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Australopithecus afarensis lived between3.85 and 2.95 million years ago.

（图解：阿法南方古猿生活在385至295万年前）

New evidence suggests hominins firstdeveloped outsized brains by scavenging fatty animal marrow, rather thanactively hunting for meat.

副标题：新的证据表明，古人类能第一个演化出特大号的大脑靠的是食用动物脂髓，而不是积极地猎取肉食。

NORTHERN ETHIOPIA WAS once home to a vast,ancient lake. Saber-toothed cats prowled around it, giant crocodiles swamwithin. The streams and rivers that fed it — over 3 million years ago, duringthe Pliocene — left behind trails of sediment that have now hardened intosandstone.

埃塞俄比亚北部曾经是一个巨大古湖泊的故乡。剑齿虎在它周边潜行，巨大的鳄鱼在其中游曳。三百多万年前上新世的溪水河流为其蓄积水源，留下的沉积物痕迹如今已经变硬，成为了砂岩。

Deposited within these layers are fossils:some of early hominins, along with the bones of hippos, antelope, andelephants. Anthropologist Jessica Thompson encountered two of these specimens,from an area named Dikika, in 2010.

沉积在这些地层中的是化石：一些早期人类、连同河马、羚羊和大象的骨头。2010年时，人类学家杰西卡·汤普森在一个叫迪奇卡的地区偶然发现了其中两具标本。
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At the time, she was a visiting researcherat the Institute of Human Origins at Arizona State University. Given noexplanation as to their history, she analyzed the bones and found signs ofbutchery. Percussion marks suggested someone may have accessed the marrow; cutmarks hinted that flesh was stripped from bone. To her surprise, the specimenswere 3.4 million years old, putting the butcher’s behaviors back 800,000 yearsearlier than conventional estimates would suggest. That fact got Thompson, nowan assistant professor in the Department of Anthropology at Yale University,thinking there might be more traces of tool use from those early times.

当时，她还是亚利桑那州立大学人类起源研究所的一位访问研究员。她没有就它们的历史作出解释，而是分析了那些骨头，然后找到了宰割的痕迹。上面留下的敲打痕迹表明，可能有人来取过骨髓；割痕暗示了从骨头上剥离肉的动作。让她感到惊讶的是，这些标本有340万年的历史了，这就把宰割行为从传统中估计的年代向前推了80万年。这个事实让汤普森认为，在那些很久远的历史时期中，可能存在更多的使用工具的痕迹，她现在是耶鲁大学人类学系的助理教授。

In a wide-ranging review published inFebruary’s issue of Current Anthropology, Thompson joins a team of researchersto weave together several strands of recent evidence and propose a new theoryabout the transition to large animal consumption by our ancestors. Theprevailing view, supported by a confluence of fossil evidence from sites inEthiopia, is that the emergence of flaked tool use and meat consumption led tothe cerebral expansion that kickstarted human evolution more than 2 millionyears ago. Thompson and her colleagues disagree: Rather than using sharpened stonesto hunt and scrape meat from animals, they suggest, earlier hominins may havefirst bashed bones to harvest fatty nutrients from marrow and brains.

在发表于今年二月号《当代人类学》的一份牵涉广泛的评论中，汤普森加入了一个研究团队，为的是把最近出现的若干条新证据整合到一起，并提出了一套关于我们祖先转变成食用大型动物的新理论。占主导地位的观点是由埃塞俄比亚各遗址中汇集到一起的化石证据支持的，即：使用薄片状工具（即切削器）和食用肉类的出现，导致大脑变大，在两百多万年前启动了人类演化。而汤普森和她的同事们不同意这个观点：他们提出，并不是使用磨到锋利的石器去狩猎并从动物身上刮下肉，年代更早的古人类可能是用打碎的骨头在骨髓和大脑中获取脂肪类营养。

Humans are the only primate to regularlyconsume animals larger than themselves. This nutritional exploitation,something Thompson and her colleagues call the “human predatory pattern,” haslong been synonymous with the flesh-eating, man-the-hunter view of humanorigins.

