We get mail

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Recently the PT crew received an email with the subject line “A legitimate question about Evolution with no agenda.” As you might expect, the dual disclaimers–“no agenda” and “legitimate”–immediately raised a few eyebrows. “No agenda”? Hmmmmm. Well, I suppose it’s possible, though numerous previous encounters with creationists’ faux naivete have left me a dab cynical.

The email reads

Subject: A legitimate question about Evolution with no agenda
Date: Sun, 5 Jun 2011 16:48:13 -0700
From: [redacted]
To: [Enable javascript to see this email address.]

Dear Panda’s Thumb crew:

I’m not a scientist, I’m a retired history teacher with a masters in that field.

I’m not writing because I have any agendas. I’m trying to get my questions answered and I’m having trouble doing it since I don’t know any evolutionary biologists whom I could ask. Those I have written to do not reply. I’m asking for the perspective of an evolutionary biologist who might answer a student with questions who is not hostile to evolutionary biology.

If you don’t have the time to reply, or don’t want to, please write me and tell me that.

Here are my questions about macroevolution. My goal is to understand how scientists explain how macro-evolution works in a real life situation, in this case between reptiles evolving into birds, since this is postulated as occurring:

*Reptiles                 Birds*
Lay eggs                lay eggs
    fly                    fly

have feathers?      have feathers
cold blooded?       warm blooded

Would being cold blooded show up in the fossil record? If not, how and why would a reptile adapt over millions of years into warm-blooded? How would anyone know whether a feathered reptile was now a bird if one is/may be cold blooded and one is warm blooded? Where is the proof?

Same topic different question: We know that horses and donkeys can interbreed to produce a mule, which is sterile. Using this explanation for cross breeding, how does that fit with macroevolution? In other words, could a flying, feathered semi-reptile mate with a full bird (or any other combination), and not be sterile? Even over millions of years, since there would be no progeny and the variant would die.

Third question: If a reptile/bird evolved, wouldn’t it also need a reptile/bird to mate with to carry on the new species? If one, a male, for instance evolved, and no female evolved at the same time and in the same place, wouldn’t that end the cycle of macroevolution?

Thank you for your time.

Sincerely,

You see the difficulties, and it seems clear why the evolutionary biologists to whom he claims to have written haven’t bothered to reply. I see three main reasons.

First, while our correspondent claims to have no agenda, the general tenor and content of the questions suggests otherwise. While he may be telling the truth, the questions have a distinctly creationist flavor and over the years I’ve learned to be wary of such self-professed innocence. Like all who have been in this game for a couple of decades, I’ve seen it before too often. But we’ll go on anyway.

Second, a number of the specific questions are underlain by misconceptions about science in general and biology in particular that render them incoherent. In order to address the incoherent questions one would first have to address the underlying misconceptions. Most working evolutionary biologists don’t have that kind of spare time. (John Scalzi has some apposite remarks in a somewhat different context.)

Finally, to all appearances our correspondent has expended little effort to find answers for himself. An easy and obvious way of responding is by pointing the correspondent to some web resources. For example, there’s the Berkeley evolution site which is rich in resources for learning about evolution. Then there are search engines for the processional literature. For example, a search on Google Scholar for [birds dinosaurs evolution] produces 25,600 hits. Searching on [evolution endothermy birds] produces 4,860 hits. On the first page of each search there are several useful and trustworthy references. (I emphasize that these are Google Scholar searches, not plain Google searches.) And of course there’s PubMed, where both searches get some hits mostly having to do with genetic, metabolic, or molecular research.

Of course, the reader has to exercise some judgment in discriminating among the Google Scholar hits, and a long-time teacher like our correspondent should know that. But there’s no indication in his email that our correspondent has looked for answers on his own; he wants a working professional to take the time to spoon-feed him. I hope that in his teaching career he taught students do a better job of self-directed research than he’s done here.

I won’t attempt a comprehensive answer to the questions here. Doing so would require require tens of thousands of words, most of them devoted to clearing away the underbrush of misconceptions (“proof”?) and I prefer that our correspondent do some of his own work. Rather, I’ll address just a few of the misconceptions underlying the questions and provide some resources so he has a leg up on the work necessary to find answers if he’s as genuinely interested as he claims to be.

Consider the second and third sets of questions in the email. Our correspondent asks

Same topic different question: We know that horses and donkeys can interbreed to produce a mule, which is sterile. Using this explanation for cross breeding, how does that fit with macroevolution? In other words, could a flying, feathered semi-reptile mate with a full bird (or any other combination), and not be sterile? Even over millions of years, since there would be no progeny and the variant would die.

Third question: If a reptile/bird evolved, wouldn’t it also need a reptile/bird to mate with to carry on the new species? If one, a male, for instance evolved, and no female evolved at the same time and in the same place, wouldn’t that end the cycle of macroevolution?

Shades of Kirk Cameron and Ray Comfort and their crocoduck!. PZ Myers dealt with the ‘where’s the mate?’ topic a couple of years ago.

