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Darwin Strikes Back (of molecules and men)

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Proponents of Intelligent Design have used the notion of irreducible complexity to bludgeon evolution theory by insisting that complex biological structures ranging from the human eye to the bacterial flagellum could not have evolved in stages because none of the intermediate versions would have functioned properly. They have never offered evidence for this notion of irreducible biological complexity, they simply declare it by fiat as an inescapable logical conclusion. Unfortunately for Intelligent Design, scientists are striking back and providing detailed evidence about the evolution of complex biological structures.

Intelligent Design advocates chose poorly when they selected the compound eye of vertebrates as one example of a complex biological structure that could not have evolved in stages. Even first-year biology students know about eye spots in planarians which are simple pigment patches at the front of the worm that are connected to their simple nervous system. They can only sense light versus dark, but that is enough for them to get by as planarians. There are many intermediate forms of eyes in the animal kingdom ranging from simple pits in the skin lined with receptor cells, all the way up to the compound eyes of animals with their cornea and lens arrangement. Fossils of trilobites that are over 500 million years old show they possessed eyes very similar to those of modern day insects. Our complex eyes clearly evolved from the simpler eyes in ancestral species, and the presence of the critical light-receptive pigment called “opsin” in all animals highlights this shared ancestry. The same molecule is used to sense light in worms, jellyfish, eagles and humans.

But what about the evolution of complex molecular structures, such as Intelligent Design’s perennial favorite, the bacterial flagellum? For details on how the flagellum most likely evolved stepwise from a bacterial secretory system, see:


Scientists are increasingly using genetics and molecular biology to dissect probable evolutionary steps in the formation of various molecular devices in animals, and one such recent study by Ken Kosik and colleagues has looked at cellular junctions in certain species of sponges.

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Yes, sponges really are primitive animals, not just absorbent kitchen cleaning items. Sponges are among the simplest of multicellular animals, and they lack internal organs, including a nervous system. However, the mobile larval form of a species of sponge which has been studied extensively has been found to possess the majority of genes for making a critical part of neural synapses, even though the sponge larvae do not have nerve cells. Instead, they have cells called flask cells.

The flask cells of these larval sponges have many features of primitive sensory cells, including a cilia and secretory vesicles. Despite the fact that the larva have no nervous system, they nonetheless possess approximately 70% of the genes required to make the complex structure of neural synapses known as the “postsynaptic density” (PSD). PSD’s are the receptive part of a synapse which receives signals in the form of neurotransmitters released by other nerve cells. So if these sponges don’t have a nervous system, why would their larvae need so many genes associated with synapses?

The answer is that they appear to be using these genes to make signaling structures that are distantly related to neural synapses in animals. The genes in these sponges show a remarkable similarity to the related genes in animals that possess nervous systems, including the structural elements that hold the molecules into a functional array. The authors note that these proto-synaptic structures are not only likely candidates for the evolutionary stepping stones to synaptic contacts between neurons, they may represent prototypical cellular junctions in general which could have led to the development of many specialized junctions between cells found in later-evolving animals.

The take home message from such studies is that the same genes and molecules are used over and over again by different animals to perform many different functions, and that these simple building blocks can be mixed and matched in differing ways to produce increasingly complex molecular devices and organ systems. This derived complexity in no way undermines the notion of evolution, it fortifies the theory immensely. Rather than being another gap in human knowledge about evolution, molecular biology is demonstrating how very complex biological structures can evolve from simpler systems by making use of modular units that can be combined in many different ways, with each change making the system function more robustly. Eye spots are just fine for worms, but not for eagles, and yet the 530 plus million years of evolution between them provided innumerable opportunities for step by step improvements in vision.

Intelligent Design proponents don’t provide us with scientific data, they provide us with uninformed commentary and conjecture. Their arguments may work well with the uneducated public, but they are not based on scientific facts. The main underpinning of their arguments rests entirely on the concept of irreducible complexity. But Darwin is striking back with scientific data that shows how life is like a self-assembling Lego set, mixing and matching simple building blocks to make increasingly complex structures. When Darwin strikes back, he does so with great vigor and eloquence.
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John R. Moffett PhD is a research neuroscientist in the Washington, DC area. Dr. Moffett's main area of research focuses on the brain metabolite N-acetylaspartate, and an associated genetic disorder known as Canavan disease.

