The Dawn of Our Own Genus: The Rise of Early Homo | The BioLogos Forum

A form can have transitional characteristics and yet still go extinct. If a series of traits evolves over time and proliferates through a related set of taxa, most of them are still going to go extinct. That doesn’t mean they don’t have transitional characteristics. The focus is on the traits, not the forms, themselves. This is why things look like a mosaic in the fossil record. Take the origin of bipedalism: some of the traits evolved in the transition from the late Miocene apes to forms like Ardipithecus. The rest of the traits that form the bipedal complex evolved later down the road and are found in Au. anamensis, a form which might represent the crown group for later hominins. A writer a few years back wrote that from Au. anamensis to Au. afarensis represented the best evidence for anagenetic speciation that he had ever seen but he was quick to point out that a systematic analysis doesn’t permit that kind of conclusion, only that they had many traits in common and that afarensis had traits that were derived in the direction of later hominins. Traits for terrestriality then showed up in later australopithecines and early Homo. The australopithecines, themselves, then diverged in different directions, with different traits showing up in different forms.

I’m not sure we are connecting here. There is a difference between a transitional characteristic or trait, and something that looks like a transitional characteristic or trait. A trait cannot be transitional, unless it actually transitions. If it ends up in an endpoint, it is no longer transitional. A trait is not transitional merely because it resembles something. We merely call that a similar characteristic. It must have resulted in something.

A butterfly and a bird and a bat all have wings and can fly. In that way they resemble each other. But we would not consider these characteristics transitional in spite of their similarity. Of course this seems to be obvious. Yet, even in situations where similarities are closer in appearance and function, we cannot maintain that a trait is transitional unless we can demonstrate that a transition actually took place. We need to prove that the fossil we find is not an end point. If it is an endpoint, then it is not transitional, and the similarity of the traits is irrelevant.

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This is probably the coolest thing anyone has done on Discourse so far. Thank you so much for investing in this dialogue.

Hope it helps. I am not sure what to do after this.

Thankyou for the diagram. As Brad said, cool drawing. I understand the concept. I have taken a couple genetics courses. My point is that to say a trait is transitional,
without a fossil or concrete evidence to prove it is transitional, one
cannot say it is transitional. You cannot say a trait is transitional
just because two species happen to have similar traits. A transition must
actually have occurred. It cannot be a just-so-story. You cannot say, I
believe they must have transitioned. If they transitioned then they must
have certain similarities. They have certain similarities, therefore they
transitioned. That is an error in logic. Scientifically, there must be
evidence not only of the similarities, but also of the hypothesized
transition.

In a case where a supposedly transitional fossil is found after the
footprints of a presumed descendant, we no longer have evidence that the
presumed intermediate existed before its presumed descendant. It changes the lines drawn from A to B etc into question marks instead of solid lines. We can
speculate on the transitional traits, but without an actual transitional,
which is actually speculation anyway, due to lack of genetic evidence, and
due to lack of observational data, we no longer have any evidence of the
sequence which we would expect. We cannot prove that the transition did
not progress in the opposite direction, for example, with a tetrapod
having its feet halfway change to fins, for example, and then ending up in
an endpoint from the other direction.

Using a human analogy, for example, it is possible to have a “double” (as
in acting or movies) which more closely resembles a person, than that
person’s actual twin or sibling, yet, we know that the one who resembles
less closely will be more closely related. We can demonstrate that thru
genetic testing, but not by mere resemblance alone. Similarities by
themselves cannot prove descent.

You write: “It cannot be a just-so-story. You cannot say, I
believe they must have transitioned. If they transitioned then they must
have certain similarities. They have certain similarities, therefore they
transitioned. That is an error in logic.”

This is not an error in logic. It is a logical deduction from evidence. Evolutionary theory predicts what should be found in the fossil record and, lo and behold, it is. If we found something that was radically different, then it would nullify the theory. We haven’t.

You write: “in a case where a supposedly transitional fossil is found after the
footprints of a presumed descendant, we no longer have evidence that the
presumed intermediate existed before its presumed descendant.”

