Wednesday, 3 July 2013

Tasteless Rebuff to Intelligent Design

Normal mouse testes. Streaks are healthy sperm tails
Losing the “taste” for sperm | The Scicurious Brain, Scientific American Blog Network

Scientists investigating the sense of taste have discovered something which illustrates nicely something Intelligent Design pseudo-scientists would much rather you weren't aware of.

As reported by Scicurious in Scientific American a couple of days ago, discussing a paper published in PNAS, a team of scientists were researching the sense of taste and found something really quite unexpected and fascinating.

Taste depends on receptors which are composed of several protein subunits which, being proteins, are coded for by specific genes. If one or more of these proteins is defective or absent it can affect the sense of taste, often in very specific ways. Two of these receptor subunits have the scientific names TAS1R3 - which is a component of two different receptors, for sweet and for umami - and GNAT3 which is essential for "basic taste". The researchers had bred mice in which either one or the other of these two subunits were absent and wanted to see what would happen if both were absent in an individual mouse. It turned out to be surprisingly difficult to breed them.

Abnormal mouse testes. No sperm and strange dark blobs
It turned out that male mice with both these subunits missing were sterile. They simply did not have functioning testes and produced no sperm. These proteins are also needed for normal testicular development and sperm production - something which, at first sight would appear to have nothing at all to do with a sense of taste. Clearly, a protein, or rather the gene which codes for it, which evolved for one process has been co-opted for a different use at some point in mammalian evolution.

Now, a serious professional liar for the Discovery Institute, or for one of the many online Creationist book marketing and money-making scam sites, will tell you that structures like taste receptors are 'irreducibly complex', depending on being fully formed for their function with no obvious way in which it could have evolved gradually. So, they will argue, they could not have arisen by a gradual evolutionary process and must have been designed at produced as fully-developed structures.

In the fruit fly Drosophila, the vestigial gene plays a critical role in wing development. In fact, if these flies are homozygous for the recessive form of the vestigial gene (vg), they will develop short wings, and they will be unable to fly as a direct result. Along with regulating wing development, the vg gene is also pleiotropic. Indirectly, the gene changes the number of egg strings in a fly's ovaries, alters the position of bristles on a fly's scutellum, and decreases the length of a fly's life (Caspari, 1952; Miglani, 2002).

Scitable - Pleiotropy: One Gene Can Affect Multiple Traits, Ingrid Lobo, 2008
What they would rather not tell you is that structures can arise fully formed by incorporating pre-existing components which evolved gradually for an entirely unrelated purpose.

Examples of this include the flagellum, which Creationist frauds still cite as an example of irreducible complexity and which could not have evolved gradually, despite the fact that plausible mechanism for its evolution has been described and are widely accepted. The "Type III Secretion System", out of which the so-called proton motor of the flagellum may well have evolved, for example, includes very similar structures which evolved for an entirely different function and which themselves could have evolved gradually.

In fact, there are multiple examples of a single gene affecting multiple traits - the technical term for this is pleiotropy
The phenotypic effects that single genes may impose in multiple systems often give us insight into the biological function of specific genes. Pleiotropic genes can also provide us valuable information regarding the evolution of different genes and gene families, as genes are "co-opted" for new purposes beyond what is believed to be their original function (Hodgkin, 1998). Quite simply, pleiotropy reflects the fact that most proteins have multiple roles in distinct cell types; thus, any genetic change that alters gene expression or function can potentially have wide-ranging effects in a variety of tissues.

Scitable - Pleiotropy: One Gene Can Affect Multiple Traits, Ingrid Lobo, 2008
Several examples are given in the above article on pleiotropy.

Of course, the ID charlatans, loons and liars market their wares to customers who can't tell a bird from bat and have no problem with talking snakes, and want above all for them to stay that way. They would rather their dupes imagined that evolution means every new structure has to evolve in isolation and is somehow estopped from using pre-existing structures, without explaining how a perfectly natural, undirected and unintelligent process could be prevented from incorporating any suitable structures, proteins, processes, metabolic pathways, etc into a mechanism if using it gave the genes an advantage which would make them more likely to produce descendents.

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1 comment :

  1. Irreducible complexity is an argument that even though proved wrong multiple times the creationists will still use. The reason for this is simple though....they have nothing else to cling. Additionally they are running out of creative ways to lie, as scientists break their arguments in minutes nowadays.

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