Behavioral Synchronization In Chacma Baboons

There is a newly published paper by Andrew J. King and Guy Cowlishaw on factors that promote or constrain group synchronization among Chacma baboons (Papio ursinus) in central Namibia. The paper "All together now: behavioural synchrony in baboons" is available online as pdf for free.

 A mother and infant Chacma baboon (Papio ursinus). Flickr photo from Arno & Louise.

Synchronized behavior is defined as behavior performed by individuals in unison. For example, you can say that a group of animals moving through its environment is synchronized in the direction of the movement. Or a group of animals feeding is synchronized in its behavior. Synchronized behavior has its costs and benefits. Group synchronization is costly to achieve, and according to this article, due to age - sex differences, morphological - physiological differences, heterogeneous feeding terrain and visual isolation between group members. The benefit of group synchronization increases foraging benefits and reduces predation risk. A large group who travels together can easily find food or spot predators.

An example of synchronized behavior. A group of baboons traveling in a synchronized direction in Tanzania. Photo from Hole In The Donut Travels.

Interestingly, this research found that the probability of the group to synchronize increases with the number of pregnant females in the group but decreases with the number of sexually swollen females in the group. They think that females that are sexually swollen are not shy about advertising their receptivity to the males in the group. The males, in turn, would zealously guard these sexually swollen females from other males thus disrupting behavioral synchronization. Pregnant females, on the other hand, promotes group synchronization because individuals are not fighting or distracted by mating opportunities.

Read more from the press release, Brazen Baboons: Flighty Females Disrupt Group Harmony.

References:
King, AJ. Cowlishaw, G. 2009. All together now: behavioural synchrony in baboons. Elsevier Retrieved October 31, 2009, from http://static.zsl.org/files/king-cowlishaw-animal-behaviour-2009-910.pdf

PR.com. 2009. Brazen Baboons: Flighty Females Disrupt Group Harmony. Retrieved October 31, 2009, from http://www.pr.com/press-release/188486

Chimps Mourn The Death Of Their Own

A picture is worth a thousand words. So, I'm gonna just let the photo do most of the talking. Ever since this photo was published it has gone viral everywhere. Read about this news story at National Geographic and an in depth explanation of the photo here.

This photo is not surprising because it is well documented that chimpanzees mourn the death of their own. I guess the reason why it went viral is because the sheer volume of individuals mourning the death of this female chimpanzee. It looks almost human-like and behaviors that are human-like tend to evoke empathy in humans.

Effects Of Global Warming On Endangered Primate Species

A study was done by Penn State Graduate students Ruscena Wiederholt and Biology professor Eric Post on how the effects of global warming, such as El Niño and El Niña, on endangered primate species. Focusing on New World Monkeys, Wiederholt and Post studied the trend of abundance and population dynamics in four genera of Atelines: the muriqui (Brachyteles hypoxanthus, formerly B. arachnoides) of Brazil, the woolly monkey (Lagothrix lagotricha) in Colombia, Geoffroy's spider monkey (Ateles geoffroyi) of Barro Colorado Island in Panama, and the red howler monkey (Alouatta seniculus) in Venezuela.

The results of the team's analyses were spectacular. All four monkey species showed drops in abundance relating to large-scale climate fluctuations. Even though the monkey populations were separated by large distances, the three fruit-eating species had synchronous responses to large-scale warming. During El Niño warming events, trees produced more fruit than usual. Then, during the subsequent La Niña cooling events, the trees produced much less fruit, resulting in a local scarcity or even famine.


Some ecologists have speculated that high production of fruit during El Niño events may have been triggered by the increase in solar radiation, despite lower-than-usual rainfall. However, high productivity during an El Niño event might also use up the stored reserves of the trees, which would have difficulty recovering during the subsequent La Niña events, when weather was wet, cloudy, and cool. This mechanism would explain why the fruit-eating monkeys showed a delayed response to the El Niño events after a lag of one or two years.

