Primate Tales: Edgar and the Appearance of Pyrrhic Victory in Biology

by Joseph T. Feldblum (Leakey Foundation Grantee) and Deus C. Mjungu (Leakey Foundation Baldwin Fellow)

pyrrhic victory
1. A victory or goal achieved at too great a cost.

Chimpanzees live in distinct communities, with mostly friendly relationships within groups and aggressive territorial interactions between groups. Every once in a while, a group of males (and more rarely a few females) will get together, approach a territorial boundary, and in silent single file, stopping often to stand upright and survey the valley below, go on a patrol. I never observed one and was always uncertain about whether I wanted to. It’s undoubtedly a fascinating behavior but would jeopardize the lives of some of the chimps that I grew attached to over three field seasons in Gombe National Park, Tanzania. If a patrol comes across a lone individual from a neighboring community, they often attack and kill them. But if they come across a group of similar size, they’ll usually stick to calling loudly and threateningly at each other from a safe distance. The key predictor of violence, it seems, is party size asymmetry.

This makes the behavior of the males in the Mitumba community in Gombe all the more puzzling. For more than four years, the alpha male in Mitumba has been Edgar, a ruler with an iron fist if ever there was one.  Every other community member is terrified of Edgar, screaming and grunting their submission at the first sign of trouble. And strangely, other than the sickly adult male Rudi, who died after my first field season in Gombe National Park, all the other males are young adolescents.

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This unusual demographic structure has an insidious explanation. Edgar, and Rudi back when he was still alpha, are known or suspected to have killed off several of the other males in the community who could have challenged their positions. Forest, who would be 20 now and newly full size, was brutally attacked by Edgar more than four years ago, and subsequently disappeared. Now it seems that Apple, one year younger, has met the same fate, as he hasn’t been seen in more than a year following a similar attack.

Edgar eating a colobus monkey. Photo credit: Ian C. Gilby

So Mitumba males now number only Edgar and a couple adolescent males, certainly not intimidating numbers for border protection. Why would Edgar endanger his group by weakening it so severely?  Wouldn’t such behavior be maladaptive?

Probably not. It’s important to remember that natural selection operates on individuals, not on groups.  So although the group’s success could be hampered by Edgar’s brutality, his individual success is probably enhanced. From genetic analysis, we’ve found that Mitumba alpha males increased their share of paternities after killing off rivals, and Edgar is likely experiencing similar success judging by the fear he inspires.

Chimpanzees live in complex societies, and males must both compete with group-mates for access to females and cooperate against rival groups. Natural selection will hone the balance between these strategies, but no balance point will be ideal in all cases. Indeed, researchers at Mahale, another field site in Tanzania, have suggested that severe competition between males in a small community may have contributed to its dissolution and the emigration of most of its females into a neighboring group. Only time will tell if Edgar’s despotism will be his undoing, or whether selection will prove him a successful, if brutal, tactician.

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pyrrhic victory. Unabridged. Random House, Inc. (accessed: January 3, 2018).


Save the Date to Celebrate!

Save the Date for The Leakey Foundation’s 50th anniversary gala!

The celebration will take place on Thursday, May 3, 2018, at the St. Regis in San Francisco and we invite you to join us to celebrate 50 years of exploring, discovering, and sharing the human story.

Check back soon for more details.

For information on sponsorship opportunities, or to purchase a table, please call or email Kristin Berger, Development Director, at (415)561-4646 extension 16.


Introducing Our Fall 2017 Grantees

The Leakey Foundation held our fall 2017 granting session on December 2, 2017. Our Board of Trustees unanimously approved 23 research grant proposals for funding.

Here are some numbers from our fall 2017 granting cycle:

There were 96 applications for research grants this cycle.

40% of the proposals were categorized as behavioral, and 60% were paleoanthropology.

416 reviews were submitted to our grants department this cycle. Thank you to our reviewers! We could not do it without you.

We would like to congratulate all of our new grantees, and we look forward to sharing news and information about them and their research along the way!

Brendan Barrett of the University of California, Davis


Brendan Barrett, University of California Davis:  Stone tool use & taxonomic status of Coiba Archipelago capuchins

Leveda Cheng, Max Planck Institute for Evolutionary Anthropology:  Behavioural and endocrinological correlates of intergroup encounters in bonobos

Alba García de la Chica, University of Barcelona:  Behavioral, hormonal and life-history correlates of pairbonding in owl monkeys

Sharon Gursky, Texas A&M University:  The function of ultrasonic vocalizations in spectral tarsiers.