人类是唯一一种习惯性食用体型比自己更大的动物的灵长类动物。这种对营养物质的利用，被汤普森和她的同事们称为“人类掠食模式”，长久以来，这和人类起源中吃生肉、狩猎者的观点是同义词。

Because large animals such as antelope packa serious micro-and-macro-nutrient punch, scientists have thought their meatcontributed to humanity’s outsized brains. A consensus arose in the 1950s thatour ancestors first hunted small animals before moving on to larger beastsaround 2.6 million years ago. Flaked tool use and meat eating became definingcharacteristics of the Homo genus.

由于羚羊这样的大型动物在微观和宏观层面上都富有营养效力，科学家们已经认为它们的肉对人类特大号的大脑是有所贡献的。五十年代的时候出现过一个共识，即我们的祖先一开始捕猎的是小型动物，直到约260万年前才转换到捕猎大型野兽。薄片状工具的使用和吃肉成了人属的本质特征。
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“It’s a very appealing story,” says Thompson. “Right around that timethere appeared to be the first stone tools and butchery marks. You have theorigins of our Homo genus. A lot of people like to associate that with what itmeans to be human.”

“这是一个非常有吸引力的故事”，汤普森说。“就在那个时期，似乎出现了第一件石器和宰割痕迹。这就找到了我们这个人属的起源。有很多人喜欢把这一点和它对人类的意义联系在一起。”
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Then, starting in the mid-1980s, anopposing theory arose in which Homo’s emergence wasn’t so tightly coupled withthe origins of hunting and predatory dominance. Rather, early hominins firstaccessed brain-feeding nutrients through scavenging large animal carcasses. Thedebate has rolled on through the decades, with evidence for the scavengingtheory gradually building.

然后，从八十年代中期开始出现了一种相反的理论，认为人属的出现，和狩猎与吃肉为主的起源之间的关系没有那么紧密。相反，早期的古人类是靠以大型动物的尸体为食来获取补脑的营养物质。这场争论已经一路持续了几十年，食腐理论的证据也逐渐建立起来。

The new paper goes further: Harvestingouter-bone meat would have come at significant costs, the authors argue. Thechance of encountering predators is high when scraping raw flesh from acarcass. Chewing raw meat without specialized teeth doesn’t give much energeticbenefit, studies have shown. In addition, meat exposed to the elements willquickly rot.

这篇新的论文又进了一步：那些作者的主张是，获取外部骨骼上的肉会付出巨大代价。从尸体上搜刮生肉时，遭遇掠食者的可能性会很高。研究已经显示，在没有特化牙齿的情况下去咀嚼生肉，从精力方面考虑并不会带来太多益处。此外，暴露在自然环境中的肉很快就会腐烂。

Marrow and brains, meanwhile, are lockedinside bones and stay fresh longer. These highly nutritional parts are also aprecursor to the fatty acids involved with brain and eye development. And moreeasily than flesh-meat, bones could be carried away from carcass sites, safefrom predators.

与此同时，骨髓和大脑被锁在骨头内部，保持新鲜的时间会更久。这些营养价值很高的部分也是负责大脑和眼睛发育的脂肪酸的一种前体。而且比取肉更容易的是，骨头是可以从尸骸所在地拿走的，如此就能保证安全，不会受到掠食者的威胁。
（译注：前体物质，是指能直接被微生物在生物合成过程中结合到产物分子，而自身结构不发生过多变化，但产物的产量可以获得较大提高的一类化合物）

Conventional thinking has been that thebehavioral package of early hominins was to go after meat and marrow together,explains Briana Pobiner, a paleoanthropologist at the Smithsonian Institution,who did not contribute to the new paper. But in the new paper, she says, “Thisteam has shown that marrow may have in fact been more important. It’s a nuance,but an important nuance.”

没有参与这篇新论文的史密森学会古人类学家布里安娜·波宾纳解释到，在传统的想法中，早期人类的行为包模式就是同时猎取肉和骨髓。但在这篇新论文中，她说，“该团队已经展示出，可能骨髓一直都是更重要的目标。这是一个微妙的差别，但却是一个很重要的微妙差别。”

The Pliocene — between 5.3 and 2.6 millionyears ago — was an era of dramatic change. An intensely variable and coolingclimate transformed vast swaths of rainforest into mosaics of grassland andsavanna. Large clearings spawned ecological niches for opportunistic andversatile hominins like Australopithecus, a likely contender for the Homoancestor, and Kenyanthropus to fill in. Larger predators may well have leftcarcasses for them to scavenge.

