Tag Archives: primates

When is the best time to give birth?

After, not before, you get to the hospital, I always say.

But seriously, Robert Martin, the famous primatologist, has an interesting piece in Psychology Today exploring this question. Go read it. I’ve got a few thoughts spurred by this research I’ll list briefly here.

First, it seems that wild primates give birth during their daily down-time, the period of time that they are generally inactive. Dirunal primates do so more at night, nocturnal primates do so more during the day. Various reasons have been proposed. I’ve not read the primary literature on this, but in my ignorance I wanted to propose a possible (maybe additional, maybe already covered) idea. It has been suggested that this is to avoid predation. It could also be the case that the down time itself happens when it does for the same reason, to avoid predation while resting. Consider just diurnal primates for a moment. Resting is probably a time that primates are more likely to be preyed on for one specific reason: they don’t have as many eyes scanning from as many angled over a large area. This would apply only to social primates, especially those that sometimes forage in multi-species groups. So, resting times would be times of lower vigilance, so those times are ideally placed during times when predators are less active. Nocturnal/crepuscular primates are least active during the part of the day that primates are less active, and diurnal primates that start to hunt in the morning may have fed by them.

I quickly add that this is a counterintuitive idea (the part about resting being placed during the low-risk time of the day). The assumption is usually that resting means you are quiet and hard to find, so less susceptible to predation. But the predators already know where the primates are, and can find them. Being more active may make primates more visible to other primates including human primatologists (arboreal monkeys can be hard to spot when they are just sitting there … usually you spot them when branches are swaying and calls are sounding). So it would be a tradeoff between increased vigilance associated with foraging (because you are out and about and observant), decreased vigilance associated with foraging (because you are busy stuffing your face with goodies), increase vigilance because you are resting (because you can sit there and look around without distraction) and decreased vigilance because you are resting (because you are zoning out and if you are hiding among thick vegetation have less of a view). Being a primate is complicated.

Like other diurnal primates, humans seem to give birth more at night. This is perhaps the baseline starting point for humans further developing a nocturnal active phase to their activities, which for a long time has been thought an important part of evolution. We social beings invent fire and this produces a sitting around the fire thing where we use language to do stuff. Sex too. Diurnal primates not only feed and move about during the day, but also have sex during the day, and in the open. The human pattern is to generally have sex at night, and more privately. This is what happens, perhaps, when you take a monogamous bird/gibbon-like mating system and deploy it in a highly social primate.

So the night time behavioral niche includes a number of activities, including sex, gossip, and popping out babies. All closely related things.

Anyway, go read Robert Martin’s article.

Global Warming Negatively Impacts Wild Monkey Diets

Yes, yes, we hear it all the time: More CO2 is good because plants love CO2

That is a rather dumb thing to say for a number of reasons; nature is not simple. You don’t change one variable and expect other variables to respond as though we were turning a garden hose up or down. For example, while plant growth might be enhanced with more CO2 in the atmosphere, there is no reason to think this would be linear, or similar across all plants. You have to dance with the one who brung ya. The plants we have are the plants that have been under Darwinian selection optimizing growth and maintenance physiology for gazillions of plant generations. Changing a fundamental variable may have little effect (and in fact, CO2 increase only enhances growth somewhat, and for only some plants) and may even have negative effects.

A new paper out in Ecology looks at the nutritional value of plants in a Ugandan rainforest and finds that the nutritional value of the leaves eaten by some Colobine monkeys there has declined, because fibre has increased at the expense of usable protein. From the abstract:

Global change is affecting plant and animal populations and many of the changes are likely subtle and difficult to detect. Based on greenhouse experiments, changes in temperature and rainfall, along with elevated CO2, are expected to impact the nutritional quality of leaves. Here, we show a decline in the quality of tree leaves 15 and 30 years after two previous studies in an undisturbed area of tropical forest in Kibale National Park, Uganda. After 30 years in a sample of multiple individuals of ten tree species, the mature leaves of all but one species increased in fiber concentrations, with a mean increase of 10%; tagged individuals of one species increased 13% in fiber. After 15 years, in eight tree species the fiber of young leaves increased 15%, and protein decreased 6%. Like many folivores, Kibale colobus monkeys select leaves with a high protein-to-fiber ratio, so for these folivores declining leaf quality could have a major impact. Comparisons among African and Asian forests show a strong correlation between colobine biomass and the protein-to-fiber ratio of the mature leaves from common tree species. Although this model, predicts a 31% decline in monkey abundance for Kibale, we have not yet seen these declines.

Jessica M. Rothman, Colin A. Chapman, Thomas T. Struhsaker, David Raubenheimer, Dennis Twinomugisha, and Peter G. Waterman, 2014. Long term declines in nutritional quality of tropical leaves. Ecology

Is Curious George an Ape or a Monkey?

