"Missing Link"

[Brett89]

Iv been wandering, the Creationist use the "missing Link" as a force against evolution, they say that since all the Trasitional forms are fully developed that evolution cant possibly be correct, can anyone tell me why they are wrong?

[BGMA]

All the basics on the "missing link" canard can be found here, start at about the 9th or 10th paragraph for why the missing link is old news:

Human Evolution (http://www.freewebs.com/thebgma/a23humanevolution.html)

Enjoy!

********************************************
The Bible of the Good and Moral Atheist (http://www.freewebs.com/thebgma/index.htm)

[espritch]

All living species are "fully developed". Evolution does not posit the existence of critters with half an eyeball evolving an eye. The earliest eyes were fully formed and functional. They were just a lot simpler; the simplest eye is nothing more than a patch of light sensitive cells (like the eye of a copepod (http://en.wikipedia.org/wiki/Copepod)). More advanced eyes add additional features, but they are still fully formed functional eyes, just not as sophisticated as later versions.

Creationists try to make the claim that a missing link is an incomplete organism that is not quite one thing or another. This is not what a transitional species is. A transitional species may exhibit some traits of an earlier species and some traits of a later species, but it is still a fully formed and functional organism in it's own right.

[patchy]

Iv been wandering, the Creationist use the "missing Link" as a force against evolution, they say that since all the Trasitional forms are fully developed that evolution cant possibly be correct, can anyone tell me why they are wrong?

Brett, by any chance are you just "posing" as an evolutionist/atheist in order to better hone your arguments or something?

[Danhalen]

If we had a complete fossil record (by complete I mean from the first living thing till now), the only non-transitionals would be the first living thing, all currently living species, and any species which happened to completely die out without speciating. That leaves an incredible amount of transitionals (or "missing links").

[Ezkerraldean]

creationists have the whole "transitional fossil" thing totally wrong. in the sense of the word that is used in the media, a transitional fossil is a fossil of an organism that, with hindsight, shares characteristics with two or more other groups of organisms that later proliferated.
in reality, any organism is "transitional". often, a gradual lineage can be seen to have played out, as in tuning fork graptolites and with the suture lines of ammonites. the lineage is so smooth that there is no one "transitional".

[Brett89]

im not "posing" to answer your question

[Jet Black]

Brett, by any chance are you just "posing" as an evolutionist/atheist in order to better hone your arguments or something?

let's just deal with the questions in the OP, ok? leave personal questions to the PM system if you like.

[Jet Black]

Iv been wandering, the Creationist use the "missing Link" as a force against evolution, they say that since all the Trasitional forms are fully developed that evolution cant possibly be correct, can anyone tell me why they are wrong?

what do you mean by "fully developed?"

[Oolon Colluphid]

Iv been wandering, the Creationist use the "missing Link" as a force against evolution, they say that since all the Trasitional forms are fully developed that evolution cant possibly be correct, can anyone tell me why they are wrong?
"Fully developed" is pretty meaningless as it stands. Every (adult ;)) organism is 'fully developed', in that it is a functioning, living thing, and (if it lives long enough to have offspring) is 'successful'. Nothing makes a living by being a part-formed step on the route to something else. They're good enough in their own rights.

The concept you need to grasp here is that evolution works by modifying existing structures.

Take the old question 'what use is half a [wing etc]?' (which is at the core of their argument here).

Wings are modified tetrapod (four-legged creatures with backbones, like frogs, lizards, horses and us) forelimbs (arms). The forelimb is a modified fish fin (see Per Ahlberg or Martin B for details, or look up Tiktaalik).

(That's why they have fundamentally the same structure as a horse's leg, the one-bone, two-bones, clump-of-bones, strings-of-bones structure of the tetrapod upper-arm, arm, wrist and fingers.)

The ancestors of birds -- the half-birds, if you will -- were not half-anything. They were, at the time, busy being fully-dinosaurs. Fully bipedal (walking on two legs) dinosaurs. So their arms were free to be co-opted for another use. But at the time they were used, as you might expect, for grasping prey. From our perspective now, looking back, these arms were wings-in-waiting. But their owners made a good enough living by using them for grabbing their escaping food.

What about feathers? Feathers are modified scales. modified outgrowths of the skin. Originally, their owners used them for skin protection or whatever scales are for (sorry, look it up, I'm doing enough work here as it is :Cheeky: ). But increase the length of the scales, and you trap a little air. Which is insulation. So scales become insulators.

