The Semantics of Vervet Monkey Alarm Calls: Part I

Anti-predatory alarm calls are important  for social animals to alert others of approaching predators. Without the presence of "language", some non-human primates are known to give out different predator-specific alarm calls to alert conspecific. These non-human primates include ring-tailed lemurs (Zuberbühler et al., 1999), white-faced capuchin monkeys (Fichtel et al., 2005), Diana monkeys (Zuberbühler, 1999), Campbell's monkeys (Ouattara et al., 2009) and vervet monkeys (Seyfarth et al., 1980).

Alarm calls are typically high frequency sounds because these calls are hard to localized by predators. On the other hand, low frequency sounds are easier to localized by predators. Calls that are hard to localized by predators are selected for because conspecific can pick up on the warning but predators cannot identify the location of the caller. If an individual successfully alert its social group of approaching predator yet does not reveal its location, it will significantly decrease the chance of the caller to be detected and increase the chance of its social group to avoid predation.

Vervet monkeys. Photo from Wikipedia.

Here, I will focus on the study of predatory alarm calls in vervet monkey (Chlorocebus pygerythrus) by Seyfarth et al. (1980) in the Amboseli National Park, Kenya. Vervet monkeys are Old World monkeys that range between Eastern and Southern Africa. These monkeys are diurnal and live in closely-knit social groups. They are quadrupedal and are both terrestrial and arboreal. Like all Old World monkeys, vervet monkeys have the characteristic cheek pouches that enables them to forage and store food to be eaten later. Male vervet monkeys have blue scrotal area and a red penis. Males and females are sexually dimorphic, with males slightly larger than females.

Male vervet monkey with blue scrotal area and red penis. Photo from Something Up Her Sleeve.

Vervet monkeys are known to elicit predator-specific alarm calls. Three well-documented vervet monkey alarm calls are those for leopard, martial eagle and python. Leopard alarm calls are short tonal calls produced in a series of inhalations and exhalations. Eagle alarm calls are low pitched grunt while python alarm calls are high pitched "chutters". Different alarm calls seem to evoke different responses to individuals that heard the alarm calls. However, the first reaction of a vervet monkey upon hearing an alarm call is to look at the direction of the caller. Looking at the direction of the caller gives them clues as to why the alarm calls were made and also where the caller is facing reveals the direction of the approaching predator. You can listen to these different alarm calls on this site.

As we said before, different alarm calls evoke different responses. Leopard alarm calls would make the monkeys run up into the tree to avoid being ambushed by the leopard. Also, these monkeys would sit on the branches further away from the tree because, even though leopards can climb trees, the branches could not support the leopard's weight. When an eagle alarm call is given, vervet monkeys would make them look up, run for the nearest bush or both to avoid an approaching aerial attack. Python alarm calls would the monkeys stand bipedally and look down on the ground.

A martial eagle. Photo by Jacques S G from Flickr.

Adult vervet monkeys are more discriminatory when eliciting alarm calls. Infants and juveniles calls however, are less discriminating as they attribute most terrestrial mammals with leopard calls, flying birds with eagle calls and stick-like figures with snake calls (although, compared to infants, juveniles are more discriminant when making alarm calls). In spite of that, adult vervet monkeys seem to elicit eagle alarm calls to different species of raptors and non-raptors (see illustration below). We can infer that adult vervet monkeys attribute eagle alarm calls to birds with the same silhouette as martial eagles. As vervet monkeys get older, they seem to have a better association between predator species and types of alarm calls. Vervet monkeys generally pay more attention to adult alarm calls than those of juveniles or infants.

Alarm calls made by infant, juvenile and adult vervet monkeys in response to sightings of birds of prey (raptors) and non-raptors. The number of calls cited for each age group refers to the total number of calls that were analysed (Gould & Gould, 1999). Click on illustration for larger view of the image.

The study of vervet monkey alarm calls by Seyfarth et al. (1980) laid an important ground work to better understand the complexity of animal communications. By showing that vervet monkeys make different alarm calls to different predatory species, we can posit that vervet monkeys have the ability to categorize different species. The ability to discriminate between terrestrial mammal, flying birds and snake-like objects starts during infancy in vervet monkeys. As they get older, they are better at associating predators with specific alarm calls.

An infant vervet monkey with its mother. Photo by Lip Kee from Flickr.

