Handedness in Humans and Geladas

I thought I’d share a paper I wrote from last semester’s Comparative Psychology class on handedness in humans and geladas. Debating if I should actually follow through with this preliminary report and do some data collection. There is a YouTube video that accompanies this paper, which will appear on the bottom of the page.

Handedness can be defined as the unequal distribution of fine motor skills between the left and right hands. Simply put, handedness is the preference to use left, right or both hands when performing tasks. Humans are mostly right-handed across cultures. Here, I compare handedness in humans (Homo sapiens) to handedness in geladas (Theropithecus gelada).

Right-handedness is predominant across cultures in humans. About 85% to 90% of humans report themselves as right-handers (10). In studies of great apes, comparative analysis indicates that chimpanzees and bonobos exhibit population-level preference in right-handedness while gorillas and orangutans do not exhibit population-level preference in handedness (10). However, right-handedness seems to be uniquely human as no other primate species has such a clear bias (1, 13 & 14). The objective of this preliminary study is to elucidate whether geladas exhibit preference in handedness.

A male gelada at The Bronx Zoo.

Geladas are Old World Monkeys and can be found in the high plateau of North Central Ethiopia and Eritrea (9 & 2). Geladas are sometimes referred to as “bleeding heart monkeys” due to the presence of a naked, pink patch of skin on the chest of males and females that looks like an hourglass (2). They exhibit sexual dimorphism; males have manes and are slightly larger than females. The maximum lifespan of a gelada is about 19 years in the wild (5) and well over 30 years in captivity (9). Geladas are gramnivores; they are unique among primates because grass is their main food source but is occasionally supplemented by seeds, roots, and bulbs (3).

There are many definitions of handedness. Here, I define handedness as the preference of left, right or either hand when performing tasks. In humans, those who have a preference for using their right hand are right-handed while those that prefer using their left hand are left-handed. Those that prefer to use either hand when performing tasks are ambidextrous.

Approximate location of Broca's area and Wernicke's area. Photo from Wikipedia.

Handedness is due to the lateralization (asymmetry) of the brain hemispheres. Those that are right-handed have a more dominant left hemisphere, while those that are left-handed have a more dominant right hemisphere. In most humans, the left hemisphere of the brain is more dominant. The left brain hemisphere is also involved in language and is where Broca’s area and Wernicke’s area are located. Broca’s area is involved in speech production while Wernicke’s area is involved in language comprehension.

Right-handed preference is deep-seated in hominid evolution. Analysis of stone tools from Lower Pleistocene sites in Koobi Fora, Kenya and Middle Pleistocene sites in Ambrona, Spain showed that there is a consistent pattern of tools being produced by right-handed Homo habilis and Homo erectus (15). Preference for right-handedness may have existed as early as 1.4 to 1.9 million years ago, and might hint that the hominid brain had lateralized and was well on its way to becoming more specialized for different functions (15). Analysis of scratch patterns in incisors and canines from archaic humans (Sima de los Huesos in Atapuerca, Spain) and European Neandertals (Sima de los Huesos in Atapuerca, Spain and Vindija, Croatia) also showed that there was a persistent pattern of right handedness (6 & 7).

The prevalence of right-handedness in humans has a linear correlation with left hemisphere dominance (12). Since the left brain hemisphere plays an important role in language, brain lateralization leads to right-handedness. Thus, the prevalence of right-handedness in humans is a byproduct of human language.

The left-handed Ned Flanders from The Simpsons. Photo from SF Weekly.

The subjects for this study are from a captive population of geladas at The Bronx Zoo (Wildlife Conservation Society). There were 7 individuals present during the observations and all were male. Observations were done on two separate days between 12 P.M. and 3 P.M. The geladas were recorded using a video camera, and the recordings were later analyzed.

Geladas spend a significant amount of their time foraging (8). Site studies show that geladas spend 35.7% to 81.6% of their time foraging (8). There is a positive correlation between altitude and time spent foraging; more energy is burnt at higher altitudes, therefore more time is spent foraging (11).

A male gelada foraging with both hands.

My observations showed that geladas use either hand while foraging. They use either their left or right hands to pick up bunches of grass to eat. As my observation progressed, I became concerned that their repetitive motion of picking up grass and putting it in their mouths was not a sufficiently varied behavior to indicate handedness. Therefore, I also observed the geladas grooming.

