Fishing With Gorillas!

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Gorilla culture and tool use is currently shrouded in relative mystery when compared to our understanding of other great apes.  For example, landmark behavioural studies detailing technological variation and distribution have been published for all great apes except gorillas (e.g., bonobos, chimpanzees, orangutans).

In the major gorilla tool use study I am aware of, gorillas were observed engaging in behaviours that can only reasonably be asserted to be technologically complex.  In one situation a gorilla was observed using a stick as a walking stick to aid in balance when crossing a river.  In another situation a gorilla was observed using shrubs to construct a bridge to cross a river.  Both of these observations demonstrate that gorillas have a very complex understanding of how physical systems work.  Furthermore, it is evidence that gorillas have a well-developed understanding of physical systems that extends beyond the acquisition of food.

In most situations throughout the animal kingdom, tool use is stimulated by an inaccessible and valuable nutritional resource.  This is true for New Caledonian crows, bearded capuchin monkeys, bottlenose dolphins, and most other tool using species.  Tool use that is directed towards non-food related goals is theorized to develop later.  So considering that gorillas have already been observed using tools for non-food related goals, it logically follows that they should have a tool kit that involves tools for procuring food.

Gorilla Doctors Blog is reporting that just such an observation has now been made.  The observation was made by Jean Felix, a medical doctor who was making a routine health check on a population of gorillas in Volcanoes National Park in Rwanda.

He reported that a second ranked silverback gorilla was:

eating ants by reaching his left hand into the ant pile before putting it in his mouth. He ran away at one point – it appeared the ants were biting his arm. Afterwards, juvenile female Lisanga joined him and used a piece of wood to retract the ants from their nest.

This is an interesting observation.  It seems as though a high ranking male was unaware that access to an ant food resource required a tool in order to prevent being attacked.  Considering that this was not an official primatological study, no further data is available that I’m aware of, but the observation raises several questions:

  • Was the juvenile female teaching the silverback?
  • Why was a younger individual aware of a tool that the older individual seemed unaware of?
  • Are female gorillas more adept tool users than males?

I don’t think any primatologists have the answers to these questions at present.  But, as I stated a few months ago, I am really excited to see what future research reveals about gorilla culture and tool use.

What do you think of this observation?  Let Cadell know on Twitter!


Monkey Tool Users

You may have never heard of a bearded capuchin monkey.  In many ways it is a typical New World monkey.  However, this particular species of monkey continues to impress primatologists because it is the only known non-ape primate to use tools.  Primatologists “discovered” this in the 1990’s, but knowledge of capuchin monkey tool-use has been a part of Brazilian folklore for over four centuries, if not longer.

Although more research needs to be conducted, it appears as though they have a limited “tool-kit” consisting of specialized stones that they use to crack nuts in different savanna-like environments (Ottoni & Izar, 2008).  Interestingly, there is a high degree of intentionality in both the stone selection process, and in the strategic use of stone tools (Visalberghi et al., 2009).  Furthermore, a paper published a few days ago revealed that they have the capacity to improve the efficiency of their tool use (Fragaszy et al., 2013). Here is an awesome video via the BBC of a capuchin using a tool to crack open a nut:

What is perhaps more remarkable, is that the capuchins lower skeletal structure is well adapted to walking bipedally while carrying stones.  This could mean that stone tool use has been an integral part of the bearded capuchin’s behavioural repertoire for thousands of years (if not much longer).

So what do these discoveries mean?  In terms of primate tool-use they appear to be an extreme phylogenetic outlier.  Chimpanzees, bonobos, gorillas, and orangutans make and use tools, but the lesser apes and all other monkeys in the wild do not.

When considering the fact that all great apes make and use tools, it seems reasonable to suspect that the common ancestor of all great apes also made and used tools.  That pushes back the origin of primitive tool use to perhaps as late as 14 million years ago.  Of course, as Adam Benton of EvoAnthhas pointed out, the first empirical evidence in the paleoanthropological record of stone tool construction is 2.5 million years old.  But the nature of the paleoanthropological record is fragmentary and all great ape tools would not preserve archaeologically; therefore it is also important to consider the possibility of tool-use being ancestral for great apes.