This is still unilineal thinking. There is no evidence whatsoever that the transitional fossil is a direct descendent of the critter that made the tracks, just that they represent a radiation of forms that shows derived traits in the direction of tetrapods. How does this not constitute evidence of the hypothesized transition? What would a transitional trait look like to you? You write that the fossils don’t constitute “observational data.” How is this not observational data?

Your argument sounds suspiciously like Ken Ham’s “Were you there?” argument.

Okay… you think it is a logical deduction from evidence. I think the evidence is circumstantial and could lead to a different conclusion. How do you distinguish is the question. Let’s take apart the logic.

You say, If they transitioned then they must have certain similarities.
They have certain similarities.
Therefore they transitioned.

But your logic is missing something. The first statement is true. But you know that things have similarities when no transition has taken place. If you said, " If Tom builds houses, they are likely to have some similar characteristics. These houses have similar characteristics. Therefore Tom built them." However, you know that other builders might also have some of the same similar charcteristics in their building. A similarity is necessary for the theory, but it is not proof. It can only be used in the negative sense, to disprove the theory. Therefore disimilarity would indicate the theory doesn’t work.

An obvious example is wings of butterfly, bird, bat. You would not argue a transition there because the similarities do not overcome the differences. The only way that the evidence can prove transition, is if you first believe the transitions must have taken place. If I say it is merely a species that existed for awhile and then went extinct, you would need to demonstrate that species transitions actually take place on the order of changing appendages and organs. And that this trait actually transitioned, and didn’t just appear spontaneously on its own and then eventually become extinct.

The evidence is circumstantial because you cannot observe the process. How do you know it is not just blind luck that something was found to match the theory. You cannot replicate the process. So the observational evidence needs to show a “fish” giving birth to a half-fish. Otherwise the half-fish is merely its own distinct species, and you don’t know if it was transitional or not. Nor do you know if the traits themselves are transitional or not.

Just because a characteristic is halfways between two other characteristics, is not proof that it is transitional. Transition is quite a different concept from variability, and it is easy to confuse the two.

I did not say that the so-called transitional fossil is a descendant of the critter that made the tracks… I said that it could be an descendant or an ancestor; we have no way of knowing. For the same reason, it may be neither an ancestor nor a descendant.

I don’t believe I said that fossils were not observational data. They are definately data. But they are not conclusive data for the theory. Similarity does not prove process. This is especially true when we do not have genetic analysis for the fossils.

Okay, have it your way, I think unilineally. But so do you. You know that a transitional trait must appear between the original species and the descendant species. That is why it was predicted to be found where it was. That is why the find was so exciting. The fact that you also may find it in a wide variety of times and places afterwards is irrelevant. If the transitional trait only appears after both of the antecedant and descendant species are already in full evidence, then we cannot argue the transition process itself. We cannot specify the direction of the transition, if the trait is not found in time between the two.

If we find evidence of tetrapods before we find evidence of the transition trait, then we no longer have evidence of the presumed transition. It’s not proof that it didn’t happen, but we do not have the evidence it did either.

You are failing to take into account how science works. Science works by testing hypotheses. Inherent in this is the fact that we can never know for sure if our hypotheses are correct. All we can know is whether or not they are wrong. If, however, we construct a hypothesis and fail to reject it, then we move on. Evolutionary theory is based on thousands of such hypotheses. What you are asking is something that is impossible in the scientific world, that we would know something for sure. As far as the evidence leading to a different conclusion, that is the heart and soul of science: hypothesis testing. If someone has a better idea of what happened, they are free to put that forth to be tested.

It is not circular. If we find fossils in one stratum that have a certain set of features, and then find fossils that have another set of features, and in between them, we find fossils with half-formed or a mosaic set of features that are in between the two sets of fossils, it is not circular reasoning to hypothesize that one group was ancestral to the other group in some way. Neither is it illogical.

As far as the bird wing and the butterfly wing are concerned, they are analogous—they do not arise from the same body elements. The wings of a bird and the wings are a bat are homologous–they DO arise from the same body elements. Therefore, the bird and the bat are more similar to each other than either is to the butterfly.

