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[recessiontime]

[NYC_Gal]

Gender changing fish:

http://earthsky.org/biodiversity/how-can-some-fish-change-from-female-to-male

[pangaea]

Gender changing frog:

http://findarticles.com/p/articles/mi_m1200/is_n9_v137/ai_8784789/

[recessiontime]

Gender changing humans:
http://www.usrf.org/news/010308-guevedoces.html

(NOT SURGERY, it's all natural)

(nudity, NSFW)

[nautilus]

[nautilus]

[nautilus]

[nautilus]

Series of Eyes
How do we see? In the 19th century the anatomy of the eye was known in great detail, and its sophisticated features astounded everyone who was familiar with them. Scientists of the time correctly observed that if a person were so unfortunate as to be missing one of the eye's many integrated features, such as the lens, or iris, or ocular muscles, the inevitable result would be a severe loss of vision or outright blindness. So it was concluded that the eye could only function if it were nearly intact.

Charles Darwin knew about the eye too. In the Origin of Species, Darwin dealt with many objections to his theory of evolution by natural selection. He discussed the problem of the eye in a section of the book appropriately entitled "Organs of extreme perfection and complication." Somehow, for evolution to be believable, Darwin had to convince the public that complex organs could be formed gradually, in a step-by-step process.

He succeeded brilliantly. Cleverly, Darwin didn't try to discover a real pathway that evolution might have used to make the eye. Instead, he pointed to modern animals with different kinds of eyes, ranging from the simple to the complex, and suggested that the evolution of the human eye might have involved similar organs as intermediates.

Here is a paraphrase of Darwin's argument. Although humans have complex camera-type eyes, many animals get by with less. Some tiny creatures have just a simple group of pigmented cells, or not much more than a light sensitive spot. That simple arrangement can hardly be said to confer vision, but it can sense light and dark, and so it meets the creature's needs. The light-sensing organ of some starfishes is somewhat more sophisticated. Their eye is located in a depressed region. This allows the animal to sense which direction the light is coming from, since the curvature of the depression blocks off light from some directions. If the curvature becomes more pronounced, the directional sense of the eye improves. But more curvature lessens the amount of light that enters the eye, decreasing its sensitivity. The sensitivity can be increased by placement of gelatinous material in the cavity to act as a lens. Some modern animals have eyes with such crude lenses. Gradual improvements in the lens could then provide an image of increasing sharpness, as the requirements of the animal's environment dictated.

Using reasoning like this, Darwin convinced many of his readers that an evolutionary pathway leads from the simplest light sensitive spot to the sophisticated camera-eye of man. But the question remains, how did vision begin? Darwin persuaded much of the world that a modern eye evolved gradually from a simpler structure, but he did not even try to explain where his starting point for the simple light sensitive spot came from. On the contrary, Darwin dismissed the question of the eye's ultimate origin:

How a nerve comes to be sensitive to light hardly concerns us more than how life itself originated. He had an excellent reason for declining the question: it was completely beyond nineteenth century science. How the eye works; that is, what happens when a photon of light first hits the retina simply could not be answered at that time. As a matter of fact, no question about the underlying mechanisms of life could be answered. How did animal muscles cause movement? How did photosynthesis work? How was energy extracted from food? How did the body fight infection? No one knew.

To Darwin vision was a black box, but today, after the hard, cumulative work of many biochemists, we are approaching answers to the question of sight. Here is a brief overview of the biochemistry of vision. When light first strikes the retina, a photon interacts with a molecule called 11-cis-retinal, which rearranges within picoseconds to trans-retinal. The change in the shape of retinal forces a change in the shape of the protein, rhodopsin, to which the retinal is tightly bound. The protein's metamorphosis alters its behavior, making it stick to another protein called transducin. Before bumping into activated rhodopsin, transducin had tightly bound a small molecule called GDP. But when transducin interacts with activated rhodopsin, the GDP falls off and a molecule called GTP binds to transducin. (GTP is closely related to, but critically different from, GDP.)

GTP-transducin-activated rhodopsin now binds to a protein called phosphodiesterase, located in the inner membrane of the cell. When attached to activated rhodopsin and its entourage, the phosphodiesterase acquires the ability to chemically cut a molecule called cGMP (a chemical relative of both GDP and GTP). Initially there are a lot of cGMP molecules in the cell, but the phosphodiesterase lowers its concentration, like a pulled plug lowers the water level in a bathtub.

Another membrane protein that binds cGMP is called an ion channel. It acts as a gateway that regulates the number of sodium ions in the cell. Normally the ion channel allows sodium ions to flow into the cell, while a separate protein actively pumps them out again. The dual action of the ion channel and pump keeps the level of sodium ions in the cell within a narrow range. When the amount of cGMP is reduced because of cleavage by the phosphodiesterase, the ion channel closes, causing the cellular concentration of positively charged sodium ions to be reduced. This causes an imbalance of charge across the cell membrane which, finally, causes a current to be transmitted down the optic nerve to the brain. The result, when interpreted by the brain, is vision.