Howler monkeys also showed declines with warm and dry El Niño events, but their population fall was out of sync with that of the fruit-eating species. The mechanism is not yet clear, but Wiederholt has some ideas. She notes, "Primate researchers have seen elevated adult female mortality and lowered birthrates among red howlers in drought years. Since leaf flush often occurs at the start of the wet season, a prolonged dry season might delay the availability of this resource for the howlers and perhaps cause them nutritional stress."


Warmer temperatures also may cause leaves -- the howlers' primary food -- to mature faster, which would accelerate the leaves' acquisition of toxins and other chemical defenses against monkeys. The factor that the scientists found was most influenced by changes in climate was the monthly maximum number of tree species that were fruiting. Climate changes also were highly correlated with the monthly maximum number of species that were flowering and with annual seed production. The length of the dry season also was highly correlated with annual flower production. Thus, vegetation responses to climatic conditions substantially altered the food resources available to primates, which in turn influenced the decline or rise in monkey abundance.

Read the rest of the article from EurekAlert!

Modern Humans Are Still Evolving But Will Modern Men Get Wimpier?

Two interesting articles that went into my inbox today: Modern man a wimp says anthropologist and Darwin Lives! Modern Humans Are Still Evolving.

A cover illustration from Australian anthropologist Peter McAllister's new book entitled "Manthropology" and sub-titled "The Science of the Inadequate Modern Male." Photo from REUTERS/Hachette Publishing/Handout.

Modern man a wimp says anthropologist  from Reuters, summarizes Peter McAllister's book Manthropology: The Science of the Inadequate Modern Male. Using various data from Neanderthals and ancient aboriginal populations, McAllister concludes that modern men are inferior than their predecessor in running, jumping, and even sheer brute. "Any Neanderthal woman could have beaten former bodybuilder and current California governor Arnold Schwarzenegger in an arm wrestle", McAllister said. John Hawks from John Hawks Weblog has a lot to say about this in his post Is modern man a "wimp"? I think Hawks is spot on with his post.

The Time article, Darwin Lives! Modern Humans Are Still Evolving, is about a study in a contemporary Massachusetts population led by Stephen Stearns and his team of scientists from Yale University. Using correlations between women's physical characteristics such as height, weight, blood pressure, and cholesterol levels with the numbers of offspring produced, they found that "stout, slightly plump, but not obese" women tend to have more offspring as oppose to women with very low body fat count, as well as women with lower blood pressure and lower cholesterol levels.

Stearns explains that women with very low body fat count, low blood pressure and low cholesterol levels do not ovulate. Ovulation is, of course, when the matured ovarian follicle ruptures and discharge an ovum (or the egg). While human females ovulate about once a month, female chickens ovulate once a day. Of course, we refer to chicken ovum as chicken eggs.

Stearns and his team thinks that the characteristics for producing maximum offspring (stout, slightly plump, higher blood pressure and cholesterol levels) were passed down from mothers to daughters. Separating social and cultural factors using statistical analysis, Stearns and his team were able to conclude that these characteristics were passed down genetically. "Variations in reproductive success still exist among humans, and therefore some traits related to fertility continue to be shaped by natural selection" Stearns says. So women who have more children are more likely to pass down these traits to their offspring.

It explains the notion that modern humans are still evolving because variation in reproductive success means that there are selective pressure that favor certain traits. Interesting to note that while fertility is being shaped by natural selection (as per Stearn and his team's study), artificial selection is also shaping the width of female pelvis and the average brain size of infants being born. Mothers with a narrow birth canal (smaller pelvis size) puts both her and her infant in jeopardy during childbirth. The infant will be stuck in the birth canal due to restricted space. An infant with a larger than average brain size will also get stuck in the birth canal. Both scenarios will likely kill the infant and mother. However the advent of Caesarean section negates the restriction of a narrow birth canal and allows infant with larger brain size to be born.

So, we can see that modern humans are evolving through variation in reproductive success, female pelvis size and average infant brain size is also evolving through artificial selection though it is too early to say which direction the selection is favoring.

When It Comes To Being The "Missing Link", Ida -- You Are NOT The Candidate

Main slab of Darwinius masillae (specimen PMO 214.214), new genus and species, from Messel in Germany. Photo from Wikipedia.

