In the early 1960s Wilt Chamberlain was one of only three players in the National Basketball Association (NBA)listed at over seven feet. If he had played last season, however, he would have been one of 42. The bodies playing major professional sports have changed dramatically over the years, and managers have been more than willing to adjust team uniforms to fit the growing numbers of bigger, longer frames.

The trend in sports, though, may be obscuring an unrecognized reality: Americans have generally stopped growing. Though typically about two inches taller now than 140 years ago, today's people-especially those born to families who have lived in the U. S. for many generations-apparently reached their limit in the early 1960s. And they aren't likely to get any taller. "In the general population today, at this genetic, environmental level, we've pretty much gone as far as we can go," says anthropologist William Cameron Chum-lea of Wright State University. In the case of NBA players, their increase in height appears to result from the increasingly common practice of recruiting players from all over the world.

Growth, which rarely continues beyond the age of 20, demands calories and nutrients-notably, protein--to feed expanding tissues. At the start of the 20th century, under-nutrition and childhood infections got in the way. But as diet and health improved, children and adolescents have, on average, increased in height by about an inch and a half every 20 years, a pattern known as the secular trend in height. Yet according to the Centers for Disease Control and Prevention, average height--5 '9" for men, 5'4" for women--hasn't really changed since 1960.

Genetic maximums can change, but don't expect this to happen soon. Claire C. Gordon, senior anthropologist at the Army Research Center in Natick, Mass ensures that 90 percent of the uniforms and workstations fit recruits without alteration. She says that, unlike those for basketball, the length of military uniforms has not changed for some time. And if you need to predict human height in the near future to design a piece of equipment, Gordon says that by and large, "you could use today's data and feel fairly confident."

AL's friend Rachel invited him to go to the lake for the day with her family. Rachel really hoped he'd say yes.

AL turned Rachel down. 【小题1】 He worried that her family and others at the lake would see what he saw when he looked in the mirror a strange excuse for a man.

The truth about guys.

Many people think of guys as being carefree when it comes to their appearance. 【小题2】Guys might think that they shouldn't worry about how they look, but body image can be a real problem for them. Unlike girls, guys are less likely to talk to friends and relatives about their bodies and how they're developing. Without support from friends and family, they may develop a negative self-image.

Why is body image important?

Body image is a person's opinions, thoughts, and feelings about his or her own body and physical appearance. 【小题3】 Body image is part of someone’s total self-image. So how a guy feels about his body can affect how he feels about himself. If he gets too focused on not liking the way he looks, a guy's selfesteem can take a hit.

How does puberty （青春期）affect body image?

Although body image is just one part of our self-image, during the teen years, and especially during puberty, it can be easy for a guy's whole self-image to be based on how his body looks.

【小题4】

It could be in your genes （基因）.

Lots of guys can have high expectations for puberty, thinking they'll develop quickly or in a certain way. 【小题5】 You can look at your uncles, grandfathers, and even female relatives, to get an idea of the kinds of choices your genes may have in store for you.

Why should mankind explore space? Why should money, time and effort be spent exploring and researching something with so few apparent benefits? Why should resources be spent on space instead of on conditions and people on Earth? These are questions that, understandably, are very often asked.

Perhaps the best answer lies in our genetic makeup as human beings. What drove our ancestors to move from the trees into the plains, and on into all possible areas and environments? With the wide spread of a species, human beings can get high chance of survival. Perhaps the best reason for exploring space is this genetic tendency to expand wherever possible.

Nearly every successful civilization has explored, because by doing so, any dangers in surrounding areas can be identified and prepared for. Without knowledge, we may be completely destroyed by the danger. With knowledge, we can lessen its effects.

Exploration also allows minerals and other potential resources to be found. Even if we have no need of them right now, they will perhaps be useful later. Resources may be more than physical possessions. Knowledge or techniques have been acquired through exploration. The techniques may have medical applications which can improve the length or quality of our lives. We have already benefited from other spinoffs including improvements in earthquake prediction, in satellites for weather forecasting and in communications systems. Even nonstick pans and mirrored sunglasses are byproducts of technological developments in the space.

While many resources are spent on what seems a small return, the exploration of space allows creative, brave and intelligent members of our species to focus on what may serve to save us. While space may hold many wonders and explanations of how the universe was formed or how it works, it also holds dangers. The danger exists, but knowledge can help human beings to survive. Without the ability to reach out across space, the chance to save ourselves might not exist.

While Earth is the only planet known to support life, surely the adaptive ability of humans would allow us to live on other planets. It is true that the lifestyle would be different, but human life and cultures have adapted in the past and surely could in the future.