Most of us are vaguely familiar with [the tenets of Neo-Darwinism], which state roughly that from random mutations and recombinations in the replication of an organism's genome, new traits can emerge, that the process of natural selection causes organisms with beneficial new traits to survive and replicate, and that from the accumulation of more new traits over a long period of time new species will form. This is how the many varied species on earth [evolved, or] came to be ...
ID proponents claim that some traits are too complex, "irreducibly complex," to have emerged by the processes of random mutation and natural selection.
For example, the flagellum is an appendage some bacteria have sticking out that allows them to swim. It is sort of like a microscopic rotating paddle. Flagella are composed of around 30 protein subunits from different genes that work together like a machine to create motion.
If we delete just one of the genes for a subunit, the whole thing can stop working. This is how they determine it is "irreducible."
Since the parts don't work separately, ID proponents say, for Darwinian evolution have created the system, there would have to have been numerous mutations all at one time, because natural selection wouldn't select an incomplete system that doesn't yet work. But, since the system has so many parts, it simply couldn't have evolved from mutation all at once ...
[But] their examples of "irreducible complexity" are in fact reducible. The bacterial flagellum is the most frequent example cited by ID proponents.
The 30 or so protein components do need each other to make a functioning flagellum. However, they didn't need to evolve together, as ID people claim, to be selected by evolution.
The question is whether fewer than the 30 subunits of the flagellum could have had any other function. By comparing gene sequences for similarity with computers, we can see that the answer is clearly "yes."
The pore-forming base of the flagellar structure is very similar to the base of the type III secretion system, which allows many bad bacteria, like Salmonella, for example, to infect host cells.
Other parts of the flagellar structure are also similar to the sex-pilus (yes, bacteria can have "sex" too), that allows conjugation and gene transfer.
In Actinobacillus, an operon of just seven genes, and only three with homology to flagella and secretion system genes, forms its own rudimentary secretion system, dubbed the tad operon. This bacteria lives in your mouth and is mostly responsible for making the slime that forms on your teeth when you don't brush. Without the secretion system, it can't make slime.
In fact, an even more rudimentary homologous secretion system, with just four genes, is found in many other bacteria (including the Mycobacteria we study in my lab).
Irrefutably, the complexity of the flagellum is reducible. The ID people will probably go on to think of new "irreducible" examples of complexity, and the real scientists with some free time and a blog will reduce those as well.
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Originally Posted by ksquared
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