The ancestral version of feathers, then -- the half-feathers -- were not half-anything. They were, at the time, busy being fully-insulating scales. From our perspective now, looking back, these scales were feathers-in-waiting. But their owners made a good enough living by being insulated by elaborated scales.

We now know that the group of animals from which birds evolved were bipedal (ie with free arms) dinosaurs with feather-like coats (probably for insulation). We've found their fossils, you see. But these transitional forms -- as we can now see them to be -- were 'fully' insulated theropods. Only with hindsight can we see that they were half-birds!

They weren't trying to become birds. It's just that one group of them found that they could make a living slightly differently, which meant different selection pressures, which led to further adaptations. One such different way of living was going up trees after food. (Pace, cursorial-flapping proponents if any are present.)

So, what good is half a wing? That is, a forelimb with proto-feathers. Well, as Richard Dawkins has explained at length, if you are up a tree and fall, it is precisely 1% better than a 49% wing at breaking your fall rather than you breaking your neck. That is, as an aerofoil, a surface area for catching air and so parachute to safety.

And there is a whole range of heights one might fall from. There is, obviously, some height from which you can fall, where 50% of a wing (that is, of surface for air catching and so safe parachuting) saves your life, while 49% of one doesn't quite break your fall enough (splat). Similarly, there's undoubtedly some height from which 10% aerofoil is enough (safety), but 9% isn't (splat); and from which 73% is just enough (safety) but 72% isn't (splat). And so on.

So, smooth gradients of potential improvement. Small gradual steps, each a subtle advantage over those without. Each of which was good enough in its own right. It had to be, or it would not leave descendants. Only with hindsight (which is what you watch deer with) were they part-anything, at the time they were fully themselves.

So of course these creatures were "fully developed". What else would they be? All they were not is fully developed birds (or whatever).

Hope that helps :).

[nogods4me]

I've been missing Link, ever since they cancelled The Mod Squad.

[Wolfie]

Excellent clarification, Oolon!

I always thought the missing link was Bill Bailey - part man, part troll.

[Berthold]

Konrad Lorenz said that we are the "missing link" :) .

[Brett89]

ok, i understand now, thanks oolon

[Oolon Colluphid]

ok, i understand now, thanks oolon
You're welcome :)

I've just (this morning BST) started listening to the audiobook version of Dawkins's The Ancestor's Tale, and realise that I was inadvertently -- unconsciously -- repeating part of the opening section of that book (even, it seems, some of the phrases crept in -- "Nothing makes a living by being a part-formed step on the route to something else" and "only with [the conceit of] hindsight" are straight out of Dawkins... weird how the mind works like that, it's been at least a couple of years since I read it!

"Part-formed." "More evolved." "Becoming more like..." These ideas are possible only with the conceit of hindsight. At the time, they made no sense.

As Dawkins (literally!) says:
A living creature is always in the business of surviving in its own environment. It is never unfinished.
[...]
That is not the way it was at the time. Those Devonian fish had a living to earn. They were not on a mission to evolve, not on a quest towards the distant future.
[...]
The gap [between fish and amphibians] comes with hindsight. There was nothing resembling a gap at the time, and the classes that we now recognise were no more separate, in those days, than two species.
[...]
As we wander in imagination through some long dead epoch, it is humanly natural to reserve a special warmth and curiosity for whichever otherwise ordinary species in that ancient landscape is our ancestor. It is an intriguingly unfamiliar thought that there is always one such species. It is hard to deny our human temptation to see this one species as on the mainline of evolution, the others as just walk-on parts, sidelined cameos.

(punctuation and italics as per the Dawkins / Ward reading)
... or, if we're looking at (say) bird ancestry, it's hard not to look for the ancestral bird species, and think of it as being 'on the road to becoming' a bird. *

But that is only how it seems to us, now. At the time, the creatures were busy being themselves.

I mention all this at length because, reintroducing myself to this book has brought home just how brilliant it is at answering questions such as the one in the OP. Brett, I seriously recommend you pick The Ancestor's Tale up from your library. Or if you PM me I can sort you out with mp3s of the audio.


* And I may as well use that point as a springboard for mentioning another concept you need to understand. At any one time in the past, there was a particular species that was ancestral to later ones. And as above, it was just one of many, "no more separate, in those days, than two species". A group of related species, then.

