If Modern Humans Are So Smart, Why Are Our Brains Shrinking?

既然现代人类如此聪明，为什么我们的大脑正在缩小？

Here are some leading theories about the why the human brain has been getting smaller since the Stone Age.

关于人类大脑从石器时代开始越来越小的原因，这里有一些领先的理论。

John Hawks is in the middle of explaining his research on human evolution when he drops a bombshell. Running down a list of changes that have occurred in our skeleton and skull since the Stone Age, the University of Wisconsin anthropologist nonchalantly adds, “And it’s also clear the brain has been shrinking.”

“Shrinking?” I ask. “I thought it was getting larger.” The whole ascent-of-man thing.

“That was true for 2 million years of our evolution,” Hawks says. “But there has been a reversal.”

John Hawks在解释他关于人类进化的研究时，丢出了一个令人震惊的结论。当时他正在梳理自石器时代以来，我们的骨骼和颅骨发生的一系列变化，这位威斯康星大学人类学家补充道，”大脑一直在缩小，这也是明确的。”

“缩小？”我问，”我以为是越来越大了”。事关整个人类的进步啊。

Hawks说：”对200万年的演变历程来说，你是对的，但是有一个逆转。”

He rattles off some dismaying numbers: Over the past 20,000 years, the average volume of the human male brain has decreased from 1,500 cubic centimeters to 1,350 cc, losing a chunk the size of a tennis ball. The female brain has shrunk by about the same proportion. “I’d call that major downsizing in an evolutionary eyeblink,” he says. “This happened in China, Europe, Africa—everywhere we look.” If our brain keeps dwindling at that rate over the next 20,000 years, it will start to approach the size of that found in Homo erectus, a relative that lived half a million years ago and had a brain volume of only 1,100 cc. Possibly owing to said shrinkage, it takes me a while to catch on. “Are you saying we’re getting dumber?” I ask.

他一股脑地说出了一串令人沮丧的数字：在过去的2万年中，人类男性大脑的平均体积已经从1,500立方厘米(cc)减少到了1,350cc，减少了一个网球的大小。女性大脑缩小了大致相同的比例。他说：”以进化的时间尺度看，我想这算得上眨眼就小了一大圈。这发生在中国、欧洲、非洲——所有我们看到的地方”。如果我们的大脑尺寸在未来2 万年中以这种速度不断下降，那么它将接近50万年前我们直立人亲戚的大脑体积，脑容量只有1100cc。可能正是由于上述脑容量缩小，我花了一些时间才反应过来，我问”你意思是我们正在变蠢吗？”

Hawks, a bearish man with rounded features and a jovial disposition, looks at me with an amused expression. “It certainly gives you a different perspective on the advantage of a big brain,” he says.

虎背熊腰的胖子Hawks，乐呵呵地逗趣地看着我，”这肯定会让你对大脑容量的优势有新的认识”。

After meeting with Hawks, I call around to other experts to see if they know about our shrinking brain. Geneticists who study the evolution of the human genome seem as surprised as I am (typical response: “No kidding!”), which makes me wonder if I’m the world’s most gullible person. But no, Hawks is not pulling my leg. As I soon discover, only a tight-knit circle of paleontologists seem to be in on the secret, and even they seem a bit muddled about the matter. Their theories as to why the human brain is shrinking are all over the map.

同Hawks会面之后，我打电话给其他专家，看看他们是否知道我们大脑正在缩小这事。研究人类基因组进化的遗传学家似乎像我一样惊讶（典型的回答：”别开玩笑！”），这让我想知道我是否是世界上最可笑的人。但不，Hawks并没有跟我开玩笑。我很快发现，似乎只有一个紧密的古生物学家圈子在研究这一秘密，甚至他们似乎对此都有点混乱。他们有关为何人类大脑正在缩小的理论正在如雨后春笋般涌现。

Some believe the erosion of our gray matter means that modern humans are indeed getting dumber. (Late-night talk show hosts, take note—there’s got to be some good comic material to mine here.) Other authorities argue just the opposite: As the brain shrank, its wiring became more efficient, transforming us into quicker, more agile thinkers. Still others believe that the reduction in brain size is proof that we have tamed ourselves, just as we domesticated sheep, pigs, and cattle, all of which are smaller-brained than their wild ancestors.

