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Which of your hands do you use most?Very few of us both use both of our hands well．Most of us are right-handed．Only about five people out of a hundred are left-handed．New-born babies can take things with either of their hands, but in about two years they like to use their right hands．Scientists don’t know why this happens．They have studied it．They think our animal ancestors(祖先)were right-handed, but this may not be true．Monkeys are our closest relations in the animal world．Scientists have found that monkeys like to use one of their hands more than the other．But it can be either hand．Next time you visit the zoo, watch the monkeys carefully．You’ll see that some of them will swing with their right hands and others will use their left hands．But most human-beings use their right hands better, and most things are designed for the right-handed people．This makes life difficult for the left-handed ones．

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　　Sharks frighten most of us, but Daniel Weaver, a shark scientist, swims with them for a living! We asked him some questions about this unusual job．

　　So Daniel, what’s it like to be a shark scientist?

　　Well, it’s a great job．I often travel to faraway places like South Africa and Fiji to study sharks．On the other hand, a shark scientist sometimes does boring desk work, such as writing reports．Also, shark scientists don’t usually get paid a lot．

　　What qualities(品质)do you need to become a shark scientist?

　　Shark scientists need to be wise and strong．They enjoy working outdoors and they have to be cool and patient(耐心)．They also have to be quite brave!

　　So do you think it’s a dangerous job?

　　Well, sharks have up to 15 rows of sharp teeth．However, sharks hardly attack(攻击)humans．There are over 350 kinds of sharks in the world and only about 10 are dangerous to us．In fact, dogs kill more people every year than sharks! Humans kill over 12 million sharks a year for food and sport!

　　How do you become a shark scientist?

　　A shark scientist usually studies Marine Science or Zoology at university．It’s also good to get some work experience in an aquarium(水族馆)．In my opinion, I have the best job in the world!

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　　Jeanne Calment took up skating at age 85, made her first movie appearance at age114．and held a concert in the neighborhood on her 121 st birthday．

　　When it comes to long life, Jeanne Calment is the world’s recordholder．She lived to the ripe old age of 122．So is 122 the upper limit(限制)to the human life span(寿命)?If scientists come up with some sort of pill or diet that would slow aging, could we possibly make it to 150－or beyond?

　　Researchers don't entirely agree on the answers．“Calment lived．to 122, SO it wouldn't sul33rise me if someone alive today reaches 130 or 135,”says Jerry Shay at the University of Texas．

　　Steve Austad at the University of Texas agrees．“People can live longer than we think．”he says．“Experts used to say that humans couldn’t live past 110．When Calment blew past that age, they raised the number to 1 20．So why can’t we go higher?”

　　The trouble with guessing how old people can live to be is that it’s all just guessing．“Anyone can make up a number．”says Rich Miller at the University, of guessing

　　　Michigan．“Usually the scientist who picks the highest number gets his name in Time magazine．”

　　Won’t new anti－aging techniques keep us alive for centuries?Any cure, says Miller, for aging would probably keep most of HS living until about 120．Researchers are working on treatments that make the life span of mice longer by 50 percent at most．

　　So, if the average(平均)human life span is about 80 years, says Miller,“adding another 50 percent would get you to 120．”

　　So what can we learn from this little disagreement among the researchers?That life span is flexible(有弹性的), but there is a limit, says George Martin of the University of Washington．“We can get flies to live 50 percent longer．”he says．“But a fly'snever going to live 150 years．”Of course, if you became a new species(物种), one that ages at a slower speed, that would be a different story, he adds．

　　Does Martin really believe that humans could evolve(进化)their way to longer life?“It’s pretty cool to think about．”He says with a smile．

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