But where do the bearded capuchins fit into this picture?  These primates are displaying a type of technological ability that was thought to have emerged approximately 2 million years ago with the origin of our genus.  Is this simply an extreme and unexpected example of convergent evolution?

Capuchin stone tool-use wouldn’t represent the first time that animal behaviourists have been surprised by cultural and technological diversity in the animal kingdom.  Over the past few decades anthropologists and biologists have uncovered an unprecedented amount of cultural variety among cetaceans and birds, including New Caledonian crow tool use that appears to be cumulative (Hunt & Gray, 2003).

In my initial judgment of this perplexing situation, I would lean towards accepting the parsimonious conclusion: that capuchins have convergently evolved the ability to use stone tools.  However, some researchers have proposed that we must not rule out the alternatives.  It could be that stone tool-use among primates emerged 35 million years ago, with the origin of the first monkey species.  Or it could be the case that stone tool use has been adapted and then lost by several monkey and ape species over the past 35 million years.  If either of these scenarios is true, we must explain why all other known contemporary monkeys have no stone tool kits.

Either way, this is yet another great example of animals forcing us to question our relationship to the past and our own divergent behaviour.

Love evolution?  You can find more of Cadell’s thoughts on evolutionary anthropology via Twitter!


Dean, L.G., et al.  2012.  Identification of the social and cognitive processes underlying human cumulative culture.  Science, 335: 1114-1118.

Fragaszy, D.M., Liu, Q., Wright, B.W., Allen, A., & Brown, C.W.  2013.  Wild bearded capuchin monkeys (Sapajus libidinosus) strategically place nuts in a stable position during nut-cracking.  PLoS ONE, 8: e56182.

Hunt, G.R. & Gray, R.D.  2003.  Diversification and cumulative evolution in New Caledonian crow tool manufacture.  Proceedings of the Royal Society, 270: 867-874.

Ottoni, E.B. & Izar, P.  2008.  Capuchin monkey tool use: Overview and implications.  Evolutionary Anthropology, 17: 171-178.

Visalberghi, E., Addessi, E., Truppa, V., Spagnoletti, N., Ottoni, E., Izar, P. & Fragaszy, D.  2009.  Selection of effective stone tools by wild bearded capuchin monkeys.  Current Biology, 19: 213-217.

Related Advanced Apes content:

Universality of Preadaptation for the Human Condition

The Evolution of Primate Sleep

Diurnality, Nocturnality, and Cathemerality

Are Humans Monogamous?

Humans, like most other animals, are sexual beings. However, unlike other animals, we are an intensely cultural species. This makes understanding our sexual nature incredible difficult. As biological anthropologist Jonathan Marks remarked: “Culture is inseparable from being human [and therefore] cannot be scraped off, like the icing on a cake, to reveal the human nature below.” (Marks, 2009).

As a primatologist, if I study the sexual behaviour of a ring-tailed lemurhamadryas baboon, or white-handed gibbon, it is relatively easy to characterize their socio-sexual system, and test for the selection pressures that may have led to its development. However, the evolutionary history of these species was dominated by biological evolution. In contrast, the human condition was produced via the interaction of biology and culture, a uniquely co-evolutionary process (Wilson, 2012).

As a result, is it possible to understand our sexual nature? Do we have a sexual nature at all? Or is our sexual behaviour simply a product of complex social systems contingent upon cultural evolution? Hopefully our understanding of the evolution of primate behaviour, as well as sexual selection theory, will help us answer these questions.

Primatologists have been researching primate socio-sexual systems and developing sexual selection theory for over four decades. Over this time period we have come to realize that pairbonding in one-male/one-female sexually exclusive units is rare. In fact, only 3% of primates are known to have evolved monogamous social systems. And phylogenetic studies have shown that all monogamous systems are derived states that have convergently evolved 7-10 times (Fuentes, 1998). Behavioural studies have also shown that monogamous behaviour tends to be flexible and conditional on numerous ecological variables. As a result, ancestral non-monogamous sexual states are often used as alternatives to monogamy in different circumstances.

