A mammoth is any species of the extinct genus Mammuthus, proboscideans commonly equipped with long, curved tusks and, in northern species, a covering of long hair. They lived from the Pliocene epoch (from around 5 million years ago) into the Holocene at about 4,500 years ago, and were members of the family Elephantidae, which contains, along with mammoths, the two genera of modern elephants and their ancestors.

A Like their modern relatives, mammoths were quite large. The largest known species reached heights in the region of 4 m at the shoulder and weights of up to 8 tonnes, while exceptionally large males may have exceeded 12 tonnes. However, most species of mammoth were only about as large as a modern Asian elephant. Both sexes bore tusks. A first, small set appeared at about the age of six months, and these were replaced at about 18 months by the permanent set. Growth of the permanent set was at a rate of about 2.5 to 15.2 cm per year. Based on studies of their close relatives, the modern elephants, mammoths probably had a gestation period of 22 months, resulting in a single calf being born. Their social structure was probably the same as that of African and Asian elephants, with females living in herds headed by a matriarch, whilst bulls lived solitary lives or formed loose groups after sexual maturity.

B MEXICO CITY – Although it’s hard to imagine in this age of urban sprawl and automobiles, North America once belonged to mammoths, camels, ground sloths as large as cows, bear-size beavers and other formidable beasts. Some 11,000 years ago, however, these large-bodied mammals and others – about 70 species in all – disappeared. Their demise coincided roughly with the arrival of humans in the New World and dramatic climatic change – factors that have inspired several theories about the die-off. Yet despite decades of scientific investigation, the exact cause remains a mystery. Now new findings offer support to one of these controversial hypotheses: that human hunting drove this megafaunal menagerie to extinction. The overkill model emerged in the 1960s, when it was put forth by Paul S. Martin of the University of Arizona. Since then, critics have charged that no evidence exists to support the idea that the first Americans hunted to the extent necessary to cause these extinctions. But at the annual meeting of the Society of Vertebrate Paleontology in Mexico City last October, paleoecologist John Alroy of the University of California at Santa Barbara argued that, in fact, hunting-driven extinction is not only plausible, it was unavoidable. He has determined, using a computer simulation, that even a very modest amount of hunting would have wiped these animals out.

C Assuming an initial human population of 100 people that grew no more than 2 percent annually, Alroy determined that if each band of, say, 50 people killed 15 to 20 large mammals a year, humans could have eliminated the animal populations within 1,000 years. Large mammals in particular would have been vulnerable to the pressure because they have longer gestation periods than smaller mammals and their young require extended care.

D Not everyone agrees with Alroy’s assessment. For one, the results depend in part on population-size estimates for the extinct animals – figures that are not necessarily reliable. But a more specific criticism comes from mammalogist Ross D. E. MacPhee of the American Museum of Natural History in New York City, who points out that the relevant archaeological record contains barely a dozen examples of stone points embedded in mammoth bones (and none, it should be noted, are known from other megafaunal remains) – hardly what one might expect if hunting drove these animals to extinction. Furthermore, some of these species had huge ranges – the giant Jefferson’s ground sloth, for example, lived as far north as the Yukon and as far south as Mexico – which would have made slaughtering them in numbers sufficient to cause their extinction rather implausible, he says.

E MacPhee agrees that humans most likely brought about these extinctions (as well as others around the world that coincided with human arrival), but not directly. Rather he suggests that people may have introduced hyperlethal disease, perhaps through their dogs or hitchhiking vermin, which then spread wildly among the immunologically naive species of the New World. As in the overkill model, populations of large mammals would have a harder time recovering. Repeated outbreaks of a hyperdisease could thus quickly drive them to the point of no return. So far MacPhee does not have empirical evidence for the hyperdisease hypothesis, and it won’t be easy to come by: hyperlethal disease would kill far too quickly to leave its signature on the bones themselves. But he hopes that analyses of tissue and DNA from the last mammoths to perish will eventually reveal murderous microbes.

F The third explanation for what brought on this North American extinction does not involve human beings. Instead its proponents blame the loss on the weather. The Pleistocene epoch witnessed considerable climatic instability, explains paleontologist Russell W. Graham of the Denver Museum of Nature and Science. As a result, certain habitats disappeared, and species that had once formed communities split apart. For some animals, this change brought opportunity. For much of the megafauna, however, the increasingly homogeneous environment left them with shrinking geographical ranges – a death sentence for large animals, which need large ranges. Although these creatures managed to maintain viable populations through most of the Pleistocene, the final major fluctuation – the so-called Younger Dryas event – pushed them over the edge, Graham says. For his part, Alroy is convinced that human hunters demolished the titans of the Ice Age. The overkill model explains everything the disease and climate scenarios explain, he asserts, and makes accurate predictions about which species would eventually go extinct. “Personally, I’m a vegetarian,” he remarks, “and I find all of this kind of gross – but believable.”

