Missing link

[12thPaladin]

<----- This is a representation of "Ardi" Ardipithecus Ramidus, reconstructed from fossil fragments and possibly the earliest Hominid.
Thought to have lived 4.4Ma ago and pre-dates "Lucy" Australopithecus by about 500Ka.
Some say Ardi may well be Lucy's direct ancestor and as such would indeed be the missing link but there seems to be some contention.
I've read a fair bit but to be honest it's a lot to take in.
I was wondering if anyone could shed some light on this in simple terms, preferably without providing links that link to links that lead back to square 1.
Has any recognised scientific body come up with a definitive answer?

[WaldoMcFroog]

Firstly, the term "missing link" is horrible and not really used by scientists. Evolution is a continuum, a gradual change from one thing into another over a long period of time. Think of it as analogous to looking at a rainbow and how red gradually becomes violet. Sure, you can point at a place on the bow and say, "that's yellow" but you can't easily point out where orange stops and yellow begins. Species is like saying 'yellow'; you can clearly tell it's different from another one, but there was lots of small iterative changes to get there.

The really short answer is to note that unless you can extract some DNA, the best possible case for any given specimen of fossil is that you can observe some features that are present in later species but not proposed earlier species, and some that are found in proposed earlier species but not the later species. This would demonstrate that there existed a species from a given time period that showed the features one would predict to see if evolution were correct. If you found one which lacked key features that existed in both the earlier and later specimen, you could reasonably assume what you have could not be an ancestor of the later species.

What you cannot prove is that your specimen is definitely decended from the earlier species or that it definitely gave rise to the later species; you are simply showing that a species of the sort that ought to exist if evolution is true did in fact exist.

[chakka35]

Waldo has said it all, but I'd like to know, 12thPaladin, what you mean by the 'missing link' in the first place, please.

[12thPaladin]

Thanks for your answers.

chakka35,
Homo ergater and Homo habilis are both thought to have shared a common ancestor, a species as yet unknown,a missing link perhaps to Australopithecus.

Ardipithecus is thought by some to be the ancestor of Australopithecus, another missing link, in as much as (to my understanding) the jury's still out.

My question rephrased then:

Is it yet accepted that Ardi was Lucy's direct ancestor?

[12thPaladin]

*ergaster

[12thPaladin]

WaldoMcFroog,
Your rainbow analogy; would be nice if the fossil record was complete.

[jake-the-peg]

What would a "complete" fossil record look like?

I doubt the entire notion of species. It seems a rather human invention that breaks down when you start looking at it carefully.

[12thPaladin]

Sorry, you'll have to explain your thinking on that jake

[jake-the-peg]

So the classic idea is that two different species cannot interbreed and produce fertile offspring.

We'll put aside how specific that seems to be to larger animals and how you might apply that to asexual reproduction

Let's consider Dogs - they can interbeed with Wolves notionally a seperate species and If you found a Dachund fossil and a Labrador one nobody would try and tell you they were the same species.

Then let's look at lions and tigers - Clearly seperate species?

Yet they can interbreed and the female offspring are fertile so you can have Li-tigons and ti-ligers and all sorts.

I think Waldo referenced a list of known seperate species that can interbreed (cant find it immediatly) a while back - it was reasonably long.

So this leads me to the question of what a complete fossil record would look like - what's missing? - or can you just go on forever saying "oh we're looking for the missing link between this one and the last one that was found"

[12thPaladin]

The fossil record is not complete. I did not suggest it was.
Inter species breeding is not a new concept.

Not to be sidetracked, my question is:

Is it yet accepted that Ardi was Lucy's direct ancestor?

[jake-the-peg]

I didn't suggest the fossil record was complete I merely asked what a complete fossil record would look like - what are we missing?

The point is that the very notion of species - saying this is a member of one species and that is not is at the very least questionable.

The idea of a fossil record is based on the idea of species and our ability to distinguish them.

As I pointed out with the dogs analogy this is also questionable

[12thPaladin]

Jake,
Regards to the fossil record, there are huge gaps, the resultant speculative theories prompted this question. There was research into Lucy's ancestry but the conclusions (to my knowledge) have yet to be made public.
I'm not a paleontologist, are you?
An honest simple question.

[12thPaladin]

Not to be sidetracked, my question is:

Is it yet accepted that Ardi was Lucy's direct ancestor?

[WaldoMcFroog]

As I stated in my initial response, no evolutionary scientist would ever make such a claim.

I don't understand what's the matter with the rainbow analogy. It doesn't require the fossil record to be complete, which is lucky, because we know full well it isn't and won't ever be.

[12thPaladin]

WaldoMcFroog,

There's no doubting the rainbow theory of evolution, if it were a linear one track event, however to my mind it makes no provision for diversity and ignores the Darwinian idea of ' branches on trees'

[12thPaladin]

Actually, ignore that last post.

[12thPaladin]

Is it yet accepted that Ardi was Lucy's direct ancestor?

Straightforward question, didn't expect a debate.

[WaldoMcFroog]

I've told you the answer twice but you just keep on about my anology...

[12thPaladin]

OK, you don't know if Lucy is descended from Ardi, that was was question.
That's fine.

[chakka35]

I punctuted my question badly, 12thPaladin. I should have asked what you mean by THE missing link. If we go back 6 million years we arrive at the common ancestor of humans and chimps. Is that the link you mean? Back another million years and we get the common ancestor of chimp, human and gorilla. Is it that one?

I cannot imagine how many common ancestors there are between homo sapiens and bacteria, let alone the original primitive life. Which is why I always ask what people (and the popular press) mean by "the missing link".

[12thPaladin]

chakka35,
A link between Sahelantropus tchadensis (reclassified as a Lemur) and Ardipithecus kadabba would be huge.

Do you have any answers?