Ida or "Aunt Ida" as many might recall from this summer of craziness sent shock waves around the nation as it was herald the missing link between prosimians and anthropoids (primates and human). Deserving of its own genus, Ida was given the name Darwinius masillae by Franzen et al. (2009) as they describe this specimen in their paper. Darwinius to celebrate the bicentennial celebration of Darwin's claim to fame "Origin of Species" and masillae for the location where Ida was discovered (Messel Pit, Germany).


Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology was published this summer. Soon thereafter, the general public expressed sheer amazement and curiosity, especially the press who were all too excited to report such breaking news. Hence, "Aunt Ida" became synonymous with "Ida" due to the general public's warm family reception. Others, such as the religious nuts were quick to point out that Ida was just another god(s) creation and the notion of a "missing link" is preposterous. Even Google participated in this frenzy, much to the chagrin of religious right-wing, featuring Ida in Google's logo on May 20th, 2009.

Ida as Google icon. Illustration from Google.

American Museum of Natural History soon announced that you can see Darwinius masillae in their Extreme Mammal exhibit (which I later find out that it is just a cast). The Discovery Center at Times Square also got into the game by exhibiting Darwinius masillae. All these publicity and attention makes one wonder. Is this just a publicity stunt on a premature discovery and discussion? Not to mention all the money they made from this discovery "that changes everything".

I, for one, was on the fence. While I was amazed and interested with the discovery, all these publicity stunt just does not bode well with me. I chose not to write about Ida's discovery in this blog, not because I was too lazy to add my one cent but rather I'd prefer to sit back and listen to all the discussions. One, I'm not a paleontologist nor am I an expert on skeletal morphology. I'd love to know if  Darwinius masillae actually groomed each other though.

So what made me wrote this blog entry? My inbox is filled with new articles about Darwinius masillae but this time disproving its role as the missing link. A new paper, published by Seiffert et al. (2009), concludes that Darwinius masillae is closely related to the genus Afradapis (an adapiform or adapoid). They also conclude that Darwinius masillae sits on the dead end of the evolutionary branch, without leaving any descendants let alone being the missing link for humans. Thus the title "missing link" is not befitting of this 47 million year old Eocene primate.

Phylogenetic position of the adapiforms Afradapis and Darwinius within primates. Photo from Wired.

So now that you have both sides of the story, what's your opinion on  Darwinius masillae? I'm betting my bananas that Darwinius masillae is just another product of a highly publicized discovery. Not to undermine the important discovery of this new genus but quoting my undergraduate professor, Dr. Sara Stinson, "There is no such thing as a missing link. We know where everything goes". She's right ... in fact the idea of a "missing link" is just an agent used by those who do not believe in evolution. You know, like the idea of Crocoduck (Hint: Kirk Cameron).

Further readings:
Bone Crunching Debunks ‘First Monkey’ Ida Fossil Hype from Wired.
So Ida's not the "missing link": questions and answers with Erik Seiffert from Times Online.
'Eighth wonder' Ida is not related to humans, claim scientists from Guardian.co.uk.
Darwinius on Wikipedia.

References:
Franzen, JL. Gingerich PD. Habersetzer, J. Hurum, JH. von Koenigswald, W. Smith, BH. 2009. Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology. PLos ONE 4(5): doi:10.1371/journal.pone.0005723.

Seiffert, ER. Perry, JMG. Simons, EL. Boyer, DM. 2009. Convergent evolution of anthropoid-like adaptations in Eocene adapiform primates. Nature 461, 1118-1121 doi:10.1038/nature08429.

Chimpanzees: Ask And You Shall Receive

A new study published by Shinya Yamamoto, Tatyana Humle and Masayuki Tanaka on PLoS ONE found that chimpanzees willing to help one another. All they have to do is ask.

Ask and you shall receive. Video from NewScientist.

Using two tool-use scenarios (a stick tool-use and a straw tool-use), both chimpanzees were placed in adjacent booths with non-corresponding tools. The chimpanzee in a stick tool-use scenario was given a straw while the chimpanzee in a straw tool-use was given a stick. Successful use of tool resulted in a reward, a carton of juice. A spontaneous tool transfer was observed between paired chimpanzees, mostly following the request of the recipient. Even though reciprocity was not always observed, the chimpanzees continue to assist their partners as long as their partner requested help.