The ability to over generalize during infancy is evident in both vervet monkeys and humans. For example, upon learning the word "dog", human infants would refer to quadruped mammals they see as "dog". As the infant grows, so does the ability to associate the semantic meaning of words they learned. However, the acquisition of alarm calls in vervet monkeys is different than the acquisition of speech (language) in humans. Alarm calls in vervet monkeys are instinctual and not learned. Humans, however, have to learn their language. Failing to do so during the "critical period" generally will result in the inability to learn language in later years. Feral child are examples of human infants that lack linguistic input during their critical period of language acquisition.

Most of us interpret animal alarm calls as an uncontrollable auditory response to fear or pain, akin to humans yelping if we had our finger caught in a door. While this is not entirely false, some animal calls actually convey information from the caller to the listener. Seyfarth et al. (1980) posit that vervet monkey alarm calls are actually basic semantic signals or symbolic signals because each alarm calls seem to mean something to these vervet monkeys. While we don't know if these alarm calls actually mean "leopard" or "run up to the tree", we do know that it conveys specific information to their conspecific about approaching predators.

I will be blogging Part II of this post later this week, where I will explain in details the experiments done by Seyfarth and Cheney on vervet monkey alarm calls.

References:
Cawthon Lang KA. 2006 January 3. Primate Factsheets: Vervet (Chlorocebus) Taxonomy, Morphology, & Ecology. http://pin.primate.wisc.edu/factsheets/entry/vervet. Accessed 2011 March 9.

Fichtel, C. Perry, S. Gros-Louis, J. 2005. Alarm calls of white-faced capuchin monkeys: an acoustic analysis. Animal Behaviour 70(1): 165-176. doi: 10.1016/j.anbehav.2004.09.020.

Gould, JL. Gould, CG. 1999. The Animal Mind. Scientific American Library.

Ouattara, K. Lemasson, A. Zuberbühler, K. 2009. Campbell's Monkeys Use Affixation to Alter Call Meaning. PLoS ONE 4(11). doi:10.1371/journal.pone.0007808.

Seyfarth, RM. Cheney, DL. Marler, P. 1980. Monkey responses to Three Different Alarm Calls: Evidence of Predator Classification and Semantic Communication. Science 210(4471): 801-803.

Zuberbühler, K. Jenny, D. Bshary, R. 1999. The Predator Deterrence Function of Primate Alarm Calls. Ethology 105: 477–490. doi: 10.1046/j.1439-0310.1999.00396.x.

Zuberbuhler, K. 2000. Referential labelling in Diana monkeys. Animal Behaviour 59(5): 917-927. doi: 10.1006/anbe.1999.1317.

Crested Gibbons: Song Structure as Indication of Phylogenetic Relatedness

The genus Nomascus are one of the four genus that occurs in the Hylobatid family. Males have erect crown hair thus giving this genus its common name, crested gibbons. Crested gibbons are sexually dichromatic; males and females of the same species have different fur coloring and markings.The males tend to have black fur while females have orange to yellow fur. All species of Nomascus are either endangered or critically endangered. Like all gibbons, their trademark is their species-specific songs that they sing to communicate to each other. These songs, unlike those from song birds, are instinctual and are not learned (Thinh et al., 2011). Gibbons are the only monogamous ape.

Nomascus leucogenys mother and male offspring.

A new study, published this month on BMC Evolutionary Biology by Thinh et al. (2011) found that crested gibbons have species-specific song that can be used to differentiate the Nomascus species and also predict the phylogenetic relatedness of this genus. In this study, 6 Nomascus species were used as analysis: N. nasutus, N. concolor, N. leucogenys, N. siki, N. annamensis and N. gabriellae. The researchers used 92 out of 175 song recordings for acoustic analysis, analyzing 440 great calls (duets between males and females) and 447 male calls from 92 gibbon groups at 24 locations to confirm the relationship between song structure and phylogeny in Nomascus.

Video of Cao Vit gibbons (N. nasutus) singing. Notice the sexual dichromatism that occurs in males and females.

The researchers were able to tell the 6 Nomascus species apart by just listening to their song acoustics, albeit some with greater difficulties than others. N. nasutus and N. concolor could clearly be identified from their song acoustics. N. leucogenys, N. siki, N. annamensis and N. gabriellae on the other hand, have songs that are similar in structure but with minute differences. They also found a significant correlation between song structures and genetic similarity, which means that Nomascus species that are more closely related have similar song structures. This would account to N. leucogenys, N. siki, N. annamensis and N. gabriellae having same song structures but with minute differences in them because they are very closely related.

