Kibale Chimpanzee Project

Richard Wrangham on human self-domestication in the Wall Street Journal

We differ from our ancient ancestors in ways similar to how dogs differ from wolves. Download the pdf file here:

Humans: The Domesticated Primate (pdf)



Get your KCP t-shirt for World Chimpanzee Day

July 14, 2018 is World Chimpanzee Day! In anticipation of this exciting occasion, we are offering the first Kibale Chimpanzee Project t-shirts, featuring our fabulous, color logo by artist Eric Losh. For every donation of $30 (US) that we receive by the end of June, we will send you one super-soft, heather gray t-shirt for World Chimpanzee Day. (Donors outside the US, please include an additional $5 for shipping.)

Donations can be made through the Paypal link on our website: Under “Special Instructions” please enter your shipping address, and indicate the style (men’s or women’s) and size (S-XXL) that you prefer. Shirts will be shipped in early July.

Your donation will support KCP’s conservation and education efforts in Kibale National Park and the surrounding communities, including scholarships for local children to attend secondary school.

New book from Harvard University Press.

Now available from Harvard University Press! Chimpanzees and Human Evolution systematically compares us with our closest living relatives, attempting to account for the evolution of both similarities and differences. Contributors include current and former KCP researchers – Richard Wrangham, Martin Muller, Melissa Emery Thompson, Katie Slocombe, Sherry Nelson, Herman Pontzer, Ian Gilby, Brian Hare, and Michael Wilson. From the Press:

“Knowledge of chimpanzees in the wild has expanded dramatically in recent years. This comprehensive volume, edited by Martin Muller, Richard Wrangham, and David Pilbeam, brings together scientists who are leading a revolution to discover and explain what is unique about humans, by studying their closest living relatives. Their observations and conclusions have the potential to transform our understanding of human evolution.

Chimpanzees offer scientists an unmatched view of what distinguishes humanity from its apelike ancestors. Based on evidence from the hominin fossil record and extensive morphological, developmental, and genetic data, Chimpanzees and Human Evolution makes the case that the last common ancestor of chimpanzees and humans was chimpanzee-like. It most likely lived in African rainforests around eight million years ago, eating fruit and walking on its knuckles. Readers will learn why chimpanzees are a better model for the last common ancestor than bonobos, gorillas, or orangutans. A thorough chapter-by-chapter analysis reveals which key traits we share with chimpanzees and which appear to be distinctive to Homo sapiens, and shows how understanding chimpanzees helps us account for the evolution of human uniqueness. Traits surveyed include social behaviors and structures, mating systems, diet, hunting practices, tool use, culture, cognition, and communication.

Edited by three of primatology’s most renowned experts, with contributions from 32 scholars drawing on decades of field research, Chimpanzees and Human Evolution provides readers with detailed up-to-date information on what we can infer about our chimpanzee-like ancestors and points the way forward for the next generation of discoveries.”

Comprehensive, judicious, authoritative, up-to-date, well written, and thoroughly fascinating to anyone interested in either species.—Steven Pinker, author of The Better Angels of Our Nature

Explaining the distribution of a chimpanzee social custom

By Richard Wrangham

In a new Current Biology paper based on almost 1000 photographs of social grooming, Kanyawara researchers have shown for the first time that variants of chimpanzee social behavior can be passed from mother to offspring, and last for a lifetime.

During the many decades that Jane Goodall spent observing chimpanzees in Gombe National Park, Tanzania, there is one kind of social grooming that she never saw. The missing kind is called high-arm grooming, a style whose significance was first realized by Gombe researchers Bill McGrew and Caroline Tutin when they visited another Tanzanian chimpanzee research site in Mahale Mountains National Park in 1972. There they saw high-arm grooming for the first time. They instantly suggested it to be a social tradition. Since then it has become renowned as the classic example of chimpanzee social culture.

The pattern was well known to the team of Mahale researchers led by Toshisada Nishida. Every now and again, a pair of grooming chimpanzees each raised their opposite arms (left to left, or right to right). They would hold them in contact for up to about two minutes at a time while continuing to groom with their other hands. Nishida had assumed that all chimpanzees practiced this striking salute.