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John....    As you well know we are... by Bob Gormley on Friday, Jun 29, 2007 at 5:05:33 PM
Yes, we do disagree on this, despite agreeing on p... by John R Moffett on Friday, Jun 29, 2007 at 5:21:27 PM
Then....    All creationists are ir... by Bob Gormley on Friday, Jun 29, 2007 at 5:32:28 PM
Gormley, you know that I didn't say that creat... by John R Moffett on Friday, Jun 29, 2007 at 5:38:44 PM
Not your exact words.... but you got the message a... by Bob Gormley on Friday, Jun 29, 2007 at 5:50:22 PM
Ok...    I scanned one of the scien... by Bob Gormley on Friday, Jun 29, 2007 at 6:01:33 PM
They're not scientific arguments, but more int... by mike on Friday, Jun 29, 2007 at 5:24:02 PM
If we are created by God, then one being is not be... by Bob Gormley on Friday, Jun 29, 2007 at 5:37:37 PM
Just because you haven't seen it, doesn't ... by Bob Gormley on Friday, Jun 29, 2007 at 5:44:45 PM
John: In his meandering around the universe in "Th... by Professor Emeritus Peter Bagnolo on Friday, Jun 29, 2007 at 5:39:20 PM
Darwin was a great writer. He knew how to turn a p... by John R Moffett on Friday, Jun 29, 2007 at 5:46:15 PM
Being among other things, a cultural/physical Anth... by Professor Emeritus Peter Bagnolo on Friday, Jun 29, 2007 at 6:03:59 PM
Why is creationism so maddeningly unscientific?If ... by Bob Gormley on Friday, Jun 29, 2007 at 6:26:14 PM
What the scientists were saying was complicat... by John R Moffett on Friday, Jun 29, 2007 at 6:43:05 PM
I get what your saying. OK... I definitely believe... by Bob Gormley on Friday, Jun 29, 2007 at 7:09:30 PM
Well, there is one thing going for you (actually t... by Professor Emeritus Peter Bagnolo on Friday, Jun 29, 2007 at 8:00:59 PM
Interesting info. Pete.    &nb... by Bob Gormley on Friday, Jun 29, 2007 at 8:05:09 PM
BUT, ALAS, PROBABLY NOT IN OUR LIFETIME. INTERESTI... by Professor Emeritus Peter Bagnolo on Friday, Jun 29, 2007 at 8:40:13 PM
take the crystal off the Rolex and break the hand.... by Blue Pilgrim on Saturday, Jun 30, 2007 at 7:38:21 AM
Hi Pilgrim,Prions are a very interesting example. ... by John R Moffett on Saturday, Jun 30, 2007 at 9:39:55 AM
John, interesting article as usual and Gormly, God... by Professor Emeritus Peter Bagnolo on Saturday, Jun 30, 2007 at 10:13:21 AM
Yeah...    It's time for a brea... by Bob Gormley on Saturday, Jun 30, 2007 at 10:33:38 AM
Sammy Sosa, has been in my prayers since 2004, for... by Professor Emeritus Peter Bagnolo on Saturday, Jun 30, 2007 at 10:39:46 AM
That's OK,     as long as ... by Bob Gormley on Saturday, Jun 30, 2007 at 12:37:06 PM
But we do not agree that little has changed in man... by tabonsell on Saturday, Jun 30, 2007 at 8:02:17 PM
Why don't you jump in the lake bonsell?Just an... by Bob Gormley on Saturday, Jun 30, 2007 at 8:07:30 PM
 As the article below shows:Ancient armies ha... by Bob Gormley on Saturday, Jun 30, 2007 at 8:24:04 PM
From another article:1.71 meters equals 5' 6&q... by Bob Gormley on Saturday, Jun 30, 2007 at 8:35:25 PM
I don't particularly want to draw a red herrin... by Geraldo on Sunday, Jul 1, 2007 at 5:20:01 AM
I am a professor Of Cultural Anthropology, and I a... by Professor Emeritus Peter Bagnolo on Sunday, Jul 1, 2007 at 9:32:35 AM
Gosh! - Am I really speaking with an authentic sci... by Geraldo on Monday, Jul 2, 2007 at 7:10:28 AM
Well, "professor"; there was a PBS series a while ... by tabonsell on Monday, Jul 2, 2007 at 1:17:36 PM
Am visiting this article for the second time. Lov... by Sheila Jackson on Sunday, Jul 15, 2007 at 4:35:24 PM