有人认为，我们大脑灰质的朽蚀意味着现代人类确实越来越蠢。 （深夜谈话节目主持人，请注意，这里有一些不错的逗乐材料，注意挖掘。）其他权威提出了相反的意见：随着大脑缩小，其布线变得更有效率，将我们变成更快更敏捷的思想家。还有人认为，大脑尺寸的减少证明我们已经驯服了自己，正如我们驯养的绵羊，猪和牛一样，所有这些动物的大脑都比野生祖先小。

The more I learn, the more baffled I become that news of our shrinking brain has been so underplayed, not just in the media but among scientists. “It’s strange, I agree,” says Christopher Stringer ,a paleoanthropologist and expert on human origins at the Natural History Museum in London. “Scientists haven’t given the matter the attention it deserves. Many ignore it or consider it an insignificant detail.”

我听到的越多，就越困惑，因为我们大脑尺寸缩小的消息不仅仅是在媒体中，甚至在科学家中都被严重轻视。 “这很奇怪，我同意。”伦敦自然历史博物馆的人类学家和人类起源专家 Christopher Stringer说，”科学家们对此问题没有给予应有的重视。许多人忽视它，或认为它是一个微不足道的细节。”

But the routine dismissal is not as weird as it seems at first blush, Stringer suggests, due to the issue of scaling. “As a general rule,” he says, “the more meat on your bones, the more brain you need to control massive muscle blocks.” An elephant brain, for instance, can weigh four times as much as a human’s. Scaling is also why nobody seems too surprised by the large brains of the Neanderthals, the burly hominids that died out about 30,000 years ago.

但是，Stringer表示，由于比例关系的问题， 通常的轻视并不像乍看起来那样奇怪。 “作为一条通则，”他说，”你骨头上的肉越多， 就越需要大脑控制大量的肌肉块”。例如，大象大脑的重量是人的四倍。正是因为比例关系，没人对尼安德特人的巨大大脑感到惊讶，这些结实的人科动物3万年前就绝迹了。

The Homo sapiens with the biggest brains lived 20,000 to 30,000 years ago in Europe. Called the Cro-Magnons, they had barrel chests and huge, jutting jaws with enormous teeth. Consequently, their large brains have often been attributed to brawniness rather than brilliance. In support of that claim, one widely cited study found that the ratio of brain volume to body mass—commonly referred to as the encephalization quotient, or EQ—was the same for Cro-Magnons as it is for us. On that basis, Stringer says, our ancestors were presumed to have the same raw cognitive horsepower.

拥有最大大脑的智人（homo sapiens）生活在2万到3万年前的欧洲。他们被称为克罗马侬人（Cro-Magnons），桶状胸，拥有巨大而突出的下颚以及巨大的牙齿。因此，他们的巨大大脑经常被归因于强壮，而非智慧。 一项被广泛引用的研究发现，我们和克罗马侬人脑质量与身体质量的比值（通常称为脑化指数或EQ）是相同的，这也支持以上说法。在此基础上，Stringer说，我们的祖先被认为（与我们）具有相同的原始认知能力。

Now many anthropologists are rethinking the equation. For one thing, it is no longer clear that EQs flatlined back in the Stone Age. Recent studies of human fossils suggest the brain shrank more quickly than the body in near-modern times. More important, analysis of the genome casts doubt on the notion that modern humans are simply daintier but otherwise identical versions of our ancestors, right down to how we think and feel. Over the very period that the brain shrank, our DNA accumulated numerous adaptive mutations related to brain development and neurotransmitter systems—an indication that even as the organ got smaller, its inner workings changed. The impact of these mutations remains uncertain, but many scientists say it is plausible that our temperament or reasoning abilities shifted as a result.

现在很多人类学家正在重新思考这个公式。一方面，现在已经不再清楚，EQ值是否自石器时代就无甚变化。最近对人类化石的研究表明，在近现代，大脑比身体缩小得更快。更重要的是，对基因组的分析使——现代人类与我们祖先别无二致（包括我们如何思考和感受），只是更精致罢了——这一说法显得可疑。在大脑缩小的同时，我们的DNA积累了许多与脑发育和神经递质系统相关的适应性突变，这表明器官变小，其内在运作也发生变化。这些突变的影响仍未确定，但是许多科学家相信我们的气质或推理能力因此而发生了转变。

Numerous phone calls later, it dawns on me that the world’s foremost experts do not really know why our organ of intellect has been vanishing. But after long ignoring the issue, some of them have at least decided the matter is of sufficient importance to warrant a formal inquiry. They have even drawn some bold, albeit preliminary, conclusions.