Those questions illustrate three common misconceptions. First, of course, they presuppose that speciation occurs only in giant steps–a ‘reptile’ morphed into a ‘reptile/bird’ and thence into a ‘bird’ in giant steps, and each new step is so different from its parents and siblings that it couldn’t breed with them. Second, they illustrate typological thinking, the notion that an individual must be a member of one or another crisp class and that there’s a chasm between the classes. Third, they illustrate a pervasive Inability to think in population terms. In general, populations evolve, not a single individual. Our correspondent uses the singular–“reptile” and “bird”–which masks the reality that (in the cases he cites, at least) it’s populations that evolve.

Let me expand just a bit in hopes that our correspondent reads this; I’ve notified him of this post.

For the most part, animal evolution occurs incrementally in populations

First, I ask our correspondent to consider this: Every generation of a sexually reproducing population is a member of the same species as its immediate parent generation, and yet after many generations–hundreds or thousands of generations or more–the last generation of the sequence of generations could be a different species than the first generation.

The correspondent’s questions imply that we must be able to classify one generation (or one individual member of a generation) as a new species, reproductively isolated from its immediate predecessor generation, somewhere along the line of those hundreds or thousands of generations, but that would be an arbitrary labeling decision and would not accurately map the continuity of evolution. It does not recognize the biological reality that the two generations, the parent generation and its immediate offspring generation, are not reproductively isolated–are not members of different species in the sense that the offspring generation surely could successfully interbreed with the immediate parent generation. An expert given the entire generational sequence from dinosaurs to birds would be utterly stumped in trying to find a sharp species boundary between any pair of succcessive generations, and that is precisely the point (this very appropriate formulation stolen from Andrea Bottaro of the Thumb). Natura non facit saltus, while not universally true, is a good rule of thumb in evolution, whether via natural selection or genetic drift. If our correspondent understands that he’ll be on his way to understanding why his questions make little sense.

Consider an obvious analogy. There was never a time when a child in an ancient Vulgar Latin-speaking population could not converse with its parents and siblings and peers in a mutually comprehensible language (teenagers’ slang aside!), yet over centuries/generations the (geographically dispersed) population of Vulgar Latin speakers incrementally diverged into separate populations of Italian speakers, French speakers, Spanish speakers, Portugese speakers, and speakers of dozens of other Romance languages. Today, after many centuries/generations, those languages are largely mutually incomprehensible (and many are extinct, along with–AFAIK–the original Vulgar Latin) yet there was never a time when a pair of Vulgar Latin-speaking parents suddenly produced a Latin/Spanish-speaking child unable to comprehend its parents’ or siblings’ language. Over centuries/generations the languages (populations) diverged until they became mutually incomprehensible (they ‘speciated’), but there was never a time when an offspring generation couldn’t speak with its parent generation.

About that giant-step speciation

In general, speciation occurs incrementally as two populations diverge over lots of time/generations. If a subpopulation becomes isolated from its parent population, say by some geological event, then over time/generations (via natural selection and/or processes like founder effects and genetic drift) the isolated subpopulation may incrementally diverge from the original parent population. If the isolation is extended, that incremental divergence can widen and may result in speciation in the sense that if the geological barrier is subsequently eliminated, the two populations will have become sufficiently different as to no longer successfully interbreed, and the subpopulation would then be classified as a new species (on the Biological Species Concept definition of “species”).

However, there are exceptions. Speciation may not necessarily require geological or geographic isolation. For example, sympatric speciation may be occurring in Rhagoletis pomenella right now in my backyard (I have both apple trees and haws there). See here for a recent genetic analysis of the two populations. The “races” (subspecies?) of R. pomenella are becoming reproductively isolated by their different hosts, and host-related behavioral and genetic changes are accompanying and producing that reproductive isolation, leading to incipient speciation. But for a contrary view see this recent paper for data that contradict the hypothesis that the host-shifting radiation of R. pomonella is due just to recent sympatry but rather is likely based on long-standing genetic variation generated allopatrically in the deeper past. So while the radiation of subpopulations in the (sexually reproducing) R. pomonella instance is recent, it may have deeper genetic roots produced by geological/geographic separation. For another candidate instance of sympatric speciation see here (PDF). (See also here; hat tip to Wesley Elsberry for flagging it to me.) I’ll also mention that in spite of our correspondent’s mule example, not all hybrids are sterile, and hybridization is one way speciation can occur.

But that’s a side issue. In some circumstances speciation can occur in a single step of a single individual offspring if the organism can reproduce itself without benefit of sexual interaction with other members of the species. That’s not uncommon in plants–polyploidy in self-fertilizing plants can give rise to a new species in one step of a single offspring–and (more rarely) it can happen in parthenogenic animals. A Google Scholar search on [polyploidy speciation] turns up 11,400 hits while a search on [parthenogenic speciation] gets 5,740 hits. Just last month I wrote a brief note on the rapid creation in the laboratory of a new species of parthenogenic whiptail lizard.