Map shows the distribution of all 7 Nomascus species. Illustration from ExtraWildlife.com

The authors also found that song similarities among species correspond to geographic location. They found a large difference in song structures between the most northern species and the most southern species, and a gradual difference when compared from the northernmost species to the southernmost species. This gradual difference in song structure, from the most northern species to the most southern species, supports the hypothesis that the genus originated from the north and successively migrated to the south. N. hainanus (omitted in the study) and N. nasutus are basal among crested gibbons (Nomascus). Together, these two species form a clade. N. concolor branched off first, then following by the rest of the Nomascus species; N. leucogenys, N. siki, N. annamensis and N. gabriellae. 

The cladogram of the genus Nomascus. Illustration from  Thinh et al. (2011).

Reference:
Thinh, V.N. Hallam, C. Roos, C. Hammerschmidt, K. 2011. Concordance between vocal and genetic diversity in crested gibbons. BMC Evolutionary Biology 11: 36 DOI: 10.1186/1471-2148-11-36

These primates are busy!

I realized I have not updated my blog for almost a month now, so first and foremost, apologies to my avid readers. I know I have left you high and dry without any post! Since my last post, I have started volunteering at Prospect Park Zoo. The zoo has a special place in my heart (especially the hamadryas baboons) because it is there that I did my research for my Honors Thesis. I never thought I would enjoy working with kids but they DO ask the darndest things. Of all the kids that had asked me questions or talked to me, one really stood out. The kid asked if I know who Steve Irwin is and that he (the kid) enjoys his (Irwin's) work. Can you believe it? The kid even recited how primates are different than other mammals. I think he's gonna grow up to be me. I'm cereal.

Have you seen the new ASP website? It's quite spiffy. I actually contributed some photos to the site ... can you spot them?

The annual Monkey Day is fast approaching. Celebrated annually on December 14th, Monkey Day not only celebrates the simian that lend its name to the festival, it also celebrates anything primate (prosimians, monkeys and apes). Over at Serious Monkey Business, Ashlee is starting a Monkey Day Blog Carnival. If you are interested in contributing to the carnival, please contact her.

A friend of mine started a new blog, The Primate Chronicles. Kayley is a graduate student at University of Calgary and does her fieldwork in Belize. Check it out.

Call for submissions: The next edition of Four Stone Hearth will be hosted by Archive Fire on December 8th. If you have wrote or saw interesting Anthropology posts around the web, please send it to ambientdisorder at gmail dot com. Afarensis, current host of the blog carnival, needs hosts for future editions. If you are interested, please email Afarensis, afarensis1 at sbcglobal dot net.

All over the blogosphere and Twitter-land, Anthropological primates are choosing sides. Are you "Team Jacob" or "Team Edward"? Errr .... I mean, are you "for" or "against" removing the word "science" from  American Anthropological Association (AAA)'s mission statement. The controversy with removing the word "science" from mission statement even reached CNN. Some of the interesting blog posts on this subject matter includes:

• Why anthropology is ‘true’ even if it is not ‘science’ and Ethnography as a solution to #AAAfail by Savage Minds.
• Anthropology, Science, and Public Understanding by Neuroanthropology.
• What is a generous interpretation of the AAA mission statement change? by Context and Variation.
• Removing science from anthropology: Parallels with medicine by Respectful Insolence.
• No Science, Please. We're Anthropologists by Psychology Today.
• American Anthropological Association's Long-Range Plan, a rebuttal to the brouhaha.

What's your stand? I don't really have a strong reaction to this, probably because I am not an AAA member. I understand the initial shock of disbelieve or just a general WTF to the decision. But seriously, are they just fishing for publicity? Those damn non-science Anthropologist!

Last but not least, to my Jewish readers, Happy Hanukkah. Chag Sameach!

Legopithecus rosalia kenneyi

Wordless Wednesday are, well, meant to be "wordless" but I've gotten a lot of questions about my Wordless Wednesday post yesterday so I've decided to include more photos and write a little bit about these cute critters.

