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Ardipithecus ramidus sheds new light on evolution

#1 User is offline   PassedOut 

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Posted 2009-October-01, 13:10

Fascinating new studies show that our 6-million-year-old ancestors looked less like chimps than was previously conjectured. Both chimps and humans have evolved considerably over that period: Fossils Shed New Light on Human Origins

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Researchers in the U.S. and Ethiopia on Thursday made public fossils from a 4.4-million-year-old human forebear they say reveals that the earliest human ancestors were more modern than scholars assumed and deepens the evolutionary gulf separating humankind from today's apes and chimpanzees.

The highlight of the extensive fossil trove is a female skeleton a million years older than the iconic bones of Lucy, the primitive female figure that has long symbolized humankind's beginnings.

An international research team led by paleoanthropologist Tim White at the University of California, Berkeley, unveiled remains from 36 males, females and young of an ancient prehuman species called Ardipithecus ramidus, unearthed in the Awash region of Ethiopia since 1994. The creatures take their scientific name from the word for root in the local Afar language. They are not the oldest known homind fossils but they comprise the most complete set discovered so far.

"It is not a chimp and it is not human," said Dr. White. "It gives us a new perspective on our origins. We opened a time capsule from a time and place that we knew nothing about."

Although the differences between humans, apes and chimps today are legion, all shared a common ancestor six million years or so ago. These fossils suggest that creature--still undiscovered--resembled a chimp much less than researchers have always believed.

It must be an exciting experience for scientists like Tim White and his team to work on such a spectacular project. Well done!
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#2 User is offline   Winstonm 

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Posted 2009-October-01, 13:33

Not chimp and not human - wow, the first chump. Sounds irreducibly complex, to me.
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#3 User is offline   Phil 

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Posted 2009-October-01, 14:26

Nothing new. I'm sure I played against a Ardipithecus ramidus in the Main Bridge Club the other day.
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#4 User is offline   MattieShoe 

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Posted 2009-October-01, 15:02

Hmm, interesting... I'm not sure I buy it though. Or maybe it just depends on how you envision 6-million-years-ago apes.

Here's a rough cut

40 million years ago, new world monkeys split off from us.
25 million years ago, old world monkeys split off from us.
18 million years ago, gibbons split off from us.
14 million years ago, orangutans split off from us.
7 million years ago, gorillas split off from us.
6 million years ago, chimps/bonobos split off from us (chimps and bonobos split from each other about 2 million years ago I think)

Now I think ALL of those look remarkably similar to us and each other. The closer you get to the bottom, the more closely they resemble us. Of course, they've all been evolving in the last X million years too, but well... Monkeys have tails. Apes don't. So you can reasonably assume that we lost our tails between 25 million and 18 million years ago. You can do the same thing for just about any feature you want to determine about when it showed up. 7 million years ago, our ancestors could have evolved into chimps, bonobos, gorillas, or humans. It's a good bet to say the features all four of us share were already present in those ancestors.
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#5 User is offline   jdonn 

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Posted 2009-October-01, 15:06

So what is it you don't buy then?
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#6 User is offline   barmar 

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Posted 2009-October-02, 20:56

Although the usual assumption is that features common to different species now were also in their shared ancestor, that's not always the case. It's not uncommon for a gene to go dormant during one period of evolution, and then awaken later on. If the gene was dormant before the split, and then awakens in both lineages after the split, this can result in a shared trait developing in parallel.

Read about evo-devo. The genome is full of genes that are waiting to be switched on. It probably wouldn't be too hard for us to re-evolve tails.

And saying "chimps/bonobos split off from us" is misleading. It's more appropriate to say "6 million years ago, a species split up into two lineages, one leading to chimps/bonobos, the other leading to homo sapiens." That species was not "us", nor was it "them", it was most likely something that has since gone extinct while the new species lived on and evolved.

#7 User is offline   mike777 

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Posted 2009-October-02, 21:09

I am always amazed that evolution from 4million years ago gets so much news coverage and yet evolution over the next 100 or 40 years, man/machine gets so little.
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#8 User is offline   MattieShoe 

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Posted 2009-October-02, 21:41

It's just the very last sentence that bugs me. A skeleton from millions of years after the split looks more human than expected, therefore the common ancestor must look more human and less like a chimp? They may be totally right, but I think it'd have to be based on more evidence than the article mentions. Why wouldn't it suggest that the human branch evolved more dramatically in the missing million plus years? Given the similarities between chimps, bonobos, gorillas, and gibbons, I'd think the simpler explanation would be that we've changed more significantly physically than they have in the last several million years. I'm not in the field or anything... The last sentence just seems to be jumping to a conclusion.

I know the "chimps/bonobos split off from us" could sound a bit wrong but it's so much less wordy. :-)

I guess it's possible to have parallel evolution via repressed genes expressing at a later date, but... Well, with tails. All monkeys have em, all apes don't. I suppose it's possible that at the time of the splits among apes, they had them and then they all lost them at a later date, but it seems much more likely that they lost them before the split.

On the other hand, given billions of years of evolution, all sorts of unlikely things have happened. Whales and hippos being so closely related still sort of boggles my mind.
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#9 User is offline   barmar 

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Posted 2009-October-03, 21:33

MattieShoe, on Oct 2 2009, 11:41 PM, said:

It's just the very last sentence that bugs me. A skeleton from millions of years after the split looks more human than expected, therefore the common ancestor must look more human and less like a chimp?

They didn't say it looked more human, just less chimpy. The usual assumption is that the common ancestor was alot like chimps and bonobos, and we evolved greatly away from that. What they're saying now is that the common ancestor wasn't much like either species, and both branches underwent significant changes since the split.

The assumption comes from a long-standing, anthropocentric belief that we're "more evolved". But there really isn't such a thing. All species have evolved the same amount, just in different directions. Humans evolved a big brain, symbolic thought, and language; gazelles and cheetas evolved fast running; eagles evolved great flying ability and eyesight, etc.

To be precise, we haven't all evolved by exactly the same amount. Geneticists can actually tell the rate of beneficial mutations in different lineages, to see how quickly selection pressure was causing the species to evolve. But these differences are minor compared to the common rate across all species.

#10 User is offline   jdonn 

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Posted 2009-October-03, 21:41

MattieShoe, on Oct 2 2009, 10:41 PM, said:

It's just the very last sentence that bugs me. A skeleton from millions of years after the split looks more human than expected, therefore the common ancestor must look more human and less like a chimp? They may be totally right, but I think it'd have to be based on more evidence than the article mentions. Why wouldn't it suggest that the human branch evolved more dramatically in the missing million plus years? Given the similarities between chimps, bonobos, gorillas, and gibbons, I'd think the simpler explanation would be that we've changed more significantly physically than they have in the last several million years. I'm not in the field or anything... The last sentence just seems to be jumping to a conclusion.

- You claim they said "must" but they actually said "suggests".
- As barmar said, they didn't say "more like a human" they said "less like a chimp". Not the same thing.
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