But no one argues that the evolution of birds from small carnivorous dinosaurs occurred in one step via polyploidy. It was an incremental process over many tens or hundreds of thousands of generations. A professional review by Kevin Padian (though a tiny bit dated) is here (PDF). It’s worth noting that the review addresses in passing our correspondent’s question about endothermy and fossils. For a fairly recent pop-science overview of the evolution of endothermy in general see here.

There’s much more that could be said, of course.

While our correspondent focuses exclusively on the fossil evidence for ‘macroevolution’ of birds from reptiles, the most powerful evidence for “macroevolution” is from comparative genetics and molecular biology, and a complete answer would require considerable expansion of that evidence. Fossils aren’t irrelevant, of course. Donald Prothero’s Evolution: What the Fossils Say and Why It Matters has a dozen pages in Chapter 12 on the evolution of birds. But there are other examples, too. Take, for instance, the evolution of mammals. So continuous is the fossil record of the transition from reptiles to mammals that we’re reduced (again!) to an almost arbitrary separation, with mammal-like reptiles on one side of the transition and reptile-like mammals on the other.

It’s disappointing to have to respond like this to one who has the academic credentials our correspondent claims. While I have not publicly identified the correspondent here, some research (well, single-digit seconds of Googling) found him, and judging from his writings elsewhere on the web he’s not quite as agenda-free as he claims. But never mind. Just some modest effort and the URL of Google Scholar would have provided him with the professional resources to address the questions, and the URLs of the Berkeley/NCSE evolution site or the TalkOrigins Archive would provide the background necessary for a lay person to understand the misconceptions underlying our correspondent’s questions. But that requires intellectual effort, and there’s no evidence that our correspondent has expended that effort. This post is over 2,000 words now and it barely scratches the surface of our correspondent’s misconceptions . I hope it’s enough to stimulate him to do his own research and thinking, but I have to say I’m not optimistic.

215 Comments

I did my own shot on this at:

http://www.vectorsite.net/taevo.html

If you like, pass that back to him, and he can give me feedback, which I would find interesting. Unless, of course, he just wants to play games, in which case I will immediately put a block on his email.

Well, whether you corespondent learned anything or not I enjoyed reading it, so thanks.

OK, after following up the link, I will just HAVE to read Scalzi’s OLD MAN’S WAR. I will buy it from Amazon and he will get the royalty. Even if I don’t like it, I owe him that much.

mrg said:

I did my own shot on this at:

http://www.vectorsite.net/taevo.html

If you like, pass that back to him, and he can give me feedback, which I would find interesting. Unless, of course, he just wants to play games, in which case I will immediately put a block on his email.

That’s a great resource. Thanks!

I’ve invited the questioner to this comment thread; we’ll see.

RBH said:

That’s a great resource. Thanks!

Why, thank you, though it does need some work – and nobody reads it. Google competition too great I should think.

My INTRODUCTION TO RADAR TECHNOLOGY, in contrast, top of the charts – which is really not all that surprising because there’s maybe three other competing documents on the internet, and they’re sketchy.

A distinction sort of like being the tallest building in Loveland, Colorado … which, to no surprise for those familiar with the Great Plains, is the crop silo.

Richard B. Hoppe Wrote:

Finally, to all appearances our correspondent has expended little effort to find answers for himself.

In the ~14 years that I have following the “debate” I have seen that odd behavior in everyone from the most committed geocentrist to the “pesudoskeptic” who claims to not accept “creationism” either (yet makes sure not to ask questions of it).

I caution that they often do scour the literature, only to give a “gotcha” to anyone who calls them clueless, and to mine data and quotes to spin more incredulity. Then when you ask them questions about their “theory” most refuse to answer any, and all eventually evade the questions. Many also demand links that they could easily find themselves - just as they found the person to “debate.”

mrg said:

OK, after following up the link, I will just HAVE to read Scalzi’s OLD MAN’S WAR. I will buy it from Amazon and he will get the royalty. Even if I don’t like it, I owe him that much.

Old Man’s War–read it: interesting premise. The sequels–don’t bother. He relies more and more on less and less believable deus ex machina plot devices.

Oh, and on topic, I wonder if the history teacher disputes that horses and donkeys share a common heritage. One must be a pretty hard-core creationist to insist that they’re separate “kinds,” yet they can no longer interbreed. How about Irish wolfhounds and teacup poodles? Is there anyone who doubts that they were bred from a common ancestor? Yet they’re morphologically so separated now that they can’t mate with each other. Artificial insemination? Possibly, if the dam is the wolfhound.

Just Bob said:

Old Man’s War–read it: interesting premise. The sequels–don’t bother. He relies more and more on less and less believable deus ex machina plot devices.

Ah, the story is maintained by an Intelligent Designer: “The scriptwriter did it!”

Here are my questions about macroevolution. My goal is to understand how scientists explain how macro-evolution works in a real life situation, in this case between reptiles evolving into birds, since this is postulated as occurring: *Reptiles Birds* Lay eggs lay eggs fly fly have feathers? have feathers cold blooded? warm blooded Would being cold blooded show up in the fossil record?