This means that although monogamy is expressed within our order, it is not common, and it is certainly not a stable evolutionary strategy. Furthermore, no primate exhibits exclusive monogamous behaviour over an entire lifetime. Take for example, the gibbon, a lesser ape classically used as an example of primate monogamy. Researchers originally believed that the gibbon was both socially and sexually monogamous. They lived in one-male/one-female adult pairs, and appeared to remain exclusively pairbonded with one individual for decades. However, long-term studies have revealed that 12% of gibbon copulations are “extra-pair” copulations that their pairbonded partner is unaware of (Reichard, 1995). Essentially, gibbons get married and then cheat.

But why even form these systems in the first place? Even though monogamy is rare, and very rarely exclusive over the course of an individual lifespan, it has evolved 7-10 times independently within our order. There must be some important benefits to being exclusive.

Surprisingly, there may be as many as four different selection pressures for the behaviour: male defense of resources, infanticide reduction, direct male care, and male mate guarding. However, none of these pressures is universally necessary, and it is likely that a different combination of these pressures has caused different “types of monogamy” to evolve in different primate species currently defined as monogamous or pairbonded.

This information can all be a little overwhelming and hard to make sense of. Monogamy is rare, never completely explicit, and the evolutionary benefits are highly variable. What can this mess tell us about human sexuality?

It is evident that pairbonds between adult males and females has been a massive component of human socio-sexual systems both throughout history and in contemporary times. Did we evolve to organize ourselves in this way? Were early modern humans in the Middle Paleolithic living in systems we would classify as monogamous? Or did our ancestors organize themselves in different sexual systems? And if monogamy was uncommon in the past, why does it appear to be the system that has been culturally promoted throughout most of written history by various culture groups?

There are some important evolutionary clues regarding the composition of our ancestral socio-sexual system. The biggest comes from our pronounced sexually dimorphic traits. Human males are on average taller, heavier, and stronger. Our level of dimorphism is moderate when compared to say, gorillas, which are highly sexually dimorphic. However, our level of dimorphism is characteristic of a species with a moderately polygynous mating system with higher levels of male-male competition for mates, than female-female competition for mates. Past behaviours do not fossilize, but our dimorphism indicates a combination of moderate male harem building and strong female mate choice for large body size.

During the formation of early city-states between 5,000-10,000 years ago, several human populations made a transition from a traditionally hunter-gatherer lifestyle to a settled agricultural existence. Many evolutionary theorists contend that during this transition, the demands of agricultural life distorted human mate choice patterns. Humans were increasingly sedentary and had to prepare and maintain a plot of land for an entire lifetime. This new system required long-term investment from two adult individuals. Also, for the first time in human history, individuals could accumulate substantial wealth and surplus resources. As a result, males could use a lifetimes worth of resources as leverage against other males in competition for access to mates. In order to level the playing field, it is likely that many early city-states promoted monogamy, to avoid male harem building and avoid the collapse of early agricultural networks (Sanderson, 2001).

So does this mean that we are all naturally polygynous? Are cultures that promote monogamy simply the product of the early agricultural city-states attempt to promote equality of mating opportunity between disproportionately wealthy males?

You may have guessed that it isn’t that simple. From a neurological perspective humans really are designed to pairbond. Chemicals like oxytocin and vasopressin are released in our brains when we establish long-term sexual relationships with one individual. Studies have also shown that humans that form long-term pairbonds live longer and are psychologically healthier. Pairbonds also serve important evolutionary functions.

Quinlan & Quinlan (2007) conducted a massive cross-cultural study on human pairbonds in order to understand what specific pressures may have selected for pairbond formation. They discovered that human pairbonds form and are most stable cross-culturally when paternal investment and male-male competition is high. Their results indicated that a pairbond with little paternal investment is nearly worthless to women. As a result, the bond quickly disintegrates. Interestingly, pairbond stability was also unstable when male contribution was disproportionately higher than female contribution. The most stable pairbonds formed with equal contribution rates (Figure below). Pairbonds were also the most prevalent and stable when male-male competition for mates was high. Combined, this indicates that monogamous human socio-sexual systems are most likely when subsistence requires reciprocal cooperation, and when females have more control over mate choice than males.

Disparity in mate choice may be important because males, by nature, are less choosy. Females invest more matter and energy into producing eggs than males invest in sperm. Consequently, potential male fecundity increases with increase in mating partners, whereas female fecundity does not (Trivers, 1972). Ergo, it shouldn’t surprise us that reducing male mate choice is key to establishing stable pairbonds.

