Chimp Females Who Leave Home Postpone Parenthood

Imani the chimpanzee, a newcomer to her group, lounges with her son at Gombe National Park in Tanzania. Photo by Ian Gilby, Arizona State University.

DURHAM, N.C. — New moms need social support, and mother chimpanzees are no exception. So much so that female chimps that lack supportive friends and family wait longer to start having babies, according to researchers who have combed through the records of Jane Goodall’s famous Gombe chimpanzees.

Wild chimpanzee females in western Tanzania who leave home or are orphaned take roughly three years longer to start a family.

The researchers analyzed more than 50 years’ worth of daily records for 36 female chimps born in Gombe National Park. Stored in the Jane Goodall Institute Research Center at Duke University, the records are part of a larger database containing close observations of hundreds of wild chimpanzees, going all the way back to Goodall’s first field notes from the early 1960s.

Some female chimpanzees stay with the group they were born into their entire lives. Others pull up their roots and move to a new group when they reach adolescence, presumably to avoid inbreeding.

The average age of first-time moms varies a lot, the researchers found. Females that stay home deliver their first infant around age 13. For migrants, it’s 16.

Several factors may contribute to the delay, the researchers said. Like all newcomers, they get pushed around, mostly by resident females. Having left their family and friends behind, they must jostle for position in the pecking order of a new and unfamiliar group.

“It’s a tough integration period,” said Kara Walker, postdoctoral associate in the department of evolutionary anthropology at Duke.

In contrast, stay-at-home females benefit from better support. Females also started reproducing earlier if their own mothers were around while they were growing up, particularly if their moms were high-ranking — in part because females with high-ranking moms get better access to food.

Their head start on motherhood means these early bloomers have the potential to produce more offspring over their lifetimes, said Anne Pusey, James B. Duke professor of evolutionary anthropology and director of the Jane Goodall Research Institute Center at Duke.

“This really raises the question of why some females stay and others go,” Pusey said.

The results also suggest that a lengthy journey from childhood to adulthood — long thought to be unique to the human branch of the primate family tree — may have deeper roots than previously thought.

“This suggests that chimpanzees are, developmentally, much more similar to humans than was previously believed,” says Christopher Walker, assistant professor of anatomy at NC State University.

The study appears online Nov. 20 in the Journal of Human Evolution.

This research was supported by the Jane Goodall Institute, the National Science Foundation (DBS-9021946, SBR-9319909, BCS-0452315, IOS-LTREB-1052693, DGE-1106401), the National Institutes of Health (R01 AI 058715) and grants from the Leakey Foundation and Margot Marsh Foundation.

CITATION: “Maturation is Prolonged and Variable in Female Chimpanzees,” Kara K. Walker, Christopher S. Walker, Jane Goodall and Anne E. Pusey. Journal of Human Evolution, Nov. 20, 2017.

Grantee Spotlight: David Samson

David Samson is from the University of Toronto, Mississauga. He was awarded a Leakey Foundation Research Grant during our spring cycle for his project entitled “What drives sleep flexibility? A comparative investigation of circumpolar and equatorial hunter-gatherers.” 

David Samson (L)

Humans are a remarkable species. We live in large social networks, persist in inhospitable places, fashion complex tools, and communicate using language. While we exhibit many morphological and behavioral differences to other primates – our cognitive capacity likely played a crucial role in our success.

My research investigates the biology, ecology, and evolution of primate sleep. I believe the effects of sleep on our lineage were profound. For example, in humans, sleep is critical for immune strength, working memory, attention, decision-making, and visual-motor performance, yet how sleep affects such processes remains unknown for most non-human primates.

To investigate this research question, I use pioneering, non-invasive technology to study human and non-human primates with a broad phylogenetic scope. In addition, I engage with the emerging field of evolutionary medicine by using my findings to understand human sleep disorders within an evolutionary framework. The ultimate goal of my research is to further our understanding of human evolution.

Scientists Discover New Orangutan Species


The newly discovered species of orangutan, Pongo tapanuliensis. Photo: Maxime Aliaga

Funded in part by The Leakey Foundation

Scientists have long recognized six living species of great ape aside from humans: Sumatran and Bornean orangutans, eastern and western gorillas, chimpanzees, and bonobos. But researchers reporting in Current Biology on November 2 have now made it seven, based on a collection of evidence showing that an isolated population of orangutans living in Sumatra is actually its own unique species. They’ve named the new species the Tapanuli orangutan (Pongo tapanuliensis).