后来的很多通电话让我逐渐明白，世界上最重要的专家们真的不知道为什么我们的智力器官正在凋零。但是虽然长期以来忽视这个问题，其中有些专家至少已经认识到这件事情是相当重要的，需要进行正式调查。他们甚至得出了一些大胆的，但尚不成熟的的结论。

DUMBING DOWN

弱智化

In search of a global explanation for our cranial downsizing, some scientists have pointed to a warming trend in the earth’s climate that also began 20,000 years ago. Since bulky bodies are better at conserving heat, larger frames may have fared better in the colder climate. As the planet warmed, selection might have favored people of slighter stature. So, the argument goes, skeletons and skulls shrank as the temperature rose—and the brain got smaller in the process. Stringer thinks there is something to that idea, but he doubts it is the whole explanation. As he points out, comparable warming periods occurred many times over the previous 2 million years, yet body and brain size regularly increased.

为了寻求我们颅骨尺寸缩小的综合解释，一些科学家指出，地球气候变暖趋势也在2万年前开始。由于体积较大的物体更易保存热量，因此在较冷的气候条件下，较大的体格可能会更好。随着地球变暖，自然选择可能偏爱较小巧的身材。所以说，随着温度的升高，骨骼和头骨萎缩，大脑在这个过程中变小了。Stringer认为这样的想法有一定的道理，但他不认为这是事情的全貌。他指出，类似的气候变暖在过去两百万年来发生了很多次，但身体和脑部尺寸却基本是增加的。

Another popular theory attributes the decrease to the advent of agriculture, which, paradoxically, had the initial effect of worsening nutrition. Quite simply, the first farmers were not very successful at eking out a living from the land, and their grain-heavy diet was deficient in protein and vitamins—critical for fueling growth of the body and brain. In response to chronic malnutrition, our body and brain might have shrunk. Many anthropologists are skeptical of that explanation, however. The reason: The agricultural revolution did not arrive in Australia or southern Africa until almost contemporary times, yet brain size has declined since the Stone Age in those places, too.

另一个流行理论认为大脑尺寸的下降与农业的出现有关，与多数人的印象相左，农业的最初效果其实是营养恶化。道理很简单，第一批农民从土地上挣扎出来的生活并不是很成功，他们满是谷物的食谱缺乏对促进身体和大脑生长至关重要的蛋白质和维生素。为了应对长期营养不良，我们的身体和大脑可能会缩小。然而，许多人类学家对这一解释持怀疑态度。原因：农业革命几乎直到现代才到达澳大利亚和南部非洲，然而这些地方自石器时代起大脑尺寸同样已经下降了。

Which brings us to an unpleasant possibility. “You may not want to hear this,” says cognitive scientist David Geary of the University of Missouri, “but I think the best explanation for the decline in our brain size is the idiocracy theory.” Geary is referring to the eponymous 2006 film by Mike Judge aboutan ordinary guy who becomes involved in a hibernation experiment at the dawn of the 21st century. When he wakes up 500 years later, he is easily the smartest person on the dumbed-down planet. “I think something a little bit like that happened to us,” Geary says. In other words, idiocracy is where we are now.

这给我们带来了一个令人不快的可能解释。 密苏里大学认知科学家David Geary说，”你可能不想听到这个消息，但是我觉得对大脑衰落的最佳解释就是蠢蛋进化论。”Geary指的是2006年的Mike Judge执导的同名电影，电影讲述了一个普通人在二十一世纪初参与了一项冬眠试验。当他500年后醒来时，他很容易的成为这个愚蠢行星上最聪明的人。 “我觉得有些类似的事情发生在了我们身上，”Geary说。换句话说，愚昧世代就是我们的现在。

A recent study he conducted with a colleague, Drew Bailey, led Geary to this epiphany. The aim of their investigation was to explore how cranial size changed as our species adapted to an increasingly complex social environment between 1.9 million and 10,000 years ago.Since that period predates the first alphabets, the researchers had no written record with which to gauge the social milieu of our predecessors. Consequently, the Missouri team used population density as a proxy for social complexity, reasoning that when more people are concentrated in a geographic region, trade springs up between groups, there is greater division of labor, the gathering of food becomes more efficient, and interactions among individuals become richer and more varied.

最近Geary和同事Drew Bailey进行的一项研究使他顿悟。他们的研究旨在探索我们这个物种为适应日益复杂的社会环境，颅骨尺寸在190万年前到1万年前期间如何变化。因为这个时间段早于文字的出现，研究人员没有书面记录来衡量我们祖先的社会环境。因此，密苏里团队以人口密度作为社会复杂性的代表，推断当更多的人集中在一个地理区域时，群体之间的贸易就会发生变化，分工越来越多，食物的采集变得更有效率，人与人之间的交互变得更加丰富多彩。

Bailey and Geary found population density did indeed track closely with brain size, but in a surprising way. When population numbers were low, as was the case for most of our evolution, the cranium kept getting bigger. But as population went from sparse to dense in a given area, cranial size declined, highlighted by a sudden 3 to 4 percent drop in EQ starting around 15,000 to 10,000 years ago. “We saw that trend in Europe, China, Africa, Malaysia—everywhere we looked,” Geary says.