Possibly. Check out - i.e. google - the relationship between homeothermy/poikilothermy (warm- and cold-bloodedness) and body size, bone structure, anatomy, etc., etc. Keep in mind that the fossil record is incomplete; changes which could be seen in fossils might easily not be, by chance.

If not, how and why would a reptile adapt over millions of years into warm-blooded?

The “if not” is not a logical connection between the previous question and this one. Be that as it may, information about the potential fitness advantages of warm-bloodedness may also be easily googled (the “why”). Keep in mind that there are plenty of (presumably) well adapted cold-blooded species still extant. There’s no reason why reptilian ancestors of modern warm-blooded species would not, over millions of years, accumulate changes in their metabolism to allow them to become warm-blooded (and thus no longer reptiles) (the “how”).

How would anyone know whether a feathered reptile was now a bird if one is/may be cold blooded and one is warm blooded?

As Richard has explained in the post, the “now a bird” part of this question is often meaningless, or arbitrary (in the predominant cases where the changes such as those from cold-blooded to warm-blooded, scaled to feathered, etc. are gradual ones).

Where is the proof?

Proof of what? And bear in mind that science doesn’t deal in proof, but preponderance of evidence. The evidence is that there were feathered “reptiles”.

Same topic different question: We know that horses and donkeys can interbreed to produce a mule, which is sterile. Using this explanation for cross breeding,

This is not an “explanation” for “cross breeding”, as stated.

how does that fit with macroevolution?

Sterile offspring of interspecific matings do not lead to evolution. Or to macroevolution (however you may wish to define it). Except for the rare parthenogenetic or clonal species as Richard has pointed out. If mules could reproduce asexually - voila! macroevolution.

In other words, could a flying, feathered semi-reptile mate with a full bird (or any other combination), and not be sterile? Even over millions of years, since there would be no progeny and the variant would die.

Richard has dealt with this nicely.

Third question: If a reptile/bird evolved, wouldn’t it also need a reptile/bird to mate with to carry on the new species? If one, a male, for instance evolved, and no female evolved at the same time and in the same place, wouldn’t that end the cycle of macroevolution?

Again, Richard has answered this nicely. Reptile/birds did, of course evolve (that is, there were transitional forms between cold-blooded, non-feathered ancestors of birds and the extant warm-blooded feathered species). They mated nicely among their variable populations on their gradual evolutionary path. The cycle of macroevolution is … who knows what.

On a side note about the warm-blooded vs cold-blooded question - as I understand it, crocodiles are cold-blooded descendants of warm-blooded species. The evidence is that their bodies have equipment that makes sense for self-heating bodies but doesn’t make sense for bodies whose ancestors never had that feature.

Henry J said:

On a side note about the warm-blooded vs cold-blooded question - as I understand it, crocodiles are cold-blooded descendants of warm-blooded species. The evidence is that their bodies have equipment that makes sense for self-heating bodies but doesn’t make sense for bodies whose ancestors never had that feature.

I thought crocodilians are warmblooded, though, inefficiently warmblooded, what with them having diaphragms and relatively large bodies that retain body heat.

The best extant example of the connectedness of the generations between species are “ring species”. Ring species should be real clinchers to fence sitters of speciation.

The one problem I have is between chimps and humans. I can understand the ebb and flow of point mutations in a population, or other small “reversible” mutations. But that merging of chromosomes thing seems to me to be a real problem. That seems to me to be a unique, once in an eon event that is unlikely to be repeated.

I presume that, all other things being equal, having ones’ genes arranged in a different number of chromosomes might not be a problem for successful reproduction. I presume that the machinery of cellular reproduction is probably flexible enough to allow that, and to match up the necessary genes when needed. (I recall reading about living adults who don’t have the normal number of chromosomes, so it clearly can happen.)

Similarly, introns seem to be unique, one-off events which, from a naive perspective, would require a similar “match” in a sexual partner to successfully be passed on.

I presume that the spread in a population of both introns and any rearrangement of genes in chromosomes could be accounted for by “genetic drift”? Or “neutral drift”? (whatever the term is). Such unique yet non-fatal mutations could be passed on as recessive genes to succeeding generations, until they actually became useful.

Are those reasonable presumptions? Is that an approximately reasonable layman’s perspective?

Thanks.

I believe it was Robert Bakker who made a strong case for at least some dinosaurs being warm-blooded. And part of his case WAS fossil evidence–microscopic structure in dinosaur bone that looked more like the bone of warm-blooded animals than that of cold-blooded ones, IIRC.

Just Bob said:

I believe it was Robert Bakker who made a strong case for at least some dinosaurs being warm-blooded. And part of his case WAS fossil evidence–microscopic structure in dinosaur bone that looked more like the bone of warm-blooded animals than that of cold-blooded ones, IIRC.

No, it wasn’t Bakker - though he did publicize it and cited other evidence, such as comparisons of predator/prey ratios in dinosaurs with those of mammals - who originally made a strong case. It was his undergraduate mentor, John Ostrom, who did, having discovered Deinonychus in the mid 1960s (Based on his detailed examination of Deinonychus’s skeleton, Ostrom realized that he was dealing with a far more active dinosaur than what others had contended for decades.) and then, approximately a decade later, revived the dinosaur ancestry of birds hypothesis first proposed by Thomas Henry Huxley.