Unfortunately, the researchers say, there are only about 800 Tapanuli orangutans left. Those that remain are under threat from loss of lowland habitat and hunting, which makes this newly discovered species among the most threatened great ape species in the world.

“It isn’t an everyday event that we find a new species of great ape, so indeed the discovery is very exciting,” said Michael Krutzen of the University of Zurich in Switzerland, senior author of the study.

The Leakey Foundation is proud to have supported this research. Donate today and help fund the next big discovery.

“Great apes are among the best-studied species in the world,” added Erik Meijaard of the Australian National University. “If after 200 years of serious biological research we can still find new species in this group, what does it tell us about all the other stuff that we are overlooking: hidden species, unknown ecological relationships, critical thresholds we shouldn’t cross? Humans are conducting a vast global experiment, but we have near-zero understanding of what impacts this really has, and how it could ultimately undermine our own survival.”

The newly discovered species of orangutan, Pongo tapanuliensis. Photo: Andrew Walmsley

The new orangutan species lives in the Batang Toru area in North Sumatra, Indonesia. While there had been rumors, no one was sure that this population of orangutans existed until 1997. They live south of what had been the known range for Sumatran orangutans.

Earlier studies suggested that the group differed from other orangutans behaviorally and at the genetic level, but it wasn’t clear that those differences were enough to support its designation as a new species. The breakthrough came in 2013, when the research team including Meijaard got access to a skeleton belonging to a Batang Toru orangutan killed in a human-animal conflict. Careful studies of the animal revealed consistent differences in its skull and teeth.

A sophisticated analysis of 37 orangutan genomes now shows that the deepest split in the evolutionary history of living orangutans occurred more than three million years ago, between the Batang Toru population and Bornean orangutans to the north of Lake Toba. Bornean and Sumatran orangutans separated only much later, less than 700,000 years ago. Behavioral and ecological evidence lends further support for the notion that the orangutans living in Batang Toru are a separate species, the researchers said.

Skull of Pongo tapanuliensis. Photo: Nater et al.

“The Batang Toru orangutans appear to be direct descendants of the initial orangutans that had migrated from mainland Asia, and thus constitute the oldest evolutionary line within the genus Pongo,” said Alexander Nater, also of the Unversity of Zurich. “The Batang Toru population was connected to populations to the north until 10,000 or 20,000 years ago, after which it became isolated.”

The findings mean that there are now 800 fewer Sumatran orangutans than previously thought. The Tapanuli orangutans are also severely threatened by hunting and the proposed development of a hydroelectric dam that would flood large parts of their best habitat if implemented. That’s especially discouraging given that previous analyses suggest a mortality rate of less than one percent per year would still be enough to drive the Tapanuli orangutans extinct.

“If even 8 out of 800 animals per annum were killed or otherwise removed from the population, the species might be doomed,” the scientists caution.

The researchers say the most important thing now is to work with organizations already in the area and Indonesian government authorities to urge support for more effective conservation measures to protect the Batang Toru area. They also want to learn more about the relationship of the Tapanuli orangutan to now-extinct orangutan populations that used to live in other parts of Sumatra.

This work was financially supported by the University of Zurich, the Swiss National Science Foundation, The Leakey Foundation, the A.H. Schultz Foundation, the UZH Research Priority Program ”Evolution in Action,” the Arcus Foundation, Australian National University, an ANU Vice Chancellor Travel Grant, Australia Awards Scholarship-DFAT, an ERC Starting Grant, EMBO, Fundacio Zoo Barcelona, the Julius-Klaus Foundation, MINECO/FEDER, the Gates Cambridge Trust, and the Department of Anthropology at the University of Zurich.

Current Biology, Nater et al.: “Morphometric, Behavioral, and Genomic Evidence for a New Orangutan Species” DOI: 10.1016/j.cub.2017.09.047

Grantee Spotlight: Carrie Miller

Carrie Miller is a PhD candidate from the University of Minnesota. She was awarded a Leakey Foundation Research Grant during our spring 2017 cycle for her project entitled “Does paternity certainty elicit protection and support of offspring by male gelada monkeys?”