The authors argues that these results further prove the evidence for altruistic behavior in chimpanzees without direct personal gain or immediate reciprocation. These results also highlight the importance of "request" as a cause for prosocial behavior in chimpanzees, between kins or non-kins and also interaction between dominant and non-dominant individuals.

When compared to humans, chimpanzees do not perform acts of voluntary altruism. Unlike humans,  chimpanzees do not necessarily act altruistically by just observing another chimpanzee struggle to achieve its goal. Chimpanzees cannot accurately understand others' desires in the absence of communicative signals such as a request.

Further reading on NewScientist.

Reference:
Yamamoto, S. Humle, T. Masayuki, T. 2009. Chimpanzees Help Each Other upon Request. PLoS ONE 4(10): e7416. [doi:10.1371/journal.pone.0007416]

The Uncanny Valley: Humans and Macaques

The uncanny valley hypothesis posits that when robots and other human facsimiles look and act almost like humans, it causes a response of revulsion among human observers. The "uncanny valley" refers to the dip in the graph of the positivity of human reaction as a function of a robot and other human facsimiles's life-likeness (see below).

Hypothesized emotional response of human subjects is plotted against anthropomorphism of a robot, following Mori's statements. The uncanny valley is the region of negative emotional response towards robots that seem "almost human". Movement amplifies the emotional response. Photo from Wikipedia.

It is the reason why we prefer cartoon characters than CGI characters that look realistic. For example, you are more likely to like the Homer Simpson on the left than the one on the right.

Read about the uncanny valley hypothesis here.

Now this is the interesting part. Using long-tailed macaques (Macaca fascicularis) as test subjects, Steckenfinger and Ghazanfar (2009) found that these monkeys' visual behavior actually fell into the uncanny valley, which mirrors the behavior of humans. These macaques looked longer at real faces and unrealistic synthetic faces than realistic synthetic faces.

The unrealistic synthetic faces, realistic synthetic faces and real faces. Actual images used in Steckenfinger and Ghazanfar's experiment.

The authors did not conclude why the visual cues of these macaques fall into the uncanny valley, though they did suggest that it has an evolutionary basis.

Remember the picture above? If not, read my blog entry on Contagious Yawning in Chimpanzees. I see you yawn. I wonder if those chimpanzees will yawn if given more realistic synthetic faces.

Reference:
Steckenfinger, SA. Ghazanfar, AA. 2009. Monkey Visual Behaviors Falls Into The Uncanny Valley. Proceedings of the National Academy of Sciences Retrieved October 15, 2009, from http://www.pnas.org/content/early/2009/10/07/0910063106.full.pdf+html [10.1073/pnas.091006310]

Discovering Ardi on Discovery Channel Tonight

The face of Ardi. Photo from Discovery Channel.

Discovering Ardi premiers tonight (Sunday, 10/11) on Discovery Channel at 9pm ET/PT. About the show, according to Discovery Channel's website.

Following publication in the journal Science on the discovery and study of a 4.4 million-year-old female partial skeleton nicknamed "Ardi," Discovery Channel will present a world premiere special, DISCOVERING ARDI, Sunday October 11 at 9 PM (ET/PT) documenting the sustained, intensive investigation leading up to this landmark publication of the Ardipithecus ramidus fossils.
UNDERSTANDING ARDI, a one-hour special produced in collaboration with CBS News will air at 11 PM (ET/PT) immediately following DISCOVERING ARDI. The special is moderated by former CBS and CNN anchor Paula Zahn and includes research team members Dr. Tim White, Dr. Yohannes Haile-Selassie, Dr. Giday WoldeGabriel, Dr. Owen Lovejoy, and science journalist Ann Gibbons
The scientific investigation began in the Ethiopian desert 17 years ago, and now opens a new chapter on human evolution, revealing the first evolutionary steps our ancestors took after we diverged from a common ancestor we once shared with living chimpanzees. "Ardi's" centerpiece skeleton, the other hominids she lived with, and the rocks, soils, plants and animals that made up her world were analyzed in laboratories around the world, and the scientists have now published their findings in the prestigious journal Science.
"Ardi" is now the oldest skeleton from our (hominid) branch of the primate family tree. These Ethiopian discoveries reveal an early grade of human evolution in Africa that predated the famous Australopithecus nicknamed "Lucy." Ardipithecus was a woodland creature with a small brain, long arms, and short legs. The pelvis and feet show a primitive form of two-legged walking on the ground, but Ardipithecus was also a capable tree climber, with long fingers and big toes that allowed their feet to grasp like an ape's. The discoveries answer old questions about how hominids became bipedal.
The international research team weighed in on the scope of the project and its findings:

"These are the results of a scientific mission to our deep African past," said project co-director and geologist, Dr. Giday WoldeGabriel of the Los Alamos National Laboratory.

"The novel anatomy that we describe in these papers fundamentally alters our understanding of human origins and early evolution," said project anatomist and evolutionary biologist, Professor C. Owen Lovejoy, Kent State University.

Project co-director and paleontologist Professor Tim White of the Human Evolution Research Center at the University of California Berkeley adds, "Ardipithecus is not a chimp. It's not a human. It's what we used to be."
DISCOVERING ARDI begins its story with the 1974 discovery of Australopithecus afarensis in Hadar, northeastern Ethiopia. Nicknamed "Lucy," this 3.2 million year old skeleton was, at the time, the oldest hominid skeleton ever found. As the Discovery Channel special documents, Lucy's title would be overtaken twenty years later by the 1994 discovery of "Ardi" in Ethiopia's Afar region in the Middle Awash study area. It would take an elite international team of experts the next fifteen years to delicately, meticulously and methodically piece together "Ardi" and her lost world in order to reveal her significance.

Female Orangutan Mating Strategies

There is a published paper by Knott et al. (2009) from next month's Proceedings of The Royal Society B about female Bornean orangutans and their reproductive strategies. The authors propose that female orangutan's mating strategies is a product of coevolution from male coercion and also selective resistance.

There are two morphs in male orangutans; flanged or unflanged. Both are secondary sexual characteristics (traits that distinguish the two sexes of a species but are not part of the genitalia). Flanged males are usually adult dominant males. Unflanged males are either juveniles (who haven't developed their secondary sexual characteristics) or non-dominant adult males. These adult unflanged males might develop a flange when they become a "dominant" male or might never develop one in their lifetime. High levels of forced copulation in orangutan is common, especially by unflanged males. Orangutans are polygamous and males generally do not spend anytime with the female after copulation. Orangutans are usually solitary (with the exception of mother and infant pair), due to scarcity of food sources.

The authors found that females, when near ovulation, mated cooperatively only with prime flanged males. When the conception risk for these females was low, they willingly associate and mate with unflanged males. These observations supported the hypothesis that, together with concealed ovulation, facultative association is a mechanism of female choice in a species where females can rarely avoid coercive mating attempts. Female resistance reduces copulation time and may provide an additional mechanism for mate selection. However, female mating strategies is important to avoid aggressive interactions from flanged males and also as infanticide avoidance.

Reference:
Knott, CD. Thompson, ME. Stumpf, RM. McIntyre, MH. 2009. Female reproductive strategies in orangutans, evidence for female choice and counterstrategies to infanticide in a species with frequent sexual coercion. Proceedings of The Royal Society B Retrieved October 9, 2009, from http://rspb.royalsocietypublishing.org/content/early/2009/10/06/rspb.2009.1552 [doi:10.1098/rspb.2009.1552]

Extended Habitat For Greater Bamboo Lemurs Found

 A Greater Bamboo Lemur (Prolemur simus) feeding on Giant Bamboo in Ranomafana National Park, Madagascar. Photo from Wikipedia.

Good news for Madagascar and lemur conservationists! Scientists have spotted bamboo lemurs in 11 sites east of the island where its populations were thought to have disappeared, AFP has reported.

The Greater Bamboo Lemur (Prolemur simus) is one of the most endangered primates in the world. Endemic to Madagascar, its name suggest that their primary food source is bamboo. Their specialized diet limits its range.

