LONDON — IN the late 17th century, the Dutch naturalist Anton van Leeuwenhoek looked at his own dental plaque through a microscope and saw a world of tiny cells “very prettily a-moving.” He could not have predicted that a few centuries later, the trillions of microbes that share our lives — collectively known as the microbiome — would rank among the hottest areas of biology.

伦敦——17世纪后期，荷兰博物学家安东·范·列文虎克(Anton van Leeuwenhoek)用显微镜查看自己的牙菌斑时，看到了一大群“非常可爱地动来动去的”微小细胞。他没有预见到，几个世纪后，与我们共存的数以万亿计的微生物——统称为微生物群落——将跻身生物学研究中最热门领域的行列。

These microscopic partners help us by digesting our food, training our immune systems and crowding out other harmful microbes that could cause disease. In return, everything from the food we eat to the medicines we take can shape our microbial communities — with important implications for our health. Studies have found that changes in our microbiome accompany medical problems from obesity to diabetes to colon cancer.

这些微小的伙伴帮助我们消化食物，锻炼我们的免疫系统，并清除其他可能致病的有害微生物。反过来，我们摄取的从食物到药物的各种东西，都可能会改变身体内的微生物群落——这对我们的健康存在重大影响。研究发现，微生物群落的变化，伴随着从肥胖症到糖尿病再到结肠癌等各种健康问题。

As these correlations have unfurled, so has the hope that we might fix these ailments by shunting our bugs toward healthier states. The gigantic probiotics industry certainly wants you to think that, although there is little evidence that swallowing a few billion yogurt-borne bacteria has more than a small impact on the trillions in our guts. The booming genre of microbiome diet books — self-help manuals for the bacterial self — peddles a similar line, even though our knowledge of microbe-manipulating menus is still in its infancy.

随着这些相关关系的明朗，人们也希望，通过引导体内微生物向更加健康的状态发展，我们或许可以治疗这些疾病。庞大的益生菌行业当然希望你会这么想，虽然没有多少证据表明，吞下酸奶中的数十亿细菌，对我们肠道中数以万亿的微生物群落有多大影响。蓬勃发展的微生物群落减肥食谱——细菌自己的自救手册——也在宣扬类似的口号，即使我们对饮食影响微生物的了解才刚刚起步。

This quest for a healthy microbiome has led some people to take measures that are far more extreme than simply spooning up yogurt. In September, the archaeology writer Jeff Leach used a turkey baster to infuse his guts with the feces of a Hadza tribesman from Tanzania. Doctors have carried out hundreds of fecal transplants, particularly to treat people with unshakable infections of the diarrhea-causing bacterium Clostridium difficile. The procedure has been spectacularly successful, far more than conventional antibiotics.

由于想拥有健康的微生物群落，一些人采取了远比喝酸奶更加极端的做法。今年9月，考古故事作家杰夫·利奇(Jeff Leach)使用一支滴管，把坦桑尼亚哈扎(Hadza)部落成员的粪便注入自己的肠道。医学界已经进行了数以百次的粪便移植，特别是在患者感染了难以去除的导致腹泻的艰难梭菌(Clostridium difficile)时。该疗法成效显著，远远超过了传统的抗生素。

But Mr. Leach did not have C. difficile. He experimented on himself because he views the Western microbiome as “a hot microbial mess,” he wrote on his blog. Poor diets, antibiotics and overly sanitized environments have gentrified the Western gut, he wrote, “potentially dragging us closer to ill health.” The Hadza, with their traditional hunter-gatherer lifestyle, carry diverse microbial communities that are presumably closer to a healthier and disappearing ideal. Hence the stunt with the turkey baster. Mr. Leach billed it as “(re)becoming human.”

可是，利奇并没有感染艰难梭菌。他在博客上写道，之所以在自己身上做尝试，是因为他认为西方人的微生物群落“乱七八糟”。糟糕的饮食、抗生素的使用和过度消毒的环境让西方人的肠道娇生惯养，他写道，“可能让我们更接近于不健康。”由于保持着传统的狩猎采集生活方式，哈扎人有多样的微生物群落，想必处于正在逐步消失的更加健康的理想状态。因此，他用滴管做了这个惊人尝试。利奇标榜此举是“（重新）变成人类”。

This reasoning is faulty. It romanticizes our relationships with our microbes, painting them as happy partnerships that were better off in the good old days. It also invokes an increasingly common trope: that there is a “normal” or “healthy” microbiome that one should aim for. There is not. The microbiome is complex, varied, ever changing and context-dependent — qualities that are the enemies of easy categorization.

这种思路是错误的。它把我们与微生物之间的关系浪漫化了，将其描绘成快乐的伙伴关系，而在美好的往昔，这种关系更加和睦友好。此外它还蕴含着一个越来越流行的主题：世界上存在着一种“正常”或“健康”的微生物群落，人们应该去追求它。其实这根本就不存在。微生物群落很复杂多样、不断变化、与环境密切相关——由于这些特质，它不能被简单地分门别类。

“Healthy” microbes can easily turn rogue. Those in our guts are undoubtedly helpful, but if they cross the lining of the intestine and enter our bloodstream, they can trigger a debilitating immune response. The same microbes can be beneficial allies or dangerous threats, all for the difference of a few millimeters.