I was up in Philadelphia for the Halloween weekend and no trip to Philadelphia is complete without me going to The Philadelphia Zoo. While there, I managed to catch the Creatures of Habitat exhibit. The exhibits are made from LEGO bricks (OMG childhood memories) and my favorite were definitely the ones I've posted on my Wordless Wednesday post yesterday. 

They are, of course, the Golden Lion Tamarins (Leonpithecus rosalia) but the folks that made them did have a sense of humor. If you actually read the signs posted by the exhibit, you'll realize that the Latin name for these critters are Legopithecus rosalia kenneyi. Hah! Legopithecus (Lego ape). Brilliant. Although, for argument sake, Golden Lion Tamarins are not apes but monkeys. 

But why the kenneyi subspecies name? One of the artists that made these Lego sculptures is Sean Kenney, in which I would think where the subspecies name comes from (It's probably an Easter egg). I wonder what they plan to do with these sculptures when the exhibition is done. I'd love to get my fingers on one (maybe two). Here are more Lego Golden Lion Tamarin pictures from the Creatures of Habitat exhibit. Enjoy!

Only 12 individuals of this subspecies left!

 HAHAHA! Brilliant.

 Grooming.

 Pirate tamarin. Yarrr!

 Golden Lion Tamarin using a tool (stick). Not sure they do though ...

Wordless Wednesday

Ape behavior inside the exhibit and holding area

An insightful paper published by Ross et al. (2010), compares zoo-living ape behavior inside their holding and exhibit areas in Lincoln Park Zoo, an accredited member of Association for Zoos and Aquarium (AZA). Zoo animals usually have at least two areas where they are housed (excluding some aquatic animals): the holding area and the exhibit area. During visiting hours and at night, zoo animals are housed in their exhibit area. In the morning, before the zoo opens, they move into the holding area to receive husbandry care and their morning food ration.

The gorilla exhibit area in Lincoln Park Zoo. Photo from Things You Should Do.

One of the chimpanzee from the study, Kipper (now deceased), from Lincoln Park Zoo interacting with a child. Photo by Chicago Tribute.

Holding and exhibit areas differ in size, design and functionality. A study by Ross and Lukas on 11 AZA-accredited zoos shows that holding areas are usually about 40 times smaller than exhibit areas (Ross et al., 2010). At the Lincoln Park Zoo, the holding area is about 9.3% of the size of the exhibit area (for both gorillas and chimpanzees). Whereas the exhibit area is designed for the complexity and to mimic the natural environment of its animal inhabitant, the holding area is usually designed for simplicity and functionality to meet husbandry needs.

Seven gorillas (2 males, 5 females; N = 7) and seven chimpanzees (3 males, 4 females; N = 7) were observed in this study. I should point out that the authors of the study is by no means criticizing Lincoln Park Zoo. It is an informal observation of behavioral changes for these animals in different environment. The result of the study shows that:

Gorillas
Inside the holding area - Increased locomotion and affiliative behavior. Also showed increased rates of aggression, self-directed behavior (subject touches, manipulates or examines the body, skin, or hair) and solitary play. Were in close proximity with each other.

Inside the exhibit area - Increased feeding and foraging behavior and also sexual behavior.

Chimpanzees
Inside the holding area - Increased aggression. Increased rate of scratching and self directed behavior (subject touches, manipulates or examines the body, skin, or hair). Were in close proximity with each other.

Inside the exhibit area - Increased feeding and foraging behavior.

Schematic representation of a typical holding area suite for an individual chimpanzee or gorilla social group at the Regenstein Center for African Apes. Shaded areas indicate animal enclosures; noncolored areas are sections of human activity (caretakers and data collectors). (Ross et al., 2010)

Both gorillas and chimpanzees showed increased aggression accompanied with self directed behavior when inside holding area. Increase in aggression can sometimes be attributed to overcrowding and self directed behavior generally means that an animal is nervous. Being constrained in a smaller space increases the chance of mixed-sex and mixed-dominance encounters thus resulting in agonistic and submissive observations. When inside exhibit areas, both apes exhibited an increase in feeding and foraging behavior. This presumably is due to their feeding and foraging habit in the exhibit area. If I remember correctly, one of the major breakthrough in exhibiting apes (and most animals) is to encourage foraging behavior throughout the day. It is no surprise that these apes exhibit these behaviors.

