MadSci Network: Evolution

Re: why didn't animals bleed to death before blood clotting formed?

Date: Wed Oct 19 14:45:11 2005
Posted By: Matthew Champion, Staff Scientist
Area of science: Evolution
ID: 1128602212.Ev


That is an interesting question. You are actually addressing one of the points creationism (ID = Intelligent Design) makes to describe why evolution requires a higher-power in order for life to exist. This tenant of ID is referred to as "Irreducible Complexity" and states that some systems are so complex that they cannot function without any component, therefore they could not have evolved as a lesser functional arrangement. Watchmakers and blood clotting are two of the favorite examples/analogies of this.

Having said that, I will try and answer your question. The fault of irredicible complexity lies in two points:

  1. Just because we do not have an explanation does not mean it has a supernatural origin. This means that the null hypothesis of explaining blood clotting is not necessarily intelligent design. If we cannot describe a phenomenon with our current models, this does not mean God did it.

  2. If something cannot function without all of its parts, this does not mean each part didn't have some other function before it became part of the blood clotting machinery or the bacterial flagellum…

The biological answer to your question is yes, a lot of organisms probably did bleed to death before the ability to clot the circulatory fluid was evolved. Nature doesn't have to be perfect, it just has to work. Haemophiliacs can and did survive before modern medicine, just with a different quality of life. Millions of organisms on this planet do not have clotting systems and manage to survive and thrive quite well in spite of it. Insects, one of the most successful collection of species on the planet do not have clotting of their haemolymph as you would likely understand it, but they thrive extremely well in virtually every environment on Earth.

With the recent trial on ID v. Evolution there has been a lot of press on this lately. Two great essays I have read yet on the issue were written by

William Saletan for Slate. The article can be found here:

Rick Weiss and David Brown also wrote an essay for the Post which can be read here: dyn/content/article/2005/09/25/AR2005092501177.html

Overall, the beauty of evolution as a model is that it is testable and falsifiable… Truth be told, as scientists we are often wrong. Most of the experiments we perform and models we make are not correct. There are observations in evolution that our current models and certainly Charles Darwin do not adequately explain. This does not mean that a higher power did it. Issac Newton's laws on Gravity did not explain the behaviors people observed when atoms interacted at a very small scale. This does not mean that God then created molecules. Our theories and laws had to be rethought, and new physical models were written to explain and predict these interactions, we call it quantum mechanics.

Evolution is a fact. It is the observation that organisms change over time. The mechanism by which this occurs is completely up for debate in science. Some people think it is slow and gradual, a very Darwinian approach. Others believe in the late Steven J Gould's theory that things are pretty stable for a long time, then there is a sudden burst of evolution in response to rapid changes in environment or circumstances. This is called the 'punctuated equliibrium.' The truth likely lies somewhere in the middle with examples of both occurring in nature. Any model that describes evolution without invoking a higher power thus negates ID as there are an infinite number of possibilities for the observation that life changes over time, why shouldn't these be taught as well?

This may be more than you wanted on Evolution, but it is important to try and spread correct information about how the basic process of observing and explaining occurs. I will close with this somewhat macabre analogy:

There were a lot of theories as to how Lincoln was assassinated. It was North, the South, Pro slavery Groups, a second gunman, John Wilkes Booth, etc. etc. In the end, the President was dead. The observation that he was shot is decoupled from theories that explain it.

Thanks for your question.

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