First things first....for all his criticisms, Mr. McLatchie did concede one point in favor of my earlier essay, which was that I had demonstrated small changes over time in a satisfactory manner:
Tim gives us one or two other uncontested examples of the occurrence of natural selection in the wild, reminding us that “[Evolution] is about divergence, not progression. To ‘evolve’ does not mean ‘to get stronger’ or ‘to get better,’ or to ‘improve’. It simply means to ‘change.’” Well, no one is going to dispute that living species change over time, or even that this change is, in part, facilitated by natural selection.
So I will consider my introductory point "made" and will not waste any more time on it. Alright! Moving on...
EVOLUTION AND EMBRYOLOGY
...with regard to the change in "body types" being unlikely: yes, in a single generation, or in even several successive generations, a population is very, very, very unlikely to exhibit any major changes to its morphological arrangement --- limb placement, the addition or subtraction of major features (such as a tail, limb, eye, or fin), and so on --- but that is not what happens. The "mutations" which Mr. McLatchie refers to as "unlikely to be beneficial" during embryonic development are, of course, generally not responsible for the major morphological changes observed in evolution! There is very little, if any, real "body plan mutation" -- in fact, there is much debate over whether such a scaled mutation is even possible. Dr. Richard Dawkins goes into the various sides of this debate in his book, The Blind Watchmaker, detailing the "mutationists" (who believe that mutations are somehow naturally inclined toward "beneficiality" or "directional evolution") and the "Darwinian evolutionists" (his own school, which holds that (A) mutations are introduced basically at random, not in any sense "directional" or otherwise biased towards improvement, and (B) the process of embryonic development may "restrict" certain kinds of change such that they are basically impossible --- such as wings growing on the backs of organisms in the human lineage, something which has never been observed in the fossil record). Any such sudden, large-scale mutation --- even assuming it were possible --- occurring in a single generation would be so large that it would be, as Mr. McLatchie indicates, very, very unlikely to be beneficial, and would be significantly more likely to inhibit or outright kill the fledgeling organism. But of course, that is not the type of mutation we are addressing when we refer to "macroevolution."
No....as I said before, "macroevolution" (as creationists describe it) is literally just "microevolution," "stacked" upon itself and extended over a long period of time; but more importantly, when macroevolutionary changes (as scientists describe them) occur, they occur on the same level as microevolutionary changes --- they do not suddenly appear as massive mutations, they represent a "milestone point" of sorts wherein the "new" species is "officially" no longer able to interbreed with the "parent" or "ancestor" species, due often to a simple, small mutation that was preceded by many other small mutations. An example of this would be if a particular population of a certain species had mutated sex cells that prevented them from forming offspring with members of other populations of that species; we would then say that this population was "speciated" from all other populations.
Argue that "macroevolution" doesn't occur, fine; but to deny that they are the same process, differing only on a scale of time and succession, renders this discussion impossible, because that's what scientists are talking about when they say "macroevolution." That's the only way macroevolution can happen, is through the lens of microevolution. If you deny this simple fact, then at the risk of being forward I must say that we are no longer talking about the same concept. And so it is this conjoined concept that I will be addressing henceforth.
MACRO-EVOLUTION: MICRO-EVOLUTION TIMES A MILLION
With that considered....almost any "microevolutionary" mutation is, in theory, possible --- which is to say, a reptile's claws may change in size from generation to generation, and if the change proves beneficial, this mutation may be preserved. Or, a bird's feathers may change ever-so-slightly in size or color or length. This change is "microevolutionary," indeed --- too small to justify claims of speciation in any short number of generations. However, this change is also cumulative, and this much can (and has) been demonstrated before, in cases such as Darwin's finches, the Endler guppy experiments, and the aforementioned Pod Mrcaru lizards, all of which are denied by evolution-deniers (and yet for reasons that are inconsistent with the Darwinian understanding of evolution). Each of those examples demonstrated cumulative evolutionary changes --- small increases, "stacked" upon one another to create greater changes to specific features. If bigger heads improve surivival in a population, than any increase in head size will likely be preserved (because the conditions necessary for survival will lead to nature unconsciously "embracing" traits which, to whatever degree, cause an organism to become more suited to those conditions), thus these adaptations will "stack" to result in a much larger net increase in head size across many generations, leaving the descendants with noticeably larger heads than the ancestors. And at no point does this change suddenly cease to be possible; it's a matter of the degree of change, not the type of change.