The notion that the evidence is circumstantial is correct We cannot observe the process but we can observe the results of the process. The same is true in a capital murder trial. A crime scene is reconstructed because the dead person cannot tell us what happened. The evidence is circumstantial. That doesn’t mean it is unimportant or cannot be used to recreate past events. That is exactly how it is done. All historical sciences are done this way and, as a means of understanding the workings the past, it works very well. Just because we were not there to observe the process does not mean we cannot infer what happened based on what we know of the processes.

BTW, speciation is observable in the modern world. Here is an example: A closer look at a classic ring species - Understanding Evolution

James, it didn’t take too long into the article in the link you provided, to find out that the ring species actually still could interbreed (cross breed) and sometimes did even with the presumably most distant lines genotypes. Which implies no speciation, unless the definition of species has changed. It is simply a selection from a variety of traits into a narrower variety, or less variable genome. The argument would apply to saying that europeans and africans and asians were demonstrating speciation.

I’m glad you acknowledge the evidence is circumstantial, and that we don’t know for sure. If you say the thinking is not circular, then you have to admit that in the example of Tiktaalik fossil, along with the pre-dated tetrapod fossil footprint, that the circumstantial evidence indicates the tetrapod existed before Tiktaalik. Until we find another tiktaalik prior to the footprint, we cannot say it was transitional towards the tetrapod. To say that the trait is transitional, we would have to find at least one fossil with the trait prior to the fossil footprint. It might theoretically be transitional, but we have no evidence, not even circumstantial evidence. We can say there is a mosaic, but we cannot say what the direction of the mosaic has been, not without evidence.

I work in science and understand full well how science works. I understand testing of hypothesis. I just judged in a highschool science fair last week, and was confronted by all the successes and failures of scientific rigor vs quasi scientific thought and jumping to conclusions which is so common in school age science. Our hypotheses can be determined correct, from a statistical perspective, if the null hypothesis is rejected. This depends to a large degree on how the hypothesis is worded as well as the degree of certainty that we set as our standard. The degree of certainty depends on replications, rejections of outliers, and controlled conditions. It is incorrectly assumed in observational science, that if one observation is measured numerous times, that the scientific rigor is good. However, it is the observation itself that must see repeats, not just the measurement of one observation. If a controlled experiment requires only ten observations, that would compare to a survey (observation science) requiring a multitude more in order to be valid, because it is not a controlled experiment. In my mind it would compare more to a survey of people’s opinions requiring a much larger sample size, to draw a conclusion of correlation from the data.

How is a crime scene different, and how is it similar to paleontological discovery? First, evidence can generally be contained and controlled at a crime scene. The longer the scene is not controlled, the less valid the evidence becomes, mostly because people do not know what was altered, removed, or added, or destroyed. Yes, some knowledge will help understand the scene, eg. bullet direction and patterns, direction of broken glass, decline of body temperature, etc. But the crime scene must be correlated to alibis, circumstantial witnesses, and to other evidence. Often, a conviction will not occur, due to lack of evidence for a particular suspect… he may have wiped all prints, got rid of the murder weapon, and moved the body. A crime scene is similar to a fossil site in this way, if we realize that nature itself gets rid of a lot of evidence, and if we realize that animal behaviour of animals that we have not met, becomes guesswork. In a crime scene, if there are no fingerprints, no blood, no emissions, then we assume no presence. But we cannot be sure. In geology, we know we cannot be sure, and have evidence this is not even a good theory. Absence of fossils does not demonstrate absence of life. And we have a lack of motivation for anyone hiding the evidence.

You just gave a rather verbose version of “how can you know, you weren’t there.” In fact, that’s the underlying theme of nearly all your posts.

“We know we cannot be sure.” Never to your satisfaction, I suppose. But for anyone who is reading this thinking that it’s a discourse between equally valid viewpoints, I just want to step in to say–as Jim has said over and over–you’re not properly representing the phrase “transitional fossil”. You keep saying that it “didn’t transition”. That’s not what’s meant by “transitional fossils” and “transitional forms”. You’re using the verb, “transition” in a phrase where there is no verb. Re-read the article. Re-read Jim’s multiple replies to you.