This all matters regarding our evolutionary interpretation of monogamy. The Quinlan & Quinlan study provides solid data that there are important adaptive functions of monogamy actually being played out among human societies today, regardless of culture. It shows that there are important ecological and environmental mechanisms that can increase (or decrease) the probability that humans will exhibit monogamous behaviour.

But are we getting closer to our answer? Of course humans can be monogamous, but are they monogamous?

After analyzing the data and theory evolutionary studies has to offer, it seems evident that we are a sexual hybrid. Within certain socio-cultural and environmental settings, humans are biologically capable of engaging in the most intensely monogamous behaviour within the Order Primates, and perhaps the entire animal kingdom. Pairbonding has really strong neurological effects that have been selected for, and offer us some really important long-term benefits.

However, as with other “monogamous” primates, polygyny is almost certainly our ancestral state. And like other “monogamous” primates, in certain circumstances we can use our ancestral state as a viable alternative to monogamy.

In conclusion, it may be a general rule among primates that species with derived monogamous socio-sexual systems are by nature highly flexible sexually and exist as sexual beings conditionally upon important ecological variables.

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Also posted via Svbtle:


Fuentes, A.  1998.  Re-Evaluating Primate Monogamy.  American Anthropologist, 100: 890-907.

Marks, J.  2009.  Nature/Culture.  pp. 260-279.  In: Why I Am NOT A Scientist.  Berkely: University of California Press.

Quinlan, R.J. & Quinlan, M.B.  2007.  Evolutionary Ecology of Human Pair-Bonds: Cross-Cultural Tests of Alternative Hypotheses.  Cross-Cultural Research, 41: 149-169.

Reichard, U.  1995.  Extra-pair copulations in a Monogamous Gibbon (Hylobates lar).  Ethology, 100: 99-112.

Sanderson, S.K.  2001.  Explaining Monogamy and Polygyny in Human Societies: Comment on Kanazawa and Still.  Social Forces, 80: 329-335.

Trivers, R.  1972.  Parental investment and sexual selection.

Wilson, E.O.  2012.  The Social Conquest of Earth.  New York: W.W. Norton.

The Adaptation Program

Ready for some evolutionary theory?

Yesterday, I read a famous scientific article on adaptation by evolutionary biologists Stephen J. Gould and Richard Lewontin, titled “The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme” (Gould & Lewontin, 1979).  Gould & Lewontin criticize what they call the “adaptationist programme” school of thought within evolutionary biology.  The adaptationist program is:

“The notion of near omnipotence of natural selection in forging organic design and fashioning the best among possible worlds. This programme regards natural selection as so powerful and the constraints upon it so few that direct production of adaptation through its operation becomes the primary cause of nearly all organic form, function, and behaviour.”

— Stephen J. Gould & Richard Lewontin

As a result, Gould & Lewontin claim that proponents of the adaptationist program are unwilling to consider alternatives to adaptation as an explanation for an organism’s morphology or behaviour.  Furthermore, they accuse evolutionary biologists of creating adaptive stories that cannot be validated by empirical testing.  Within this school of thought, adaptive argument after adaptive argument are employed, without consideration for any non-adaptive argument.  And in the absence of any adaptive explanation, Gould & Lewontin claim that researchers would rather attribute this failure to an “imperfect understanding of where an organism lives and what it does” as opposed to considering a non-adaptive explanation (e.g., genetic drift).  Consider the following example for the type of thinking that Gould and Lewontin are critiquing:

“How Tyrannosaurus used its tiny front legs is a scientific puzzle; they were too short even to reach the mouth. They may have been used to help the animal rise from a lying position.”

— (Gould & Lewontin, 1987)


Gould and Lewontin point out that just because the Tyrannosaurus front legs cannot reach the mouth, does not mean you can just create an untestable adaptive story about what other potential ways they may have used them.  The Tyrannosaurus front legs may not have been adaptive at all.  They may have simply been allometrically scaled down homologues in an allosaur ancestor.

