Richard W. Wrangham’s research while affiliated with Harvard University and other places

The use of tools to drink water is well‐documented in wild chimpanzees, but the specific function of this behavior is unclear. Here we use a large data set of drinking behaviors spanning 14 years of observation from the Kanyawara community of chimpanzees living in Kibale National Park, Uganda, to test two possible functions of leaf‐sponges and other drinking tools. On the one hand, chimpanzees may use tools to access water that is hard to reach, which predicts that chimpanzees will preferentially use tools to drink at tree holes and crevices compared to all other locations. Conversely, chimpanzees may use these tools to filter stagnant water, in which case they would use tools more often at holes and puddles compared to running water sources (e.g., streams). We compared both likelihood of using a tool to drink at different locations, as well as overall rates of drinking, and found chimpanzees in this community most often drink from streams without tools. However, when they do use tools, they preferentially do so to drink at tree holes. Given known age and sex effects on tool use in chimpanzees, we also examined demographic variation in drinking tool use to understand the emergence of this behavior. While females use tools more often than males overall—in part driven by differences in drinking rates at different locations—both males and females use tools more frequently at tree holes than other locations when they do drink there. Finally, comparisons by age indicate that this selectivity strengthens over development with older chimpanzees showing a more pronounced effect of using tools more often at tree holes, suggesting that younger chimpanzees may exhibit exploratory tool use behavior. These results pinpoint the specific function of tool use during drinking and further suggest that even simple tools may require learning for use in appropriate contexts.

Objectives Self‐domestication theory and preliminary data suggest that western chimpanzees ( Pan troglodytes verus ) could have smaller brains than eastern chimpanzees ( P. t. schweinfurthii ), but no large‐scale studies of chimpanzee endocranial volume (ECV) have tested this. This study compares ECV of wild adult P. t. verus and P. t. schweinfurthii , along with femoral head diameter (FHD; an index of body size), bizygomatic breadth (BZB) and palate length (PAL). Materials and Methods Adult crania of P. t. schweinfurthii (60 females, 90 males, from Uganda and Democratic Republic of Congo) and P. t. verus (43 females, 37 males, from Liberia and Ivory Coast) were sampled. ECV was measured using 3 mm diameter glass beads, and FHD, PAL, and BZB with digital calipers. Quantities of interest were estimated using Bayesian inference. Results No meaningful differences were found between subspecies on average in ECV, FHD, or the relationship between ECV and FHD. Within countries and subspecies, ECV varied widely among individuals, partly because males had higher ECV on average than females. When sex was controlled for, ECV was unrelated to FHD. Within subspecies there was no evidence of meaningful differences in average ECV among countries. PAL was the only measure that differed between subspecies on average, being shorter in P. t. verus females. Discussion Current data show that within sexes, mean ECV is similar between P. t. verus and P. t. schweinfurthii . This suggests that average brain size in chimpanzees has remained unchanged for ~0.7 million years, in contrast to orangutans ( Pongo ) and humans.

Conservation funding is currently limited; cost-effective conservation solutions are essential. We suggest that the thousands of field stations worldwide can play key roles at the frontline of biodiversity conservation and have high intrinsic value. We assessed field stations’ conservation return on investment and explored the impact of COVID-19. We surveyed leaders of field stations across tropical regions that host primate research; 157 field stations in 56 countries responded. Respondents reported improved habitat quality and reduced hunting rates at over 80% of field stations and lower operational costs per km2 than protected areas, yet half of those surveyed have less funding now than in 2019. Spatial analyses support field station presence as reducing deforestation. These “earth observatories” provide a high return on investment; we advocate for increased support of field station programs and for governments to support their vital conservation efforts by investing accordingly.

The speciation process that led to the separation of bonobos (Pan paniscus) from chimpanzees (P. troglodytes) is estimated to have begun between 0.8 and 2.6 million years ago (Takemoto et al. 2017), most likely between 1.5 and two million years ago (Fontsere et al. 2022). Since then, the two species have accumulated substantial differences in morphology, physiology, behavior and cognition. Of particular importance for social behavior, bonobos tend to occur in more stable parties and to have stronger associations among females (Kano 1982, 1992; Furuichi 2009, 2011, 2023). In this chapter, I consider potential explanations for the evolution of these differences. I conclude that bonobos have likely evolved from a chimpanzee-like ancestor, and have been subject to selection against male aggressive behavior, or “self-domestication.” I then consider ecological explanations for this process. I focus on the “No gorillas” hypothesis, which proposes that bonobo evolution was strongly influenced by their experiencing reduced scramble competition for food compared to chimpanzees.

Based on evidence of selection against alpha-male behavior in the earliest Homo sapiens, I suggest that by 300,000 ya (years ago) language would have been sufficiently sophisticated to contribute to peacemaking between groups. Language also influenced the social landscape of peace and war, and groups' ability to form coalitions.

Research in African ape sanctuaries has emerged as an important context for our understanding of comparative cognition and behavior. While much of this work has focused on experimental studies of cognition, these animals semi-free-range in forest habitats and therefore can also provide important information about the behavior of primates in socioecologically-relevant naturalistic contexts. In this "New Approaches" article, we describe a project where we implemented a synthetic program of observational data collection at Ngamba Island Chimpanzee Sanctuary in Uganda, directly modeled after long-term data collection protocols at the Kibale Chimpanzee Project in Uganda, a wild chimpanzee field site. The foundation for this project was a strong partnership between sanctuary staff, field site staff, and external researchers. We describe how we developed a data-collection protocol through discussion and collaboration among these groups, and trained sanctuary caregivers to collect novel observational data using these protocols. We use these data as a case study to examine: (1) how behavioral observations in sanctuaries can inform primate welfare and care practices, such as by understanding aggression within the group; (2) how matched observational protocols across sites can inform our understanding of primate behavior across different contexts, including sex differences in social relationships; and (3) how more robust collaborations between foreign researchers and local partners can support capacity-building in primate range countries, along with mentoring and training students more broadly.