A How busy is too busy? For some it means having to miss the occasional long lunch; for others it means missing lunch altogether. For a few, it is not being able to take a “sickie” once a month. Then there is a group of people for whom working every evening and weekend is normal, and frantic is the tempo of their lives. For most senior executives, workloads swing between extremely busy and frenzied. The vice-president of the management consultancy AT Kearney and its head of telecommunications for the Asia-Pacific region, Neil Plumridge, says his work weeks vary from a “manageable” 45 hours to 80 hours, but average 60 hours.

B Three warning signs alert Plumridge about his workload: sleep, scheduling and family. He knows he has too much on when he gets less than six hours of sleep for three consecutive nights; when he is constantly having to reschedule appointments; “and the third one is on the family side”, says Plumridge, the father of a three-year-old daughter, and expecting a second child in October. “If I happen to miss a birthday or anniversary, I know things are out of control.” Being “too busy” is highly subjective. But for any individual, the perception of being too busy over a prolonged period can start showing up as stress: disturbed sleep, and declining mental and physical health. National workers’ compensation figures show stress causes the most lost time of any workplace injury. Employees suffering stress are off work an average of 16.6 weeks. The effects of stress are also expensive. Comcare, the Federal Government insurer, reports that in 2003-04, claims for psychological injury accounted for 7% of claims but almost 27% of claim costs. Experts say the key to dealing with stress is not to focus on relief – a game of golf or a massage – but to reassess workloads. Neil Plumridge says he makes it a priority to work out what has to change; that might mean allocating extra resources to a job, allowing more time or changing expectations. The decision may take several days. He also relies on the advice of colleagues, saying his peers coach each other with business problems. “Just a fresh pair of eyes over an issue can help,” he says.

C Executive stress is not confined to big organisations. Vanessa Stoykov has been running her own advertising and public relations business for seven years, specialising in work for financial and professional services firms. Evolution Media has grown so fast that it debuted on the BRW Fast 100 list of fastest-growing small enterprises last year – just after Stoykov had her first child. Stoykov thrives on the mental stimulation of running her own business. “Like everyone, I have the occasional day when I think my head’s going to blow off,” she says. Because of the growth phase the business is in, Stoykov has to concentrate on short-term stress relief – weekends in the mountains, the occasional “mental health” day – rather than delegating more work. She says: “We’re hiring more people, but you need to train them, teach them about the culture and the clients, so it’s actually more work rather than less.”

D Identify the causes: Jan Elsnera, Melbourne psychologist who specialises in executive coaching, says thriving on a demanding workload is typical of senior executives and other high-potential business people. She says there is no one-size-fits-all approach to stress: some people work best with high-adrenalin periods followed by quieter patches, while others thrive under sustained pressure. “We could take urine and blood hormonal measures and pass a judgment of whether someone’s physiologically stressed or not,” she says. “But that’s not going to give us an indicator of what their experience of stress is, and what the emotional and cognitive impacts of stress are going to be.”

E Eisner’s practice is informed by a movement known as positive psychology, a school of thought that argues “positive” experiences – feeling engaged, challenged, and that one is making a contribution to something meaningful – do not balance out negative ones such as stress; instead, they help people increase their resilience over time. Good stress, or positive experiences of being challenged and rewarded, is thus cumulative in the same way as bad stress. Elsner says many of the senior business people she coaches are relying more on regulating bad stress through methods such as meditation and yoga. She points to research showing that meditation can alter the biochemistry of the brain and actually help people “retrain” the way their brains and bodies react to stress. “Meditation and yoga enable you to shift the way that your brain reacts, so if you get proficient at it you’re in control.”

F The Australian vice-president of AT Kearney, Neil Plumridge, says: “Often stress is caused by our setting unrealistic expectations of ourselves. I’ll promise a client I’ll do something tomorrow, and then promise another client the same thing, when I really know it’s not going to happen. I’ve put stress on myself when I could have said to the clients: ‘Why don’t I give that to you in 48 hours?’ The client doesn’t care.” Over-committing is something people experience as an individual problem. We explain it as the result of procrastination or Parkinson’s law: that work expands to fill the time available. New research indicates that people may be hard-wired to do it.