Even though this paper was published in 1979, it still resonates with evolutionary theorists today.  TheWeb of Knowledge website indicates that it has been cited over 2,000 times, and is generally considered a “citation classic” throughout academia.  I can definitely understand why: while I was reading it, I started to get nervous.  I consider myself a human evolutionary theorist, and I frequently attempt to employ adaptive theory that will explain contemporary morphology and behaviour.  I started to wonder: “Am I a part of the adaptationist program that Gould and Lewontin were denouncing over forty years ago?”

In order to find out I had to go back and look at some of my old papers, including a recently accepted publication for Folia Primatologica and my nearly completed Master of Science thesis.  If I had been a part of the adaptationist program, I had become so unknowingly, and I would have to question my entire evolutionary theory education.

My initial fear quickly turned to relief.  After analyzing both papers, I realized that I had unknowingly benefitted from reading (and implementing) decades of evolutionary research that had built on the suggestions of Gould and Lewontin.  Instead of falling victim to the adaptationist program, I had incorporated a pluralistic approach to theory that considered non-adaptive explanations.  In my Folia Primatologica paper I collected data on chimpanzee night nesting patterns between two different forest blocks in Cameroon.  What I discovered was that there were differences in patterns of night nesting that were dependent on the level of human presence.  I concluded that in areas where humans were present, chimpanzees felt less safe, and consequently were less likely to nest terrestrially during the night.  In terms of theory, this means that terrestrial night nesting is likely an adaptation to an environment with low predation levels.  I did not just create an adaptation story; I had empirical evidence to support my claim for an evolutionary adaptation.

Likewise, I did not assume adaptation in my Master of Science thesis while investigating the potential for ring-tailed lemur cathemeral behaviour.  An animal can be considered cathemeral if “the activity of an organism […] is distributed approximately evenly throughout the 24 hours of the daily cycle, or when significant amounts of activity, particularly feeding and/or traveling, occur within both the light and dark portions of that cycle” (Tattersall, 1987: 201).  In my analysis I consider both an adaptive (stable evolutionary strategy) and non-adaptive (evolutionary disequilibrium) hypothesis for cathemerality.  The adaptive hypothesis proposes that cathemerality is a stable and deep-rooted activity pattern among ring-tailed lemurs that is dependent on environmental and ecological variables.  The non-adaptive hypothesis proposes that cathemerality is a transitional state between nocturnality and diurnality made possible by the rapid extinction of subfossil lemurs and raptors approximately 2,000 years ago (Van Schaik & Kappeler, 1996).  Therefore, we should expect there to be a mismatch between cathemeral lemurs activity pattern and biological adaptation.

The fact that I had been unaware of the adaptationist program critiqued by Gould & Lewontin in 1987, and yet still avoided the pitfalls of logic that accompanied it, reveal how powerful and influential their paper has become.  I strongly recommend reading it.  In today’s field of evolutionary biology, theorists have realized that not all organisms are perfectly adapted to their environments, and that you cannot simply create an adaptive story without sufficient evidence to indicate probability.  However, even though I personally had not become part of an adaptationist program, it is still important that I read this paper.

I have started to think about adaptation, and adaptive evolutionary theory in a different way.  It is now clear to me that adaptation is a concept that can only completely solve evolutionary puzzles for extant organisms.  As soon as we apply evolutionary theory to extinct organisms, we can only solve evolutionary puzzles on a gradation of probability.  It is true that we can collect empirical evidence supporting adaptive theory, but that can only reveal that a certain adaptation is the likely cause of a trait.  For example, evolutionary theorists believe that humans became bipedal as an adaptive response to an increasingly terrestrial existence in a woodland-mosaic environment.  This can be tested via evidence from fossilized remains, paleoclimatic data, and modeling the behaviour of our closest relatives (e.g., chimpanzees and bonobos).  These data all strongly suggest that there were real environmental pressures for a transition to bipedality after the split from our common ancestor with chimpanzees and bonobos.  These pressures likely remained strong until the emergence of our contemporary genus (e.g, Homo).  However, these data can only allow us to conclude with a high probability of certainty.  They cannot be used to allow us to conclude with 100% certainty.  Therefore, if a certain trait like bipedalism appears to be adaptive, we will always have competing hypotheses.  A complete theory of bipedality will always be near-completion, but never definitive.  The more data we collect, the stronger our current hypothesis may become.  However, that may be the best we can do since our early-bipedal ancestors are now extinct.