If you want to reject the evidence as not compelling, fine. You may stay with the one percent. But in doing so, don’t misrepresent the definition of transitional fossils. Your logic is no different than Duane Gish. If we show you two fossils, you’ll say there’s no “link” between them. If we show you three links between them, you’ll say that there are now four gaps. It’s debate tactics. It’s not the way scientists talk. You already demonstrated this when you said there were amphibian footprints in 150 mya strata of the Grand Canyon. You demonstrated this again when you said that Tiktaalik prints can’t be any older than Neil Shubin’s. I rejoice that you’re on our forum, and I’m glad you’ve taken a couple of genetics courses. (As well as judged a science fair.) Just be careful to represent the facts correctly, and to only refute that which is actually being claimed.

@ brute One does not like to be accused of improperly representing something. Perhaps because I have degrees in both science and arts (philosophy/english), the way concepts are expressed are as significant to me, as are the concepts themselves. Transitional fossil is a concept. Transitional is an adjective. Transition is a verb. Even a verb used as a noun still expresses an action… or at least it acknowledges an action. When the term transitional fossil is used, it implies a fossil that was transitional from one form to another form; by that I don’t mean that that particular dead animal was the transition, but certainly the species to which the fossil belonged needs to be transitional between two forms in order to be legitimately called “transitional”. Of course, it may be possible to redefine transitional to refer to something halfway between something, like the number 5 is transitional between 3 and ten, or the white house is between the green house and the blue house. But I doubt that is the intent. The verb is the intent, even if the word transition is used to describe a trait in an animal long after the actual transition took place.

If the fossil (or fossil species) itself is not claimed to be intermediate, but only the traits it possesses are named as transitional, as Jim was saying, then one should not call a non-transitional fossil a transitional fossil - that is a misnomer, which contributes to poor communication and misperception. Rather one should say that it is a fossil species which has some traits that appear to be transitional.

Am I arguing that “how can you know, you weren’t there”? Yes, well certainly that is a starting point. But I acknowledge there can be evidence in spite of not being there. The point is, is the evidence real and convincing, or is the prisoner assumed guilty before proven? You mistated what I said. I did not say that Tiktaalk prints can’t be older than Neil Shubin’s tiktaalik fossils. I said that tetrapod footprints were older than his tiktaalik fossils. As long as tetrapod fossils are older than tiktaalik or similar types of proposed intermediates (transitionals), then we do not have evidence that the proposed transitionals are actually intermediates between species. I mean even if the order was right, we would not have irrefutable proof, but if the order is wrong, then we have even less warrant for drawing a definitive conclusion from a science based perspective.

Why do I say that even if the proposed order was right, we would not have irrefutable proof? Well, this example is perfect. Before the footprints were discovered, we didn’t know about them, yet they were there, and so we now know that tetrapods existed previously. But even if there were no footprints, the mere absence of fossils does not prove the absence of species. This is a very difficult obstacle to overcome. While presence of fossils demonstrates something, the absence of fossils demonstrates very little, if anything. The same argument that says that we have not seen or discovered all the intermediate species, either because we just haven’t found them, or because they left few fossils, or because they didn’t leave any fossils, also applies to the theory that a large number of species existed without leaving any fossils in earlier and later sedimentary times than the layers in which we now find them.

You write: "If the fossil (or fossil species) itself is not claimed to be
intermediate, but only the traits it possesses are named as
transitional, as Jim was saying, then one should not call a
non-transitional fossil a transitional fossil - that is a misnomer,
which contributes to poor communication and misperception. Rather one
should say that it is a fossil species which has some traits that appear
to be transitional. "

That is exactly what I am arguing. The traits are transitional. They show up in mosaic fashion in a number of different forms. The writers of the article on the Ledi jaw argue that some traits align it with early Homo and some traits align it with Au. afarensis. The catch is that you have to give the organism of which the jaw is representative a taxonomic name because the jaw exists synchronically. The traits are changing over time but the Ledi jaw is a static creature that has a mix of those traits. Is it a transitional form? Only in so much as it has a set of traits that differ from those forms around it that that fall within that phylogenetic branch.