Curious George is called a “little monkey” in all of the Curious George literature, TV shows, and movies. But Curious George has no tail, and generally, that means you are an ape. But, there is one monkey with no tail, or at least one that is vestigial and not visible: The Barbary Macaque (Macaca sylvanus). For this reason, some have suggested that George is a monkey, specificaly, a Barbary Macaque or perhaps a close previously undiscovered species.

However, one of the main features distinguishing between monkeys and apes is the intermembral index. This is simply the relative proportion of the forelimbs and hind limbs. Apes have short legs and long arms (unless you are a Man in a Yellow Hat variety of ape) while monkeys have more even length limbs. The image above compares a young Chimpanzee to stand in for the apes, a Barbary Macaque, and Curious George, with the limb lengths marked off with a red line.

This seems to indicate the George is an Ape.

Also, note that the Man in the Yellow Hat originally kidnapped George in a Jungle.

There is another possibility, that Curious George is an undiscovered type of primate that is technically a Monkey but with certain Ape features. We are not certain of the genetic heritage of the mysterious ape Sungudogo, so perhaps George is one of those.

Note that these comparisons are being made among Old World Primates. If New World Primates are included in the mix, there may end up being more questions than answers.

Amazingly cute new primate species in Borneo

The Slow Loris (Genus Nycticebus) is a category of prosimian (primates that are neither monkey or ape) that lives in southeast Asia. Most prosimian species live on the island of Madagascar, but there are several African and Asian forms, all of which are nocturnal. The Slow Loris is special because it is the only primate we know of that has a toxic bite.

ResearchBlogging.orgThe total number of nocturnal primates known has increased considerably over the years and I’d wager there are many more to be found. “Technological advances have improved our knowledge about the diversity of several nocturnal mammals,” said Rachel Munds from the University of Missouri Columbia. “Historically many species went unrecognized as they were falsely lumped together as one species. While the number of recognized primate species has doubled in the past 25 years some nocturnal species remain hidden to science.”

Tomorrow, a paper will be released providing the diagnosis of a new species of slow loris. From the abstract:

The slow lorises … once included only two species, but recent taxonomic studies resulted in the description of three additional species; … The Bornean loris in particular is characterized by pelage and body size variation. In this study, we explored facemask variation in the Bornean loris (N. menagensis). Differing facemask patterns, particularly influenced by the amount of white on the face, significantly clustered together by geographic regions, separated by notable geographic boundaries. Our results support the recognition of four species of Bornean lorises: N. menagensis, N. bancanus, N. borneanus, and N. kayan. Genetic studies are required to support these findings and to refine further our understanding of the marked variability within the Bornean loris populations

Previously, one species of Bornean slow loris, with three subspecies, was recognized. The present study elevates the three subspecies to species status and add the fourth as a new discovery. Obviously, this significantly increases our conception of diversity in the nocturnal Bornean rainforest. One of the biggest threats to these animals is the pet trade. “The pet trade is a serious threat for slow lorises in Indonesia, and recognition of these new species raises issues regarding where to release confiscated Bornean slow lorises, as recognition by non-experts can be difficult,” said co-author Professor Nekaris, from Oxford Brookes University.

The study used 25 photographs and 27 museum specimens including the type specimens for two of the previously designated subspecies. A large number of features were examined and measured, of which eight showed variation across the sample, thus showing promise to use as in classification. Here is an example of one of the traits, called “Crown”:

Various fancy statistical analysis were done to produce two “functions” (combinations of variables) that separate the samples as indicated in this graph:

These traits clearly sort out the groups, and these groups have geographical distinctions as well.

Group 1 is on the island of Bangka and in the southwestern portion of Borneo south of the Kapuas River and east to the Barito River; this group’s boundaries appear not to extend all the way east to Barito River. Group 2 is found in central Borneo, north of the Kapuas and Mahakam Rivers. It is often found in higher ele- vations, but is not restricted to them. The boundary of Group 3 overlaps in part with Group 1, as it is found north of the Kapuas River, but its range ex- tends as far east as the Barito River. Finally, Group 4 inhabits the southern Philippines and northern and eastern Borneo, primarily in coastal and low- land areas. It does not range south of the Mahakam River.

So there are now four species: N menagensis, N. bancanus, N. borneanus and N. kayan. That last one is the new designation, and is named for a river flowing through the region in which it lives..

