The phenomenon of symbiotic homeostasis is a direct assault to traditional evolutionary theory. Homeostasis, by definition, is resistance to change. This is the process by which certain physiological functions are maintained in equilibrium through negative feedback loops. These loops are common processes in many biochemical reactions of all living things. The human body reacts to increasing ambient temperature by vasodilation and sweating, for example, thereby cooling the body down by allowing greater heat to be exchanged from the body to the environment. Take out any component of the equation and you have pyrocephallacy. But how on earth might this have come about?
If any single component of the negative feedback system is removed, then the system breaks down and homeostatis cannot be achieved. Subscribers to the theory of evolution have yet to provide evidence which would describe a plausible progression of evolutionary designs in humans which would have allowed for this complex system to occur, and it does appear to fall under the category of irreducible complexity. Just by looking at the image, one can see that omitting either receptors or effectors at any point along the way would lead to a complete breakdown of the entire cycle. Darwin pointed out that if any structure could not have come about by a serial progression then the entire theory fails. Michael Behe describes irrecucible complexity as "a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning. An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive 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."
Irreducible Complexity and Michael Behe on Intelligent Design Behe has pointed to irreducibly complex structures such as the camera eye and flagella to make his case. But what about functional aggregates? Behe points to blood clotting cascades and immunological responses as irreducibly complex as well. This makes a lot of sense. The mousetrap is often cited as a comparative analogy. If you remove any part of the mousetrap, it no longer functions. So how could it have come about by a serial progression of steps through evolution?
A bigger issue is that of the entire complex which makes up the feedback loops seen above, and how these loops apply not only in biochemical processes, but ecological interactions as well. The best example of such that I can think of are symbioses. Symbiosis, literally speaking, is two or more separate organisms (species) living together. Examples include coral reefs which make up a large and important component of marine systems, mycorhizzae which contribute to the health of boreal forests, and even malaria (plasmodium) which threatens large populations of humans in a variety of places around the world. All of these symbioses are of global reach. In fact, there are numerous examples of how symbioses are universal. Everywhere you look in biology, you are likely to find a symbiosis. I used these three examples for a good, logical reason too. And that is because each of them are slightly different types of symbiosis. It is first and foremost important to understand that there are three gradations of symbiosis: parasitism-commensalism-mutualism. Many people assume symbiosis to infer the last of these three, but that is a flawed use of the term, technically speaking. Symbioses do not always benefit both species. In the case of corals, both species benefit. This is a mutualism. In the case of mycorhizzae, only one benefits the other is unaffected. This is a commensalism. In the case of the third example, the parasite that causes malaria benefits, which the host human is affected negatively, health-wise. This is a parasitism. But all three examples are symbioses. Now to the interesting part. There are numerous examples in nature of these three distinct systems, but there are absolutely no definitive examples of the intermediary steps that one would expect if one were expecting these associations between organisms to have evolved.
.
