10.02.2009

welcome back ardi

A fossilized skeleton of an early human ancestor has been found in Ethiopa. The discovery - nicknamed "Ardi" for Ardipithecus ramidus - is one million years older than the previously oldest found skeleton, the one known as Lucy. From National Geographic:
Scientists today announced the discovery of the oldest fossil skeleton of a human ancestor. The find reveals that our forebears underwent a previously unknown stage of evolution more than a million years before Lucy, the iconic early human ancestor specimen that walked the Earth 3.2 million years ago.

The centerpiece of a treasure trove of new fossils, the skeleton—assigned to a species called Ardipithecus ramidus—belonged to a small-brained, 110-pound (50-kilogram) female nicknamed "Ardi."

The fossil puts to rest the notion, popular since Darwin's time, that a chimpanzee-like missing link — resembling something between humans and today's apes — would eventually be found at the root of the human family tree. Indeed, the new evidence suggests that the study of chimpanzee anatomy and behavior—long used to infer the nature of the earliest human ancestors—is largely irrelevant to understanding our beginnings.

(Interactive time line: how the Ardipithecus ramidus discovery changes human evolutionary theory.)

Ardi instead shows an unexpected mix of advanced characteristics and of primitive traits seen in much older apes that were unlike chimps or gorillas (interactive: Ardi's key features). As such, the skeleton offers a window on what the last common ancestor of humans and living apes might have been like.

Announced at joint press conferences in Washington, D.C., and Addis Ababa, Ethiopia, the analysis of the Ardipithecus ramidus bones will be published in a collection of papers tomorrow in a special edition of the journal Science, along with an avalanche of supporting materials published online.

"This find is far more important than Lucy," said Alan Walker, a paleontologist from Pennsylvania State University who was not part of the research. "It shows that the last common ancestor with chimps didn't look like a chimp, or a human, or some funny thing in between." (Related: "Oldest Homo Sapiens Fossils Found, Experts Say" [June 11, 2003].)

Ardi Surrounded by Family

The Ardipithecus ramidus fossils were discovered in Ethiopia's harsh Afar desert at a site called Aramis in the Middle Awash region, just 46 miles (74 kilometers) from where Lucy's species, Australopithecus afarensis, was found in 1974. Radiometric dating of two layers of volcanic ash that tightly sandwiched the fossil deposits revealed that Ardi lived 4.4 million years ago.

Older hominid fossils have been uncovered, including a skull from Chad at least six million years old and some more fragmentary, slightly younger remains from Kenya and nearby in the Middle Awash.

While important, however, none of those earlier fossils are nearly as revealing as the newly announced remains, which in addition to Ardi's partial skeleton include bones representing at least 36 other individuals.

"All of a sudden you've got fingers and toes and arms and legs and heads and teeth," said Tim White of the University of California, Berkeley, who co-directed the work with Berhane Asfaw, a paleoanthropologist and former director of the National Museum of Ethiopia, and Giday WoldeGabriel, a geologist at Los Alamos National Laboratory in New Mexico.

"That allows you to do something you can't do with isolated specimens," White said. "It allows you to do biology."

That National Geographic story has lots more, plus excellent links. This short video from CBC News is also good.

Some years ago, I read and blogged briefly about Origins Reconsidered (here, and again here), written by Richard Leakey, son of pioneering paleontologists Mary and Louis Leakey, with science writer Roger Lewin.

I loved thinking about these early hominids as our ancestors - remembering that every human on this earth shares a common link, all of us one species. We share much more than that, of course. We share all the human emotions and desires, we share this planet, we share all our incredible human capacities, for better and worse. But I found something very profound, almost spiritual, in contemplating the fact that every single one of us, every human that has ever inhabited this planet, is part of the same huge family tree.

I saw this story on "The National" last night, which brings me to something else I appreciated: the story was reported with no mention of so-called controversy or other so-called theories. I know those kooks exist in Canada, but CBC doesn't put on them on the news unless it's a story about "creationists". In the US, I think you'd be hard-pressed to find a TV news outlet that doesn't include ignorant wackos in their story on this, or at least incorrectly emphasize that evolution is a "theory," misusing the word.