The conservation and research project responsible for this work has a web page with cute pictures, interesting videos, and more information on conservation related matters: Prof Anna Nekaris’ Little Fireface Project

Munds, Rachel, Nekaris, K.A., & Ford, Susan (2012). Taxonomy of the Bornean Slow Loris, with new species Nycticebus kayan (Primates, Lorisidae) American Journal of Primatology, 75, 46-56 : 10.1002/ajp.22071

Understanding Sex Differences in Humans: What do we learn from nature?

Nature is a potential source of guidance for our behavior, morals, ethics, and other more mundane decisions such as how to build an airplane and what to eat for breakfast. When it comes to airplanes, you’d better be a servant to the rules of nature or the airplane will go splat. When it comes to breakfast, it has been shown that knowing about our evolutionary history can at times be a more efficacious guide to good nutrition than the research employed by the FDA, but you can live without this approach. Nature works when it comes to behavior too, but there are consequences. You probably would not like the consequences.

The question at hand is this: Should men and women be given fundamentally different rights? Would it be OK if men and women had different pay for the same job, or different access to jobs? Would it be OK if men and women were treated differently by the law in a way that accounted for the behavioral differences between them that arise from their biology which, in turn, may be partly a function of their evolutionary history? Should men and women have different status because of their gender? Similar questions can be extended to people that are biologically different in other ways, such as by age, gender orientation, physical handicap or, should it be proven a valid categorization, race. But for now, let’s stick with the basic adult male vs. female difference.

Continue reading Understanding Sex Differences in Humans: What do we learn from nature?

What is Dunbar's Number?

The term “Dunbar’s Number” refers to a particular hypothesis by primatologist Robin Dunbar. It is a very simple idea with rather complex implications, and it is one of those simple ideas that gets more complicated than ideal as we look into it more and more. Eventually, the idea is required by many who contemplate it to do more work than was ever intended, and in this way seems to fail, though it really doesn’t. I personally think Dunbar’s number is useful if it is properly understood, so I want you to give it a chance, and to help you do that I’d like to use an analogy.

I’m thinking of a number called Carrier’s Number. Carrier, in this case, refers to the company that installs air conditioners and heaters. Carrier’s number is the temperature in degrees F at which you, sitting there in your chair, notice it is too warm so you get up and go turn on the air conditioner. It is best measured as a post hoc number…we watch and wait, flies on the wall, as the room heats up, and when a person gets up and flips on the air conditioner, the temperature at that point was carrier’s number for that person at that time.

One might argue that a post hoc measure like this isn’t much use in science because in science we like to predict things. But just because carrier’s number is best measured pot hoc does not mean that it only exists post hoc. It existed before the test subject got up, we just didn’t know what it was. For a large number of test subjects, we should be able to estimate carrier’s number (it is probably in the upper 70’s F). However, this will vary across cultures, across seasons, humidity, as clothing styles change (in the days of Polyester Leisure Suits, it is said that Carrier’s Number went down by about four degrees) and so on. The fact that it varies does not make it a bad number. In fact, its variation and reasons for it can make it an extra good number depending on what one is trying to do with it.

Dunbar’s number is the number of full blown social interactions you can manage. This number is lower or higher across species of social primates, as it tracks adaptive suites of sociality and the ability of brains to manage sociality. So, you can measure Dunbar’s number across primate groups by looking at how large effective primate groups get across species and figuring that the number is just about that maximum group size. Or, you could estimate Dunbar’s number (retrodict it, as it were) by looking at relative brain size, if we assume that brain size is linked to Dunbar’s number, all else being equal. In this way, Dunbar’s number is a way of linking primate sociality with brain evolution, which was the original idea.

In modern society, and in human historical contexts, we may see Dunbar’s number in a lot of places. This is the number at which, more or less, groups start to break down (in some societies) and villages split. Military units max out at about Dunbar’s number (companies are about 100 in size) and so on. This does not mean that Dunbar’s number and its associated dynamics explain everything. It might mean that the breakdown of social interactions can be more important than, say, resource limitations, on human group fission and fusion. That is exactly what many anthropologists have been suggesting for decades. Dunbar’s Number is simply this concept quantified somewhat and expanded to primates.

There are variations and adjustments. Some organisms have apparent smaller brain size because their diets cause a different body size, so that has to be adjusted for (leaf-eating monkeys may small relative brain size because their bodies are large, not because their brain is small, for example). What a fully blown social interaction is may vary. A group of primates may have a subgroup that hardly ever interacts with the others. Perhaps pre-adolescent monkeys don’t count for as much as sexually mature monkeys, so if there happens to be a baby boom a couple of years back, the group size if you count everyone is higher than Dunbar’s number. Or perhaps the group includes two or three social geniuses who temporarily facilitate an extra large group size, or temporarily force an extra small group size, for some reason.