“健康”微生物也能摇身变成祸害。我们肠道中的微生物无疑很有益处，但如果它们穿过肠壁，进入血液，就可能触发一种使人生病的免疫反应。同样一群微生物既可以是有益的盟友，也可以是危险的威胁，相差不过是毫厘之间。

Conversely, “unhealthy” configurations of microbes can be normal, even necessary. Ruth E. Ley at Cornell University and colleagues demonstrated this in dramatic fashion when they found that microbiomes go through a huge upheaval by the third trimester of pregnancy. They end up looking like the microbiomes of people with metabolic syndrome — a disorder that involves obesity, high blood sugar and a higher risk of diabetes and heart disease. These communities might indicate someone on the verge of chronic disease — or merely motherhood. Packing fat and building up blood sugar makes sense when you are nourishing a growing fetus.

相反的，“不健康”的微生物配置可以是正常的，甚至必要的。康奈尔大学(Cornell University)的露丝·E·雷(Ruth E. Ley)和她的同事们，惊人地展示了这一点。他们发现，孕妇的微生物群落会在妊娠晚期里经历翻天覆地的变化，其最后的状态会像代谢综合征患者一样。代谢综合征常常伴随着肥胖、高血糖，而病人患糖尿病和心脏病的风险也会提高。这些微生物可能显示人快患上了慢性病，也可能表示快当妈妈了——在滋养一个不断成长的胎儿时，堆积脂肪、提高血糖是十分合理的。

Here is another example. Common medical wisdom says that healthy vaginal microbiomes are dominated by the acid-making Lactobacillus group that creates an inhospitable environment for disease-causing microbes. But Larry J. Forney at the University of Idaho and colleagues found that a quarter of women didn’t fit this pattern, despite being perfectly healthy. They also showed that their vaginal communities can change dramatically and rapidly, even over a single day, flitting in and out of states that are supposedly conducive to disease, but with neither clear causes nor ill effects.

还有另一个例子。医学界通常认为，健康的阴道微生物群落，主要由制造酸性环境的乳杆菌(Lactobacillus)组成，从而创造一个不适宜致病微生物存活的环境。然而，爱达荷大学(University of Idaho)的拉里·J·福尼(Larry J. Forney)和同事们却发现，有四分之一的女性不符合这种情况，尽管她们都很健康。这些研究对象还显示出，她们的阴道菌群可能会非常剧烈地迅速变化，甚至同一天内都会这样变化，时而处在人们以为容易患病的状态，时而不然，但是既找不到明确的原因，也没有产生致病效果。

If you tried to determine a woman’s health by analyzing her vaginal microbes, the results would be hard to interpret and might be outdated by the time they arrived.

如果你试图通过分析阴道微生物来判断一名女性的健康状况，结果恐怕会很难判读，而且等到分析结果出来，情况可能已经变了。

This befuddling complexity is not confined to the vagina. Earlier this year, Patrick D. Schloss at the University of Michigan analyzed microbes from 18 different body parts on 300 volunteers. They were all healthy, with nary a dental cavity among them. And yet, Dr. Schloss found that their microbes varied greatly, and flipped between different states, for as yet inexplicable reasons.

这种让人困惑的复杂性并不限于阴道。今年早些时候，密歇根大学(University of Michigan)的帕特里克·D·施洛斯(Patrick D. Schloss)分析了300名志愿者18个不同部位的微生物群落。他们都很健康，连龋齿都没有。然而施洛斯却发现，他们身上带有的微生物差异巨大，而且会在不同的状态之间交替变化，而其中的原因尚无法解释。

The dynamic nature of the microbiome partly explains the enthusiasm that surrounds it. If scientists identify changes in the human genome that increase the risk of disease, it is hard to rewrite those genes or to find drugs that target them. But the microbiome could theoretically be altered through probiotics, fecal transplants or other means. It is, as some researchers say, the only “organ” that can be replaced without surgery.

微生物群落多变的性质部分解释了为什么人们对它产生了这么大的兴趣。就算科学家认定人类基因的变异可能会提高疾病风险，也很难改写基因，或者找到靶向药物。然而，理论上微生物群落可以通过益生菌、粪便注入或其他手段来调节。就像一些研究人员所说的，它是不必做手术就可以更换的仅有的“器官”。

But how can you tell when it needs replacing? A bloom of C. difficile is an obvious problem, but most other communities are not so easily classified. The microbiome is a teeming collection of thousands of species, all constantly competing with one another, negotiating with their host, evolving, changing. While your genome is the same as it was last year, your microbiome has shifted since your last meal or sunrise.