9 comments:

Stephanie said...

Fascinating story, thanks!

James said...

It's a great find. And this bit of the NG article is vitally important:

The fossil puts to rest the notion, popular since Darwin's time, that a chimpanzee-like missing link—resembling something between humans and today's apes—would eventually be found at the root of the human family tree.

The "missing link" concept is at least 100 years out of date, but creationists -- up to and including US senators -- still bring it up.

Likewise this bit:

"It shows that the last common ancestor with chimps didn't look like a chimp, or a human, or some funny thing in between."

People still come up to Richard Dawkins (and other biologists) and ask "If we're descended from chimps, why are there still chimps?", which shows an amazingly profound misunderstanding of the entire concept.

I've just finished Dawkins's The Greatest Show On Earth and am currently reading Jerry Coyne's Why Evolution Is True -- they're both great books on the foundational evidence for evolution.

L-girl said...

If I ever read anything not for school again, I would be interested in Coyne's book.

"If we're descended from chimps, why are there still chimps?", which shows an amazingly profound misunderstanding of the entire concept.

Last night on The National, I enjoyed Bob McDonald's (this guy) explanation of this. He said in passing that apes are just as evolved as humans - the two kinds of primates branched out and evolved separately. I may not be reproducing it exactly right, but he made it so simple and clear, really nice.

deang said...

Your last paragraph is so true. US programs and publications would feel compelled to give "equal time" to "another view," that of creationists, while calling long-established scientific conclusions "controversial." And in the US the word controversial is tacked onto words as though it connotes an innate quality, as though certain scientific finds or certain public figures are intrinsically controversial. That's a trend I remember first noticing at the start of the Reagan years - suddenly, feminism was "controversial", the EPA was "controversial", wide public opposition to nuclear weapons was "controversial". And now it's just normal US rhetoric.

L-girl said...

That's a trend I remember first noticing at the start of the Reagan years - suddenly, feminism was "controversial", the EPA was "controversial", wide public opposition to nuclear weapons was "controversial". And now it's just normal US rhetoric.

Yes! I have the same impression of when that trend started, which coincides with the rise of 24-hour cable news and great leaps in media conglomeration.

James said...

US programs and publications would feel compelled to give "equal time" to "another view," that of creationists, while calling long-established scientific conclusions "controversial."

It's so much easier to publish two press releases and call it "balance" than it is to actually find out which represents reality.

Last night on The National, I enjoyed Bob McDonald's explanation of this. He said in passing that apes are just as evolved as humans - the two kinds of primates branched out and evolved separately. I may not be reproducing it exactly right, but he made it so simple and clear, really nice.

You've got it exactly right. One of the interesting points with Ardi is that she not only lacks many human-like features, she lacks many chimp-like features as well, such as prominent canines. This means that chimps gained those canines after the split, rather than humans losing them -- and this is exaclty what you'd expect under common descent.

impudent strumpet said...

That's a trend I remember first noticing at the start of the Reagan years - suddenly, feminism was "controversial", the EPA was "controversial", wide public opposition to nuclear weapons was "controversial". And now it's just normal US rhetoric.

Let's see what happens if we appropriate that.

"The controversial Harper government"

"Catholicism, a controversial christian sect."

"The controversial US health insurance industry"

L-girl said...

I'm down with that!

"The controversial anti-abortion movement"

"Capital punishment, which remains controversial..."

"The controversial "War on Terror"..."

James said...

By the way, another highly recommended book on evolution is Your Inner Fish by Neil Shubin. It deals with the discovery of Tiktaalik, the splendid transitional fossil between fish and amphibians that was discovered in northern Canada a few years back.

I haven't read it yet, but it's on my list for after I finish Coyne's book. Both Coyne & Dawkins refer to it in their books.