Each, however, had its own "living to earn". And that means each had its own adaptations peculiar to living that way. These, in the lingo, are called 'autapomorphies'. Because these critters shared a common ancestry, they had features in common, features they inherited (like the framework of limb bones I mentioned). These get called 'symplesiomorphies' -- shared ancestral features. And finally, the group had its own set of 'derived' ('evolved', if you like) characteristics, which get called 'synapomorphies'.

('Sym', together; 'apo', away from [the ancestral version]; and 'morphy', shape. An aut-apo-morphy is the species's own unique features.)

So what am I wittering about? This: there were a bunch of critters around at any one time. One of them was undoubtedly ancestral to later ones. But -- and it's a huge 'but' -- fossilisation (getting your remains to survive for millions of years) is a very chancy process. Most creatures get eaten, by bacteria even if not in our more usual sense of crunched within another's jaws.

Then the remains have to get preserved in rock, not crushed by it as it forms, nor eroded away later, or subducted beneath a continental shelf, and so on.

And then, we've got to find the fossil!

What does this all suggest? The obvious conclusion is that what we find as fossils are but a tiny, tiny fraction of what was alive at the bit of time we're looking at. And that means, the chances that this 'ere particular fossil, 'the one wot we just dug up', was a member of the very species we think of as special, the particular species on the "mainline"... the chances that the fossil was one of those, is very small. It could be. But we can't expect it to be.

So, we don't. Instead, we have to assume that all fossils are the "sidelined cameos". We don't know that the fossil left descendants, so we cannot assume any fossil is directly ancestral. 'Related to the ones that were' is all we can hope for.

Imagine that all your family -- great-grandparents, parents, sisters and brothers and cousins (first, second, third cousins, and so on), are all buried in one cemetary (apologies for those still alive, this is a thought experiment, right? :D). Then throw a hoop over your shoulder. What's the chances of the hoop landing over the headstone of your paternal grandad, your particular ancestor? Slim, right? Probably, we'll get your second cousin twice removed.

So, how do we know that those skeletons are actually members of your family? How, with fossils, do we know that fossil X is related to later fossil Y?

You can probably guess. By comparing the details of the anatomy. By working out, very carefully, what are ancestor-like features, shared derived features, and unique derived features (those hideous words symplesiomorphies, synapomorphies and autapomorphies... that's why I mentioned them.) It's not guesswork, it's hardwork. Others here are far more qualified than I am to explain how it's done, if you're interested.

But the overall point here -- yes, there was one ;) -- is that fossils are transitional (some say they all are), but not (necessarily) directly ancestral. They have features that, with 'the conceit of hindsight', we can see were 'on the general road to' becoming something later. But they were unique, 'valid' species in their own rights. And fossil X probably wasn't on the main line, but a related side branch.

And this is crucial, if difficult to get your head around, because you will find creationists who will pick on some feature of a fossil species, and declare that because it has some unique feature (that is, an autapomorphy), it wasn't ancestral. Well duh. Shared features ('primitive' and 'derived'), folks!

That is why 'family trees' (called 'cladograms', from 'clade', group) (eg this (http://www.nature.com/nature/journal/v440/n7085/images/440747a-f1.2.jpg)) show the species branching off.

In short, a fossil species probably isn't directly ancestral. This tells us nothing at all about what it really was, its 'phylogenetic' position. For that, we look at what it's like. (In detail, with measurements ;).)

So beware creationist misinformation on that sort of thing. The infamous 'March of Progress' picture -- parodied eg:

http://www.talkorigins.org/faqs/homs/evolve.jpg

... not only suffers from the conceit of hindsight (the species weren't marching to anywhere!). It also suggests that knocking members of it out of the 'line leading to' us means that the ladder of progress collapses. Well it's not a ladder, and discovering, for instance, that Australopithecus afarensis wasn't directly ancestral does not matter. It is still 'transitional', in that it shared features in common with later species and earlier ones.

Hope that makes sense and helps.

[RBH]

Oolon, it's a shame you aren't a teacher.

Oh. Wait. In effect you are. Here. Thanks!

RBH

[Berthold]

Actually, Oolon's job description in his profile is encompassing enough that he could be one.

Of course, also a gaol warden or a tax collector :devil1: .

[Oolon Colluphid]

It says 'Paper Pusher'? :eek: :D

[Berthold]

Oh, so you have made it a bit more specific than it used to be. It still can be a lot :) .