creoles at first.  The English past tense –ed ending may have evolved from the verb 'do'.  'It ended' may once have been 'It end-did'.  Therefore it would appear that even the most widespread languages were partly created by children.  Children appear to have innate grammatical machinery in their brains, which springs to life when they are first trying to make sense of the world around them.  Their minds can serve to create logical, complex structures, even when there is no grammar present for them to copy.


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