Youth crimes and violence are【C1】_____out of the headlines. We are all shocked【C2】__another young person is【C3】__on our streets. And each of these personal tragedies【C4】__wider social problems that we are a long way from solving. For a college community, nothing is【C5】_____terrible than the death of a student. And every grieving family or devastated friend is an urgent plea for us to do something. We need to avoid simplistic or knee-jerk responses.

This complex problem can’t be【C6】_____to a single cause and won’t be【C7】__with a single solution. Contributory【C8】__include poverty and inequality; drugs; knife-carrying; the【C9】_____of guns; mental health issues; and the lack of constructive alternatives.

So what can be done? There are no quick【C10】_____. This is a national problem that requires action at every 【C11】__of society. Young people need to be at the heart of any response, and colleges can help to【C12】__them. For example, the Student Commission on Knife Crime in London has【C13】__an impressive manifesto for change. Adults need to be【C14】__in young people’s lives. We cannot give【C15】__anyone. Those drawn into criminality or violence are also victims. They need support to【C16】__a way out and start making a positive contribution. We must also【C17】__in young people. Over the past decade, public spending on youth provision has been【C18】__cut. With more resources, we could show young people that they are a precious and valued part of society,【C19】__a problem to be managed. Colleges and schools have a role to play in a coordinated multi-agency response—one that is long-term and【C20】_____.

What’s a man? Or, indeed, a woman? Biologically, the answer might seem obvious. A human being is a(n)【C1】_____who has grown from a fertilised egg which【C2】__genes from both father and mother. A growing band of biologists,【C3】__. think this definition incomplete. They【C4】__people not just as individuals, but also as ecosystems. In their view, the descendant of the fertilised egg is【C5】__one component of the system. The others are trillions of bacteria, each equally an individual,【C6】_____are found in a person’s gut, his mouth, his skin and all of the crevices and orifices that exist in his body’s surface.

A【C7】_____adult human harbours some 100 trillion bacteria in his gut alone. That is ten times as many bacterial cells as he has cells【C8】__from the sperm and egg of his parents. These bugs, moreover, are【C9】__. Egg and sperm provide about 23,000 different genes. The microbiome, as the body’s commensal bacteria are collectively known, is reckoned to have around 3 million.【C10】__, many of those millions are variations on common themes, but equally many are not, and even the number of【C11】_____that are adds something to the body’s genetic mix.

And it really is a system, for evolution has【C12】_____the interests of host and bugs. In exchange for raw materials and shelter the microbes that live in and【C13】__people feed and protect their hosts, and are thus integral to that host’s well-being. Neither wishes the other harm. In bad【C14】__, though, this alignment of interest can【C15】_____. Then, the microbiome may misbehave in ways which cause disease.

That bacteria can cause disease is no【C16】_____. But the diseases in question are. Often, they are not acute infections of the【C17】__20th-century medicine has been so good at dealing with. They are, rather, the chronic illnesses that are now,【C18】__in the rich world, the main focus of medical attention.【C19】__, from obesity and diabetes, via heart disease and asthma to neurological conditions such as autism, the microbiome seems to play a(n)【C20】_____role.