Bailey和Geary发现人口密度确实跟大脑大小密切相关，但却是以一种令人惊讶的方式相互关联。当人口数量较少时（正如我们进化史的多数时段那样），颅骨不断变大。但是随着人口在一个特定区域从稀疏到密集，颅骨大小出现下降，尤其引人注目的是在1,5000到10,000年前，EQ值突然下降了3到4个百分点。 Geary说，”我们在欧洲、中国、非洲，马来西亚——任何我们研究的地方都看到这一趋势。”

The observation led the researchers to a radical conclusion: As complex societies emerged, the brain became smaller because people did not have to be as smart to stay alive. As Geary explains, individuals who would not have been able to survive by their wits alone could scrape by with the help of others—supported, as it were, by the first social safety nets.

观察结果让研究人员得出了一个激进的结论：随着复杂社会的出现，大脑变得更小，因为人们不必那么聪明才能活着。如Geary解释道，那些不能靠自己的智慧独自生存下来的个人，可以在其他人的帮助下勉强度日，这有赖于最早的社会安全网。

Geary is not implying that our beetle-browed forebears would have towered over us intellectually. But if Cro-Magnons had been raised with techno-toys and the benefits of a modern education, he ventures, “I’m sure we would get good results. Don’t forget, these guys were responsible for the ‘cultural explosion’“—a revolution in thinking that led to such startling new forms of expression as cave paintings, specialized tools, and bones carved into the first flutes. In terms of raw innate smarts, he believes, they probably were as “bright as today’s brightest” and might even have surpassed us.

Geary并不是意指我们粗眉毛的祖先有着高于我们的智慧。但是，如果克罗马侬人在科技玩具和现代教育中成长，他大胆预言，”我相信我们会得到不错的结果。不要忘了，这些家伙带来了’文化大爆炸’“——一场造就了令人吃惊的新型表达形式的思维革命，这些表达形式包括洞穴绘画，专门的工具和骨雕长笛。他认为，在天生聪慧方面，他们可能 “和今天最聪明的人一样聪明”，甚至可能超过了我们。

Still, Geary hesitates to use words like genius or brilliant in describing them. “Practically speaking,” he explains, “our ancestors were not our intellectual or creative equals because they lacked the same kind of cultural support. The rise of agriculture and modern cities based on economic specialization has allowed the very brightest people to focus their efforts in the sciences, the arts, and other fields. Their ancient counterparts didn’t have that infrastructure to support them. It took all their efforts just to get through life.”

不过，Geary对使用天才或卓越这样的词汇来描述他们颇为踌躇。 他解释说，”实际上，我们的祖先并是我们智力或创造力的对手，因为他们缺乏同样的文化支持。以经济专业化为基础的农业和现代城市的兴起，使最聪明的人们将精力集中在科学，艺术和其他领域。我们的古代对手没有这样的基础来支持他们，所有的努力只是为了维生。”

SMALLER BUT SMARTER

更小但更聪明 When I follow up with Hawks, the anthropologist who first tipped me off about our missing gray matter, I assume that his interpretation of the trend will be like Geary’s. But even though Hawks does not doubt the findings of the Missouri team, he puts a completely different (and, in his view, more uplifting) spin on the data.

Hawks最早向我介绍了我们消失的灰质，当我再次向他询问时，我以为他对这一趋势的解读会与Geary相似。但是，尽管Hawks并不怀疑密苏里团队的发现，但他基于该数据提出了完全不同（他认为更令人振奋）的观点。

Hawks spent last summer measuring skulls of Europeans dating from the Bronze Age, 4,000 years ago, to medieval times. Over that period the land became even more densely packed with people and, just as the Missouri team’s model predicts, the brain shrank more quickly than did overall body size, causing EQ values to fall. In short, Hawks documented the same trend as Geary and Bailey did in their older sample of fossils; in fact, the pattern he detected is even more pronounced. “Since the Bronze Age, the brain shrank a lot more than you would expect based on the decrease in body size,” Hawks reports. “For a brain as small as that found in the average European male today, the body would have to shrink to the size of a pygmy” to maintain proportional scaling.