We may never have 100% certainty of the adaptive selection pressure for bipedality

In the future, I will likely be a better researcher for being cognizant of Gould & Lewontin’s landmark paper “The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme.”  I will still attempt to use adaptive theory, but I will be aware that adaptation cannot explain all morphology and behaviour.  I should probably use this experience as evidence that I need to read more Stephen J. Gould.


Gould, S.J. & Lewontin, R.C.  1979.  The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme.  Proc. R. Soc. Lond. B.  205, doi: 10. 1098/rspb.1979.0086

Tattersall, I.  1987.  Cathemeral activity in primates: A definition.  Folia Primatologica, 49: 200-202.

Van Schaik, C.P., & Kappeler, P.M.  1996.  The social systems of gregarious lemurs: lack of convergence with anthropoids due to evolutionary disequilibrium?  Ethology, 102: 915-941.

Building The Genetic Bridge

Now that scientists have decoded the genome for humans and all great apes, we can now start to identify all of the functional genes that make us different.  One such gene was discovered recently: MIR941-1 (Hu et al. 2012).  This gene encodes human specific microRNA that is not present in our closest relatives, or any other known mammals.  And it may be the start to building a complete understanding of what functionally separates our genetic structure from the rest of the animal kingdom.

What Does It Do?

MIR941-1 regulates cellular differentiation and neurotransmitter signaling.  Specifically, it plays a role in human-specific cognitive functions like language and speech, and it also affects pathways that increase the human lifespan.  What is most interesting is that when there is a problem with the brain region producing miR-941 microRNA, people display “mental retardation, developmental delay, as well as speech and language defects.” (Hu et al., 2012).

Exercise Caution

To clarify, this is not the gene responsible for human intelligence.  In all likelihood there is not one-single gene that gives us the cognitive capacity we enjoy over other animals.  Uncovering the complex genetic relationships and pathways that make us human will be a very long process, and will likely include the discovery of other genes similar to MIR941-1.  But it is still an important discovery because it shows us that scientists now have the data and technology to start “building the genetic bridge” that separates humans from great apes.

All too often, the popular scientific media exaggerates the importance of interesting genetic discoveries, because they want to break a simplistic story of the one gene that makes us special.  FOXP2 was a gene that was described in this way back in 2003.  Jerry Coyne gives a fantastic explanation of how this was done with the discovery of miR-941 on his blog Why Evolution Is True.  A basic rule of thumb would be to never believe any post that claimed there was a very basic Mendelian inheritance pattern between a few genes and our uniqueness.  As evolutionary scientists have discovered over the past few decades, genes that are related to cognitive functioning very rarely display this type of pattern.  More research should reveal other genes that play an important role in our uniqueness from the great apes, but is exciting to know that we have identified one key gene and region of the brain that seems to play a very important role.

When Did It Appear?

Future research on this specific gene should also help us understand more about our evolution as a species.  At the moment, we know that the gene appeared very rapidly between 6-1 million years ago.  This is critical because it is the period of human evolution when our ancestors evolved from early stem hominins to ancestral Homo.  Unfortunately, it does not tell us anything about when this critical gene became fixed, and consequently, what species first acquired it.  Understanding this development in more detail may help us to understand a great deal more about the evolution of human language.  Theories in the 1980s and 1990s posited that human language emerged during the Upper Paleolithic, a mere 40,000 years ago (Diamond, 1994; Klein, 1995).  However, more recent anatomical (Nishimura, 2002), cultural (Bar-Yosef, 2002), primatological (Dunbar, 2001), and genetic data (Enard et al., 2002) has revealed that the first modern humans that emerged 200,000 years ago, likely had what we would call modern human language.  The discovery of MIR941-1 could push that date back even further.  If a gene that plays a unique and specific role in enabling human language and speech existed as early as 1 million years ago, it is likely many ancient hominids had more complex language abilities than do contemporary great apes.

Concluding Thoughts…

This discovery is extremely interesting.  It could represent the start of our attempt to understand all of the genes that are functional and unique to our species.  However, genetics is very complicated, and it should not be viewed as the gene that separates us from the great apes.  Future research will need to be conducted to both better understand the significance of the role MIR941-1 has in modern day human populations and our ancestors.  Future research will also be needed to better understand what other genes play a role in our cognitive abilities.  It is an exciting time to study human origins – as I’m sure it always has – and hopefully always will.