We know now that birds are highly derived coelurosaur dinosaurs (http://www.ucmp.berkeley.edu/diapsi[…]osauria.html) distantly related to gigantic “cousins” like Albertosaurus and Tyrannosaurus.

Scott F said:

The one problem I have is between chimps and humans. I can understand the ebb and flow of point mutations in a population, or other small “reversible” mutations. But that merging of chromosomes thing seems to me to be a real problem. That seems to me to be a unique, once in an eon event that is unlikely to be repeated.

It was most likely unique, ocurring in a single individual.

I presume that, all other things being equal, having ones’ genes arranged in a different number of chromosomes might not be a problem for successful reproduction. I presume that the machinery of cellular reproduction is probably flexible enough to allow that, and to match up the necessary genes when needed. (I recall reading about living adults who don’t have the normal number of chromosomes, so it clearly can happen.)

The type of rearrangement with Human Chromosome 2 is a special kind of Robertsonian translocation called a centric fusion. In mammals, centric fusions often have little or no effect on the fertility of the offspring of individuals whose chromosome numbers differ by that fusion. In humans, the negative effect of centric fusions on the fertility of heterozygotes is minimal, approximately 10%.

I presume that the spread in a population of both introns and any rearrangement of genes in chromosomes could be accounted for by “genetic drift”?

In the case of Human Chromosome 2, not entirely. It’s true that , all other things being equal, chromosome rearrangements whose heterozygote is selected against, even only mildly, can spread only via drift. However, in human females, fusions are preferentially passed to the eggs during oogenesis (a phenomenon known as ‘meiotic drive’), which offsets the selection against the heterozygote considerably.. In addition, populations that are subdivided into local breeding groups (called ‘demes’) increase the probability that the rearrangement will become fixed in one subpopulation. If there is a high level of local extinction and recolonization among these demes, the probability of the rearrangement spreading from the deme in which it has become fixed and eventually becoming fixed is enhanced. Paleoanthropological work has shown that the human lineage, for most of its history, possessed almost the ideal structure for the fixation of this kinmd of fusion.

Hope this helps.

I presume that the spread in a population of both introns and any rearrangement of genes in chromosomes could be accounted for by “genetic drift”? Or “neutral drift”? (whatever the term is). Such unique yet non-fatal mutations could be passed on as recessive genes to succeeding generations, until they actually became useful.

It might be drift, or it might be situated near other DNA that does have some advantage. Or for all I know, a rearrangement might sometimes be of some selective advantage; I wouldn’t assume that such can’t happen.

I was transferring some of my old laserdiscs to DVD the other night, in particular the four-part THE DINOSAURS! series made for PBS in the early ’90s. That’s where Bakker (if I remember right) made a popular-level presentation on dinosaur bone structure and the predator-prey ratio pointing to warm-bloodedness in dinosaurs. This might be what gets remembered, no matter who originally worked it out?

I’m not an anti-religionist, and have no anti-religionist agenda you understand, but I do have some questions which I should like the religionist community to address.

Now, the world is how old? And please, a little more evidence than a re-re-re-translated text would be welcome.

If fish were not the ancestors of amphibians, and these did not evolve into reptiles, birds and mammals, over hundreds of millions of years, what is your brilliant idea? (Please, remember, the Book has already been excluded as physical evidence, you need to do better.)

As I said, I have no axe to grind, I am merely interested in truth, hearing Both Sides, and letting the populace decide.

Mr Hoppe, did this coward add his name to this tripe, or like most religionists, did he/she/it hide behind annonimity?

Second, a number of the specific questions are underlain by misconceptions about science in general and biology in particular that render them incoherent. In order to address the incoherent questions one would first have to address the underlying misconceptions. Most working evolutionary biologists don’t have that kind of spare time. (John Scalzi has some apposite remarks in a somewhat different context.)

Reading Scalzi’s comments brought back memories from many years ago when some guy tracked me down and wanted some free advice on building a “free energy machine” of some sort. He said he had this idea and wanted me to explain how he should build it. (I guess most physicists get one of these characters from time to time.)

I told him it wouldn’t work; it really made him mad.

Why isn’t that person asking something honest, like how we know that birds evolved from non-bird reptiles?

I’m not certain that an agenda is being pursued by this individual, but it clearly follows the agenda of pseudoscientists.

Here’s a question: How are the fossil record, genetics, and morphology explained without evolution (“macroevolution” as IDiots call it)?

I’d like to see this purported retired history teacher fall for such BS if plagiarism were detected in a student’s work. The student can ask, “How do you account for the changes that you see between my work and what I supposedly copied? If you can’t explain the psychological and cognitive causes of the differences between the two, you haven’t shown derivation.”