Chimpanzee subjects in a single enclosure in a holding area suite, during a period of free access (following training and research protocols). Photograph was taken from the central caretaker area. (Ross et al., 2010)

These apes reacted differently when inside their holding area than in their exhibit area because they are exposed to different sensory. Apart from the difference in size and complexity, these two areas also differ in the degree of human interaction, cross-species presence, environmental factors and time spent between these two areas. An understanding of these differences and motivational factors is important in promoting optimized environments for captive apes. The authors encourage that zoos would consider species-specific functional, physical and social preferences when designing enclosures for apes regardless of frequency of use.

Reference:
Ross, S. Wagner, K. Schapiro, S. Hau, J. 2010. Ape behavior in two alternating environments: comparing exhibit and short-term holding areas. American Journal of Primatology 72: 951–959. doi: 10.1002/ajp.20857

New Gibbon Species Discovered

A new gibbon species have been discovered by researchers, led by Christian Roos, from the German Primate Center (Deutschen Primatenzentrums) and was published on Vietnamese Journal of Primatology. The northern buffed-cheeked gibbons (Nomascus annamensis) live in the rainforests of Annamite Mountains, situated around Vietnam, Laos and Cambodia. The northern buffed-cheeked gibbons were once thought to be the yellow-cheeked gibbons (Nomascus gabriellae) but vocalization and genetic research prove that both are distinct species.

The northern buffed-cheeked gibbon males (left) have a black pelt that shimmers silver in sunlight. The chest is brownish in color and the cheeks are deep orange-golden. The crest is very prominent in males. Females (right) are orange-beige in color and lack the characteristic crest. Photo by Tilo Nadler, Endangered Primate Rescue Center, Vietnam.

"The discovery of a new species of ape is a minor sensation", Christian Roos warns. All crested gibbons (genus Nomascus) are either endangered or critically endangered with Hainan black crested gibbons (Nomascus nasutus hainanus) the most critically endangered, totaling to only 20 individuals. The sharp decline of Hylobatids can be contributed to illegal hunting and loss of habitat. “Knowledge of their biology and exact distributions is essential for effectively protecting the animals. Only if we know where which species is found and how many individuals there are can we start with serious conservation actions", Roos adds.

Comparison between the northern buffed-cheeked gibbon male (left) and the yellow-cheeked gibbon male (right). Photo of the yellow-cheeked gibbon from The Gibbon Network.

Comparison between the northern buffed-cheeked gibbon female (left) and the yellow-cheeked gibbon female (right). Photo of the yellow-cheeked gibbon from The Gibbon Network.

Gibbons are mostly monogamous, pair-bonding primates that are strongly territorial. These vocal displays or songs, usually a duet between a mated pair and sometimes their offspring, can be heard from as far as 1km away. Gibbon songs are territorial displays, perhaps if a gibbon can hear another gibbon sing then it is  encroaching a mated pair territory. Oh, in case you are wondering, gibbons do not have tails (they are apes).

For more about this discovery:
New ape species uncovered in Asia on Mongabay.com
New gibbon species discovered in Indochina on Informationsdienst Wissenschaft

Thinh, VN. Mootnick, AR. Thanh, VN. Nadler, T. Roos, C. A new species of crested gibbon, from the central Annamite mountain range. Vietnamese Journal of Primatology 1(4), 2010, 1-12.

P/S - Anyone able to find Thinh et al. (2010) publication online or the Vietnamese Journal of Primatology is not available online?

Wordless Wednesday

Allogrooming in Verreaux's Sifaka

Finally a paper about grooming patterns! On "early view" in American Journal of Primatology, is Rebecca J. Lewis's Grooming Patterns in Verreaux's Sifaka (free abstract). If you would like to read the article, let me know and I can send you the whole article in pdf.

I can definitely relate to the first sentence of this paper's abstract, "Lemur grooming has received very little attention in the literature". It has became apparent to me when I was visiting different graduate schools that professors would comment "Well, there aren't much grooming going on in the species that I study so you'll just be wasting time". While it is important to collect data on species that groom a lot, it is also important to document grooming patterns in species that don't groom a lot so that we can compare these data. Why don't these species groom as much? What alternative strategies are they using instead of grooming?