A female gelada grooming herself.

There are two types of grooming in geladas: autogrooming (self grooming) and allogrooming (social grooming). Grooming is not only important for hygienic reasons but also important for strengthening social bonds (4). A study by Dunbar suggests that the major reason for grooming is the satisfaction of physical contact between the groomer and the individual being groomed (4).

From my observations, allogrooming starts with the individual being groomed initiating eye contact with the groomer. Then, the individual lies down and presents the area that needs to be groomed. Sometimes, a groomer simply approaches the individual they want to groom and starts grooming them. My observations showed that there is also no preference for which hand is used by geladas during grooming. The geladas used either hand for both autogrooming and allogrooming. The decision to use their left or right hand seemed to be determined by the area of the body that needed grooming.

From my observations, it seems that the geladas use either hand for foraging and grooming. The geladas at The Bronx Zoo seem to exhibit ambidexterity because they have no preference for their left or right hand, unlike humans who are predominantly right-handed.

Handedness is correlated with brain hemisphere dominance. For most humans, the left brain hemisphere is dominant and is also involved in language. Thus, the prevalence of right-handedness is a byproduct of human language. None of the geladas I observed at The Bronx Zoo exhibited preference for handedness. This is probably due to the fact that geladas do not have language; therefore, their left brain hemisphere is not dominant and does not lead to right-handedness. Besides foraging and grooming, more behavioral repertoire should be used in future analysis to further elucidate the preference in gelada handedness.









 References

 1. Cashmore, L., Uomini, N., & Chapelain, A. (2008). The evolution of handedness in humans and great apes. Journal of Anthropological Sciences, 86, 7-35.

 2. Dunbar, R.I.M., &; Dunbar, P. (1975). Contributions to Primatology: Social Dynamics of Gelada Baboons (Vol. 6). Basel, Switzerland: S. Karger AG.

 3. Dunbar, R.I.M. (1984). Reproductive Decisions. Princeton, New Jersey: Princeton University Press.

 4. Dunbar, R.I.M. (2008). The social role of touch in humans and primates: Behavioural function and neurobiological mechanisms. Neuroscience and Biobehavioral Reviews, 34(2), 260-268.

 5. Falk, D. (2000). Primate Diversity. New York and London: W.W. Norton & Company.

 6. Frayer, W.D., Fiore, I., Lalueza-Fox, C., Radovčić J., & Bondioli, L. (2010). Right handed Neandertals: Vindija and beyond. Journal of Anthropological Sciences, 88, 113-127.

 7. Frayer, W.D., Lozano, M., de Castro, J.M.B., Carbonell, E., Arsuaga, J.L., Radovčić J., Fiore, I., & Bondioli, L. (2011). Laterality: Asymmetries of Body, Brain and Cognition, doi:10.1080/1357650X.2010.529451

 8. Gron, KJ. (2008, September 3). Primate Factsheets: Gelada baboon (Theropithecus gelada) Taxonomy, Morphology, & Ecology. Retrieved May 11, 2011, from www.pin.primate.wisc.edu/factsheets/entry/gelada_baboon

 9. Hiller, C. (2000). "Theropithecus gelada" (On-line), Animal Diversity Web. Retrieved May 11, 2011, from www.animaldiversity.ummz.umich.edu/site/accounts/information/Theropithecus_ gelada.html

10. Hopkins, W.D. (2006). Comparative and Familial Analysis of Handedness in Great Apes. Psychology Bulletin, 132(4), 538–559.

 11. Iwamoto, T., & Dunbar, R.I.M. (1983). Thermoregulation, Habitat Quality and The Behavioural Ecology of Gelada Baboons. Journal of Animal Ecology, 52, 257-366.

12. Knecht, S., Dräger, B., Deppe, M., Bobe, L., Lohmann, H., Flöel, A., Ringelstein, E.-B., & Henningsen, H. (2000). Handedness and hemispheric language dominance in healthy humans. Brain, 123 (12), 2512-2518

13. McGrew, W.C., & Marchant, L.F. (1997). On the other hand: Current issues in and meta-analysis of the behavioral laterality of hand function in nonhuman primates. American Journal of Physical Anthropology, 104(25), 201-232.

 14. Steele, J. & Uomini, N. (2009). Can the Archaeology of Manual Specialization Tell Us Anything About Language Evolution? A Survey of the State of Play. Cambridge Archaeological Journal, 19, 97-110.