Duna Susie Lee, New York University:  The role of testosterone in the modulation of parental behaviors in female rhesus macaques

Elizabeth Mallott, Northwestern University:  Response of primate gut microbiome function to increased faunivory

Caroline Schuppli, University of Zürich:  Orangutan mothers’ adaptive strategies to make their infants develop fast

Meagan Vakiener, The George Washington University:  Weaned age in gorillas using trace element distributions in teeth

Melissa Wilson Sayres, Arizona State University:  Quantifying the variation and heritability of X-inactivation

Dr. Fredrick Kyalo Manthi of the National Museums of Kenya


James Blinkhorn, University of Liverpool:  The Late Acheulean to Middle Palaeolithic transition in South Asia

Breanne Clifton, University of Connecticut:  Using phytoliths to reconstruct hominin adaptations and microhabitats during the Acheulian-MSA transition in the Kapthurin Formation, Kenya

Dylan Gaffney, University of Cambridge:  The initial colonisation of insular rainforests by archaic and modern hominins

Christopher Gilbert, Hunter College, City University of New York:  Primate evolution, chronology, and biogeography in the Indian Lower Siwaliks

Kevin Hatala, Chatham University:  Paleoecological investigation of 1.5 Ma footprint sites near Nariokotome, Kenya

Hannah Hilbert-Wolf, James Cook University:  Dating hominin fossils in the East African Rift, Malawi

Tania King, University College London:  Neanderthal occupation of the southern Caucasus: Chronological and biogeographic framework

Amanda Leiss, Yale University:  Paleoenvironmental context of ESA archaeology: An analysis of Gona fauna.

Fredrick Manthi, National Museums of Kenya:  Investigations of Middle Pleistocene sites in Natodomeri, northwestern Kenya

Laurent Marivaux, Institut des Sciences de l’Evolution de Montpellier (ISEM):  Oligocene and Miocene platyrrhine primates from Tarapoto, Peruvian Amazonia

Steffen Mischke, University of Iceland:  Environment of early hominins outside of Africa: The Nihewan Basin

Jonathan Reeves, The George Washington University:  Movement ecology and Pleistocene hominin land-use: Perspectives from Koobi Fora

Sileshi Semaw, CENIEH:  Gona Palaeoanthropological Research Project

Frido Welker, Max Planck Institute for Evolutionary Anthropology:  Towards complex Pleistocene hominin proteomes using multiple proteases.

Grantee Spotlight:  Thomas Plummer

Thomas Plummer is a Professor of Anthropology at Queens College, City University of New York, and a member of the New York Consortium in Evolutionary Primatology. He was awarded a Leakey Foundation research grant in our spring 2017 cycle for his project entitled “Excavation of ca. 2.6 Ma Oldowan sites at Nyayanga, Kenya.”

Thomas Plummer in Kenya.

Leakey Foundation funding was awarded to investigate the foraging ecology of Oldowan hominins at Nyayanga, Homa Peninsula, Kenya. The appearance and spread of Oldowan archeological sites ca. 2.6 – 1.7 million years ago (Ma) reflects an important adaptive shift in human evolution.  Stone technology gave hominins the potential to work a wide variety of materials, including nutrient-dense foods (e.g., animal carcasses, underground storage organs) that could be acquired or prepared with tools.  But many of the traits routinely used to characterize the Oldowan (transport of lithic raw material beyond what is normally exhibited by living nonhuman primates, large mammal butchery, repeated use of the same spots on the landscape to create a stacked sequence of archeological material) more clearly exemplify Oldowan occurrences 2 Ma and younger.  Lithic transport dynamics and the activities that Oldowan tools were used for at the dawn of the industry are only poorly understood.

Magnetostratigraphy and biostratigraphy suggest that Nyayanga is ca. 2.6 Ma, but unlike most other early Oldowan sites, artifacts are frequently associated with well-preserved fossils.  Past surface collections recovered a wide variety of fauna, a Paranthropus sp. upper molar, Oldowan tools, and fossils with stone tool butchery marks.  We will be excavating three sites that were tested in 2016 and already have yielded spatially associated accumulations of stone tools and fauna, including artifacts associated with a partial skeleton of a hippopotamid.

