As a society we might want to rethink the time and money spent on education, so that these resources can benefit a greater percentage of the population. Ideally, both high schools and colleges can prepare individuals for the ever-changing roles that are likely to be expected of them.

High school degrees offer less in the way of preparation for work than they might, or than many other nations currently offer, creating a growing skills gap in our economy. We encourage students to go on to college whether they are prepared or not, or have a clear sense of purpose or interest, and now have the highest college dropout rate in the world.

We might look to other countries for models of how high schools can offer better training, as well as the development of a work ethic (勤奋工作的美德) and the intellectual skills needed for continued learning and development. I recommend Harvard’s 2011 “Pathways to Prosperity” report for more attention to the “forgotten half” (those who do not go on to college) and ideas about how to address this issue.

Simultaneously, the liberal arts become more important than ever. In a knowledge economy where professional roles change rapidly and many college students are preparing for positions that may not even exist yet, the skill set needed is one that prepares them for change and continued learning.

Learning to express ideas well in both writing and speech, knowing how to find information, and knowing how to do research are all-solid background skills for a wide variety of roles, and such training is more important than any particular major in a liberal arts college. We need to continue to value broad preparation in thinking skills that will serve for a lifetime.

Students also need to learn to work independently and to make responsible decisions. The lengthening path to adulthood appears exacerbated (恶化) by parental involvement in the college years. Given the rising investment in college education, parental concern is not surprising, but learning where and when to intervene will help students take more ownership of the outcomes of these increasingly costly educations.

Have you ever wondered how an ecosystem functions? Why do there exist so many mosquitoes and so few tigers? What makes the numbers of diverse species? Now scientists have figured out mathematical models of food webs, noting who eats whom and how much each one eats.

Drawing upon the models, scientists have discovered some key principles operating in food webs. Most food webs, for instance, consist of many weak links rather than a few strong ones. When a predator (掠食动物) always eats huge numbers of a single prey (猎物), the two species are strongly linked; when a predator lives on various species, they are weakly linked. Food webs may be dominated by many weak links because that arrangement is more stable over the long term. If a predator can eat several species, it can survive the extinction of one of them. And if a predator can move on to another species that is easier to find when a prey species becomes rare, the switch allows the original prey to recover. The weak links may thus keep species from driving on another to extinction.

Mathematical models have also revealed that food webs may be unstable, where small changes of top predators can lead to big effects throughout entire ecosystems. In the 1960s, scientists proposed that predators at the top of a food web had a surprising amount of control over the size of populations of other species — including species they did not directly attack.

And unplanned human activities have proved the idea of top-down control by top predators to be true. In the ocean, we fished for predators such as cod on an industrial scale, while on land, we killed off large predators such as wolves. These actions have greatly affected the ecological balance.

Scientists have built an early-warning system based on mathematical models. Ideally, the system would tell us when to adapt human activities that are pushing an ecosystem toward a breakdown or would even allow us to pull an ecosystem back from the borderline. Prevention is key, scientists say because once ecosystems pass their tipping point (临界点), it is remarkably difficult for them to return.