15. Toth, N. (1985). Archaeological Evidence for Preferential Right-Handedness in The Lower And Middle Pleistocene, and Its Possible Implications. Journal of Human Evolution, 14(6,) 607-614.

Keeping up with the Hominin

In less than a week, some of you will be shuffling back to school as Fall session begins. Every new semester, without a doubt, you'll be able to pick out the smart ass in the class. You know, the ones that sit in front of the class and always have their hands up when the professor asks a question (think Hermione Granger). But what if you are the smart ass? Have no fear, you're reading the right post.

"Hominin - the group consisting of modern humans, extinct human species and all our immediate ancestors (including members of the genera Homo, Australopithecus, Paranthropus and Ardipithecus)."

- Australian Museum.

A lot had happened this year with hominin research and some would redefine conventional understandings of this group. Below is a list of new studies that came out this year that I find quite interesting on hominin. Read up so you can show off in class with your knowledge of current hominin research. You know, just so you can make sure that your adjunct is really paying attention of what he/she is doing instead of begrudgingly teaching a class because he/she has to. Or maybe you have a geeky classmate you want to impress. Or if you're like me, you just wanna be the smartest in class because Asian Fail is not an option. So, enjoy ... and if they question you, tell them I said so.

Australopithecus africanus and Paranthropus robustus

• Male philopatry and female dispersal in both A. africanus and P. robustus. Is this a strategy to prevent inbreeding and mate choice by females? Ancient Hominid Males Stayed Home While Females Roamed, Study Finds

Paranthropus boisei

• Seems like we'll have to re-evaluate P. boisei's nickname, "Nutcracker Man". Recent study showed that P. boisei didn't eat nuts but instead used its big teeth to chew on grasses and sedges. No nuts for 'Nutcracker Man': Early human relative apparently chewed grass instead

From left to right: Comparison of upper jaw, P. boisei and H. sapiens. Photo from PhysOrg.

Homo erectus

• H. erectus were the first to controlled fire but it wasn't just used for warmth. New study shows that H. erectus were the first to cook their food (with fire) and process their food with tools. Homo Erectus Processed Food Like Humans, Harvard Scientists Say

• Stone artifacts, mostly flakes from stone tools, from the Dmanisi site in Georgia (the country, not the state) might suggests that H. erectus evolved outside of Africa. However, no conclusive evidence can be made due to the poor conditions of fossils found near these artifacts. Human ancestors in Eurasia earlier than thought

• H. erectus reached South Asia earlier than previously thought, between 1.5 to 1 million years ago according to Acheulean tools. Go east, ancient tool makers

• Findings from Solo River Terrace (SoRT) in Indonesia shows that H. erectus never coexisted with H. sapiens. Using three dating techniques: U-series, Electron Spin Resonance (ESR) and argon-argon, scientists found H. erectus went extinct between 143,000 to 550,000 years ago. H. sapiens are thought to reached Indonesia about 40,000 years ago. Human Ancestor Older Than Previously Thought; Finding Offers New Insights Into Evolution

An Acheulean hand ax found in India (South Asia) indicates that H. erectus moved to South Asia shortly after the invention of stone tools, around 1.6 million years ago. Photo from ScienceNews.

Homo neanderthalensis

• Neandertals probably died off because there were too many early humans to compete with. According to a statistical analysis, the Périgord region of southwestern France has the highest concentration of Neandertals and early humans. The ratio between Neandertal to early human was 1 to 10. There were just too many humans for Neanderthals to survive

• Mousterian culture might have lasted longer than previously thought and Neandertals might have spread as far as northern Russia in the mountains of Polar Urals, near the Arctic Circle. Last Neanderthals Near the Arctic Circle?

• Neandertals were predominantly right-handed, according to their teeth. Also, humans have been predominantly right-handed for at least 500,000 years. Neanderthal ancestors were mostly right-handed

Homo floresiensis (the Hobbits)

• The debate whether H. floresiensis is a separate species or just microcephalic H. sapiens continues on. New study shows that the measurement of the Hobbit skull is within the range of microcephalic H. sapiens. Taking the measure of a hobbit

From left to right: Homo floresiensis (LB1) and Homo sapiens.

