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From Hypothesis to Theory

Post of the Month: October 2005


Subject:    Re: Can anyone enlighten me?
Date:       9 October 2005
Message-ID: WI92f.3117$D8.2463@okepread03

> What are the requirements to make a theory acceptable to science? How does
> this come about?
> I would go further than that and ask, in light of the fact that evolution is
> said by some to transcend theory and has become a fact; what is the process
> for moving from hypothesis to theory to fact.
> Are there any set rules and reg's and who puts them in place?

I'll try to illustrate this using the concept of continental drift in contrast to evolution.

Around 1900 scientists knew that the earth had regions where earthquakes occurred, and regions with volcanoes, and ocean trenches and belts of minerals and other geologic features and activities, but they didn't know why all of these were distributed as they are. In other words, geology was a catalog of facts without any unifying explanation to tie the facts together.

Around 1915 Alfred Wegener noticed many of these features could be related to each other if one were to assume that the continents were moving (drifting across the Earth's surface). Wegener supported his theory of continental drift to explain why coastlines had their particular shape, why mountain ranges and mineral belts occurred on opposite sides of oceans and why the fossil record diverged on different continents.

Geologists examined the theory and how the theory related to the data, and most decided that there was not enough data to conclusively support the theory. Continental drift was 'an explanation' of Earth geology, but it was not the 'only explanation' and was not clearly superior to all other explanations. So after a decade or so of debate it was not so much rejected as just ignored. You see, facts (observations) can support multiple theories (explanations), and scientists are cautious about accepting one theory above another unless the evidence is truly compelling.

Then during and after World War 2 there was a great increase in the study of the geology of the ocean floor. Now here is the crux of the matter. The only theory which could logically explain the new data gathered was the theory of continental drift. All the other theories failed to predict key elements in the geology of the sea floor. Well, at that point the theory of continental drift gained wide acceptance and by the early 1970s was the dominant theory of Earth geology. Over the last several decades the 'theory of continental drift' has been modified with the new data to become what we call today the 'theory of plate tectonics'.

But there is another part to this story of continental drift. Continental drift is not 'just a theory' any more. The basic concept of continents moving has been experimentally verified. We know for a fact that the Americas are moving westward away from Europe at several centimeters a year. Likewise other continents have been measured to move. So continental drift is both a 'fact' and a 'theory'. The fact is the actual measurement of continent motion, and the theory is the explanation of why continents move and produce geologic activity.

Ok, so how does this relate to evolution? Well before 1860 biologists knew that life was complex, and they knew there were relationships between species, and they knew that present life was different from fossil life. But they didn't know why. Darwin's theory explained why and how all life is related. It explains it better than any competing theory. In fact, it consistently predicts things that no other theory can predict. So it is the dominant theory in biology about how life is related.

Now, just like the theory of continental drift, evolution has changed to incorporate new data. It now incorporates data on DNA, mutations, genetic drift, punctuated equilibrium, etc. But most of the basic concepts of evolution as proposed by Darwin are still part of the theory.

And there is another similarity between evolution and continental drift. Evolution has been observed. There is documented data (facts) of species changing into other species. So evolution is both a fact (it's been observed) and a theory (it explains how all life is related).

Let's compare this to Intelligent Design. Intelligent design fails to explain why life is related. It fails to explain the pattern of fossil change over time. It fails to explain the fact of life forms evolving. There is not one single positive piece of data that supports intelligent design instead of evolution. So intelligent design is an explanation of life, but it fails the test both as a theory which explains facts, and it fails to be a fact. All explanations are not equal in science. Only those explanations which explain the majority of the facts becomes a theory. The theory which convinces the majority of experts in the field becomes the dominant theory.

Evolution is a robust, fruitful theory, that is accepted by the vast majority of biologists.


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The Inverted Human Retina

Post of the Month Runner-Up: October 2005


Subject:    Re: Is the Backwards Human Retina Evidence of Poor Design?
Date:       27 October 2005

>Research by ophthalmologists has clearly shown why the human retina must
>employ what is called the "inverted" design. An inverted retina is where the
>photoreceptors face away from the light, forcing the incoming light to
>travel through the front of the retina to reach the photoreceptors.

The ICR article attempts to explain the inverted eye "design" mainly on the basis of two points: 1) the photoreceptors are embedded in a layer of retinal pigment epithelial cells which perform important functions and 2) the photoreceptors have a very high metabolic rate which requires a good circulatory system to support them. Both of these points are quite valid, to be sure. However, neither of them supports the "essential" nature of the inverted design.

Point 1 (the "need" for the epithelial cells to surround the receptors): It is quite possible, and would seem "natural" to any intelligent designer, to design the eye with a surface layer of receptors embedded in an epithelial layer just below that would provide the necessary supportive functions. Immediately below this would be the neural processing layers, out of the way of the light path. The olfactory system has the receptor ciliary portion of the cells on the surface of the nasal sensory epithelium and the neural portions buried below. The auditory system has the receptor hair cells on the upper surface of the basilar membrane surrounded by elaborate membrane systems and the neural portions buried below.

Point 2 (the "need" for an adequate circulatory supply): This is extremely puzzling. Most people who discuss the retina know that the light must pass through the nervous system on the way to the photoreceptors. But most people, including the authors of this note, ignore the fact that the light must also pass through the blood supply, the retinal blood vessels! The arteries and veins that supply the retina are also in the light path! This point renders the argument in the paper completely false. The capillary network in the pigment epithelial layer, so essential to photoreceptor function, must be derived from the blood vessels that lie in the light path. A far superior design would be as outlined above: Superficial photoreceptors underlain by a pigment epithelial layer and a rich blood supply underlain, in turn, by the retinal neural processing layers. The receptors would be the first elements in the light path, they would be surrounded by the proper supportive tissue, they would have a good circulatory supply, and they would still maintain close contact with the neural processing circuitry.

The real problem here that nature (evolution) had to solve is that the retina is really a portion of the central nervous system, not a peripheral sense organ. For some unknown reason -- an evolutionary accident? -- it developed with a "cortical"-like structure with everted cell layers (neurons on the surface like the cortex) instead of the original CNS arrangement (neurons lining the central canal like the spinal cord). It could have been different. Again, look at the olfactory system. The olfactory bulb is also an outgrowth of the CNS, not a peripheral sensory organ. But the receptors were added externally, the "natural" way. The eye can get away with the inverted "backwards" design because it really is not that poor. As the article points out, cells tend to be quite transparent so that there is essentially no absorptive loss in the pathway. The scattering and diffraction really is quite minimal so that the overall acuity of the retina still approaches the physical wavelength limit on resolving power even given the bad design.

Obviously, if the design really were that "poor" we vertebrates would never have developed keen vision. The backwards retina should really be cited more as an example of incredibly silly and inept design, not as "poor quality". We (especially hawks) really do have quite good vision despite the backwards nature of the design.

[Return to the 2005 Posts of the Month]

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