However while high-arm grooming has now been recorded from eight wild populations across Africa, it is entirely absent in three. Strikingly, the three that lack high-arm grooming are found in different subspecies (Gombe and Budongo in the east, Bossou in the west), supporting the notion of the differences being due to culture rather than genes. In Kanyawara, and probably throughout Kibale, high-arm grooming can be seen almost every day.

High-arm grooming was originally called hand-clasp grooming, but that term does not capture the fact that the style of contact between the uplifted arms varies widely. Sometimes chimpanzees indeed clasp their raised hands together (called palm-to-palm clasping). However at other times their arms are in contact only at the wrist, or along the forearm. The frequency of palm-to-palm clasping varies extensively among populations from less than 5% to more than 80% of high-arm grooming events.

This variation in the frequency of palm-to-palm clasping has been an intriguing mystery. Could palm-to-palm clasping be a sign of mutual friendship? Does it signify membership in a particular social network? Or does it indicate shared ages, or dominance ranks? Our new paper rules out those ideas and finds a surprisingly simple pattern. Whether or not a chimpanzee clasps another’s palm during high-arm grooming depends on whether their mother did so. Palm-to-palm clasping is a social custom passing down matrilines.

There is much yet to find out. Kanyawara mothers vary in their frequency of palm-to-palm clasping with their family from less than 10% to more than 90% of occasions. Where does that variation come from? And most importantly, why do they high-arm groom at all? When members of matrilines with different rates of palm-to-palm clasping engage in high-arm grooming, one of them has to abandon their preference. So who wins? Our current data do not give any indication that the “winner” is higher-ranking, or older, or female, or anything else. But with 1000s more photographs, maybe a pattern will emerge. If we are lucky we might then find out whether this social custom has a social meaning larger than doing what Mum did.


New KCP research in PNAS

Birth rates can be a good indicator of the viability and health of great ape populations. While apes reproduce slowly as a rule, richer and more stable food resources lead to faster production of offspring, putting members of these endangered species on a path towards population growth. In Kanyawara, chimpanzee birth rates have increased noticeably over the past 2 decades. Our alpha female, Outamba, has produced infants every 3.5 years, a startling 2 years faster than the average wild chimpanzee. But is there a downside to having all of these babies? Life history theory suggests that, because mothers have limited resources to devote to reproduction, they may face tradeoffs between producing many offspring and investing in the quality of each. While these tradeoffs are almost inevitable, evidence for them has eluded anthropologists studying humans and other primates.

In a recent issue of the Proceedings of the National Academy of Sciences, the Kibale Chimpanzee Project team tested this prediction by examining the influence of reproductive rates on offspring growth. We found that an immature chimpanzee’s size had a strong positive relationship with the interval to its next sibling’s birth. In other words, when mothers could afford to reproduce faster, they did so at the expense of their offspring’s growth. Remarkably, chimpanzee juveniles did not manage to make up for these early growth deficits later on, but remained small throughout their adolescent years. These tradeoffs could come about because mothers who reproduce quickly exhaust their supplies of energy to feed infants. Alternatively, when a mother produces two offspring in quick succession, she might withdraw nutritional support from the first in order to feed the second. Our data support the second interpretation. It was mothers like Outamba, who were in the best energetic condition during lactation, that produced the smallest offspring. Instead of using surplus energy to enhance their current offspring, these mothers appeared to bank it so that they could afford to produce a new infant sooner. Because wild chimpanzee mothers cannot afford to feed two infants at the same time, they have to wean one infant in order to feed the next. The weaned infants then have to feed themselves, even if they have not yet learned how to be efficient foragers or developed the digestive system to fully process raw plant foods. For humans, this is less of a problem. Human infants continue to receive nutritional support from their mothers and other family members long after they finish nursing, and cooked foods are both calorie rich and easy to digest.

KCP is dedicated to research that is non-invasive. One of the big challenges that we have faced is how to estimate the body size and energetic condition of our animals without weighing them. Weighing is both impractical and disruptive, as it would require baiting scales with food. Over the years, we have developed novel assays for urinary biomarkers of muscle mass and energy balance that enabled us to complete this study. With this toolkit, we can begin to answer many new questions about growth and body size. Stay tuned!

Apes Seizure Database reveals extent of illegal trade

GRASP (Great Apes Survival Partnership) just released this short video on the illicit trade in great apes. Narrated by KCP co-director Dr. Richard Wrangham, it introduces the Apes Seizure Database, an important new tool to fight the global traffic in great apes.