Homo sapiens (early and modern humans)

• Early humans have been playing hanky panky with Neandertals and possibly the Denisovans. Proof? A toe bone and its DNA. Stone Age toe could redraw human family tree

• A particular segment of our X-chromosome were inherited from Neandertals. This supports the hypothesis that early humans interbred with Neandertal. However, only non-African humans have this segment. Confirmed: All non-African people are part Neanderthal

• Might not be a conscious decision, but apparently early humans that left Africa interbred with Neandertal to protect themselves against diseases. This is probably an unintended result more than an active thought process. First modern humans protected themselves against disease after leaving Africa by 'interbreeding with Neanderthals'

*Bouchra child, Homo sapiens*

• Dr. Harold Dribble and his team found the skull of "world's oldest human child" dated around 108,000 years old in Morocco and nicknamed it Bouchra. The boy died when he was 8 years old. This specimen has not been described in any scientific paper so watch out for it soon. World’s Oldest Child Found in Morocco

Someone Cited My Thesis!

Some time last week, a little birdie sent me a link to what appears to be a page from American Museum of Natural History (AMNH). Said birdie also mentioned that the link has to do with my honors thesis. Along with the link was a thumbnail of a male hamadryas baboon that looked rather familiar. It took me a few seconds to realize that I am looking at Fadi, or Moja as what he is referred to by the zoo. (Follow this link for who's who at Prospect Park Zoo) Confused as to what my honors thesis, Moja and AMNH have in common, I opened the link. The link directed me to one of AMNH's Young Naturalist Awards winner, a young gentleman by the name of Henry.

Henry's winning entry is Hamadryas Baboons, Papio hamadryas: Captive vs. Wild. His research was on hamadryas baboon behaviors, where he compares the Prospect Park Zoo troops with the ones from Larissa Swedell's field work in Ethiopia. And guess what, he cited my thesis! I'm excited that someone dug up my baby and used it in their research. This is the first time (that I know of) someone actually cited my research. I'm so glad I uploaded my honor thesis on Scribd instead of just letting the bound copy collect dust in my college's library. Anyway ...

Henry's research is quite interesting. He found that there are behavioral differences between captive and wild hamadryas baboons. Also, grooming was not the highest in frequency compared to other behaviors (sitting was the highest in frequency). This could be explained by the hot weather or the fact that data for this research was only collected for about 9 hours. Nonetheless, this is heading in a good direction and a pretty good research topic for a 15 year-old. Hopefully he'll stick to his passion for primates (baboons) and go on to be the next primatologist.

Note that the male hamadryas photo "Simen, a 19-year-old Alpha Male" (above) is actually Moja, Simen's offspring. Simen can be identified with a mole underneath his left eye, which is absent in this photo. Click on the link to read my thesis, A Cross-Species Comparative Study: Grooming Patterns in Captive Populations of Hamadryas Baboons and Geladas.

20 million-year-old well preserved fossil skull: Ugandapithecus major

Map of Uganda showing the remote Karamoja region in the northeast of the country where a team of Ugandan and French paleontologists announced Tuesday they had found a 20-million-year-old ape skull, saying it could shed light on the region's evolutionary history. Illustration from PhysOrg.

A well preserved fossil skull of an ancient primate, Ugandapithecus major, has been excavated in the northeast region of Karamoja in Uganda (hence the genus name, Uganda monkey). The 20 million-year-old skull belongs to a male and probably died when it was about 10 years old, said researchers Pickford and Senut. The cranial size of Ugandapithecus major was about the same size as that of chimpanzees but its brain size is smaller. Ugandapithecus major is a tree-climbing catarrhine, an herbivore that lives around the Miocene. Although its genus name refers to it as a monkey, Ugandapithecus major is actually a hominoid (ape).

A well preserved skull of Ugandapithecus major. Photo from BBC News. 

The skull will be cleaned and prepared in France for about a year before returning it back to Uganda. Ugandapithecus major was described in 2000 by Senut et al. from a few dental and postcranial remains.

You can read Senut et al. (2000) A new genus of Early Miocene hominoid from East Africa: Ugandapithecus major (Le Gros Clark & Leakey, 1950) here (requires subscription).

