Lucy, meet Ardi

More than 4 million years since she last walked the Earth and more than 15 years since her discovery was first announced, a distant human ancestor dubbed “Ardi” was introduced to the general public on Oct 1, 2009.  Nicknames abound in this field where long scientific nomenclature is common. So, meet “Ardi”, a member of the genus Ardipithecus.

Who was Ardipithecus? When and where did they live? What can we say about their diet and behavior? How do they relate to later fossils, such as Lucy, as well as to us? Where do they fit in with regards to our closest living primate relatives, the chimps? This is an extensive array of questions, not unusual to find when fossils are discovered. Scientists rely on an equally extensive array of approaches to find answers.

Lets start with the first question: who was Ardipithecus?

The genus Ardipithecus derives its name from an Afar language word, “ardi“, which means “ground” or “floor.” By choosing this term, the scientists involved in the discovery clearly wanted to reflect the place Ardipithecus occupied in human evolution: as close to the very beginning of hominids as possible. Defining “hominid” as any fossil species closer to modern humans than to chimps and bonobos, which are our closest living relatives, Dr. Tim White stated: “This is the oldest hominid skeleton on Earth.”

After their discovery of the first Ardipithecus remains in 1992, scientists had identified the bones of 17 hominid fossils by the end of 1993. These specimens were retrieved from a cluster of localities West of the Awash River, within the Afar Depression, Aramis, Ethiopia. Hominid and associated fossil faunas, including wood, seed and vertebrate specimens, were dated to about 4.3 million years ago.

Over a period of several years, the team followed up with more excavations at the location of the original discovery. They collected 125 fragments of skulls, teeth, arms, hands, the pelvis, legs and feet. In addition to this skeleton, the area yielded a total of 110 other catalogued specimens representing body parts of at least 36 other Ardipithecus individuals.

Ardi is the most complete individual among those found, with about 45% of the skeleton intact. Ardi, an adult female, probably stood four feet tall and weighed about 120 pounds, almost a foot taller and twice the weight of Lucy

Ardi
Ardi, as shown in the Oct. 2 issue of Science.
Image (c) Tim White, 2008

When did they live?

There is more than one species within the genus Ardipithecus. Scientists distinguish between Ardipithecus kadabba (5.8 – 5.2 million years ago) and Ardipithecus ramidus (4.4 million years ago). Both discovered in the Awash valley in Ethiopia, these two species lived after the split between the human and chimpanzee lineages. They represent the earliest known hominids from Ethiopia.

Where did they live?

The remains of Ardipithecus kadabba and Ardipithecus ramidus have been found in Eastern Ethiopia. When they roamed that area, the Great Rift was a well-established geologic feature. The environment 4-to-5 million years ago was very different from that of today. The climate was cool and wet. Ardipithecus kadabba and Ardipithecus ramidus lived in an area of swamps, streams and dense tree cover, rather than in a mosaic of forest and grassland, as originally thought. This evidence has caused a re-examination of the hypothesis on the origin of upright walking.

What can we say about their behavior?

It seems that Ardi was equally at home on the ground as she was in the trees. Her feet, pelvis, legs, and hands suggest she walked upright on the ground but moved around on all fours when in the trees. The large, flaring bones of the upper pelvis were positioned so that Ardi could walk on two legs without lurching from side to side like a chimp. Ardipithecus gives us a close look at an upright walking being and a chance to evaluate the mechanisms that may have caused this behavior to evolve and remain until today.

Traditionally, scientists suggested that the evolution of upright walking was closely related to the disappearance of the forest cover and its replacement by grasslands. Creatures adapted to living in trees were now forced to cross grasslands in order to go from one island of trees to another, the thinking went. However, crossing through the grass would make them very vulnerable to predator attacks. Walking upright allowed one to see predators sooner, thus representing a beneficial adaption to a changing environment.  We now know that the origins of upright walking pre-dates the widespread disappearance of the forests and their replacement by grasslands. Bipedalism did not evolve as an adaptation to receding forest cover and expanding grasslands. Back to the drawing board, in other words.
Bipedalism is now thought to have evolved in a tree environment.

Questions remain: how and why? Among living non-human primates, researchers have observed bipedal stances in creatures such as orangutans as they move around in the trees, while chimpanzees most often stand upright when they feed on small objects in the trees. Early human ancestors, such as Ardipithecus, who lived in a tree environment, may have had similar adaptations.