Is anyone stupid enough to believe that? Then why are so many stupid enough to believe that if we don’t explain everything in evolution, derivation hasn’t been demonstrated (or for Behe, derivation has been shown by the predictions of evolution that he doesn’t actually accept as limitations)? Clearly because they’re unwilling to accept the obvious evidence, not because they’re really that dumb (well, not most of them).

And why would this person expect anyone to answer very basic misconceptions about evolution, like the Ray Comfort-type belief in the doctrine of a separate evolution of males and females?

Crack a book for once, or at least surf the web for answers, lazy unthinking person.

Glen Davidson

The idea that the chimp/human chromosones merged is fascinating, but can you explain this to the layman? I don’t understand Dave Whiskers comment re. a single individual, it seems like the creationist crocaduck.

Deklane said:

I was transferring some of my old laserdiscs to DVD the other night, in particular the four-part THE DINOSAURS! series made for PBS in the early ’90s. That’s where Bakker (if I remember right) made a popular-level presentation on dinosaur bone structure and the predator-prey ratio pointing to warm-bloodedness in dinosaurs. This might be what gets remembered, no matter who originally worked it out?

Maybe in the popular imagination, but it was John Ostrom who recognized that dinosaurs were far more active creatures - not the plodding, slow-moving variety depicted by artist Charles R. Knight or captured as such in countless Hollywood films from the 1920s until the early 1970s - based on his substantial examination of Deinonychus’s bones. This led him to look anew at Huxley’s dinosaur to bird hypothesis by examinating Archaeoptyerx, and concluding that it was a coelurosaur dinosaur.

I don’t deny that Bakker did much to promote the renaissance in dinosaur paleobiology - both in the public imagination and in science (part of the reason too was that Bakker was - and still is - a great artist as well a writer) - but there are others who have made more important contributions, not the least of which was his Yale University undergraduate professor of vertebrate paleontology, John Ostrom.

John Kwok said:

Deklane said:

I was transferring some of my old laserdiscs to DVD the other night, in particular the four-part THE DINOSAURS! series made for PBS in the early ’90s. That’s where Bakker (if I remember right) made a popular-level presentation on dinosaur bone structure and the predator-prey ratio pointing to warm-bloodedness in dinosaurs. This might be what gets remembered, no matter who originally worked it out?

Maybe in the popular imagination, but it was John Ostrom who recognized that dinosaurs were far more active creatures - not the plodding, slow-moving variety depicted by artist Charles R. Knight or captured as such in countless Hollywood films from the 1920s until the early 1970s - based on his substantial examination of Deinonychus’s bones. This led him to look anew at Huxley’s dinosaur to bird hypothesis by examinating Archaeoptyerx, and concluding that it was a coelurosaur dinosaur.

I don’t deny that Bakker did much to promote the renaissance in dinosaur paleobiology - both in the public imagination and in science (part of the reason too was that Bakker was - and still is - a great artist as well a writer) - but there are others who have made more important contributions, not the least of which was his Yale University undergraduate professor of vertebrate paleontology, John Ostrom.

Deklane, as a postscript, I’m not sure if dinosaur bone structure is still regarded as a key indicator of endothermy (Hopefully someone who has a more substantial background in vertebrate paleobiology than yours truly, will chime in.).

Please note that in lieu of “examinating” I meant to say examining.

cronk,

cronk said:

The idea that the chimp/human chromosones merged is fascinating, but can you explain this to the layman? I don’t understand Dave Whiskers comment re. a single individual, it seems like the creationist crocaduck.

Sorry about that, but frankly, it’s not a subject easy to condense into a single comment, let alone make comprehensible to a layman. It involves two highly technical disciplines, cytogenetics and population genetics, both of which have their own arcane terminology. But let me summarize with as little technical detail as possible.

The fusion that resulted in Human Chromosome 2 (HC2) involved two chromosomes breaking at their extreme ends(in an area known as the telomeres) and joining together, end-to end, with the little end fragments being lost. The telomeric regions don’t contain any genes, so this particular fusion did not result in any potentially fatal or detrimental loss of genomic information.

Fusions are a fairly common chromosomal mutation, but end-to-end fusions like this are very rare. So this fusion probably occurred only once, in a single individual’s egg or sperm. When that individual mated, one of its offspring was a hybrid, or heterozygote for the fusion (instead of having 46 or 48 chromosomes, it had 47).

Now, many types of chromosome rearrangements have a problem in heterozygotes when it comes time for them to produce gametes (eggs or sperm), because the chromosomes cannot pair up properly during meiosis. They have to contort themselves into odd configurations, and this often prevents the proper number of chromosomes making it into the gametes, and also can result in losses of genetic material during recombination.

Typically, heterozygotes for rearrangements can be expected to be semisterile, i.e., suffering a 50% loss of fertility. In evolutionary terms, these heterozygotes suffer a significant loss of fitness, and, under normal circumstances, are not expected to spread and become fixed in a population (fixed means every individual in the population has the mutation). But the fusion that resulted in HC2 is different: because the breaks occurred at the extreme ends of the original chromosomes, when it comes time for the chromosomes to pair up in the heterozygotes during meiosis, the one fused chromosome and the two individual chromosomes can pair up fairly easily without (much) contorting.