AMNH Picturing Science Tweetup: In Living Colors

Atlantic Spotted Mackerel. Stained using red dye (bones) and blue dye (cartilage)

I was excited to be invited back to another tweetup at AMNH last night. This time, I was able to get Vance to come with me and I think he had a pretty good time. The tweetup was about "Picturing Science: Museum Scientists and Imaging Technologies", a vivid photo exhibition of specimens and phenomenon. And yet again, I have forgotten to bring my camera. You know, after I've got my Nexus S, I have barely used my camera. I just need to remember that sometimes my phone can't take pretty pictures. Anyway, we were treated to some behind-the-scene tour of some of the AMNH scientists at work using imaging technologies such as computed tomography (CT) scans, scanning electron microscope (SEM), infrared photography and even dyes to color bones and cartilage (staining technique). The latter was my favorite technique as I am quite fond of stained specimens.

We picked up a button when we arrived and on the brim of the button reveals the group that we will be part of. I subconsciously just chose the button of a upper mandible of a felid. Bones, bones, bones. So we were assigned to Group #2 for a behind-the-scene tour. But before the tour, we gathered at Akeley Hall of African Mammals to mingle. There was, of course, wine and cheese. Oh yea, it's classy like that.

Led by an ichthyologist and an entomologist graduate students, the first stop for this group was a classroom-like setting where we were treated to amber, flies, ants and stained fishes. Sweet. I got to hold a piece of Baltic amber that encases a pair of flies that are still in the heat of copulation. Pretty rad. There was also amber that encases a species of previously undescribed ant. That guy has a massive pair of mandibles. We also spent some time looking at stained fishes under the microscope, although the staining technique itself is sufficient to show the complexity of fish osteology. "Fish bones are jigsaw puzzle from hell". Yep, that pretty much sums it up along with articulating a snake. The staining technique uses red dye to color the bones and blue dye to color the cartilage. Here's a writeup on how to prepare a stained fish Hidden Blades, Glowing Scorpions and Bug Genitalia: Great Science Images From the American Museum of Natural History.

Using a microscope to looking inside an amber. This particular amber has an ant in it.

Vance loves ants. So he's particularly excited.

I hold in my hand a piece of amber that has encased a pair of copulating flies, hence the "IN LOVE" and an arrow pointing at the two amorous flies.

Next stop was the imaging technology area where we got to see some cool microscopes such as SEM and CT scan in action. The SEM was used to produce detailed close-up photos of goblin spider while the CT scan was used to take thousands of armadillo lizard x-rays. These x-rays are later incorporated into a 3D program to produce a comprehensive 3D image of an armadillo lizard. Pretty neat stuff. There was also a microscope that they dubbed "microscope on steroid" and is used to scan comet dust. They mean business there. LOL!

Scanning electron microscope (SEM) on the left. Image of the carapace of a goblin spider on the right.

Using a CT scan to look inside an armadillo lizard.

"Microscope on steroid". Scanning comet dust.

As the behind-the-scene tour ends, we were ushered back into the Akeley Hall of African Mammals and got to spend more time mingling and taking in the new photo exhibition. There was a photo exhibit of Chilecebus (Chilean Monkey), an extinct primate and the only specimen of its kind ever found. Using a CT scan, the researchers were able to look inside the skull of Chilecebus to reveal its brain size and the shape of its head's semicircular canal. 

Chilecebus photo exhibit. Using a CT scan to look inside the skull of the one and only specimen found.

Chilecebus skull (left). CT scan reveals the shape of its head's semicircular canal. 

Brownie points to Denton Ebel, the Curator-In-Charge of Department of Earth and Planetary Sciences for walking us through the exhibition and explaining to us in depth the "Warhol" meteorite photo exhibit. And also thanks for all the jokes "It's perfectly round, just like tears of astronauts in space ... because they missed home". Oh yes, I forgot about the swag. This time we were ushered away with some postcards from the photo exhibition and also a scorpion sucker! Hmm ... I dunno, I don't think I am gonna eat THAT. But thanks for another great tweetup, American Museum of Natural History! Looking forward to the next one.

Buttons for the group tour (left). Scorpion suckers as parting gift (right). I dunno, but I doubt it'll taste like chicken.

You can follow American Museum of Natural History on Twitter at @AMNH for more info on the museum, upcoming events and also future tweetups. The photo exhibition, Picturing Science: Museum Scientists and Imaging Technologies, opened June 25, 2011 and ends June 24, 2012. It is free with museum admission and opens daily.