My explanation is just a sketchy overview of the biochemistry of vision. Ultimately, though, this is what it means to "explain" vision. This is the level of explanation for which biological science must aim. In order to truly understand a function, one must understand in detail every relevant step in the process. The relevant steps in biological processes occur ultimately at the molecular level, so a satisfactory explanation of a biological phenomenon such as vision, or digestion, or immunity must include its molecular explanation.

Now that the black box of vision has been opened it is no longer enough for an "evolutionary explanation" of that power to consider only the anatomical structures of whole eyes, as Darwin did in the nineteenth century, and as popularizers of evolution continue to do today. Each of the anatomical steps and structures that Darwin thought were so simple actually involves staggeringly complicated biochemical processes that cannot be papered over with rhetoric. Darwin's simple steps are now revealed to be huge leaps between carefully tailored machines. Thus biochemistry offers a Lilliputian challenge to Darwin. Now the black box of the cell has been opened and a Lilliputian world of staggering complexity stands revealed. It must be explained.

Irreducible Complexity
How can we decide if Darwin's theory can account for the complexity of molecular life? It turns out that Darwin himself set the standard. He acknowledged that:

If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But what type of biological system could not be formed by "numerous, successive, slight modifications"?

Well, for starters, a system that is irreducibly complex. Irreducible complexity is just a fancy phrase I use to mean a single system which is composed of several interacting parts, and where the removal of any one of the parts causes the system to cease functioning.

Let's consider an everyday example of irreducible complexity: the humble mousetrap. The mousetraps that my family uses consist of a number of parts. There are: 1) a flat wooden platform to act as a base; 2) a metal hammer, which does the actual job of crushing the little mouse; 3) a spring with extended ends to press against the platform and the hammer when the trap is charged; 4) a sensitive catch which releases when slight pressure is applied, and 5) a metal bar which connects to the catch and holds the hammer back when the trap is charged. Now you can't catch a few mice with just a platform, add a spring and catch a few more mice, add a holding bar and catch a few more. All the pieces of the mousetrap have to be in place before you catch any mice. Therefore the mousetrap is irreducibly complex.

An irreducibly complex system cannot be produced directly by numerous, successive, slight modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional. An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution. Since natural selection can only choose systems that are already working, then if a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop, for natural selection to have anything to act on.

Demonstration that a system is irreducibly complex is not a proof that there is absolutely no gradual route to its production. Although an irreducibly complex system can't be produced directly, one can't definitively rule out the possibility of an indirect, circuitous route. However, as the complexity of an interacting system increases, the likelihood of such an indirect route drops precipitously. And as the number of unexplained, irreducibly complex biological systems increases, our confidence that Darwin's criterion of failure has been met skyrockets toward the maximum that science allows.

The Cilium
Now, are any biochemical systems irreducibly complex? Yes, it turns out that many are. A good example is the cilium. Cilia are hairlike structures on the surfaces of many animal and lower plant cells that can move fluid over the cell's surface or "row" single cells through a fluid. Inhumans, for example, cells lining the respiratory tract each have about 200 cilia that beat in synchrony to sweep mucus towards the throat for elimination. What is the structure of a cilium? A cilium consists of bundle of fibers called an axoneme. An axoneme contains a ring of 9 double "microtubules" surrounding two central single microtubules. Each outer doublet consists of a ring of 13 filaments (subfiber A) fused to an assembly of 10 filaments (subfiber B). The filaments of the microtubules are composedof two proteins called alpha and beta tubulin. The 11 microtubules forming an axoneme are held together by three types of connectors: subfibers A are joined to the central microtubules by radial spokes; adjacent outer doublets are joined by linkers of a highly elastic protein called nexin; and the central microtubules are joined by a connecting bridge. Finally, every subfiber A bears two arms, an inner arm and an outer arm, both containing a protein called dynein.

But how does a cilium work? Experiments have shown that ciliary motion results from the chemically-powered "walking" of the dynein arms on one microtubule up a second microtubule so that the two microtubules slide past each other. The protein cross-links between microtubules in a cilium prevent neighboring microtubules from sliding past each other by more than a short distance. These cross-links, therefore, convert the dynein-induced sliding motion to a bending motion of the entire axoneme.

Now, let us consider what this implies. What components are needed for a cilium to work? Ciliary motion certainly requires microtubules; otherwise, there would be no strands to slide. Additionally we require a motor, or else the microtubules of the cilium would lie stiff and motionless. Furthermore, we require linkers to tug on neighboring strands, converting the sliding motion into a bending motion, and preventing the structure from falling apart. All of these parts are required to perform one function: ciliary motion. Just as a mousetrap does not work unless all of its constituent parts are present, ciliary motion simply does not exist in the absence of microtubules, connectors, and motors. Therefore, we can conclude that the cilium is irreducibly complex; an enormous monkey wrench thrown into its presumed gradual, Darwinian evolution.

http://www.arn.org/docs/behe/mb_idfrombiochemistry.htm


Game over kids.

[Globutron]

[nautilus]

[Globutron]

[nautilus]

[pangaea]

nautilus wrote:

[NYC_Gal]

[Underwaterbob]