I’m sorry I didn’t keep track of your posts, then. Carry on.
Wait! Can you actually show that Tiktaalik is not an extinct leaf node?
So going back to the first post where it is claimed there is
What are the transitional forms in that series? By name please, not just a link to a “tree” with a bunch of species that might or might not be that long series.
Well yes they do. God created the Pongidae (Great ape kind) on day 6, the same day He created humans. These were not created in Africa since Africa as we know it did not exist prior to Noah’s Flood. Representatives of the Pongidae were on Noah’s Ark and after the flood they dispersed with many new species developing in Africa (adaptive radiation) and some in other places such as the Orangutan.
Pongidae (Great ape kind)
Wilson and Reeder (2005) place the great apes in Hominidae with humans, but given the significant differences between us and apes compared to some of the differences between other families, this seems ludicrous. Therefore, the older designation Pongidae is used here. There are three genera and six species in this family, which includes the gorilla, chimpanzee, and orangutan. Hybrids have been documented between the two species of orangutans (Gray 1972).
Now I’m getting confused. We are talking about a metaphor here but it was my understanding that every species was a leaf node when it existed but if the bush/tree of life is thought of as existing through time then only living species are leaf nodes at this time. Leaf nodes from former times return to dust or, if the conditions are just right, leave behind fossils.
Dear Chris. Thank you for starting this thread it has been very thought provoking and I have enjoyed watching the conversation ‘evolve’ 
In your last post, you said:
Let’s assume something for a moment. 1. Let’s assume that the Hebrew for ‘kinds’ is a technical-scientific word which denotes a biological classification (and that is a big if). 2. Let’s assume that a Pongidae pair was on Ark. 3. Let’s assume that the flood was global.
If we assume that all of those things are true, there is still an astronomical amount of special pleading going in that paragraph. Firstly, there is nothing in the Genesis account to indicate that Africa did not exist, or indeed, that global geography was changed in any way by the flood. Secondly, Genesis 1 is silent about God creating a specific kind called ‘Pongidae’. Thirdly, there is also nothing in the passage to indicate that following the flood these Pongidae moved to Africa.
It strikes me that a YEC cannot conclusively prove that any of this is true anymore than an EC can conclusively prove the role of Tiktaalik as a transitional fossil. However, I am reminded of something that Ken Ham is keen to point out in conversation about evolution. He has been known to say, on several occasions, that 1. That Genesis 1-11 are eye witness accounts of what really happened (literal, word for word, accounts) and 2. True science is based on what one can empirically prove based on sensory experience.
So, I wonder,
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Has anyone ever seen one ‘kind’ of animal produce a new species according to its kind? How would one even empirically prove that to have happened?
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With regards Pogidae moving to Africa after the flood. How can one know that such a dispersal pattern took place according to the text without first deciding it did and then reading that back into the narrative?
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Scripture is (effectively) silent about the existence of the African continent in Genesis 1-11. How then does one prove based on sense experience that Africa did not exist before the flood or that a single geographical feature had been changed in any significant degree? Seems to me, that (as I was fond of saying when I was a YEC) if you weren’t there, how do you know it happened that way at all?
If I have misunderstood anything then please do correct me. However, I hope you can see why I am really struggling to take this line of argument seriously from both a scientific and exegetical perspective.
Looking forward to hearing your thoughts. Liam
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A leaf node is connected to a branch, nevertheless. That’s what I meant when I said it inhabits a branch. So it could be a branch node, could be a leaf node. In either case it inhabits a branch.
I have no idea which type of evidence it is that you feel is intolerable (“not just a link to a ‘tree’”). Would it help if I mentioned that anthropologists are quite convinced that
- Homo Erectus is definitely in the line of succession leading from the common ancestor to humans
- Neanderthals, Denisovans, and Sapiens are offshoots of H. Erectus
- Neanderthals, Denisovans and Sapiens swapped DNA from time to time.
??
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In that case, so do a salmon and a reindeer.
So as evidence of transitional fossils from ape to man you offer only those that are already considered human.
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You basically stated that you were not going to accept evidence that I might present. Then you criticize me for not presenting enough evidence. How does that make sense?
Moreover, you did not answer my question. Please do so, and I will be happy to have a productive conversation with you based on your answer.
Thanks,
Chris
Yes, that’s a good start. But I’m interested to see if there are any proposed non human ancestors…
What do you mean by non-human ancestors? Not genus homo?
Surely fish generally are part of the line of descent leading to human beings, though pinpointing one particular species of fish as unequivocally being my direct ancestor would be difficult.
True, and a species of fish on your plate would only be transitional to some future species, if it survives our appetites. It is more our cousin than our grandpa.
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Sorry I was busy over the weekend and I’m just getting to reply here now. I think it’s true that people have widely varying definitions of what “transitional form” means, so I will look up a few to see what they say.