去年夏天Hawks测量了从4000年前青铜时代到中世纪的欧洲人头骨。在此期间，这片土地上人口愈发密集，正如密苏里团队的模式所预测的那样，人类大脑比整体身材缩小得更快，导致EQ值下降。简而言之，Hawks记录了Geary和Bailey在他们较老的化石样本中所发现的相同趋势：事实上，他发现的模式更显著。 Hawks报道，”自青铜时代以来，对应身体尺寸的缩小，大脑尺寸的缩小超出了预期，”“对应如今欧洲男性大脑的平均大小，身体必须缩小到侏儒的尺寸”才能保持比例相称。

Hawks chose to focus on Europe in the relatively recent past, he explains, because there is an exceptionally large number of complete remains from that era. That allowed him to reconstruct a detailed picture of what was happening during our downsizing. The process, he discovered, occurred in fits and starts. There were times when the brain stayed the same size and the body shrank—most notably, he says, from the Roman era until medieval times. But more frequently, the brain got smaller while the body remained the same. Indeed, Hawks says, that is the overarching trend for the thousands of years he studied.

Hawks选择专注研究较为近期的欧洲，他解释是因为欧洲有大量那个年代保存完整的遗体。这使他能够重建我们大脑尺寸下降期间发生事情的详细情景。他发现，这个过程间断发生。有部分时间，最明显的是从罗马时代到中世纪，大脑尺寸不变，身体缩小。但更常见的情况是，大脑尺寸变小，身体保持不变。 Hawks说，这的确是他研究的数千年间的总体趋势。

The image of a brain dwarfed by its body conjures up dinosaurs, a group not exactly known for their intellectual prowess. But Hawks sees nothing alarming in the trend. Quite the contrary, he believes the startling decrease in our brain volume—both in absolute terms and relative to our stature—may be a sign that we are actually getting smarter.

与其身体相比明显偏小的大脑让人想起了恐龙，这是一个不为他们的智力而闻名的群体。但Hawks并不认为这个趋势令人害怕。恰恰相反，他认为我们的脑体积惊人的减少——不管是绝对值还是相对于我们的身材——可能是一个迹象，表示我们实际上变得更聪明。

As complex societies emerged, brains shrank because those previously unable to survive by wits alone could now scrape by with the help of others.

随着复杂社会的出现，大脑缩小，因为以前无法​​通过智慧生存的人们现在可以在别人的帮助下勉强生存。

This upbeat perspective is shaped by Hawks’s focus on the energy demands of the brain. The organ is such a glutton for fuel,he says, that it gobbles up 20 percent of all the calories we consume. “So although a bigger brain can presumably carry out more functions, it takes longer to develop and it uses more energy.” Brain size probably depends on how those opposing forces play out.

这个乐观的观点源于Hawks对大脑能量需求的关注。他说，这个器官极其耗能，在人体消耗的全部热量中，大脑占到20% 。 “所以虽然更大的大脑可能会发挥更大的作用，但需要更长的时间发育，并且消耗更多的能量。”大脑尺寸大小可能取决于相反力量如何发挥作用。

The optimal solution to the problem, he suggests, “is a brain that yields the most intelligence for the least energy.” For evolution to deliver up such a product, Hawks admits, would probably require several rare beneficial mutations—a seeming long shot. But a boom in the human population between 20,000 and 10,000 years ago greatly improved the odds of such a fortuitous development. He cites a central tenet of population genetics: The more individuals, the bigger the gene pool, and the greater the chance for an unusual advantageous mutation to happen. “Even Darwin knew this,” he says. “That’s why he recommended that animal breeders maintain large herds. You don’t have to wait so long for desirable traits to arise.”

最佳的解决方案，他提到， “是用最小能量产生最大智力的大脑”。Hawks承认，进化要完成这样一件作品，可能需要几种罕见的有益突变 ——几率实在渺茫。但在2万年至1万年之前的人口繁荣，大大提高了这种偶然发展的可能性。他引用人口遗传学的中心原则：个体越多，基因库越大，发生不寻常的有利突变的机会就越大。 “达尔文知道这一点，”他说。 “这就是为什么他建议动物饲养者保持大型畜群。你不必等待很长时间就能出现所需的特质。”

Hawks notes that such changes would be consistent with the many brain-related DNA mutations seen over the past 20 millennia. He speculates that the organ’s wiring pattern became more streamlined, the neurochemistry shifted, or perhaps both happened in tandem to boost our cognitive ability.