Well, maybe we are making progress. You agree that some traits appear to be transitional. How do you distinguish between traits that are transitional vs those traits that are not transitional? Let’s use dogs because they are easy to understand. Are the different sizes called transitional traits? Are the different lengths of hair called transitional traits? Are the different hair colors and jaw alignments called transitional traits? We know there is a spectrum of sizes, weights, colors, hair length, etc. There is a mosaic of traits and extent of traits. Are these all transitional traits, or are only those intermediate characteristics that lead to the endpoints called transitional; ie. if the endpoint is the Great Dane then the distinctively Great Dane traits are not transitional, but the traits of the golden lab might be transitional?

Back to the original point of this thread: humans.

Apparently, neandertals, which some people consider to be non-human, have interbred with people, and have a genome closer to modern humans than the similarity of genome of some chimps to genome of other chimps. Yet, some populations apparently do not have neandertal linkages. Which would make it strange they were ancestral in that case. Based on this it seems that neandertals are not ancestors of all humans, and were co-existant with relatively modern humans (europeans and asians but not africans). In essence, neandertals would simply be humans.

Lubenow (1998) has pointed out that the use of a statistical average of a large modern human sample (994 sequences from 1669 modern humans) compared with the mt DNA sequence from one Neanderthal is not appropriate. Furthermore, the mt DNA sequence differences among modern humans range from 1 to 24 substitutions, with an average of eight substitutions, whereas, the mt DNA sequence differences between modern man and the Neanderthal specimen range from 22 to 36 substitutions, placing Neanderthals, at worst, on the fringes of the modern range. (Dave Phillips, M.Sc.)

Sorry for the delay in responding. The whole family has either colds or the flu. It is quite true that some modern populations don’t have Neandertal markers. The most likely explanation for the populations that have no Neandertal in them, is that they migrated out of Africa subsequent to the Toba eruption, 71k years ago (which ruined everyone’s day)

Neandertals are not simply humans, as you say. The available literature is uniform in the conclusions that Neandertals and modern diverged between 300 and 400 thousand years ago (results vary depending on the genetic region used) but that when they came back together, they could, in fact, interbreed and, at least in limited fashion, did. This explains why you get Neandertal markers in European and western Asian populations. One of my friends here at work use 23andMe to get her genetic make-up and found that 2% of her genetic markers are Neandertal in origin.

Warning: I am now about to go on an extended rant:

Marvin Lubenow’s book, from which you quote is one of the worst examples of scholarship that I have found in recent memory. I could give you example after example after example of how he used out-of-date information to bolster his case, made logical errors, factual errors, misinterpreted the data and engaged in what I thought at the time to be outright deception (Yes, that is strong. Yes, that is what it looked like). He made many gratuitous statements in the book, often without backing them up with citations. Please do not use this as a reputable source. You do yourself a disservice.

Jim, thanks for your reply. Wow, what a rant! However, in your second paragraph, you cited no data to back up your claim. “The available literature” … doesn’t give anyone else a chance to make a rant like yours, nor does it explain why they are not humans. Also, the conclusion that they diverged is irrelevant to whether they are human, while the fact that they could interbreed is relevant.

I quoted Dave Phillips, not Lubenow. That aside, even a book of poor scholarship may still contain some truths. Are you arguing that what is actually stated in Dave Phillips quote is not in fact true? That there is in fact a large neandertal sample of DNA sequences (from many neandertals and not just one)? how many?

I agree data can be out of date. Yet on all sides this data is used to draw conclusions and leave impressions which are not easily erased. We have a good example of this in two cases, on both sides of the issue. The human and chimp dna was compared and said to be 99% similar. Obviously that demonstrates humans and chimps are related. However, later the similarity was downgraded to 96% or 94%. Then we discover that the genome size of chimps is 8% larger. Now we are at 87% similar. Are the people who quote these early studies to blame for the inaccuracy of the early studies? Lately I have heard that in some cases the human genome was found to be 12% larger, a complete reversal in genome size. I admit I am truly confused. I would not like to be castigated for reporting out of date data under the circumstances.

What if I said that your rant seemed somewhat gratuitous to me? (I forgive you, but still…) The real issue of the facts at hand is most important; is the comparison of the different sample sizes appropriate? Is the statement by Phillips totally inaccurate? If so, why?