Well back to the article. As you might have guessed, it's about grooming patterns in Verreaux's Sifaka (Propithecus verreauxi). What's unique about prosimians grooming is that they don't groom with their fingers, instead they groom with their dental comb. In her paper, Lewis found is that these sifakas:

• Spend very little time allogrooming. 
• Allogrooming happens on parts of the body that can be easily autogroomed (self groomed). 
• While ectoparasite loads are greater in the rainy season, the rate of allogrooming did not increase.
• Allogrooming rates are influenced by sex and rank. Sifakas groom up the rank with females receiving more grooming than males. Males also tend to groom others more than females do.
  
• Allogrooming rates increased by 50-100% during mating season. Males tend to initiate grooming during mating season but generally are not reciprocated by females.

These results suggest that Verreaux's Sifaka used grooming as a social function, not as a health function. Lewis also posits that lemur grooming patterns do not differ from anthropoid grooming patterns as much as previously thought.

Oldest Anthropoid Fossil Hails From Thailand, Said Thai Officials

So supposedly a newly publicized paper back in November 2009 confirms that the oldest primate anthropoid fossil comes from the southern province of Krabi, Thailand (according to some Thai news articles, which unfortunately I cannot find where they cited their primary sources). It was discovered 14 years ago by Thailand's Mineral Resources Department archaeologists. Siamopithecus eocaenus supposedly roamed the earth 35 million years ago and is in fact currently the oldest primate anthropoid fossil from the fossil record (again, can't find where they cited the primary source). Thanks to Mae Kai Fa for pointing out that it is the oldest "anthropoid" fossil not primate fossil, which makes more sense.

Siamopithecus eocaenus or the Siam Ape gets its name from the country it was found. Siam was the official name of Thailand until 1939, although it is still somewhat used synonymously with Thailand.

Fragments of the fossil includes the lower right molars and upper left and right molars that are attached to the eye bone. Researchers think that S. eocaenus is about the size of a gibbon, weighs around 7kg and belongs to the Amphipithecidae family.

So, I don't know. This sounds a bit like the Darwinius massilae fiasco all over again. I also wonder why no one picked up this news, except a sprinkle of Thai news websites. What do you think? The paper pointed out by these articles is possibly The Face of Siamopithecus: New Geometric-Morphometric Evidence for Its Anthropoid Status by Zollikoffer et al. (2009) that was published in The Anatomical Record on November. Unfortunately I do not have access to that journal so I can't verify whether the paper did point out that S. eocaenus is indeed 35 million years ago.

Some Thai news article:
Oldest primate fossils found by Bangkok Post.
35-mn-year-old fossil raises questions on primates' origin by Prokerala.com.
Oldest primate fossils found in Krabi by National News Bureau of Thailand (NNT).

Can I See Your Fingers Please?

That is what University of Liverpool's Emma Nelson probably would have said if she were to meet our hominan ancestors in person. Known to hold true in anthropoids (humans, apes and monkeys), the index (second digit) to ring (fourth digit) fingers ratio or 2D:4D is an indication of how much an individual were exposed to androgen (such as testosterone) in the womb. The more androgen you are exposed to, the longer the ring fingers are (and the shorter the index fingers are compared to the index fingers).

Photo of a human's left hand. From left to right: thumb, index, middle, ring and little finger. Photo modified from Wikipedia.

Nelson et al. believe that a high ratio (longer index finger, shorter ring finger) suggests monogamy (or pair-bonded) while a low ratio (shorter index finger, longer ring finger) suggests polygamy (or non pair-bonded). Simply put, individuals with high androgen level is likely to be non pair-bonded and the telltale sign is in the index and ring fingers. Also, some controversial studies had suggested that both men and women who receive high levels of androgen in the womb are more likely to be stronger, faster, and more sexually competitive.

Nelson and her researchers recently looked at the fossils of two Neandertals and one Australopithecus afarensis with complete index and ring fingers to determine their 2D:4D. They found that Neandertals had long ring fingers, suggesting that they were polygamous just like modern day primates that live in groups. A. afarensis on the other hand, had long index fingers. Nelson is puzzled by this discovery. "These were small creatures that probably lived in groups and were being eaten by predators. How do you keep from mating with different members of the group?", she said.