It makes sense that there is a limit on effective sociality, and thus, on effective social group size. Dunbar’s number is nothing other than the number you end up with because when you are making the damn graph you need a damn number to put there on one of the axes. It has been over-interpreted or over-used as a number like many of those from Physics, like the freezing point or boiling point of water, which it is not.

Desiree Schell and I spoke about Dunbar’s Number on the Skeptically Speaking that just became ready for you to download. Check it out here.

This video includes, during the last third somewhere, a discussion by Dunbar of all this.

And, here’s a few items by Dunbar you might find interesting:

  • How Many Friends Does One Person Need?: Dunbar’s Number and Other Evolutionary Quirks
  • Grooming, Gossip, and the Evolution of Language
  • Wild angry baboons on the high cliff

    We three had somehow wound our way down into the canyon without experiencing any really steep slopes, but having walked for several miles in the sandy dry riverbed, Trusted Companion, Young One, and I were now looking rather hopelessly at unsafe-to-climb cliffs on both sides, covered with imposing vegetation of the kind that sports a thorn every few inches. The sun was low enough that the canyon floor was in a dark shadow, and the air was beginning to chill down. We were far enough from the vehicle, lost enough, and sufficiently plan-free that it would be perfectly reasonable to worry that we might not make it across the remote African Savanna before the leopards and hyenas came out to hunt. It was even possible that we’d have to spend the night huddled in some spot we could convince ourselves was protected from the elements and the wild animals. All this dark and scary truth had dawned on me over the last hour as we continued heading up a seemingly endless side canyon in search of a place to climb out of this river valley known among international extreme outdoors people as one of the most treacherous in the world, and known among the more traditional local folk for its dragon-like 50-meter long human-eating snake that was supposedly mythical.
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    On the Move

    On the Move: How and Why Animals Travel in Groups, edited by Sue Boinski and Paul Garber is a compendium of academic research on … well, on how and why animals travel in groups. Notice of this book is a fitting start to a series of reviews of migration-related books that is part of Migration Week on GLB. (For an overview of the Bigness and Vastness of bird migration in particular, see A Question of Migration.)
    Continue reading On the Move

    Isabel Behncke: Evolution’s gift of play, from bonobo apes to humans

    With never-before-seen video, primatologist Isabel Behncke Izquierdo (a TED Fellow) shows how bonobo ape society learns from constantly playing — solo, with friends, even as a prelude to sex. Indeed, play appears to be the bonobos’ key to problem-solving and avoiding conflict. If it works for our close cousins, why not for us?

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    What I know about Marc Hauser, the recently ‘investigated’ Harvard primatologist

    I know Marc Hauser, and I trust him. I worked with him for a few years as a colleague on the faculty in the Anthropology department on various administrative matters (such as graduate admission and undergraduate program development) and we taught together. We are very different kinds of people, and did not always see eye to eye (well, we disagreed on one thing, once), but the same can be said of almost any two people from those days and that department, to some degree.
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    New Primate Fossil Informs Us of the Ape-Monkey Split During the Oligocene

    ResearchBlogging.orgThe newly reported Saadanius hijazensis may or may not be a “missing link” but in order for this monkey to climb onto the primate family tree, a new branch had to be sprouted. So, not only is Saadanius hijazensis a new species, but it is a member of a new taxonomic Family, Saadaniidae, which in turn is a member of a new Superfamily, Saadanioidea. Why is this important? It’s complicated. But not too complicated.

    The fossil was found while University of Michigan paleontologist Iyad Zalmout was busy looking for dinosaur fossils in western Saudi Arabia. He found the monkey, from a much later time period, instead. Ooops.
    Continue reading New Primate Fossil Informs Us of the Ape-Monkey Split During the Oligocene

    Keep an eye on the prey: You’ll find the predator

    In Robert Gardner’s documentary film Dead Birds, the men of a highland New Guinea village guard the perimeter of the territory, watchful for men of the neighboring group who may be intent on sneaking into the gardens to capture and kill an unwitting child or woman in order to avenge a prior death. But they don’t see the men sneaking through the dense riparian forest. They don’t even look for them. Rather, they see the birds fly from their preferred habitat where they are foraging or resting, startled into the open by … something. The birds belie the predator.
    Continue reading Keep an eye on the prey: You’ll find the predator

    Falsehood: Humans evolved from apes

    Is it a Falsehood that Humans Evolve from Apes?

    How about this one: Is it a Falsehood that Humans did NOT evolve from Apes????

    Yes and no. Humans descend from a population of primates from which other apes also descended (minimally the two species of living chimps) and which was part of the panoply of late Miocene forms, all related to each other, that we call apes. So yes, humans evolved from apes.
    Continue reading Falsehood: Humans evolved from apes