But again, all those are small, "microevolutionary" changes. Think of this, however: we can prove, easily, that small change is possible. And small changes are cumulative. Therefore, if they accumulate, we will see a much greater change overall than that exhibited by single mutations in short generational distances. It is by this method --- slow, gradual change, not sudden, rapid, powerful mutation --- that we see major changes in an organism's morphology. So the "dilemma," as Mr. McLatchie has painted it, is not in fact a dilemma at all; he seems to be mistaken about the very method by which gradual change accumulates. In fact, he seems to imply that there is a point at which this change ceases to be cumulative --- that a beak can change in size, or a foot can change in size, but not both; that an eye can become more or less potent, or legs can become shorter and more powerful or longer and more limber, but not both. This is false. Small changes --- wherever they occur on the body --- are cumulative, because genetics are cumulative. They start with the same embryonic blueprint, and genes add and alter additional features --- this is one way that we can detect the "trail" of evolution through the study of DNA relations between species. Thus, if small changes to individual regions of the body are possible, it logically and demonstrably follows that large chains of change can gradually accumulate which appear to affect entire regions of the body, or even the entire body itself. This is yet without even considering literal examples in which this happens --- we can arrive at this conclusion based on reasoning (and the fact of microevolution) alone.
EXAMPLES OF MICRO- AND MACRO-EVOLUTION
Speaking of literal examples....there are three somewhat famous examples which Mr. McLatchie seems wholly unaware of. At the very least I find it odd that he did not address them, even if only to try and discount them:
-) The Oenothero gigas (follow the link, then C+F "O. gigas"), a form of evening primrose, was successfully artificially speciated from the evening primrose, such that it can successfully breed with others of its kind but it cannot breed with the original species from which it was speciated.
-) Manatees (follow the link, then C+F "manatee"), in a display of common kinship with land mammals, have elephant toenails on their flippers, as well as an internal skeleton that is completely homologous to humans and other terrestrial tetrapods; it contains rudimentary pelvic bones (especially odd for a creature that supposedly has, neither currently or historically, the need of a pelvic region nor a relation to any organism that does have one), yet no hind limbs.
-) Apes and humans have been famously connected by the study of genetics; in human DNA, there is a strand which is exactly identical to two specific segments of an ape's DNA. It appears to have been formed from two chromosomes that joined together at some point during our ancestry; this is made more readily apparent by the presence of two telomeres connecting together in the center of the strand --- normally, telomeres are only present at the end of a strand, but this particular strand is the length of two telomeres, indicating that they were likely two separate strands that had been joined together to form a single strand with an elongated telomere at the center.
SPECIATION THROUGH MACRO-EVOLUTION
One means by which a population can be speciated into two species (as in the above cases) is by mutation of the receptor-ligand complex that directs sperm to fuse with the egg; this is a "microevolutionary" step (a small mutation) leading to a "macroevolutionary" event (the differentiation of species). This also, interestingly, appears to be an example of so-called "irreducible complexity" -- none of the sperm will be able to fertilize the egg if the ligand on it (the egg) mutates, nor will they be able to fuse with the egg if their (the sperm's) receptor changes, and the chance that both will mutate simultaneously is not really worth considering. Thus, the populations with mutations rendering each other incompatible become "separate species," and the ones whose mutations match up become speciated thusly.
On a side note, speaking further of "microevolution vs. macroevolution"....interestingly, Answers In Genesis (a Creationist website which works to provide cue-card arguments for would-be hack debaters) includes this very argument as #2 on a list of "Arguments that should be avoided (because further research is still needed, new research has invalided aspects of it, or biblical implications may discount it)." From AiG:
Arguments that should be avoided (because further research is still needed, new research has invalided aspects of it, or biblical implications may discount it)
1. Evolution is just a theory. (“Theory” has a stronger meaning in scientific fields than in general usage; it is better to say that evolution is just a hypothesis or one model to explain the untestable past.)
2. Microevolution is true but not macroevolution. (People usually mean that we see changes within a kind but not between kinds; however, the important distinction is that we observe changes that do not increase the genetic information in an organism.)
Even their correction is wrong, however, because we do observe changes that do increase the genetic information in an organism. A single gene can "accidentally" reproduce itself twice, creating an extra copy, which then mutates separately from the original in future generations. This results in "new information" in the genome that did not exist before the original mutation. One example of this (with which I'm sure Mr. McLatchie is familiar) is the hemoglobin of a human adult; without going into too much detail (again, Richard Dawkins has written about this one in The Blind Watchmaker, and about which he has also written about extensively elsewhere), there is evidence that the four protein chains in current human adult globins actually originated from an ancestor genome which "split" around 500,000,000 years ago into two parts; each part then later mutated separately and became a different cluster. This happened again around 400,000,000 years ago, and the alpha gene mutated again, following a similar path and giving us the zeta chain. This much is actually supported by contemporary phylogenetic analysis, as well --- other animals descended from those who existed around the time of the genome split (and which were associated with our ancestral line) also demonstrate this same split, and the same chromosomal arrangement of these genomes.