The discovery of the genus Ardipithecus and the study of the environment in which they once lived have caused us to revisit and refine the thinking on the origins of upright walking. However, we can’t be sure that bipedalism first emerged in the Awash Valley. Its origins may lie even further back in time.

Upright walking may also relate to another aspect of Ardipithecus’ behavior: monogamy. Here is where a hypothesis originally dating back to the 1980s has found new traction. Dr. Owen Lovejoy suggests that instead of fighting for access to females, a male Ardipithecus would supply a “targeted female” and her offspring with gathered foods and gain her sexual loyalty in return. Walking upright freed his hands to carry the food, thus helping him to achieve this goal.

Lucy fossil
The fossil Lucy.

How does Ardi relate to Lucy?

Ardi pre-dates Lucy by more than a million years. She was larger and heavier than Lucy. Lucy was a more adept upright walker than Ardi. Both Ardi and Lucy lived well before stone tools were in use. Their brain size was similar to that of a chimp. Both were found in the same region of Ethiopia, with Ardi’s site just 46 miles (74 kilometers) away from where Lucy’s species, Australopithecus afarensis, was found in 1974.

What traits does Ardi share with us, Australopithecines and chimps?

Like chimps, Ardi had an opposable big toe. However, she was probably not as agile in the trees as a chimp. Unlike chimps, however, she could have carried things while walking upright on the ground, and would have been able to manipulate objects better than a chimp. And, contrary to what many scientists have thought, Ardi did not walk on her knuckles, White said.

Ardi was not a chimpanzee, but she wasn’t human,” stressed White, who directs UC Berkeley’s Human Evolution Research Center. “When climbing on all fours, she did not walk on her knuckles, like a chimp or gorilla, but on her palms. No ape today walks on its palms.”

Moreover, Ardi’s small, blunt, upper canine teeth, very likely reflect amicable relationships, leaving open the possibility of pair-bonded couples living together in social units. Ardi’s dentition contrasts sharply (no pun intended) with the much larger canine teeth found in chimpanzees and gorillas, animals known for their teeth-baring threat behavior. The latter statement is a good example of how paleoanthropologists rely on various sources of information in their attempt to reconstruct past behavior, including comparative primatology. In this case, similarities in dentition between fossil and living primates form the basis for suggested similarities in behavior both past and present. While Ardi’s canines were smaller than those of chimpanzees and gorillas, Lucy’s canines were even smaller in comparison.

Ardi’s teeth also revealed her and her ilk to be omnivores, eating a wide range of foods rather than specializing in a more restrictive diet of fruit or leaves. Being an omnivore is another trait that sets Ardi apart from chimps, animals that eat primarily fruits, and and gorillas, which eat primarily leaves, stems and bark. The research team surmised that Ardipithecus spent a lot of time on the ground looking for nutritious plants, mushrooms, invertebrates and perhaps small vertebrates.

The shape of Ardi’s upper pelvis and aspects of muscle attachment in that part of the hip resemble much more an upright walking human than a knuckle walking chimp. However, the lower pelvis is much more primitive than anything found in other hominids.

Why the buzz?

When the news about Ardi was released, it generated quite a buzz, underscoring the great interest in the study of human origins. Hundreds of media outlets covered the story. Predictably, creationist outlets use the sentiment that Ardi has overturned our understanding of human evolution to make their point that scientists “do not agree” when it comes to human evolution.  In making this statement, they display a fundamental misunderstanding of how the scientific process works. Fortunately, there are a number of excellent sites that make the process of understanding the latest news both easier and much more palatable.

Quite often, scientists were quoted stating that this find was “far more important than Lucy.” It also showed that “the last common ancestor with chimps didn’t look like a chimp, or a human, or some funny thing in between.”  Questions also abound about what this will do to Lucy’s preeminent status in the world of paleoanthropology. Now that we have an older creature also capable of walking upright, so the thinking goes, will “Ardi” now become the buzzword du jour, instead of Lucy?

In my opinion this is not the right question to ask. We are not dealing with a beauty contest among fossils. Each of these finds has substantially increased our understanding of human evolution. Lucy taught us that bipedalism pre-dates the expansion of the human brain as well as tool making. With Ardi, the most important contribution seems to be that we now need to look beyond chimps (the 98% genetic overlap between humans and chimps notwithstanding) as a model for a common ancestor. What this common ancestor may have looked like and when and where it lived, remains, as of now, a great unknown.