Hawks指出，这种变化与过去2万年中的我们观察到的许多与脑相关的DNA突变是一致的。他推测，器官的布线模式变得更加合理，神经化学发生变化，或者两者相继发生变化提高我们的认知能力。

A TAMER BREED

一个更温顺的品种

Other researchers think many of their colleagues are barking up the wrong tree with their focus on intelligence as the key to the riddle of our disappearing gray matter. What may have caused the trend instead, they argue, is selection against aggression. In essence, we domesticated ourselves, according to Richard Wrangham,a primatologist at Harvard University and a leading proponent of this view.

许多研究者认为智力是解开我们消失的灰质之谜的关键，但他们的一些同行则认为这是找错方向了。他们认为，导致这种趋势的原因实际上是自然选择对攻击性的排斥。哈佛大学灵长类动物学家Richard Wrangham是这一观点的主要支持者，他认为实质上，我们驯化了自己。

Some 30 animals have been domesticated, he notes, and in the process every one of them has lost brain volume—typically a 10 to 15 percent reduction compared with their wild progenitors. Domesticated animals also have more gracile builds, smaller teeth, flatter faces, a more striking range of coloration and hair types—and, in many breeds, floppy ears and curly tails. Except for those last two traits, the domesticated breeds sound a lot like us.

他指出，对于大约30种被驯化动物，在驯化过程中，每一种的大脑体积相较其野生祖型通常都下降了10％至15％。驯养动物体型更纤弱，牙齿更小，面孔更扁平，毛发的颜色和类型范围更广， 在很多品种中有耷拉的耳朵和卷曲的尾巴。除了最后两个特征外，驯养品种听起来和我们很像。

“When you select against aggression, you get some surprising traits that come along with it,” Wrangham says. “My suspicion is that the easiest way for natural selection to reduce aggressiveness is to favor those individuals whose brains develop relatively slowly in relation to their bodies.” When fully grown, such an animal does not display as much aggression because it has a more juvenile brain, which tends to be less aggressive than that of an adult. “This is a very easy target for natural selection,” Wrangham argues, because it probably does not depend on numerous mutations but rather on the tweaking of one or two regulatory genes that determine the timing of a whole cascade of developmental events. For that reason, he says, “it happens consistently.” The result, he believes, is an adult possessing a suite of juvenile characteristics, including a very different temperament.

“当你朝着降低攻击性的方向选育，你会意外得到一些伴随而来的特征，”Wrangham说， “我怀疑，为了降低攻击性，对自然选择来说，最简单的方法是青睐那些大脑相对于身体发育慢的人”。当完全长大时，这样的动物不会表现出太强的攻击性，因为它具有更年轻的大脑，因此不会如成年的大脑那般富于攻击性。 “对自然选择，这是一个非常容易的标靶，”Wrangham认为，因为它可能不依赖于许多突变，而是依赖于一两个调节基因的调整，这些基因决定了整个发育阶段的时间轴。因此，他说：”这一直在发生。”他相信其结果就是一个拥有许多幼年特征的成年人，包括一种非常不同的性情。

To illustrate how this could happen, Wrang­ham refers to an experiment that began half a century ago in Siberia. In 1958 the Russian geneticist Dmitri Belyaev started raising silver foxes in captivity, initially selecting to breed only the animals that were the slowest to snarl when a human approached their cage. After about 12 generations, the animals evidenced the first appearance of physical traits associated with domestication, notably a white patch on the forehead. Their tameness increased over time, and a few generations later they were much more like domesticated dogs.They had developed smaller skeletons, white spots on their fur, floppy ears, and curlier tails; their craniums had also changed shape, resulting in less sexual dimorphism, and they had lower levels of aggression overall.

为了说明这种情况是如何发生的，Wrangham提到一个半个世纪前在西伯利亚开始的实验。 1958年，俄罗斯遗传学家 Dmitri Belyaev开始圈养银狐，最初的选育原则是，只繁育人类接近笼子时最后吼叫的个体。大约12代后，这些动物开始出现与驯化相关的特征，特别是前额上的白色斑块。他们的驯服程度随着时间的推移而增加，几代后，他们便更像驯养的狗。他们发展出较小的骨骼，毛皮上的白点，耷拉的耳朵和卷曲的尾巴；他们的颅骨也改变了形状，导致两性差别减小，整体攻击水平下降。

So what breeding effect might have sent humans down the same path? Wrangham offers a blunt response: capital punishment. “Over the last 100,000 years,” he theorizes, “language became sufficiently sophisticated that when you had some bully who was a repeat offender, people got together and said, ‘We’ve got to do something about Joe.’ And they would make a calm, deliberate decision to kill Joe or expel him from the group—the functional equivalent of executing him.” Anthropological records on hunter-gatherers suggest that capital punishment has been a regular feature of our species, according to Wrangham. In two recent and well-documented studies of New Guinea groups following ancient tribal custom, the ultimate punishment appears to be meted out to at least 10 percent of the young men in each generation.