Carrie Miller with a gelada monkey in Ethiopia

Recent studies suggest humans underwent an intermediate stage of polygyny within a multi-level society, similar to multi-level societies observed in gelada monkeys (Theropithecus gelada) or hamadryas baboons (Papio hamadryas). Gelada males employ a range of reproductive strategies and may practice multiple strategies over the course of their life. Leader-males invest heavily in mating effort by defending and maintaining stable breeding bonds with ‘harem’ females in their one-male unit (OMU). Because, the gelada OMU typically has just one breeding male, leader-males should have high paternity certainty. The resulting high paternity certainty makes infanticide a logical strategy for new males taking over an OMU. The multi-level social structure also results in frequent encounters with rival males in all-male bachelor groups seeking to acquire an OMU of their own. However, deposed leader-males often stay on as subordinate follower-males, perhaps to protect their offspring from infanticide following the take-over by a new male. These combined features of gelada societies suggest that males, especially recently deposed leader-males, may benefit by shifting their investment to parenting effort. However, male-immature interactions have not yet been studied in detail in geladas or other primates with multi-level societies.

Guassa Gelada Research Project field site

My project seeks to examine the role multi-level social systems of geladas, which exhibit high paternity certainty and high infanticide risk, may have played in promoting paternal care in the absence of provisioning. I will examine variation in male-immature interactions and long-term paternal effects on immatures through behavioral data collection with gelada monkeys at Guassa, Ethiopia. I will also assign paternity for immatures in the Guassa study population through genetic analysis of fecal samples.

By studying gelada male reproductive strategies and male-immature interactions we can better understand the variation in paternal care and male reproductive strategies observed across human societies. In addition, by studying these questions in a species with a multi-level social system, we will begin to understand the significant role multi-level systems played in the evolution of similar social traits in humans.

Guassa geladas

Riff Raff (infant) and Rafiki (mother)

Grantee Spotlight: Elaine Guevara

Elaine Guevara was awarded a Leakey Foundation Research Grant during our spring 2017 cycle for her project entitled “Epigenetics of primate longevity.” Guevara is a doctoral student at Yale University and a visiting student at the Center for the Advanced Study of Human Paleobiology at George Washington University.

Elaine Guevara

Humans are long-lived compared with most mammals, including our closest living biological relatives, the chimpanzees. Our exceptional longevity has been proposed to be a key part of what makes us human, potentially having coevolved with a number of other notable human characteristics, including large brain size; enhanced cognitive capacity; an extended juvenile period; social learning; behavioral complexity, including skilled foraging; and cultural innovation. Yet the genetic and physiological bases of our remarkable longevity—as well as the processes underlying human aging—remain poorly understood.

A growing body of recent research has demonstrated a critical role for epigenetics in aging. In particular, methylation—a chemical alternation to DNA that plays a role in adjusting gene expression—shows a consistent pattern of change at many different specific pieces of DNA found throughout the genome with age in humans. In facts, these alternations in methylation level are so predictable that they can be used to accurately estimate an individual’s chronological age. Moreover, slight deviations among individuals of the same chronological age in “methylation age” seem to reflect biological aging: prematurely elevated methylation age is associated with mortality risk, increased frailty, decreased grip strength and lung function, diminished cognitive performance, and increased cancer and cardiovascular disease risk. Thus, methylation age represents a valuable new approach for measuring biological aging, identifying factors that influence aging rate, and potentially uncovering the genetic regulatory changes that underlie physiological aging.

So far, change in methylation with age has primarily been studied in humans and has not been studied at all in any other primates. However, this newly discovered phenomenon offers potential for insight into species differences in aging and lifespan if considered in a comparative context. To this end, I am characterizing the pattern of methylation change with age in chimpanzees by generating genome-wide methylation data for 100 chimpanzees of ages across the lifespan, and comparing it to that data from humans. These data may allow for the identification of genes that are differently regulated with age in the two species and thereby help identify which physiological mechanisms (for example, DNA damage repair or immune function) play critical roles in human survival to advanced ages.