I think this can clearly apply to living as well as fossil organisms; all that is required is that they show what an in-between state of some trait might have looked like. So a shark has a cartilaginous skeleton, and if we were particularly interested in skeletal evolution we could say that the cartilaginous skeletons of modern sharks and rays show us a transitional form between ancient creatures with no skeletons and the many modern kinds of bony fishes and other derived bony forms. It’s not necessary to say that no ‘off-track’ evolution has occurred in order for a form to be transitional.
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group.[1] This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. Therefore, it cannot be assumed that transitional fossils are direct ancestors of more recent groups, though they are frequently used as models for such ancestors.
Wikipedia uses the word ‘fossil’ instead of ‘form’ specifically, perhaps to avoid confusion. However we still have clear acknowledgement that it is the commonalities that are important.
A transitional form is an organism that has features intermediate of its ancestors and progeny. The term is most common in evolution to refer to organisms that show certain features (wings, feathers, gills and so on) partly in development. In theory, every fossil is a transitional form if it has descendants and each living creature is a transition between its parent and its offspring.
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Because of all this, the term transitional form is often used to mean organisms that lie between two groups as cousins, not just as ancestors. For example, the echidna is not ancestral to modern mammals, but retains features of the reptile-like mammals which other mammals (the therians) lost, and is therefore transitional between ancient reptiles and therian mammals. A generally interchangeable term is intermediate form . Most iconic transitionals are the close descendants or cousins of a directly ancestral species whose fossils have not been found, or which never fossilized to begin with. (Fossilization is extremely rare.)
RationalWiki has the definition closest to what @aarceng, @Daniel_Fisher and @Chris_Falter are using saying so far, I think. It’s possible we should have been using “Intermediate form” instead for salmon and other ‘cousin’ descendants, though both uses seem very common. But I don’t think either choice of word usage makes a very big difference to the argument overall.
I think chimpanzees are an excellent example of an intermediate form between tree shrews and humans, don’t you? Anatomically speaking, is that really a statement that can be argued with?
Going back to the original question of this thread, since I want to try to answer it without getting (any more) sidetracked.
- There are both transitional and intermediate forms, although there is seldom certainty over which is which.
- Best current scientific consensus currently is that Ardipithecus ramidus, Australopithecus afarensis, Homo habilis, and Homo erectus are likely to be on, or very close to, our actual line of descent. Other fossils we don’t have as much information on yet may also be on or close to the line of descent, or one or more of the species I named may prove to be only close cousins.
Pretty certainly, species which are on our direct line of descent will also represent individuals who lived after the point of divergence, sometimes even by millions of years. It is common and expected that the body form of one population should change little, while another population finds a new ecological niche and evolves to fill it more efficiently. The fact that species can span millions of years without much noticeable change in their skeletons should not be taken as reason to eliminate those species from being on our family tree for part of that time span. It would be as silly as saying that the earliest Christians couldn’t have been Jews because look, Jews are still around in non-Christian form today!
More importantly, we are much more uncertain about individual species than we are about genera. We evolved from ancient species/individuals in the genus Homo, who evolved from older species/individuals in the genus Australopithecus, who evolved from older species/individuals all the way back to our common ancestor with Pan, the chimpanzee genus. The evidence is strong enough to say that much without fear of being overturned by future discoveries.
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Thanks for looking up the definition, Lynn. I would respectfully disagree with this take on the definition, however. Transitional fossils/forms provide links both with regard to morphology and with respect to time. This is what is meant by ancestors and progeny, I would assert.
Therefore modern sharks should not be regarded as transitional forms, as they are not intermediate in time between ancestors and progeny. On the other hand, Xenacanthus is an excellent example of a transitional fossil leading to early sharks.
Best,
Chris
I would assume that @aarceng means something like sister taxa or outgroups like this diagram:
So technically, one could say that Taxon B and C are not ‘transitional forms’ to Taxon A (let’s call that the “human” one). But all of this is just silly talk in light of how we know how evolution and common ancestry work.
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One thing I am not clear on is when do we consider these forms to be “human?”
It seems the word human is ill-defined. Homo sapiens came on the scene about 300K years ago, but in the lay literature, I see stories of evidence of “early humans” dating back 2-3 million years. And biblically, if you adhere to a time line where either the YEC idea is held or if humans were created out of a pre-existing population, you can place Adam and Eve at the dawn of agriculture and near the beginning of metal working as per Genesis 4:22 with Tubal-Cain.
Like all words, I suppose it is however you define it. I just wish there was some consistency in how we used it.
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So there seems to be some, but not universal, agreement that a transitional form/fossil should lie in time between the first appearance of the Ancestor and the first appearance of the Descendant. Thus since there is good evidence that tetrapods predate Tiktaalik by millions of years we can’t take Tiktaalik as being transitional between fish and tetrapods.
However RationalWiki as quoted by @Lynn_Munter doesn’t follow this since they say
and so it doesn’t need to be in the right time frame or in the line of descent.
Now as regards human evolution it looks like we also have some agreement between @Lynn_Munter and @Chris_Falter.
and Chris posted a graphic showing Australopithecus afarensis as an ancestor of Homo.
So they agree on the Australopithecus but not necessarily on the afarensis.
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