Bar-Yosef, O.  2002.  The Upper Paleolithic Revolution.  Annual Review of Anthropology, 31, 363-393.

Diamond, J. (Ed. Campbell, and William Schopf, J.)  1994.  The Evolution of Human Creativity.  InCreative Evolution?! (pp. 75-82).  Los Angeles: Jonas and Barlett Publishers.

Dunbar, R.  2001.  Brains on Two Legs: Group Size and the Evolution of Intelligence.  In Tree of Origin: What Primate Behavior Can Tell Us about Human Social Evolution (173-191).  London: Harvard University Press.

Enard, Przeworski, Fisher, Lai, Wiebe, Kitano, Monaco, and Paabo, S. 2002.  Molecular evolution of FOXP2, a gene involved in speech and language.  Nature, 418, 869-872.

Klein, R.  1995.  Anatomy, Behavior, and Modern Human Origins.   Journal of World Prehistory, 9(2), 167-198.

Hu, H.Y., et al. 2012.  Evolution of the human0-specific microRNA miR941.  Nautre Communications 3, Article number: 1145 doi: 10.1038/ncomms2146

Nishimura, T.  2002.  Comparative morphology of the hyo-laryngeal complex in two steps in the evolution of the descent of the larynx.  Primates, 44, 41-49.

A ‘Great’ Crisis

I have been thinking a great deal about happiness and how we can best study the happiness of our species.  I will likely expound more on this topic in the coming months but a recent study caught my eye that I found quite insightful.  The study was led by psychologist Alexander Weiss, who investigated patterns of well-being in two great ape species: chimpanzees and orangutans (Coles, 2012).  In this study, Weiss and his colleagues wanted to understand if our closest relatives share the same general life pattern of well-being that humans seem to possess.  Social scientists have established that humans experience a U-shaped pattern of well-being.  This means that as a species we tend to experience greatest mental health in youth, become far less happy throughout midlife, and then become happier again in old age (Weiss et al., 2012).  This seems to be a general pattern regardless of various socio-cultural  and economic factors.  The study by Weiss et al. (2012) provide some evidence that this U-shaped well-being curve is an evolved predisposition that we share with our closest relatives.

In the study, 508 captive great apes of varying age ranges were rated based on their ‘happiness’.  However, happiness is notoriously difficult to study.  Many social scientists are still struggling to understand how to study happiness in humans.  Researchers decided that the best way to study happiness in apes was to survey the people who knew them best: their keepers.  In the survey happiness was rated using four criteria (Callaway, 2012):

1. The animals overall mood

2. How much pleasure they got out of socializing

3. Their success in achieving goals such as obtaining food and objects they desire

4. How happy the keeper would be if s/he were that animal for a week

The results of this survey indicated that individuals in their late 20s to mid-30s were significantly less happy than individuals younger and older (Weiss et al. 2012).  These results mirror the U-shaped happiness curve found in humans and raises some interesting questions about the evolutionary pressures that would have selected for these patterns.

Admittedly, the study is intensely anthropomorphic.  As primatologist Frans de Waal suggested, it would have been nice to see a harder measure of ape happiness (e.g., stress hormone levels) (Callaway, 2012).  Furthermore, I do think future studies should incorporate a more sophisticated methodology over a longer period of time before we can conclude with certainty that great apes experience a U-shaped well-being curve.  However, I think this study does give us some insight into our own happiness because it is relatively easy for keepers to gauge the mood of the apes they know so well and because the data had such strong conclusions.  So, if you trust the methodology what does this tell us about the evolutionary pressures that produced it?  Do these results mean that we are all destined to experience a mid-life crisis to some degree, regardless of socio-economic status and/or our own personal perception of age-appropriate achievement?

