The ecological cultural and cognitive context of tool use in New Caledonian crows

人类是奇怪的动物。我们用复杂的语言交流，我们制造和使用工具来改造和利用环境，我们与同龄人分享知识和信息，我们建立了惊人复杂的社会。定义“智力”是一个有争议的话题，但大多数人都会同意人类拥有无与伦比的脑力--这一观察结果往往导致对“人类独特性”的夸大看法。但是，到底是什么让我们走上了不寻常的进化轨迹呢？是特定的生态环境促进了一个或几个关键的适应，如语言或工具的使用，这些特征在文化进化中扮演了什么角色？在其他条件不变的情况下，可以合理地假设，工具的使用和知识的积累会给其他物种的个体或群体带来优势，然而这些特征，尤其是它们的共同存在，在动物王国中是极其罕见的。只有两个物种被认为是工具技术的文化传播：黑猩猩和我的研究对象，新喀里多尼亚乌鸦。这些乌鸦生活在一个遥远的太平洋岛屿上，在那里他们使用工具从洞和裂缝中提取幼虫。他们使用至少三种不同的工具类型，包括迄今为止发现的最复杂的动物工具设计，他们甚至可能在文化上传播并逐步改进其工具技术的各个方面（有些工具形状各异）。人类是几代人积累文化信息的大师，手表或自行车等日常用品就是明证，更不用说电脑或航天飞机了。没有一个人可以从零开始设计和制造这些物品。我们建立在祖先的技术遗产上，研究表明，可能正是这种能力使我们的物种成为这样一个进化成功的故事。在新喀里多尼亚，我调查了野生乌鸦社会是如何组织的，青少年如何学习他们的技能，以及这些鸟的日常饮食中有多少是用工具获得的。我还探索了这些鸟的家乡岛屿是否有什么特别之处，可以解释它们不寻常的适应能力。事实上，它们可能为我们自己的进化历史提供了一个独特的窗口，让我们得以瞥见是什么因素推动了我们祖先的工具使用和文化的进化。但在野外研究这些乌鸦并不容易，因为它们很害羞，生活在能见度有限的茂密森林中。我的团队已经开发出微型动物携带的摄像机，可以播放电视质量的彩色视频。这些摄像机安装在乌鸦的尾巴上，并通过腿向前窥视，以产生乌鸦的眼睛看到的世界。正如我们最近在《科学》杂志上报道的那样，这项新技术使我们能够搭上野生乌鸦的便车，并对它们的日常生活有了深入的了解。它已经改变了我们对这个物种觅食生态的理解，它将在我们未来的工作中发挥关键作用。我用圈养乌鸦的对照实验来补充我的田野工作：（1）探测它们的认知能力（它们理解基本的物理原理吗？它们比其他动物聪明吗？(2)研究它们是否能模仿导师（支持工具技术文化传播的机制）;（3）探索遗传、社会和环境对特定工具形状产生的贡献（野生捕获的成年乌鸦忠实地产生某些工具形状吗？最后，我希望我的研究能更清楚地了解这些鸟到底有多“聪明”，以及它们最初的异常行为是如何进化的。最近有人提出，弗洛雷斯人不可能是一个工具使用者，因为它的大脑很小。新喀里多尼亚乌鸦证明了这一点，我对这个物种的研究可能会进一步揭示我们的进化根源。

Humans are weird animals. We communicate with a sophisticated language, we make and use tools to transform and exploit the environment, we share knowledge and information with our peers, and we build societies of astonishing complexity. Defining 'intelligence' is a contentious topic, but most would agree that humans are equipped with unsurpassed brain powers -- an observation that only too often leads to an exaggerated perception of 'human uniqueness'. But, what exactly was it that sent us on our unusual evolutionary trajectory? Was it particular ecological circumstances that facilitated one or several key adaptations, like language or tool use, and what role did these traits play in the evolution of culture? It is reasonable to assume that, ceteris paribus, the use of tools and the accumulation of knowledge would have conferred advantages to individuals or groups in other species, yet these traits, and especially their joint presence, are exceedingly rare in the animal kingdom. There are only two species for which cultural transmission of tool technology has been suggested: chimpanzees and, my study subject, the New Caledonian crow. These crows live on a remote Pacific island, where they use tools for extracting grubs from holes and crevices. They use at least three distinct tool types, including the most sophisticated animal tool design yet discovered, and they may even culturally transmit, and progressively refine, aspects of their tool technology (some tools vary in shape). Humans are masters at accumulating cultural information over generations, as evidenced by everyday items like watches or bicycles, not to mention computers or space shuttles. No single person could design and manufacture any of these objects from scratch. We build on the technological heritage of our ancestors, and research suggests it may be this capacity that made our species such an evolutionary success story. In New Caledonia, I investigate how wild crow societies are organised, how juveniles learn their skills, and how much of these birds' daily diet is obtained with tools. I also explore whether there is anything special about these birds' home island that might explain their unusual adaptations. In fact, they may provide a unique window into our own evolutionary past, permitting rare glimpses of what factors may have driven the evolution of tool use and culture in our ancestors. But studying these crows in the wild is not easy, because they are shy and live in dense forest where visibility is limited. My team has developed tiny, animal-borne video cameras that broadcast TV-quality, colour video. These cameras are mounted on a crow's tail, and peek forward through the legs to produce a crow's-eye view of the world. As we recently reported in Science, this novel technology enabled us to hitch a ride with wild crows and obtain intimate insights into their daily lives. It has already changed our understanding of this species' foraging ecology, and it will play a key role in our future work. I complement my fieldwork with controlled experiments with captive crows: (1) to probe their cognitive capabilities (Do they understand basic physical principles? Are they smarter than other animals?); (2) to examine whether they can imitate tutors (the mechanism that would support the cultural transmission of tool technology); and (3) to explore the genetic, social and environmental contributions to the production of particular tool shapes (Do wild-caught adult crows faithfully produce certain tool shapes, and what shapes do cross-fostered juveniles produce?). In the end, I hope my research will produce a much clearer picture of how 'intelligent' these birds really are, and how their unusual behaviour evolved in the first place. It has recently been suggested that Homo floresiensis could not have been a tool user because of its small brain. New Caledonian crows disprove this, and my study of this species may shed further light on our evolutionary roots.