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

人类是奇怪的动物。我们用一种复杂的语言交流，我们制造并使用工具来改造和利用环境，我们与同伴分享知识和信息，我们建立了令人惊讶的复杂社会。定义“智力”是一个有争议的话题，但大多数人都同意人类拥有无与伦比的脑力——这一观察结果往往会导致对“人类独特性”的夸大看法。但是，究竟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种或几种关键的适应，比如语言或工具的使用，这些特征在文化进化中发挥了什么作用？我们可以合理地假设，在其他条件不变的情况下，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，但这些特征，尤其是它们的共同存在，在动物王国中是极其罕见的。只有两种物种被认为有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偏远的太平洋岛屿上，在那里它们用工具从洞和裂缝中取出幼虫。他们至少使用三种不同的工具类型，包括迄今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，并逐步改进他们的工具技术（一些工具在形状上有所不同）。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证明了这一点，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之上，研究表明，可能正是这种能力使我们的物种在进化上如此成功。在新喀里多尼亚，我调查了野生乌鸦社会是如何组织起来的，幼鸟是如何学习技能的，以及这些鸟的日常饮食有多少是用工具获得的。我还探索了这些鸟的家乡是否有什么特别之处，可以解释它们不同寻常的适应能力。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，让我们得以瞥见哪些因素可能推动了我们祖先的工具使用和文化的进化。但是在野外研究这些乌鸦并不容易，因为它们很害羞，而且生活在茂密的森林里，能见度有限。我的团队开发了一种动物携带的微型摄像机，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，通过腿向前窥视，形成乌鸦的视角。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，并深入了解它们的日常生活。它已经改变了我们对该物种觅食生态的理解，并将在我们未来的工作中发挥关键作用。为了补充我的野外工作，我对圈养的乌鸦进行了对照实验：(1)探索它们的认知能力(它们理解基本的物理原理吗？它们比其他动物聪明吗？)；(2)考察他们是否能够模仿导师（支持工具技术文化传播的机制）；(3)探索遗传、社会和环境因素对特定工具形状产生的影响（野生捕获的成年乌鸦是否忠实地产生某些工具形状？交叉培育的幼鸦产生什么形状？）最后，我希望我的研究能让人们更清楚地了解这些鸟到底有多“聪明”，以及它们的不寻常行为最初是如何进化的。最近有人提出，弗洛勒斯人不可能是工具使用者，因为它的大脑很小。新喀里多尼亚乌鸦反驳了这一点，我对这个物种的研究可能会进一步阐明我们的进化根源。

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.