那么什么育种效应可能会使人类陷入同一条路径？ Wrangham给出直接的回应：死刑。 “在过去的十万年里，”他的理论是，”语言变得足够复杂，当一些恶霸屡屡欺凌你们，人们聚在一起说，’我们必须要对Joe做一些事情’。然后他们作出冷静而审慎的决定——杀死Joe或将他驱逐出团队——效果上相当于处决他。”根据Wrangham的说法，狩猎采集人类的人类学记录表明，死刑是我们物种的常规特征。最近两项记录完好的关于沿袭了古代部落习俗的新几内亚部落的研究显示， 每一代年轻人中最终会有至少10%遭受到惩罚。

“The story written in our bones is that we look more and more peaceful over the last 50,000 years,” Wrangham says. And that is not all. If he is correct, domestication has also transformed our cognitive style. His hunch is based on studies—many done by his former graduate student Brian Hare—comparing domestic animals with their wild relatives. The good news, Wrangham says, is that “you can’t speak of one group being more intelligent than the other.”

Wrangham说：”记录在我们骨头上的故事告诉我们，我们在过去5万年里看起来越来越平和。而这不是全部。如果他是正确的，驯化也改变了我们的认知风格。他的预感以研究为基础——其中许多正是由他以前的一位研究生Brian Hare完成——这些研究比较了家养动物和它们的野生亲戚。好消息是，Wrangham说， “你不能说驯养动物和它们的野生亲戚谁更聪明”。

Hare, now an assistant professor of evolutionary anthropology at Duke University, agrees. “All you can say is that wild types and domesticates think differently.”

Hare现在是杜克大学进化人类学助理教授，他也赞成，”你只可以说，野生型和驯化型思考方式不同。”

The two scientists point to the results of studies comparing the cognitive abilities of wolves and dogs. Wolves, with their larger brains, are more prone to flashes of insight, allowing them to solve problems on their own; dogs, with smaller brains, excel at using humans to help them. “Wolves seem to be a little bit more persistent than dogs in solving simple problems like how to open a box or navigate a detour,” Hare says. “Wolves persevere when dogs readily give up.” On the flip side, dogs leave wolves in the dust when it comes to tracking the gaze and gestures of their masters—or as Hare puts it, “They are very good at using humans as tools to solve problems for them.” And while dogs may appear lazy and pampered, some can survive for multiple generations in areas far removed from humans—an indication, Hare says, that they have retained an ability to adapt to the wild.

两位科学家谈到比较狼和狗的认知能力的研究结果。狼拥有较大的大脑，表现出更强的洞察力，让他们有能力自己解决问题；脑相对较小的狗，则擅长利用人类来帮助他们。Hare说：”在解决简单问题，比如打开一个盒子或绕道找路时，狼似乎比狗更坚持不懈。 “当狗准备放弃时，狼会坚持下去”。另一方面，在跟踪主人目光和手势时，狗会让狼望尘莫及，或者正如Hare所说，”它们非常擅长以人类作为解决问题的工具。”而且，虽然狗可能看起来很懒惰和娇宠，但有些可以在远离人类的地区生存多代，这表明，他们保留了适应野外环境的能力。

For more insight, Hare is now studying other primates, notably bonobos. He tells me he suspects that these great apes are domesticated chimps. As if on cue, bursts of exotic, birdlike trills suddenly drown out his voice over the phone. “Sorry about that,” he shouts over the line. “Those are the bonobos.” It turns out that as I am speaking to him, Hare is not at his desk at Duke but in a Congo forest where the bonobos live. “Bonobos look and behave like juvenile chimps,” he continues. “They are gracile. They never show lethal aggression and do not kill each other. They also have brains that are 20 percent smaller than those of chimps.”

为了更深入的了解，Hare正在研究其他灵长类动物，特别是倭黑猩猩。他告诉我，他怀疑这些伟大的猿是驯养的黑猩猩。似乎为了给我提示，一阵听起来像异域鸟鸣的颤音突然淹没了他的声音。 “抱歉，”他隔着电话喊道，”是倭黑猩猩。” 原来Hare和我通话时， 他并不在Duke大学的办公桌边，而是在倭黑猩猩生活的刚果森林里。 “倭黑猩猩的相貌和行为像青少年黑猩猩，”他继续说。 “他们纤弱，从不表现出致命的攻击性，不互相残杀。他们的大脑也比黑猩猩小20％。”

Hare thinks bonobos became domesticated by occupying an ecological niche that favored selection for less aggressive tendencies. That niche, he says, offered more abundant sources of nutrition, so a habit of fighting over meals became less important to survival. From that lineage came the bonobos, highly cooperative primates known for their peaceful ways.