Just as an aside, do you find it perfectly normal that DNA should last for 50,000 years without being totally degraded? How long does it take to degrade?

This give and take between you and me is effectively the 21st century equivalent of writing notes back and forth. That is not the same thing as a self-contained scholarly work, such as Lubenow purported to put forth. I didn’t provide you with citations for the sake of brevity. His should have been there in the first place. But, since you asked:

http://www.pnas.org/content/96/10/5581.short

http://www.sciencemag.org/content/314/5802/1113.short

That help?

With regard to the chimp/human DNA:

http://www.pnas.org/content/99/21/13633.short

The concern I had about the out-of-date data is that, in some instances, newer data undercut his position and yet he did not include it. Yes, I can provide examples of those, as well.

As far as the quote from Phillips (yes, you are correct, you did not cite Lubenow, Phillips did) is concerned, I backtracked it back to the original article from Lubenow Recovery of Neandertal mtDNA: An Evaluation | Answers in Genesis in which he argues that Krings et al (1997) use the concept of Neandertal “averages” when only one Neandertal was present. Here is what Krings et al wrote:

“Whereas these modern human sequences differ among themselves by an
average of 8.0 ± 3.1 (range 1–24) substitutions, the difference between
the humans and the Neandertal sequence is 27.2 ± 2.2 (range 22–36)
substitutions. Thus, the largest difference observed between any two
human sequences was two substitutions larger than the smallest
difference between a human and the Neandertal. In total, 0.002% of the
pairwise comparisons between human mtDNA sequences were larger than the
smallest difference between the Neandertal and a human.”

They are not saying anything about a Neandertal “average,” they are arguing that the average difference between any two modern humans is 8 substitutions. When all moderns are individually compared to the Neandertal remains, the average is 27 substitutions. Lubenow misread their results.

James, thanks for your reply. I have not yet looked at your references, but I will. Thanks much.

However, you should re-examine your last three paragraphs. After checking back and forth between your statements and Phillip’s statements, I find you both saying the same thing. Phillips does not mention a Neandertal average, only a comparison between a human average and the neandertal specimen, and a comparison between individual humans and the neandertal, as you also indicate. The problem is the neandertal sample size is apparently quite small.

Okay… the first reference you gave:

DNA was extracted from the Neandertal-type specimen found in 1856 in western Germany. By sequencing clones from short overlapping PCR products, a hitherto unknown mitochondrial (mt) DNA sequence was determined. Multiple controls indicate that this sequence is endogenous to the fossil. Sequence comparisons with human mtDNA sequences, as well as phylogenetic analyses, show that the Neandertal sequence falls outside the variation of modern humans. Furthermore, the age of the common ancestor of the Neandertal and modern human mtDNAs is estimated to be four times greater than that of the common ancestor of human mtDNAs. This suggests that Neandertals went extinct without contributing mtDNA to modern humans.

Does this abstract really make sense to you? This was 1997, almost twenty years ago… I’m not sure which of your points it demonstrates. It indicates that neandertals did not contribute mtDNA to humans but modern research indicates neandertals did contribute dna to europeans and west asians. This suggests to me that age of a common ancestor is not a predictable indicator of DNA contributions.(and vice versa). Furthermore, there is a contradiction in terms of the comparison of DNA of humans and this neandertal in this report which showed that the ranges of differences in nucleotides overlapped, compared to mtDNA where the ranges of differences also overlap. In addition, no neandertal-chimp comparison was made. However, the main problem in this study (besides the degraded DNA) is that there is only one neandertal, which is likely to skew the results.

I will look at the other references; I hope you get over your cold soon.

Hi JohnZ. I will get back to this in a bit but right now, all bets are off. I need to process this: New instrument dates old skeleton before 'Lucy'; 'Little Foot' 3.67 million years old -- ScienceDaily

New instrument dates old skeleton before ‘Lucy’; ‘Little Foot’ 3.67 million years old

This has significant implications for the study of human palaeo because, if the dates are right, it adds new wrinkles to how the australopithecines fit.