Barbara J. King

Friday Animal Blog

Genes for Altruism - Primate Diaries in Exile

October 29, 2010

I'm honored to host a prominent science blogger this week whose work consistently informs my thinking.
This guest post by Eric Michael Johnson is part of his Primate Diaries in Exile blog tour. You can follow other stops on this tour through his RSS feed, The Primate Diaries on Facebook, or by following him on Twitter.

How genes for altruism might benefit strangers as well as kin

The generosity of adoption has long been considered a unique human hallmark.

Image: Shadows of Forgotten Ancestors

ResearchBlogging.orgFor decades it was conventional dogma that humans were the only species that used tools. “Man the Toolmaker” was our celebrated designation. The hominin fossil Homo habilis (or "handy" man) was even defined within our genus primarily because the skeleton was associated with stone implements. However, when Jane Goodall discovered chimpanzees using modified sticks at Gombe to “fish” for termites, Louis Leakey famously cabled her that:

“Now we must redefine tool, redefine Man, or accept chimpanzees as human.”

By now people should stop insisting on singling out specific human behaviors and declaring them to be unique in the natural world. Invariably, whatever special attributes humans possess, other primates do in some form as well. For many years it has been argued that humans are the only primates that will adopt unrelated individuals to care for as their own. This has been conventional wisdom because it doesn’t make intuitive sense according to the rigid definition of biological fitness.

Since animals, including humans, are merely ambulatory vehicles for their selfish genes, according to the dominant framework, it would be to one's benefit to care for a niece or cousin that lost their mother but not for a stranger of which there was no genetic relation. This is because any genes that promoted such altruism towards unrelated individuals would end up losing out by using up resources that didn’t perpetuate themselves. However, these “altruistic genes” would be passed on and thrive if they were helping a kin member with similar genetic makeup. In the currency of reproductive fitness, nepotism pays.

However, a study in the journal Primates by Cristiane Cäsar and Robert John Young report on a case of adoption among a wild group of black-fronted titi monkeys (Callicebus nigrifrons) from the rainforests of Brazil.

Titi monkeys found to adopt abandoned orphans.
Image: Luiz Claudio Marigo

Since July of 2005 the team has been studying this largely unknown species, when, much to their surprise, they witnessed a new infant traveling with the group that wasn’t there previously (the authors subsequently determined that a nearby group was missing an infant). Presumably the infant got lost from its former group and ended up being saved by the latter. Even more remarkably, it was the male in the new group that provided much of the adoptive care:

“Observations of the adoptive group confirm that it was being cared for by the adult male, and initially the group’s adult female was nursing the infant alongside her biological infant. . . Thus, in the case of adoption by C. nigrifrons there is an argument to include male primates in the definition of adoption.”

This would appear to undermine the notion that only related individuals would be adopted and cared for by others. However, the authors speculate that the two groups might be distantly related, thus suggesting kin altruism as the explanation for this unique occurrence. While this could be, the coefficient of genetic relatedness would likely be much too low for such a large investment to be in the genetic interests of the adoptive parents. Furthermore, any genetic mechanism involved (let alone an epigenetic one) would be unlikely to be so precise as to differentiate a kin member from a stranger. Since any orphan they come across would have a higher chance of being from their own group (and thus closely related), a genetic “rule of thumb” would be to provide assistance to all abandoned infants so long as resources were available.

Much the same has been argued for the origin of human altruism. Since most modern hunter-gatherer populations (and presumably our hominin ancestors) live in small groups of closely related individuals, the chances of helping a kin member by behaving altruistically are very high. Our genes today are descended from such close knit communities and don’t realize that we now live in enormous populations of strangers where being generous doesn’t directly improve our reproductive fitness.

By this simple act of adopting a strange infant, these titi monkeys may be teaching us an important lesson about evolutionary strategies. While the net sum of behaviors in the natural world is for the perpetuation of their genes, such mechanisms can’t always differentiate the forest for the trees. Genes that evolved for one set of environmental constraints (in this case helping the infant of a kin member) could promote behaviors for another (helping the infant of a stranger). This should give us some hope as political commentators suggest that our world is spinning out of control as the result of factionalized groups based around instincts for kin networks. If we can extend our notion of kin from our local population to the global community, then perhaps we’ll find a way to help one another. Our genes are already primed to benefit their close relations, we just need to find a way to put them to use for the benefit of the human family.