There is still some effect on fertility, though: studies on the fertility of human heterozygotes for centric fusions in general (not just ones like HC2) show a fertility loss of about 10% at the most. So, in order to spread throughout the population, HC2 had to overcome selection against the heterozygote, at least in the early generations of fixation

This is often difficult for laymen to grasp—it seems counterintuitive. After all, shouldn’t natural selection have eliminated the fusion from the population? And yet, it became fixed in the human population despite that! The fixation of chromosome rearrangements which are selected against as heterozygotes is a classic problem in population genetics, because there are many examples of rearrangements becoming fixed in lineages of numerous organisms. It has fascinated population geneticists like Sewall Wright, Russell Lande, and Phil Hedrick who have shown the conditions under which the fixation can take place. But I’ll stop here. Does this make at least some sense so far?

Actually, it wasn’t until I read the first chapter of Dawkins’s *Greatest Show on Earth* that I understood this, and I would recommend this reading to most laypeople. Dawkins writes about the tendency/desire of people to put things into pigeonholes and discrete categories (he cites this as a version of Platonism) and about the unfortunate (?) reality of biology that things are not easily put into such discrete categories. The argument there is very good. And it is the problem with this guy’s argument.

(I would add that after reading this I understood why I had decided to go into math, where things can, except at the base level of foundations, be put into discrete categories.)

Mike Elzinga said: I told him it wouldn’t work; it really made him mad.

“What’s your honest opinion on this?”

“Won’t work.”

“ … OK, then give me your dishonest opinion instead.”

Dave Wisker said:

But I’ll stop here. Does this make at least some sense so far?

Forgive minor sniping at what is clearly an expression of good sense, but it would make more sense with paragraph breaks.

Dave Wisker Wrote:

Hope this helps.

Thanks, it does. While the chromosome fusion itself is dramatic evidence of common ancestry (unless one plays the game that the alternative is “I don’t know”), the “how” is hard to explain, even to many of us with a background in science.

If I may stray a bit more from the topic, this example will always remind me of a Ken Miller talk I saw in 2009. The audience of several hundred included many college science majors and others well-versed in evolution. So it was far from representative of the general population. I was shocked that only ~1/4 of them raised their hand when Miller asked if they were aware of this example!

Dave Wisker -

Thanks very much for your excellent comments about human chromosome 2.

Moving on, I can’t help responding to some of the questions from the original post.

Would being cold blooded show up in the fossil record?

We can’t measure the body temperature of a long dead organism, but the reasonable answer here is “yes, to fair degree of certainty, in many cases”.

We have many examples of poikilotherms and homeotherms living on the earth right now. Furthermore, the level of efficiency of homeothermy is variable. We humans have evolved such that we can, and need to, maintain a very regulated internal temperature, but some animals regulate somewhat, but to a lesser degree.

So of course, by extension from what we see in living animals, we can determine whether or not a fossil is from a homeotherm or poikilotherm to varying degrees of accuracy. After all, you’d have to be quite unreasonable to deny that the fossilized remains of a bear are from a homeotherm, or that the fossilized remains of a frog are from a poikilotherm.

In the case of some extinct, transitional lineages, it may not be easy to say, and indeed, they may not have fit neatly into either category.

If not, how and why would a reptile adapt over millions of years into warm-blooded?

What do you mean by “if not”?

Anyway, moving on to the question - no individual reptile could ever possibly live for millions of years. The scenario you describe is impossible.

Of course, what does happen is that reptiles reproduce. When they reproduce, they have descendants. Their descendants always vary slightly relative to the parents. Some of the variation is due to environmental factors, but some is due to genomic variation impacting on phenotype.

Some phenotypes maybe selected for or selected against, and if this happens, alleles associated with those phenotypes will increase in the population. Also, some alleles may spread through the population via genetic drift, depending on various factors. At various points, some descendants may branch off into new lineages via a gradual process of genetic isolation from the rest of the population.

Via this process, known as “evolution”, it is easy to see that traits associated with incrementally more regulation of internal temperature might emerge and be selected for. In addition, it is easy to note that possession of one such trait might predispose toward the positive selection for a second related trait.

How would anyone know whether a feathered reptile was now a bird if one is/may be cold blooded and one is warm blooded? Where is the proof?

This question shows a gross misunderstanding of biology.

Imagine if I’m trying to go from AA to BB and I can only change one letter at a time. AA - AB - BB. Now, the left end of this sequence is clearly a pure example of “AA”, and the right end is unequivocally an example of “BB”. Now imagine that I erase the entity in the middle. AA and BB are clearly distinct from one another. But in fact, there was a transitional step (one, in this very simplified model). There is no need to conjecture that “an AA suddenly gave birth to a BB”.

It’s arbitrary where we draw the line between feathered reptiles and birds, and many people, including me, like to refer to birds as dinosaurs, which is entirely justifiable.