Gene duplications are not the only way to produce new information, however --- we also have events such as nucleotide insertions, as well as (possibly) viral manipulation. Basically, though, there are a multitude of ways to increase information in the genome through error or mutation.
IRREDUCIBLE COMPLEXITY AND "INTELLIGENT DESIGN" CREATIONISM
Moving on to some of Mr. McLatchie's links, though, I'm curious about this statement (from a link provided by Mr. McLatchie to one of his own blog entries, "colliding with the pharyngula"):
At best, all his case demonstrated was common ancestry -- a proposition which is perfectly compatible with intelligent design.....I have to say, I don't quite understand how he can say that common ancestry is "perfectly compatible" with intelligent design, yet without major evolutionary change. What he calls "macroevolution" is commonly understood to be the primary vehicle for common ancestry! If common ancestry is demonstrable, but not by evolution, then by what method does he mean to imply that all life on earth evolved from a common ancestor? It seems mutually exclusive to say that all life we see today, in all its magnificent diversity, could have come from a common ancestor *without* major evolutionary change along the way. I'm interested in his explanation for this.
With regard to his "rebutall" of the popular rebuttal of Michael Behe's T3SS/bacterial flagellum argument....I'd like to refer to a couple of things: first, a study performed by students of the Department of Biology at the University of California at San Diego:
"[H]omologous flagellar proteins show phylogenetic clustering that suggests that the flagellar systems and Type III protein secretory systems diverged from each other following very early duplication of a gene cluster sharing many (but not all) genes. Phylogenies of most or all of the flagellar proteins follow those of the source organisms with little or no lateral gene transfer suggesting that homologous flagellar proteins are true orthologues. We suggest that the flagellar apparatus was the evolutionary precursor of Type III protein secretion systems."
--Phylogenetic analyses of the constituents of Type III protein secretion systems (Nguyen L, Paulsen IT, Tchieu J, Hueck CJ, Saier MH Jr.)What the consensus tells us is that the flagellum and the T3SS probably each had an early precursor from which they diverged, which shared many (but not all) of the necessary genes to express the complete flagellum. As luck would have it, in his report (published in 2003 at Talkdesign.org), one Mr. N.J. Matzke lays out the following model of the evolution of the flagellum --- the method by which the flagellum moved from an early, primitive state to the so-called "irreducibly complex" flagellum we see today. Also take note, each of these steps involves the modification of only a single protein:
-) A simple passive pore exists within the membrane of a single bacterium, which allows movement of proteins into the periplasm;
-) the association of a second protein makes the pore selective, allowing only specific proteins into the periplasm;
-) The F1F0 ATP Synthase associates with the pore, imparting active transport (Type III Export Apparatus);
-) Secretins and proteins, also ancestral to the flagellum, allow protein movement out of the cell. Association of a Secretin with the Type III Export Apparatus gives us the Type III Secretion Apparatus, which moves proteins from the cytoplasm to the extracellular environment;
-) An adhesive protein attempts to secrete, but becomes bound; repeating this process, proteins polymerize to form a pilus; as the pilus grows in length, the chance of finding a substrate to attach to increases;
-) Attachment of the pilus to the inner membrane increases its strength;
-) Wear/tear bends the pilus, allowing it to wiggle and thus further increasing the chance of finding a substrate;
-) The Tol-Pal system (which transports protons across a membrane) associates with the pilus, causing it to spin haphazardly, but thus allowing bacteria to escape crowded environments when nutrients are low;
-) Modification of the secretin releases any attachment between the former pilus and outer membrane; the remainder of the secretin becomes the P-ring, the former "chaperone' is modified into the F-ring --- both rings serve to stabilize the filament, allowing it to rotate freely;
-) Signal transduction proteins bind the proto-flagellum, linking its function to the state of the environment, thus forming a chemotactic flagellum.
For more of my thoughts on "irreducible complexity" and "specified complexity," you can go here. That's all I'm going to say about it in this article, though.
This is not a subject that's very easy to argue about; for one, the body of evidence that supports evolution is MASSIVE as it spans many topics (from biology to geology to geography to archeology to even astronomy). No matter where I choose to end this article, I'm going to feel like I still have much to say about evolution. But that's how these discussions work; no one person can hope to raise or rebut every possible argument for or against their position. I can only do my best to respond to the points made against me which I feel to be the most relevant and worth responding to. If I have failed to address anything very important, then feel free to leave a comment or snide remark or whatever below. Let it be known that I don't delete comments or anything, so have no fear of your argument being covered up. Although I reserve the right to ignore you or be a smartass if you try to pose as a "gotcha question" something which I have already addressed at length. Ask whatever you please but please don't waste my time! Thanks.