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We have two broad objectives for this project. First, we will expand our 2016 excavations to enlarge the collections of in situ fossils and artifacts.  This will afford us large enough samples of excavated materials to carry out meaningful analyses of hominin behaviors within their paleoenvironmental contexts.  Second, at the end of the season, we’ll need to protect the sites against rapid erosion due to rainfall and livestock trampling.  We will thoroughly backfill excavations, contour and stabilize the slopes, and work with the local landowners to limit foot traffic over areas of paleoanthropological significance.  The proposed project will document hominin behavior at one of the oldest archaeological localities discovered thus far. It will expand the geographic range of the Oldowan showing that the technology was more broadly distributed across East Africa at an earlier time than previously thought.  And it will help develop a temporal sequence of Oldowan sites (Nyayanga at ca. 2.6 Ma, Kanjera South at ca. 2 Ma, and Sare River at ca. 1.8 Ma) on the Homa Peninsula that will allow us to carry out a regional comparison of Oldowan hominin behavior through time.

Grantee Spotlight: Sean Lee

Sean Lee is a PhD candidate from The George Washington University. He was awarded a Leakey Foundation Research Grant during our spring 2017 cycle for his project entitled “The ontogeny of social behavior and facial form in Pan.” 

Sean M. Lee at the LuiKotale Bonobo Project field site in Democratic Republic of Congo. Researchers wear surgical masks to prevent disease transmission.

Chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) are our closest living relatives, and they are both equally so. Their common ancestor diverged from the lineage that eventually led to us roughly 5-7 million years ago. Then, roughly 1-2 million years ago, this chimpanzee-bonobo common ancestor split into the two great ape species that we know today. At around the same time as this “speciation,” several other great apes belonging to our very own human lineage were roaming around other regions of Africa and Asia. For better or for worse, none of these “hominins” (great apes more closely-related to humans than to chimpanzees and bonobos) exist today. Well, except for us of course! All that remains of these hominins are the signs that they left of their past existence. These signs can tell us quite a lot about human evolution, as many Leakey Foundation grantees can attest, but the limitations are obvious—we cannot study their biology in vivo, that is, in real-time, as living, breathing organisms.

Leah, an immature female bonobo. Photo by Sean Lee.

So how can living, breathing, extant primates like chimpanzees and bonobos help us? (By the way, extant means not extinct­—confusing, I know). Well, aside from being a source of sheer natural beauty that we can be in awe of, we can use them as living “models” to examine behavioral and biological processes in vivo, processes that may have been similar to those which occurred in our long-extinct hominin ancestors. Chimpanzees and bonobos are particularly well-suited to be models of human evolution because, as I mentioned before, they are our closest living relatives. But this is not the only reason—the two species also exhibit important differences between each other in terms of behavior, morphology, physiology, and cognition, despite speciating only one to a few million years ago (a relatively short amount of evolutionary time). For example, while chimpanzees are characterized by male-dominated social systems (that is, all adult males in a given social group are higher-ranking than all adult females), adult females hold the highest-ranking positions in bonobos. That’s a pretty big difference! And an important one, too, which warrants extensive study! By understanding more about how differences such as these came about in our closest living relatives we can provide a broader, comparative perspective for those anthropologists studying the bones, tools, footprints, and other signs that our hominin ancestors left behind.

Shwali, an immature male chimpanzee. Photo by Kaitlin Wellens.

For my dissertation, I will contribute to this understanding by comparing the behavioral development and physical growth of chimpanzees and bonobos. This is important because previous research suggests many of the differences between adults of these two species arise through changes in how they develop during infancy and juvenility. I say suggests because much of this research has been conducted on captive populations of chimpanzees and bonobos, in zoos, sanctuaries, or research centers. While captive animals are very informative, there is always the possibility that they do not quite resemble their wild counterparts. But this is not to say that we should rely solely on wild studies—both types of research are extremely valuable in conjunction with the other. To contribute to this joint-endeavor, I will collect data on behavioral development and physical growth from wild populations of both species—specifically, the eastern chimpanzees of Gombe Stream, Tanzania, and the bonobos of LuiKotale, Democratic Republic of Congo—to learn more about how each species grows and develops under natural conditions. So stay tuned for my Field Update to learn more about these field sites, the beautiful animals that reside there, and how my research is going!

Bonobo mother, Wilma, and her 1.5 year-old son, Watson

Immature chimpanzees grooming at Gombe Stream National Park, Tanzania