G A study in the February issue of the Journal of Experimental Psychology shows that people always believe they will be less busy in the future than now. This is a misapprehension, according to the authors of the report, Professor Gal Zauberman, of the University of North Carolina, and Professor John Lynch, of Duke University. “On average, an individual will be just as busy two weeks or a month from now as he or she is today. But that is not how it appears to be in everyday life,” they wrote. “People often make commitments long in advance that they would never make if the same commitments required immediate action. That is, they discount future time investments relatively steeply.” Why do we perceive a greater “surplus” of time in the future than in the present? The researchers suggest that people underestimate completion times for tasks stretching into the future, and that they are bad at imagining future competition for their time.

James Paul Gee, professor of education at the University of Wisconsin-Madison, played his first video game years ago when his six-year-old son Sam was playing Pajama Sam: No Need to Hide When It’s Dark Outside. He wanted to play the game so he could support Sam’s problem solving. Though Pajama Sam is not an “educational game”, it is replete with the types of problems psychologists study when they study thinking and learning. When he saw how well the game held Sam’s attention, he wondered what sort of beast a more mature video game might be.

Video and computer games, like many other popular, entertaining and addicting kid’s activities, are looked down upon by many parents as time-wasters, and worse, parents think that these games rot the brain. Violent video games are readily blamed by the media and some experts as the reason why some youth become violent or commit extreme anti-social behavior. Recent content analyses of video games show that as many as 89% of games contain some violent content, but there is no form of aggressive content for 70% of popular games. Many scientists and psychologists, like James Paul Gee, find that video games actually have many benefits – the main one being making kids smart. Video games may actually teach kids high-level thinking skills that they will need in the future.

“Video games change your brain,” according to University of Wisconsin psychologist Shawn Green. Video games change the brain’s physical structure the same way as do learning to read, playing the piano, or navigating using a map. Much like exercise can build muscle, the powerful combination of concentration and rewarding surges of neurotransmitters like dopamine, which strengthens neural circuits, can build the player’s brain.

Video games give your child’s brain a real workout. In many video games, the skills required to win involve abstract and high level thinking. These skills are not even taught at school. Some of the mental skills trained by video games include: following instructions, problem solving, logic, hand-eye coordination, fine motor and spatial skills. Research also suggests that people can learn iconic, spatial, and visual attention skills from video games. There have been even studies with adults showing that experience with video games is related to better surgical skills. Jacob Benjamin, doctor from Beth Israel Medical Center NY, found a direct link between skill at video gaming and skill at keyhole or laparoscopic surgery. Also, a reason given by experts as to why fighter pilots of today are more skillful is that this generation’s pilots are being weaned on video games.

The players learn to manage resources that are limited, and decide the best use of resources, the same way as in real life. In strategy games, for instance, while developing a city, an unexpected surprise like an enemy might emerge. This forces the player to be flexible and quickly change tactics. Sometimes the player does this almost every second of the game giving the brain a real workout. According to researchers at the University of Rochester, led by Daphne Bavelier, a cognitive scientist, games simulating stressful events such as those found in battle or action games could be a training tool for real-world situations. The study suggests that playing action video games primes the brain to make quick decisions. Video games can be used to train soldiers and surgeons, according to the study. Steven Johnson, author of Everything Bad is Good For You: How Today’s Popular Culture, says gamers must deal with immediate problems while keeping their long-term goals on their horizon. Young gamers force themselves to read to get instructions, follow storylines of games, and get information from the game texts.

James Paul Gee, professor of education at the University of Wisconsin-Madison, says that playing a video game is similar to working through a science problem Like students in a laboratory, gamers must come up with a hypothesis. For example, players in some games constantly try out combinations of weapons and powers to use to defeat an enemy. If one does not work, they change hypothesis and try the next one. Video games are goal-driven experiences, says Gee, which are fundamental to learning. Also, using math skills is important to win in many games that involve quantitative analysis like managing resources. In higher levels of a game, players usually fail the first time around, but they keep on trying until they succeed and move on to the next level.

Many games are played online and involve cooperation with other online players in order to win. Video and computer games also help children gain self-confidence and many games are based on history, city building, and governance and so on. Such games indirectly teach children about aspects of life on earth.

In an upcoming study in the journal Current Biology, authors Daphne Bavelier, Alexandre Pouget, and C. Shawn Green report that video games could provide a potent training regimen for speeding up reactions in many types of real-life situations. The researchers tested dozens of 18- to 25-year-olds who were not ordinarily video game players. They split the subjects into two groups. One group played 50 hours of the fast-paced action video games “Call of Duty 2” and “Unreal Tournament,” and the other group played 50 hours of the slow-moving strategy game “The Sims 2.” After this training period, all of the subjects were asked to make quick decisions in several tasks designed by the researchers. The action game players were up to 25 percent faster at coming to a conclusion and answered just as many questions correctly as their strategy game playing peers.