但是怎么才能确定需要更换呢？艰难梭菌激增肯定是个问题，但其他多数菌群都没那么容易归类。微生物群落包含成千上万的物种，而且总是在相互竞争并与宿主来回过招，同时演化、变异。你的基因和去年是一样的，但从上一顿饭开始，或者从太阳升起时开始，你的微生物群落已经发生了变化。

We need to start thinking about it as an ecosystem, like a rain forest or grassland, with all the complexities that entails. And just as the gorillas and leopards of African forests differ from the wolves and moose of American ones, so, too, do microbiomes vary around the world.

我们应当开始把微生物群落理解成一个生态系统，比如一片雨林或草原，其中也具有类似的复杂性。就像非洲森林里的大猩猩和豹子，不同于美洲的狼和驼鹿，世界各地人体内的微生物群落也千差万别。

Take the Hadza. Their microbial roll call is longer than a Western one, with both omissions and additions. They are the only adult humans thus far sequenced who are devoid of Bifidobacteria — a supposedly “healthy” group that accounts for up to 10 percent of the microbes in Western guts. But they do carry unexpectedly high levels of Treponema, a group that includes the cause of syphilis.

哈扎部落就是一个例子。他们拥有的微生物种类的多样性超过西方人，不过具体组合各有千秋。在目前得到测序的人群中，他们是仅有的不带有比菲德氏菌(Bifidobacteria)的成年人。这个菌群通常被认为是“健康”的，西方人肠道中的微生物，就有至多10%属于这个种类。不过，哈扎人身上却带有很高水平的密螺旋体属(Treponema)细菌，而梅毒的病原体就归于这一属。

Is this menagerie worse than a Western one? Better? I suspect the answer is neither. It is simply theirs. It is adapted to the food they eat, the dirt they walk upon, the parasites that plague them. Our lifestyles are very different, and our microbes have probably adapted accordingly. Generations of bacteria can be measured in minutes; our genomes have had little time to adapt to modern life, but our microbiomes have had plenty.

这些菌群是比西方人体内的更好还是更糟？我猜想这两个答案都不正确，这只是他们独有的菌群而已，与他们的食物、他们踩过的土地、他们感染的寄生虫相适应。我们的生活方式十分不同，我们的微生物群落可能也相应地做出了适应。数代细菌的更迭可能只需要几分钟时间，我们的基因组根本来不及适应现代生活，但是我们的微生物群落却有充足的时间进行调适。

It may be that a Hadza microbiome would work equally well in an American gut, but incompatibilities are also possible. The conquistadors proved as much. As they colonized South America, they brought with them European strains of Helicobacter pylori, a stomach bacterium that infrequently causes ulcers and stomach cancer, and these European strains also displaced native American ones. This legacy persists in Colombia, where some communities face a 25-fold higher risk of stomach cancer, most likely due to mismatches between their ancestral genomes and their H. pylori strains.

或许哈扎人的微生物群落在美国人的肠道里也同样能运转，但也有可能不兼容。历史上的西班牙征服者就证明了这一点。他们殖民南美洲之时，携带来了欧洲变种的幽门螺杆菌(Helicobacter pylori)，胃部的这种细菌会不太频繁地引起溃疡和胃癌。而且这些欧洲变种的细菌，也取代了美洲原生的细菌变种。在哥伦比亚，其后果一直延续到了今天，在一些社区，胃癌的发病率要高出25倍，极有可能是因为来自祖先的基因组，与体内的幽门螺杆菌变种并不匹配。

The microbiome is the sum of our experiences throughout our lives: the genes we inherited, the drugs we took, the food we ate, the hands we shook. It is unlikely to yield one-size-fits-all solutions to modern maladies.

微生物群落是我们一生中所有经历的总和：我们继承的基因、我们服用的药物、我们吃过的食物、我们握过的手。针对现代的疾病，得出普适性的疗法，可能性并没有那么高。

We cling to the desire for simple panaceas that will bestow good health with minimal effort. But biology is rarely that charitable. So we need to learn how tweaking our diets, lifestyles and environments can nudge and shape the ecosystems in our bodies. And we need ways of regularly monitoring a person’s microbiome to understand how its members flicker over time, and whether certain communities are more steadfast than others.

我们一直不肯放弃心中的一种执念，想要有一种灵丹妙药，不费多大力气，就能简简单单地得到健康。然而生物学却很少会这样慷慨，所以我们需要学着怎样通过调节饮食、生活方式和环境，来细微地影响体内的生态系统。我们还需要想出一个办法，来经常性地监测人体内的微生物群落，从而理解这些微生物在长时间里如何变化，一些菌群是不是比另一些更为固定。

Our microbes are truly part of us, and just as we are vast in our variety, so, too, are they. We must embrace this complexity if we hope to benefit from it.

我们的微生物群落的确是我们人体的一部分，就像人与人千差万别一样，这些微生物也千差万别。如果我们想从中受益，就必须接受这种复杂性。

Useful, thank you.