This finding opens "a new chapter for the species and for the places we can protect it by preserving the forest as the main problem is loss of habitat," Mahaoly Ravaloharimanitra, a research assistant at the Aspinall Foundation, told AFP.

The Greater Bamboo Lemur was thought to be extinct until 1980s. Currently there are no more than 300 individuals left. They use to range from western, northern and central Madagascar but are now limited to patches of forest in the southeastern part of Madagascar. Destruction of rain forest habitat by slash and burn agriculture and extensive cutting of bamboo, the lemur's primary food source.

Read more about Greater Bamboo Lemurs on Animal Info.

Self-Suckling in Barbary Macaques Before and After Infant's Death

Self-suckling is a rare behavior that occurs among Barbary macaques (Macaca sylvanus) and might have been a learned behavior. Dr. Bonaventura Majolo and his PhD. student Richard McFarland noticed this behavior while studying Barbary macaques in the middle-Atlas mountains of Morocco (2009). They published their findings, "Brief communication: Self-suckling in Barbary macaque (Macaca sylvanus) mothers before and after the death of their infant" on American Journal of Physical Anthropology last July.

Dr. Majolo and his student observed eight females with infants from two troops; "Flat face" and "Large". They found that four mothers from "Flat face" troop self-suckle themselves for a brief moment when their infant is still alive, possibly to improve milk flow when the infant change from one nipple to the other. All four of these females lost their infant due to predation or some unknown cause. They then observed these females self-suckling in bouts up to two minutes. Self-suckling was never observed between four females in "Large" troop before and after the death of an infant (only one monkey lost its infant in this troop).

Barbary macaque females from "Flat face" troop. Photo from BBC.

Majolo and McFarland think that self-suckling in Barbary macaque is cultural although they don't know why such behavior exists. It might be a response to make up for the energy they had invested in producing milk, help relieve engorged breasts, to help boost the females' immune system or even an emotional response to losing an infant.

"In humans and other species, breast-feeding reduces the stress through the release of prolactin. It is therefore possible that the self-suckling functions to reduce the stress generated by the loss of the infant ... It is interesting that we observed self-suckling in just one troop and not the other. This may indicate that self-suckling is a sort of cultural behavior. We will have to wait to see if self-suckling is consistently displayed by females in the same troop and not in the others", said Dr. Majolo.

References:

Majolo, B. McFarland, R. 2009. Brief communication: Self-suckling in Barbary macaque (Macaca sylvanus) mothers before and after the death of their infant. American Journal of Physical Anthropology 140(2): 381-383. [10.1002/ajpa.21125]

Walker, M. 2009. Grieving monkeys drink own milk. BBC. Retrieved October 5, 2009, from http://news.bbc.co.uk/earth/hi/earth_news/newsid_8287000/8287774.stm

Baby Sumatran Orangutan Born in Philadelphia Zoo

While Ardipithecus ramidus was all abuzz in the paleontology, physical anthropology, primatology and science blogosphere yesterday, the folks at Philadelphia Zoo were keeping themselves busy for another addition to their PECO Primate Reserve.

 Sugi, the proud father. Flickr photo from Kevin Burkett.

A baby was born to the zoo's resident Sumatran orangutan family (Pongo abelii), Tua (16 years old) and Sugi (13 years old), on Oct 2nd at around 8am. This is the first orangutan baby born at PECO Primate Reserve since it was opened in 1999 and also the first offspring for both Tua and Sugi. No words yet whether the baby is a boy or a girl.

According to Philadelphia Zoo's press release, both mother and baby appear to be doing well. The first 48 hours are crucial for the baby so zoo staff and veterinarians are closely monitoring both Tua and her baby. They do not know when Tua and her baby will make their debut at the PECO Primate Reserve.

Congratulations Tua and Sugi! See you soon.