Cäsar, C., & Young, R. (2007). A case of adoption in a wild group of black-fronted titi monkeys (Callicebus nigrifrons) Primates, 49 (2), 146-148 DOI: 10.1007/s10329-007-0066-x


  1. October 29, 2010 8:38 AM EDT
    For once, I get to be the first commenter! What Eric has done here is a beautiful example of how to take new data on free-ranging primates, in this case titi monkeys, and use them to think meaningfully about evolutionary patterns. That titi monkeys adopted an infant across groups reminds me that we even know of a few examples of interspecific adoptions in the animal world. It's no surprise that I resonate very keenly with Eric's focus on the great plasticity of behavioral patterns originally selected for genetically-- and the hope this plasticity gives us in our world today.
    - Barbara
  2. October 30, 2010 4:37 AM EDT
    Great blog. I live-work in Burundi (most recently); throughout Africa in the past, working in agriculture and livestock. Animal adoptions - and sometimes just animal friendships - are a most interesting aspects of animal behavior and recently I did the following (slightly tongue-in-cheek) blog on the topic:
    Sometimes altruism? That may be our interpretation of some of these relationships, but would be interested to hear more on the topic.
    - diana buja
  3. November 2, 2010 7:48 PM EDT
    See this recent detailed analysis of 18 cases of adoption in wild chimps:
    Adoption could be more common than appears among primates, possibly derived from extensite maternal/paternal care and tight social bonds. Unfortunately, the adopted 'orphans' do not do very well when they are very young.
    - Blackbird
  4. November 2, 2010 7:54 PM EDT
    I always cite (gorilla) Mandara's adoption of Baraka and rejection of her biological child, Kejana, as an excellent example of altruism, the stranger's newborn required a higher level of care than her own 11 month old. And now Baraka has returned to National Zoo, and sired an offspring by Mandara, giving us new grist for the mill of the idea of incest avoidance!
    - Melanie Bond
  5. December 17, 2010 4:27 AM EST
    To my knowledge, Hrdy (1976) was the first to review adoption in non-human primates, including its costs and benefits. Many behavioral ecologists, especially theorists, have pointed out that, in some environmental, especially local, regimes, one's kin may be one's worst enemies. Thus, cooperating with and/or demonstrating altruism towards non-kin may be a "best of a bad job" and/or may represent a situation in which Actor's genes benefit more than they would be by the same behavior(s) directed towards kin. The classic explanation for when this should occur is when competition among kin is intense (see West et al., 2002). The behaviors that you describe and others like them are not in violation of kin selection, a point made many times in the literature.
    - Clara B. Jones
  6. December 17, 2010 4:34 AM EST
    Here are the citations for my comment posted previously:

    Hrdy, S.B. 1976. The care and exploitation of non-human primate infants by conspecifics other than the mother. Advances in the Study of Behavior 6: 101-158.

    West, S.A., Pen, I., & Griffin, A.S. 2002. Cooperation and competition between relatives. Science 296: 72-75.
    - Clara B. Jones

Selected Works

Why are animals so irresistible to us? Why do we live with and care so deeply about them? From the famous "art caves" of ice-age Europe, to the ancient villages where animals were first domesticated, to stories of apes, whales, dogs, and cats doing fascinating things today, King weaves together a scenario about the animal-human bond that encompasses our past, present and future.
Can scientists discover a prehistory of religion just as they have traced the evolution of technology, language, and art? What does compassion in chimpanzees, or burial patterns in our human ancestors and Neanderthals, tell us about the origins of religion? In Evolving God, named a Top Ten Religion Book for 2007 by the American Library Association, Barbara King explores these questions.
How do chimpanzees, bonobos, and gorillas-- the African apes -- communicate using body postures and gestures? Using her many years of experience studying these apes, Barbara King answers this question in a book that offers a new perspective on the evolution of language.