Hare认为，倭黑猩猩通过占据这样一个生态位而被驯化，该生态位倾向更少的攻击性。他说，这个生态位提供了更多丰富的营养来源，所以为食物打斗的习惯对于生存来说不再那么重要。正是沿着这一进化路径，诞生了倭黑猩猩，这一以和平生活方式而闻名的高度协作的灵长类动物。

Both Wrangham and Hare see parallels between bonobo development and our own. Our self-domestication, they think, may hold the key to our species’s extraordinary motivation to cooperate and communicate —arguably the twin pillars supporting the whole of our civilization.

Wrangham和Hare都看到了倭黑猩猩与我们自己发展的共同点。他们认为，我们的自我驯化可能是我们这个物种对合作和沟通能有如此异乎寻常的意愿的关键所在——可以说合作和沟通是支撑整个文明的两大支柱。

ABOUT-FACE

大逆转 Just as I begin to absorb these varying interpretations, I am hit with the next surprise in our human evolutionary narrative: After a long, slow retrenchment, human brain size appears to be rising again. When anthropologist Richard Jantzof the University of Tennessee measured the craniums of Americans of European and African descent from colonial times up to the late 20th century, he found that brain volume was once again moving upward.

正当我开始努力消化这些不同解释时，我在人类进化叙事中收获了另一个惊喜：经过漫长而缓慢的缩小，人类大脑尺寸似乎正再次上升。当田纳西大学的人类学家Richard Jantzof测量了欧洲和非洲裔美国人从殖民时代到20世纪末期的颅骨后，他发现脑容量再次向上移动。

Since evolution does not happen overnight, one would assume this sudden shift (much like the increase in height and weight) is unrelated to genetic adaptations. Hawks, for instance, says the explanation is “mostly nutrition.” Jantz agrees but still thinks the trend has “an evolutionary component because the forces of natural selection have changed so radically in the last 200 years.” His theory: In earlier periods, when famine was more common, people with unusually large brains would have been at greater peril of starving to death because of gray matter’s prodigious energy requirements. But with the unprecedented abundance of food in more recent times, those selective forces have relaxed, reducing the evolutionary cost of a large brain.

由于进化不会在一夜之间发生，所以人们会假设这种突然的转变（很像身高和体重的增加）与遗传适应无关。例如，Hawks解释”主要是营养”。Jantz同意这个看法，但仍然认为趋势有”进化因素，因为自然选择的力量在过去200年里发生了如此大的变化”。他的理论是：在早期，当饥荒更加普遍时，由于灰质的巨大能量需求，拥有不寻常的大号大脑的人将会面临更大的死亡危险。但随着近期食品空前的丰富，这些选择性压力已经放松，降低了大脑的进化成本。

Whatever the reason for the recent uptick in cranial size, Jantz believes it is having an effect on how we think. Recent MRI studies, according to Jantz and other scientists, show that brain volume really does correlate with intelligence—at least as measured by that oft-celebrated but widely criticized metric, the IQ test. Seen from that perspective, a bigger brain sounds like good news. Then again, if aggressiveness rises with brain size, maybe not.

不管最近颅骨大小上升的原因是什么，Jantz认为这会影响我们如何思考。根据Jantz和其他科学家的说法，最近的MRI研究表明，大脑体积确实与智力有关，至少是与由广泛使用但饱受争议的智商测验得出的IQ值有关。 从这个角度看，一个更大的大脑听起来好像是个好消息。 那么，攻击性是否会随着脑部尺寸的上升而上升？也许并不会。

Perhaps, like so many things in life, our fluctuating brain size is a mixed bag—and in contrast to animal breeding, we cannot determine where evolution is taking us. “Natural selection is different from artificial selection in that it acts on every trait at once,” Stringer says. “It’s perfectly plausible our modern brain is smarter in some ways, dumber in others, and more docile overall.”

也许像生活中的许多事情一样，我们尺寸波动的大脑是一个装着混杂东西的袋子 ——与动物繁殖相反，我们无法确定进化将把我们带向何处。 “自然选择与人工选择有所不同，它可以对所有特征同时进行操作，”Stringer说。 “我们的现代大脑在某些方面比较聪明，在其他方面比较愚蠢，而整体上更温顺，这是非常合情合理的。”