Where Ardipithecus ramidus Fits In The Hominin Family Tree

Filling a gap. Ardipithecus provides a link between earlier and later hominins, as seen in this timeline showing important hominin fossils and taxa.  CREDITS: (TIMELINE LEFT TO RIGHT) L. PÉRON/WIKIPEDIA, B. G. RICHMOND ET AL., SCIENCE 319, 1662 (2008); © T. WHITE 2008; WIKIPEDIA; TIM WHITE; TIM WHITE

This is the most current human origin timeline, starting from Sahelanthropus tchadensis all the way to Homo sapiens. Ardipithecus ramidus fits between the genus Orrorin and Australopithecus. Another Ardipithecus species, Ardipithecus kadabba predates Ardipithecus ramidus.

A Step Closer To Understanding Human Origins: Ardipithecus ramidus

An artist rendition of Ardipithecus ramidus. Illustration from Science. Credit: © 2009, J. H. Matternes

A total of 11 papers are being published in this month's issue of Science on Ardipithecus ramidus and its environment, the first ever published papers on this species.  

"We thought Lucy was the find of the century," says paleoanthropologist Andrew Hill of Yale University, referring to the famous 3.2-million-year-old skeleton that revolutionized thinking about human origins. "But in retrospect, it was not."

Indeed it was not. Dubbed Ardi, the Ardipithecus ramidus skeleton was found in 1994 in Aramis, Ethiopia. Until now, we knew Lucy (Australopithecus afarensis) as the oldest known human ancestor skeleton but Ardi, also another female, predates Lucy by about 1.2 million years old. Although not the oldest fossil hominin, Ardi is by far the most complete specimen of all fossil hominin which includes most of the skull and jaw bones, pelvis, hands and feet. These parts are crucial in determining Ardi's (in essence her species's) locomotion, gait, brain size, diet and even the habitat. Ardi and 35 individuals of her species are described by authors of the 11 papers from this month's Science.

Similarities and differences between Ardipithecus ramidus and Australopithecus afarensis:

• Both A. ramidus and A. afarensis have the same average brain size as a chimpanzee. 
• A. ramidus was not a committed biped but instead a facultative biped just like a chimpanzees. They probably spend most of their time up in the trees. A. afarensis however, are most bipedal but do spend some time up in the trees.
• A. ramidus have opposable big toes, an indication that they spent most of her time in trees (arboreal). A. afarensis do not have opposable big toes, instead, all of its big toes are in line with the rest of the toes. A. afarensis are mostly terrestrial.
• A. ramidus probably climb trees to escape from predators, find food and for shelter (possibly sleeps in nests). A. afarensis possibly returned to the trees to escape from predators or for shelter.
• A. ramidus lived in the woodlands while A. afarensis lived in open savannah.
  

I know at least one of my professors, Dr. Sara Stinson, would be excited about this publication. Particularly, a female Ardipithecus ramidus with an intact pelvis. The significance of a female A. ramidus pelvis is not only an indication of its gait but also its infant and the child birth process. What was the brain size of an infant A. ramidus? Were they born precoccial or altricial?

Most researchers, who have waited 15 years for the publication of this description and analysis, agree that Ardi is indeed an early hominin. "This is an extraordinarily impressive work of reconstruction and description, well worth waiting for," says paleoanthropologist David Pilbeam of Harvard University. But he takes issue with the idea that the common ancestor of chimps and humans didn't share many traits with the African apes. "I find it hard to believe that the numerous similarities of chimps and gorillas evolved convergently," he says. Regardless, the one thing all scientists can agree on is that the new papers provide a wealth of data for the first time to frame the issues for years. "It would have been very boring if it had looked half-chimp," says paleoanthropologist Alan Walker of Pennsylvania State University, University Park.

Read more about A. ramidus from Science here and those 11 published papers here (if you are not an AAAS member, you can access the papers for free. You just need to fill out a simple registration).

Also, Kambiz from Anthropology.net has a few nice write up. Science Publishes 11 Papers On Ardipithecus ramidus and The 4.4-Million-Year-Old Ardipithecus ramidus. Ardipithecus is out! from Beast Ape & The Bleeding Heart Baboons. Ardipithecus FAQ and Losers of the day from John Hawks.

Reference:

Gibbons, A. 2009. Ancient Skeleton May Rewrite Earliest Chapter of Human Evolution. Science. Retrieved October 1, 2009, from http://sciencenow.sciencemag.org/cgi/content/full/2009/1001/1