Indeed it does not make sense for A. afarensis to be monogamous if they live in groups. Notice that Nelson et al. only used one A. afarensis fossil to get the 2D:4D. Perhaps it is not their fault that only one A. afarensis specimen had complete index and ring fingers but such are the dilemma of using fossil specimens to generalize a whole species.The result might just be a statistical outlier. However, I can't speculate the result or the implications but anyone that are familiar with statistical data knows that a small sample size leads to a higher sampling error. Also what would a 2D:4D = 1 (same index and ring finger length) be?

Interesting enough, John Hawks at John Hawk's Weblog mentioned the correlation of 2D:4D with male homosexuality (Robinson and Manning, 2000). I would know about this. In fact, my 2D:4D is indeed low.  Robinson and Manning predicted right! Maybe ...

I do find both Nelson et al. and Robinson and Manning (2000) research interesting but I would like to stress that the results are mere predictors and correlations. Take it with a grain of salt. Don't go measuring 2D:4D of your future spouse, boyfriend or girlfriend and accuse them of not being monogamous or a homosexual.

Emma Nelson and her team presented their research at this year's Society for Vertebrate Paleontology meeting held in Bristol, United Kingdom. Read more about Emma Nelson's research.

References:

Reilly M. 2009. Human Ancestors Conflicted on Monogamy. Discovery News. Retrieved September 25, 2009, from http://dsc.discovery.com/news/2009/09/24/human-monogamy.html

Robinson SJ. Manning JT. 2000. The ratio of 2nd to 4th digit length and male homosexuality. Evolution and Human Behavior 21(5): 333-345. [doi:10.1016/S1090-5138(00)00052-0]

Algeripithecus and Azibius: Anthropoids or Strepsirhines?

The mandible of Algeripithecus. Photo from Science Daily.

The debate for the origin of anthropoid points to two locations. One hypothesis supports the notion that anthropoids originated from Africa while the other argues that anthropoids originated from Asia. The model for the African origin hypothesis rests on Algeripithecus minutus, a fossil discovered in Algeria, Africa that lived 45 million years old. Algeripithecus and Azibius are Eocene primates that lived around the same time in Africa some 50 million years ago.

Much more complete craniodental fossils of Algeripithecus and Azibius were recently excavated and reveal that they might not be anthropoids but were strepsirhines instead. New data from the fossils, according to a recently published paper by Tabuce et al. (2009), suggest that Algeripithecus and Azibius were the earliest primates to branch out of the Afro-Arabian strepsirhines clade.

According to Tabuce et al. (2009), there are anatomical evidence suggesting that Azibius were nocturnal. They also found that Algeripithecus has a long, thin and forwardly inclined lower canine alveolus, features that match the long and and flat lower canine in the tooth comb (dental comb) of crown strepsirhines. These physical characteristics suggest that both Algeripithecus and Azibius are closely related to crown strepsirhines. The researchers concluded that both Algeripithecus and Azibius were not members of the anthropoid family but instead an early representative of the crown strepsirhines. Crown strepsirhines gave rise to modern day lemurs, galagos and lorises.

Tooth comb of a ring-tailed lemur (Lemur catta). Notice the two lower canines that are long, thin and forwardly inclined. Together with four lower incisors, it makes up the tooth comb. Photo from Wikipedia.

These recently excavated fossils support the origin of crown strepsirhines from Africa. However, it also challenges the hypothesis that points to Africa as the origin of anthropoids since Algeripithecus should be classified as strepsirhines instead of anthropoids (and no longer provide evidence for the Africa origin hypothesis) according to this published paper by Tabuce et al.


References:

CNRS (Délégation Paris Michel-Ange) (2009, September 15). African Origin Of Anthropoid Primates Called Into Question With New Fossil Discovery. ScienceDaily. Retrieved September 15, 2009, from http://www.sciencedaily.com­ /releases/2009/09/090915101355.htm

Rodolphe Tabuce, Laurent Marivaux, Renaud Lebrun, Mohammed Adaci, Mustapha Bensalah, Pierre-Henri Fabre, Emmanuel Fara, Helder Gomes Rodrigues, Lionel Hautier, Jean-Jacques Jaeger, Vincent Lazzari, Fateh Mebrouk, Stéphane Peigné, Jean Sudre, Paul Tafforeau, Xavier Valentin, and Mahammed Mahboubi. Anthropoid versus strepsirhine status of the African Eocene primates Algeripithecus and Azibius: craniodental evidence. Proc R Soc B 2009 : rspb.2009.1339v1-rspb20091339.