530至260万年前的上新世是一个急剧变化的时代。相当多变且凉爽的气候把大量的雨林转变成了草原和稀树草原构成的拼图。大片的空地为投机取巧且多才多艺的古人类创造了生态位，比如南方古猿，人属祖先的一个可能的竞争者，以及替代了前者的肯尼亚扁脸人。大型掠食者很可能为他们留下了可以食用的尸骸。

Evidence suggests hominins shifted theirdiet around 3.76 million years ago as they took advantage of the open spaces.By around 3.5 million years ago, some species of Australopithecus alreadyshowed increased brain sizes, up to 30 percent larger than chimpanzees ofcomparable body size. Canines had shrunk to proportions later seen in the genusHomo, and hand morphology was already more human than ape, with potential bothfor terrestrial travel and tool use.

证据表明，随着古人类充分利用了开阔地域，他们的饮食结构在约376万年前发生了转变。到了约350万年前的时候，南方古猿中一些种族的大脑已经变大了，要比身体大小相仿的黑猩猩大出30%。犬齿已经缩小到了见于之后人属的相对比例，而且手的形态已经更接近人类而不是猿了，这就同时具备了陆地旅行和使用工具的潜力。

Percussive tools, the authors argue, werethe key to the transition to large animal exploitation. Rocks could bash openbones, exposing the marrow inside. The alternative — that humans sharpenedstone against stone, creating a flaked tool to carve meat from bone — seemsmore onerous, they say. They argue that such meat carving and the associatedtool creation would likely come later.

这几位作者主张，敲打工具是转变成去利用大型动物的关键。石头可以敲开骨头，从而暴露出里头的骨髓。他们表示，替代方法似乎更为繁琐，即人类通过互击将石头磨快，打造出一种能从骨头上切下肉来的切削器。他们主张这种切肉行为乃至相关的工具打造可能出现于更晚的时期。

As to who wielded these percussiveinstruments, the timeline presents a puzzle. The earliest Homo specimen is nowdated to 2.8 million years. The Dikika fossils suggest butchery behaviors at3.4 million years ago. Homo may have emerged earlier than scientists suspected— a theory that would need more fossil evidence to support it — or anotherhominin, such as Australopithecus, may have created tools before Homo.

至于是谁在挥舞这些敲打工具，在时间轴上呈现为一个谜团。现今最早的古人类标本可以追溯到280万年前。出土于迪奇卡的化石表明，宰割行为出现在340万年前。古人类的出现也许比科学家们猜想的更早（该理论需要更多的化石证据来支持），另一种古人类，比如南方古猿，也许在人属出现之前就创造出了工具。

Some scholars aren’t convinced by thestudy’s arguments, however. For example, Craig Stanford, an anthropologist atthe University of Southern California, questions the emphasis on homininscavenging behavior appearing before hunting. “We have no examples today ofanimals that scavenge but don’t hunt,” he adds.

然而，有些学者并不信服该研究的论证。比如克雷格·斯坦福，他是南加州大学的人类学家，他所质疑的是：研究强调了古人类在狩猎行为之前就出现了食腐行为。“我们找不到任何现存动物食腐而不狩猎的例子”，他补充说。

To test the new theory, the review authorssuggest seeking out further evidence of percussive tools that predate flakedtools. Researchers could, they note, broaden the search for the signatures ofsuch instruments within both the existing fossil record and at dig sites.Thompson’s graduate students, for example, are using 3D scanning and artificialintelligence techniques to improve the identification of marks on fossils —whether they were created by early hominins, saber-toothed cats, hyenas, orother types of creatures.

为了验证这个新理论，这篇评论的作者提议，找出敲打工具在时间上早于切削器的进一步证据。他们提到，研究者可以在现存的化石记录以及遗址挖掘中，同时扩大对这类工具蛛丝马迹的搜索。比如说，汤普森的毕业生们正在使用3D扫描和人工智能技术来改善对化石上痕迹的鉴识水平，即它们是由早期人类，还是由剑齿虎、鬣狗或其他类型生物留下的。
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What they uncover could deal a blow totheir theory, but it will also, undoubtedly, enrich our understanding of howour ancestors evolved.

他们所揭示的可能会打击到他们的理论，但毫无疑问也会丰富我们对我们祖先进化方式的理解。