Explore Evolution with Lucy’s Legacy

lucy-model-face

Lucy’s Legacy, an exhibition featuring the world’s most famous fossil, recently opened at Discovery Times Square Exposition in Times Square, New York. The exhibit will remain on display until October 25, 2009.

The Lucy exhibit has been an exciting catalyst for discovery, discussion, and debate within the scientific community. In this series of blogs, Dirk presents all sides of the controversy surrounding Lucy’s existence and significance while skillfully separating fact from fiction with supporting evidence and research.
  
Do you enjoy debate about scientific theories or issues? If so, prepare yourself for a great read while perusing the following blogs by Dirk. In addition to his perspective and logic, Dirk also provides links to research and evidence that will leave you on the edge of your seat…and excited about evolution!

In fide constans… Always loyal [Lucy’s Legacy]     
Neanderthal Controversy
A Letter From Lucy: Making no bones about it. (Pun intended)
Lucy loves Houston – and she’s not leaving. Yet.
If Humans came from monkeys, than why are monkeys still around?
Evolution
 
 Neanderthals—most people know what they were, but do we know who they were or how they lived? Join Dirk as he discusses these unique people and their lifestyle.

Neanderthal Controversy 
Neanderthals on the move
Neanderthals Speak Out

Why are genetics important in the development of humans? More than just appearance, genetics play a role in where we live and even how we survive. In the following blogs, Dirk explores where genetics has contributed to history and evolution. 

Neanderthals on the move
We are all mutants
10,000 BC: The story behind the date
A major step forward – 40,000 years ago

s-legacy-exhibitSure, they’re adorable and entertaining to observe but chimps and monkeys offer far more than that! They provide valuable information about human behavior and progress. Follow-up with these blogs and read Dirk’s presentation of our connection to these magnificent animals.

Chimps using tools: Archaeology’s most fascinating discovery of 2007
The Apple Doesn’t Fall Too Far from the Tree
Monkey business
If Humans came from monkeys, than why are monkeys still around?
  
The study of fossilized remains (like Lucy and other hominids) offers an exciting opportunity to draw parallels on our own existence and physicality. What did they look like and how did they live? Dirk has explored these questions in the following blogs:

Discovering behavior: a step-by-step process
Reconstructing ancient hominid behavior
Lucy’s kitties
Paleoanthropology: making the past come alive.
Extinction doesn’t mean failure

If you ask a fossil to share the secrets it holds, it will provide invaluable information and insight into the past. But how can we piece the puzzle together? Dirk explains the wisdom of what happens when fossils meet modern technology…and dating begins (pun intended).

How do we know: dating techniques
Meet Lucy, Australopithecus afarensis. (What’s in a name?)
Teeth Tell Tales
 
Want to find out more about Lucy’s home, Ethiopia? Click below and discover a wealth of history, culture and tradition.

Timkat, an Ethiopian Epiphany celebration
The Ark of the Covenant and Aksum

In fide constans… Always loyal [Lucy’s Legacy]

The model of Lucy created for
the Lucy’s Legacy exhibition.
Photo by reality photography

The Lucy’s Legacy exhibit was reviewed in early February by a representative of the Seattle-based Discovery Institute, which promotes Creationism and Intelligent Design. In the following paragraphs, I would like to add my observations to the statements found in this review.

Let me start with a few general remarks. First, a favorite approach by Creationists is to cast doubt on the subject of evolution, particularly human evolution and to drive a wedge between faith and science. This policy, known as the Wedge Document, is publicly acknowledged by the Discovery Institute as being theirs. Second, a favorite approach of Creationist writers is to represent issues in stark black and white terms.

The 2000-word document is sprinkled with terms that drive the message home: the study of human evolution fails as a belief system; the evidence is scarce and the interpretations fast and loose and not widely accepted. Moreover, some of the evidence is misrepresented.

The writer of the document stated that there is a “paucity of actual hard evidence for human evolution.” An interesting statement, but one which considering the presence of an actual fossilized hominin fossil, fails itself to carry any water. What harder evidence can one want, but for an authentic fossil, I wonder. The same author also quotes a statement that “unless more fossils are recovered (…) there is likely to be a continuing debate on Lucy’s posture…”  Two thoughts come to mind here. It is always good to have more fossil evidence. In fact, for years paleoanthropologists have continued to find fossils every year. Our database of fossilized early humans continues to grow, courtesy of an ongoing scientific effort. This growing database has led to the formulation of answers to old questions while at the same time giving rise to new questions which we need to answer. That is the essence of scientific research; it is a never ending quest for better insights in what we can observe.