I believe that if a U-shaped curve is something we share with our closest relatives then it has probably been present for tens of millions of years throughout ape evolution and potentially primate evolution.  It is plausible to suggest that the main pressure for this U-shaped curve would be the need for increased adaptability during mid-life.  Generally speaking, young and old individuals are under less pressure to accumulate resources for survival and do not have the added burden of needing to increase biological fitness.  Perhaps being discontent increases the likelihood that an individual will put extra effort into acquiring more resources or finding a new/better mate.  It would make sense that there would be a strong selection pressure for this throughout our evolution because resources were so scarce and difficult to acquire.  Discontented middle-aged individuals would likely be able to out compete (and out survive) those middle-aged individuals that were content.

Either way, future research regarding great ape happiness needs to be conducted before we can be sure that the U-shaped curve is something they share with humans.  If future data indicate it is true, our only chance of minimizing the bottom of the U-shaped curve may be to genetically reprogram ourselves.


Callaway, E.  2012.  Great ape go through mid-life crisis.  Nature.  Accessed November 21, 2012.

Coles, J.  2012.  Great apes may have ‘mid-life crisis’, a study suggests.  BBC Nature.  Accessed November 21, 2012.

Weiss, A. et al.  2012.  Evidence for a mid-life crisis in great apes consistent with the U-shaped in human well-being.  Proceedings of the National Academy of Sciences.  doi: 10.1073/pnas.1212592109

The State of Things

A recent study (Junker et al., 2012) has detailed recent decline in suitable environmental conditions for African great apes.  As I have discussed in the past, habitat loss is a serious challenge that may lead the extinction of the great apes.  However, this study has shown conclusively that habitat loss is a larger problem than previously believed and is causing great ape populations to collapse at a faster rate than previously predicted.

Pan-African data

The three species of African great ape (i.e., chimpanzees, gorillas and bonobos) have suffered disproportionately from the affects of habitat loss, and certain geographical regions of Africa have seen greater habitat loss and faster great ape population decline than others.

Gorillas have been hit the hardest.  Since 1995 cross river gorillas have lost 59% of their habitat, eastern gorillas have lost 52% of their habitat and western gorillas have lost 31% of their habitat.  These data reveal that for gorillas, continental location seems to mean very little.  Whether in the east (52%) or west (59% and 31%) of Africa, habitat loss has been incredibly disastrous and rapid.

However, there is significant variation between the effects of this habitat loss on overall subspecies population totals.  Although all subspecies have suffered massive population decline (about half since the 1980s), two of the four subspecies may be on the verge of extinction.  There are currently 95,000 and 5,000 western lowland and eastern lowland gorillas respectively.  These totals are low enough to warrant an “endangered” status from the IUCN.  However, there are only 700 and 300 mountain and cross river gorillas remaining in the wild, which has caused several conservationists to believe they are beyond saving.

The reasons for the disproportionate population decline seems to be because both of these subspecies only live in mountain environments.  This increases the likelihood that their populations would be isolated and fragmented as a result of habitat loss.  For subspecies with such low total populations, genetic isolation due to fragmentation could cause genetic bottleneck too small to survive.  Even the most optimistic researchers have found it hard to argue against the likelihood that they will not be extant in 2020.

For bonobos and chimpanzees the data does not paint as bleak a picture, but still quantifies the plight of species struggling to deal with our increased presence.  Bonobos have suffered a 29% reduction in habitat and chimpanzees have suffered in between 11-17% reduction in habitat over the past 20 years.  The toll on overall population size has been shocking.  There are fewer than 50,000 bonobos and approximately 250,000 chimpanzees remaining in the wild.  This may not seem as bad as gorilla population decline, but it is important to remember that in the 1960s there were close to 2 million chimpanzees.

Although both chimpanzees and bonobos are more ecologically flexible than gorillas, habitat loss still poses extreme challenges to their continued existence.  Less habitat means less resources, increased fragmentation, more contact with humans (which increases the likelihood of zoonotic disease transmission) and less space to hide from poachers.  In essence, habitat loss compounds other problems that are causing chimpanzee and bonobo population to collapse at alarming rates.  In some areas of Africa populations have collapsed by more than 90% due to human-contracted disease (e.g., Ebolavirus) and increased hunting.

These data reveal more clearly than ever that great ape protected area establishment and proper management are more important than ever.  If we don’t act soon, we may be the only member of the Hominidae family remaining by 2100.


Junker et al., 2012.  Recent decline in suitable environmental conditions for African great apes.  Diversity and Distributions, 18: 1077-1091.