Posted: Dec 16, 2010 9:32 am
by Darwinsbulldog
My quick and dirty attempt. :-

“Hopeful Monsters” and “Living Fossils”

Creationist skepticism about evolution often revolves around macroevolution. Saltations, they claim, have a divine significance. The diversity and disparity of forms and kinds are the work of some creator-designer, for no natural mechanism is credible in their eyes.

Before we proceed, let us define evolution from Freeman & Herron (2007:p.800) :-

“Originally defined as descent with modification, or change in the characteristics of populations over time. Currently defined as changes in allele frequencies over time.”

Well, that is straight-forward enough. Evolutionists talk about “innovation”, but the creationists ask “Where does this innovation come from? “ Where does the information come from?” “Who was the designer of this complex life?”

“How then, can “living fossils” exist?”. Let us try to argue the creationist case. So-called “living fossils” are extant creatures that have very similar-looking ancestors in the past. The morphology does not seem to change all that much. But in a stable environment [like the sea], why do they need to change radically? A morphology that works does not need changing. Are living fossils defying evolution? Well, no, they are not. Their morphology does not change much, but what of their biochemistry or physiology? That is pretty difficult to find out from an extinct species of Coelacanth. The modern definition of evolution is not violated either, because we do not know if modern Coelacanths have the same genome as extinct ones. It seems unlikely that they would. Natural selection can only do so much, and even good genes can disappear over time. Genetic drift makes this inevitable. But where is it written in stone that a different DNA sequence cannot produce a similar morphology? “Not uncommon” and “common” differ in length by five letters, and yet the meaning is pretty much the same. Convergence of form in similar environments does not demand a convergence in genotype. So in this case, a large change of genome results in a small change in morphology.

What then of the opposite case? That of the “hopeful monster”. Some radical change in morphology would surely demand a large genetic change? Not necessarily. Innovation in evolution may take many steps [all of whom must be beneficial] for a large change in morphology. The vertebrate of cephalopod eye, the wing of a bird or bat. But are all such innovations done in tiny steps?

What of the turtle? This looks like a pretty radical re-design to me? Can natural selection handle this sort of radical departure? What would the genetic changes look like? A [supposedly] radical re-design would require natural selection to re-write the code, and make many changes all at once?

Well, actually no. Most vertebrates have their scapulars [shoulder blades] outside their ribs, and in turtles the shoulder girdles are inside their rib cage! One can see our god puzzling over this one. But he is a smart dude. Well, sometimes he is very smart, but the Recurrent Pharyngeal Nerve just caught him on a bad day??
But what of this evil evolutionist doctrine of natural selection? Can it redesign the turtle? Oh yes it can. Dumb as bricks, and it can do it with only a couple of changes! Normally, the genes responsible for ribs program the outer part of the rib primordia to grow much faster on the outside than the inside. [Actually as cartridge, but let's not quibble, the bone comes later]. The result of this “rib tissue” growing faster on the outside it that the left and right ribs grow towards each other, and often meet at the sternum, thus forming the familiar rib cage.
Now what happens if the relative timing is tweaked? Make both the inner and outer sides of the rib grow at more like the same rate. The result? The ribs grow more or less horizontally from the spinal column. The effect of that is that the shoulder blades can end up on the inside of the ribs, instead of the outside. All is required is that the outer rib tissue grow a little more slowly, or the inner rib tissue grows just a bit faster. After that, it is just a case of tweaking-dotting the “I's” and crossing the “T's”. You have a viable hopeful monster. From a tiny bit of developmental timing. This is no Michelangelo at the Sistine Chapel; this is a tiny heterochronic change. Well within the ability of a random change in a Hox gene. Dumb as horse shit. If this new developmental tweak works, then hey presto, natural selection will give it the nod. And as well know, it did. Granted, it is a bit weird-looking. But now, I hope you can see, not the stuff where one would have to invoke gods, or call on the design services of a Leonardo DaVinci.

But so far I have just given you a “just so” story. I can't do much about our living fossil, but what of our weird hopeful monster, the humble turtle?

Turtles and tortoises belong to the Order Celonia. “The two main components of the shell are the dorsal the dorsal carapace and the ventral plastron.” (Carroll, et.al. 2005: p.180). Two genes, Fgf10 and Msx [which are normally associated with limb bud growth are involved seem to have been co-opted into the development of the ribs. The structure in the turtle embryo is called the carapacial ridge. That's it really. Not hundreds or thousands of new genes required to make this huge innovation happen. Just a case of a couple of limb patterning genes getting mixed up in the formation of the ribs bud growth. A couple of pathways got their wires crossed a little, causing ribs to grow straight instead of curved. Of course, god could have done it. But so could have natural selection. I don't see why we have to invoke god here. Dumb old natural selection did it again. Turtle carapaces are no more mysterious than eyes or wings. A hopeful monster triumphs again, and does it on a shoestring of a couple of genes that got a little “lost”. Science is about methodological naturalism. It works. Hopeful monsters do not triumph that often, but this one did. No magic involved, as far as anyone can tell.

So what have we learned? Neither living fossils nor hopeful monsters seem to violate natural law. Living fossils don't change much, and as far as we know, but can still evolve [change over time] genetically. Hopeful monsters can adapt a new bauplan, a radical departure in “design” with couple of genes that got a bit lost, causing a change in rib geometry that left the shoulder blades inside, rather than on the outside. And the designer? Natural selection I would warrant. Assigning god as the causative agent to design the wing of a peregrine falcon sounds real grand. But then you also have to credit him with the recurrent pharyngeal nerve fiasco and piles in your bottom. Nor does the weird and hopeful monsters like turtles and platypus do you much good either. Because they are not all that hard to build. Not really. No forethought, no design. Just replicators such as genes reproducing like mad, making a few errors, and the natural filter of natural selection does the rest. And time. Information does not come from some magic man, it comes from the environment. Badly copied genes trip over the “right” solution. They don't even know what they are doing. They are just polymers of deoxyribose nucleic acid, for goodness’s sake. And thank goodness for that. I understand that the illusion of design is strong. The wonder of it all is immense. Creationists, I know you want to give thanks to something. I do too. But credit where it is due. Unless you can give me some real evidence of your celestial watchmaker, I am going to give good old Mother Nature the credit. She is called Natural Selection. Is it not time you did the same?

REFERENCES:-

Carroll, S. B. (2005). "FROM DNA TO DIVERSITY: Molecular Genetics and The Evolution Of Animal Design". Oxford, Blackwell.

FREEMAN, S. and J. C. Herron (2007). "EVOLUTIONARY ANALYSIS". New Jersey, Pearson, Prentice-Hall.

FURTHER READING:-

http://en.wikipedia.org/wiki/Coelacanth

http://www.sciencemag.org/content/325/5 ... ce.1173826

http://en.wikipedia.org/wiki/Hopeful_Monster

http://en.wikipedia.org/wiki/Living_fossil

http://www.pbs.org/wgbh/evolution/index.html