These statements, using the terms “paucity” and “until more fossils are recovered,” are misleading. One wonders if the author knows that the remains of 300 Australopithecus afarensis individuals are known to the scientific community, making Lucy and her kind the best known of all of early human ancestors.

Turkana Boy
Creative Commons License photo credit: ideonexus
Turkana Boy

Another lament found in the document is the “incompleteness” of her (i.e. Lucy’s) skeleton.” The author continues “only 40% was found” and “very little useful material from Lucy’s skull was recovered.” I suppose one could say that everything is in the eye of the beholder. Of course, 50% or more would have been even better. However, another way of referring to Lucy and the preservation of her skeleton is that it is amazing that so much was preserved, considering she died more than 3 million years ago. 

Factually incorrect is a statement that “Lucy still represents the most complete known hominid skeleton to date.” There are currently older and better preserved fossils, including some of the same species as Lucy. Baby Selam for example, is much better preserved. More recent than Lucy, but better preserved is an early hominid known as Turkana Boy. Lucy is still the earliest known and most complete adult Australopithecus afarensis. Things were different in 1974, when scientists could say that she was the oldest known and best preserved skeleton of a distant human ancestor. The fact that this statement now has to be qualified to reflect more recent discoveries is a testimony to the dogged work carried out by teams of paleoanthropologists in Africa. It is also an insight that ought to have been included in the Discovery Institute document, as I am sure that this is something they are aware of.

Photo by reality photography

We also get to read that Lucy’s bones were found scattered across a hillside, a vague reference to an old creationist claim that Lucy’s bones do not all belong to the same individual. The fact that this claim has been debunked does not stop creationists from repeating it. The author – it seems – seems to prefer that Lucy’s bones would have been found together as a contiguous skeleton. Aside from the fact that intentional burial did not exist in Lucy’s time and that she did die more than 3 million years ago, it would have been a miracle (pardon the pun) if she had been preserved completely intact and as a contiguous skeleton. One should not, however, raise the reader’s hopes by presenting this a something that should have happened.

I would like to end by referring the author of the Discovery Institute piece as well as all the readers to this latest development: Lucy was scanned at the University of Texas, Austin campus, after the exhibit in Houston had ended. I have no doubt that scientists will be pouring over this new dataset and that this effort will result in improving our understanding of who we are and where we came from.

Loyalty to a cause is admirable; having the ability to see countless shades of grey instead of only black and white is even more desirable.

Lucy loves Houston – and she’s not leaving. Yet.

lucy-exhibit-2-small-2-blog.jpg

The original fossilized remains of the
3.2 million year old hominid known as Lucy

Great news if you haven’t been to see Lucy yet – the exhibit has been extended through Sept. 1!

A group of officials from Ethiopia visited the museum this week to sign an agreement that allows the Museum to keep her on display for a few more months. They brought a crew from Ethiopian TV with them, and Dirk, our curator of anthropology, gave them an extensive tour of the exhibit that will be broadcast in Africa and placed in the Ethiopian Prime Minister’s permanent archive.

Almost 170,000 people – including visitors from as far away as Helsinki, Finland and Santiago, Chile – have visited Lucy so far, and I’m thrilled we’ll have her on display here for a few more months. It’s hard to describe the experience of  looking at these 3.2 million year old bits of fossilized bone, just trying to imagine what Lucy’s life was like and contemplating the astonishing journey of our species. I’m glad that many more visitors will have the opportunity to experience this for themselves.

There’s a comment book at the end of the exhibit, where people can leave their thoughts about the experience. While the exhibit did generate some controversy when it opened, most of the comments in these books, from people who have just seen the show, have ranged from gratitude to the Ethiopian people for sharing this amazing treasure with us to amazement at the discovery of Ethiopia’s rich human history.

dirk-in-lucy-gallery.jpg

Dirk Van Tuerenhout, curator of the Lucy exhibit
(second from left), gave ETV a tour of the Lucy exhibit.
Here they are in standing behind the Lucy fossil.

Have you visited Lucy yet? If so, I’d love to hear what you thought of the experience, so please leave a comment on this post if you have a moment. If not, be sure to visit this summer – the exhibit is is scheduled to open at the Pacific Science Center in Seattle on Oct. 4 (so, no more extensions!).