( fig. S20), the mechanical properties of the synthetic nacre are still not as good as that of natural nacre (35,36) (Fig. 4, B and C). Due to the larger aspect ratio of the aragonite platelets in the synthetic nacre, the platelets exhibit a "partly pullout" behavior, which leads to lower crack-resistance capability.Because the precipitation of the second phase onto the matrix relies on electrostatic force, CaCO 3 and chitin can be substituted by other precursors with opposite charges to make superior composites such as engineering ceramics (21-24) (figs. S21 and S22). Besides, as the dependence of properties of the composite materials on the characteristic length of their periodic microstructure (37), the mechanical performance of these materials can be optimized by adjusting the properties of the original matrix (38), which affect both the amount of electrostatically absorbed precipitates and the density of the nucleation sites. The fabrication of the laminated synthetic nacre is not a special case; there are other techniques, such as programmable 3D printing, for constructing predesigned macroscopic matrices that can be readily incorporated with our strategy to produce composite materials. Moreover, this strategy is also adaptable for fabricating robust bulk materials with brittle and heat-labile components ( fig. S21B). Given the importance of nano-and microscopic structures for the materials performance, we thus anticipate that our method can be extended to produce various composite materials with unique properties. Humans operate with a "theory of mind" with which they are able to understand that others' actions are driven not by reality but by beliefs about reality, even when those beliefs are false. Although great apes share with humans many social-cognitive skills, they have repeatedly failed experimental tests of such false-belief understanding. We use an anticipatory looking test (originally developed for human infants) to show that three species of great apes reliably look in anticipation of an agent acting on a location where he falsely believes an object to be, even though the apes themselves know that the object is no longer there. Our results suggest that great apes also operate, at least on an implicit level, with an understanding of false beliefs.C entral to everything that makes us humanincluding our distinctive modes of communication, cooperation, and culture-is our theory of mind (TOM). TOM is the ability to impute unobservable mental states, such as desires and beliefs, to others (1, 2). For nearly four decades, a cardinal question in psychology has concerned whether nonhuman animals, such as great apes, also possess this cognitive skill (1, 3). A variety of nonverbal behavioral experiments have provided converging evidence that apes can predict others' behavior, not simply based on external cues but rather on an understanding of others' goals, perception, and knowledge (3, 4). However, it remains unclear whether apes can comprehend reality-incongruent mental states (e.g., false beliefs) (3...

Surprisingly little is known about the eye movements of chimpanzees, despite the potential contribution of such knowledge to comparative cognition studies. Here, we present the first examination of eye tracking in chimpanzees. We recorded the eye movements of chimpanzees as they viewed naturalistic pictures containing a full-body image of a chimpanzee, a human or another mammal; results were compared with those from humans. We found a striking similarity in viewing patterns between the two species. Both chimpanzees and humans looked at the animal figures for longer than at the background and at the face region for longer than at other parts of the body. The face region was detected at first sight by both species when they were shown pictures of chimpanzees and of humans. However, the eye movements of chimpanzees also exhibited distinct differences from those of humans; the former shifted the fixation location more quickly and more broadly than the latter. In addition, the average duration of fixation on the face region was shorter in chimpanzees than in humans. Overall, our results clearly demonstrate the eyemovement strategies common to the two primate species and also suggest several notable differences manifested during the observation of pictures of scenes and body forms.

Inferring the evolutionary history of cognitive abilities requires large and diverse samples. However, such samples are often beyond the reach of individual researchers or institutions, and studies are often limited to small numbers of species. Consequently, methodological and site-specific-differences across studies can limit comparisons between species. Here we introduce the ManyPrimates project, which addresses these challenges by providing a large-scale collaborative framework for comparative studies in primate cognition. To demonstrate the viability of the project we conducted a case study of short-term memory. In this initial study, we were able to include 176 individuals from 12 primate species housed at 11 sites across Africa, Asia, North America and Europe. All subjects were tested in a delayed-response task using consistent methodology across sites. Individuals could access food rewards by remembering the position of the hidden reward after a 0, 15, or 30-second delay. Overall, individuals performed better with shorter delays, as predicted by previous studies. Phylogenetic analysis revealed a strong phylogenetic signal for short-term memory. Although, with only 12 species, the validity of this analysis is limited, our initial results demonstrate the feasibility of a large, collaborative open-science project. We present the ManyPrimates project as an exciting opportunity to address open questions in primate cognition and behaviour with large, diverse datasets.

Emotion is one of the central topics in animal studies and is likely to attract attention substantially in the coming years. Recent studies have developed a thermo-imaging technique to measure the facial skin temperature in the studies of emotion in humans and macaques. Here we established the procedures and techniques needed to apply the same technique to great apes. We conducted two experiments respectively in the two established research facilities in Germany and Japan. Total twelve chimpanzees were tested in three conditions in which they were presented respectively with the playback sounds (Exp. 1) or the videos (Exp.2) of fighting conspecifics, control sounds/videos (allospecific display call: Exp. 1; resting conspecifics: Exp.2), and no sound/image.Behavioral, hormonal (salivary cortisol) and heart-rate responses were simultaneously recorded. The nasal temperature of chimpanzees linearly dropped up to 1.5 degree in two minutes, and recovered to the baseline in two minutes, in the experimental but not control conditions. We found the related changes in excitement behavior and heart-rate variability, but not in salivary cortisol, indicating that overall responses were involved with the activities of sympathetic nervous system but not with the measureable activities of the hypothalamus-pituitary-adrenal (HPA) axis. The influence of general activity (walking, eating) was not negligible but controllable in experiments. We propose several techniques to control those confounding factors. Overall, thermo-imaging is a promising technique that should be added to the traditional physiological and behavioral measures in primatology and comparative psychology.