There are no examples of difficult-to-classify feathered animals now; as far as I know all feathered animals alive today are clearly birds. But in the past there were animals which had some traits of modern birds and some traits of reptiles that modern birds don’t share, and at least some of those were the ancestors of modern birds.

Same topic different question: We know that horses and donkeys can interbreed to produce a mule, which is sterile. Using this explanation for cross breeding, how does that fit with macroevolution?

Horses and donkeys share very recent common ancestry. That’s why they have such similar traits and can and will interbreed and produce viable offspring. However, the lineages have diverged sufficiently that they seldom produce fertile offspring.

What happened is that, in the “recent” (by evolutionary standards) past, wild horse ancestors and wild ass ancestors became genetically isolated from each other. However, before they had diverged massively, humans came along and domesticated each species (originally a different human culture for each).

Truly wild horses are now exceedingly rare http://en.wikipedia.org/wiki/Wild_horse (mustangs and the like are feral domestic horses), and so are wild asses http://en.wikipedia.org/wiki/African_Wild_Ass, and they live in different environments. Whether they might mate with each other if they happened across each other is unknown. However, the production of mules on a large scale is a purely human invention.

In other words, could a flying, feathered semi-reptile mate with a full bird (or any other combination), and not be sterile?

It is highly unlikely that ancient transitional species would theoretically be able to mate with modern birds.

Of course, no-one proposes such a thing.

What happened is that some reptiles with some bird-like traits could easily mate with some reptiles with incrementally more bird-like traits, for many iterations.

Third question: If a reptile/bird evolved, wouldn’t it also need a reptile/bird to mate with to carry on the new species?

Again, at the level of an individual expressing an incremental phenotypic adaptation due to incremental allelic variation, there is no reason to conjecture that such an individual could not mate with other members of the population.

If one, a male, for instance evolved, and no female evolved at the same time and in the same place, wouldn’t that end the cycle of macroevolution?

No. Individuals do not “evolve”. Populations evolve. It is absurd to argue that every individual with an incremental phenotypic adaptation that could be selected for is sterile within its population.

Just Bob said:

Question for the biologists: How frequent are mutations that are NOT the result of outside influences (chemicals, radiation, etc.)? Are there some organisms that are more prone to such purely “intramural” mutations than other critters?

The frequency varies, and for different reasons. Areas of the genome with extensive repeats (microsatellites, for example) are more prone to inserts and deletions than other areas. Chromosome rearrangement mutations involve chromosome breakage, and breaks tend to occur more often in areas with repeats. So some areas of the genome are mutational “hotspots”, while others are not. In humans, I think I read that the mutation rate for chromosome rearrangements is 10^-3 to 10^-4 per gamete. DNA Polymerase, the enzyme that replicates DNA is not 100% accurate and makes spontaneous errors, as do the DNA proofreading processes. In the bacterium E.coli the overall error rate for DNA replication is something like 10^-10 nucleotides per replication. The rate is similar in eukaryotes (like fruit flies and mammals), I think. There may be species-to-species differences, but I can’t think of any off the top of my head.

Dave Wisker said:

For example, consider a population of 50 individuals, 25 of whom are homozygous at a locus for allele A and 25 homozygous for a variant allele a. The frequency of A is thus 50%. Now, one day an A individual accidentally walks off a cliff in the dark. There are now 24 individuals homozygous for A and 25 homozygous for a. The frequency of A has now dropped to ~ 49%, and A’s frequency has increased for a reason that has nothing to do with the differential reproductive capacity of the allele a over A. Evolution has occurred in the population with respect to A and a without being due to natural selection.

Surely you can only make that assertion if you know the allele does not predispose an individual carrying it to nocturnal perambulation! :)

Dave Lovell said:

Surely you can only make that assertion if you know the allele does not predispose an individual carrying it to nocturnal perambulation! :)

I think that was the idea, yes ;)

Off topic I know, and a dead off topic too, but,

mrg

Not always. The DH Mosquito didn’t have “handed” engines. The P-38 Lightning did … one of the consequences of this was that if it lost an engine on takeoff, a pilot who didn’t know how to react was likely to try to compensate by revving up the live engine, which would flip the aircraft over on its back.

Another solution to the problem of engine torque that is near and dear to me is the twin tandem-tractor/pusher (or fore and aft) engine layout. This layout is rare and only one aircraft could be regarded as having been genuinely successful in service production with it.

mrg,

You may enjoy this study.

http://www.me.wustl.edu/~aiaa/AIAA_[…]ov_85x11.pdf

dornier.pfeil said: This layout is rare and only one aircraft could be regarded as having been genuinely successful in service production with it.

Oh yes, the Skymaster is very interesting. When I was down at Fort Hood in the 1970s I’d see one on occasion circling over the range area during exercises; moments later a strike fighter would pounce on some position spotted by the air controllers.

I’ve got a prototype document for my Air Vectors page on German twin-engine fighters: Bf-110, the dreadful Me-210, Me-410, Hornisse, and Do-335. Don’t know when I’ll complete it. END OT.

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This page contains a single entry by Richard B. Hoppe published on June 10, 2011 3:52 PM.

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