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Theistic Evolution: Common Descent or Common Designer?

Posted By Randall D. Isaac, Thursday, April 5, 2018

The second major scientific critique of theistic evolution in this book claims that universal common ancestry, or simply, common descent, is not supported by the evidence. Common descent is the startling hypothesis presented by Charles Darwin (and Alfred Russel Wallace) in 1859, suggesting that all life forms have descended from “…a few forms or one…” At that time, there was scant evidence to support such an audacious claim. In the next half-century, most of the data obtained seemed to point against it. Lord Kelvin noted from thermodynamics that the earth was perhaps no more than 25 million years old, ensuring that there was not enough time for all life to evolve from the same source. The fossils that were discovered during that time could not be dated with any reasonable accuracy, leaving a puzzling set of data.

At the turn of the century the tide began to change. The discovery of radioactivity opened the door to solving both major dilemmas. It provided the source of heat that Lord Kelvin needed to realize that the earth was indeed very old, in the billions of years. Radioactivity was also the key to determining the age of the fossils. Amazingly, the story told by the fossils fit dramatically into Darwin’s proposal. In addition, the rediscovery of Mendelian genetics gave credence to the crucial role of inherited traits. In another half-century, the discovery of DNA added a major corroboration to Darwin’s theory. In yet another half-century, the ability to sequence genomes provided the icing on the cake, permitting extraordinarily detailed confirmation of common ancestry. There could be no further doubt.

Or could there be? The authors of this book present two arguments that they believe nullify the firm conviction of nearly all biologists. They are so confident in the strength of their arguments that they claim evolution is not even sufficiently viable for anyone to consider integrating it with Christianity. The two arguments are

1.       There are observations that cannot be explained by common descent

2.       The alternative explanation of common design is a superior claim

I will discuss only two of the types of observations they present as being contradictory to common descent. The first is the inconsistent pattern of hybridization found in nature. They list page after page of details of families and genera in which some species hybridize and others don’t. Their point is simply that if common descent were true, then all species within a family or genus would either all hybridize or all not-hybridize. What they fail to recognize is that the ability for species to hybridize depends on more variables than the proximity of their common ancestor. Both environmental factors and the specific types of differences underlying their differentiation have a great bearing on the ability to hybridize. In other words, while it is true that a near common ancestor would increase the likelihood of the ability for two species to hybridize, other factors come into play that prevent these observations from nullifying common descent.

The second type of observation they present is the occasional lack of orthologous genes. Orthologous genes encode for the same function in different species and are almost identical. Consistent with common descent, there are only a few differences in the genetic sequence of these orthologous genes due to a slightly different history of mutations. I recall hearing Paul Nelson’s talk at the ASA 2012 meeting at Pt Loma, CA. He described genes in certain species that had no orthologous gene in an ancestral or closely-related species. His point was that if common descent were true, all genes should have orthologous forms in closely-related species. The frequency of these “orphan” genes without an orthologous gene in closely related species, however, was very low, less than 1%. I later learned from my biologist friends that even today’s highly sophisticated sequencing technology can only detect with ease about 90% of an arbitrary genome of a species. The remaining 10% or so are extremely difficult to find and are generally not worth the trouble or the cost. A missing gene in a species could well be part of the remaining 10%. Consequently, an inability to identify a small number of orthologous genes in closely-related species is not a fatal contradiction of common descent.

Other types of examples are offered but, like these two, are the result of a misinterpretation of the scientific data. Many of the issues relate to familiar claims of missing links, sudden appearance of species, rapid extinctions, or a too rapid pace of evolution. Not one of these issues represents a fundamental contradiction of evolution but rather is within the range of complexities being explored within the realm of evolution.

The second main argument presented in the book is that common design is an alternative and superior explanation for all the observations. Simply put, the theory of common design says that any similarity between species is the result of a common designer who uses a common building block to design various species. Any differences between those species is the result of that common designer recognizing the different functional needs that those species may have. Voila, all observations have been explained. Similarly, the large number of pseudogenes are predicted to have some residual value for their organism, thus explaining their existence by a yet-to-be discovered functionality. For example, the defective gene for vitamin C in primates is imagined to have some unknown function, presumably more necessary than making vitamin C.

In a later post we will explore one of the philosophical problems associated with the assertion of a common designer. Here we comment on the scientific description itself. First of all, the common designer concept is not falsifiable. A similarity and a difference between two organisms are equally “explained” by the proposed existence of a common designer, which has not been observed. No evidence could render the explanation to be false. Secondly, the hypothesis provides no basis for understanding under what conditions there are similarities and when there might be differences. The only vague rationalization is that the alleged “common designer” knew it was better to have a similarity or a difference. Finally, the assertion of a common designer is best called “creation with the appearance of common descent.” Like the concept of “creation with the appearance of age” in the young-earth claims, it cannot be scientifically or logically disproved definitively but is neither theologically nor pragmatically defensible.

Tags:  theistic evolution 

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Comments on this post...

Tony Isaac says...
Posted Tuesday, April 10, 2018
As with "creation with the appearance of age," I reject "creation with the appearance of common descent." With that said, it makes sense that the various creations by a common creator might appear to have common descent, as a side effect of having a common creator. This is not he same as creating life in such a way as to make it "deceptively" look like common descent.

As a software engineer, I can look at software and tell you 1) how skilled the creator was, 2) how intelligent the creator was, 3) how much effort was put into the design by the creator, 4) the elements of design that the creator considered important, and many other attributes of the creator. I can do this because I thoroughly understand HOW (the process by which) software (or anything) is designed and developed.

When I look at the design of life through the eyes of an engineer, I see a highly skilled, highly intelligent Creator, one who spent much effort working out the many design choices and tradeoffs, to produce thriving life forms. If indeed random chance produced all of life, then that random chance produced a creation "with the appearance of a designer."

I accept that life evolves, but I can't accept that life could have designed itself spontaneously. Perhaps that is why I'm an engineer rather than a scientist!
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David E. Singer says...
Posted Wednesday, April 11, 2018
Tony, I share your propensity to see an astute designer as I marvel at God's creation. I think this perspective is in keeping with revelation. But then I too am not a scientist nor even an engineer. I do try to fathom, as best I can, the latest scientific explanations and discoveries. I've read "The Language of God" by Francis Collins and found it convincing. Science, by definition, searches for a sequence of "natural" causes. As Randy points out, the 'common designer' concept is not falsifiable. From my perspective no miracle, by definition, is (they aren't repeatable) Falsifiability is required to pass as good science. But in the end we know that God created all that exists. But like miracles in general, we don't know how. That remains the purview of science. So, when I look at evolution as a closed system of explanation, I say there's still that missing ingredient of the Divine. I can marvel at the result without knowing exactly how it all came about but also knowing it wasn't just by accident or a consequence of random probabilities.

There's this tendency to cast revelation against science when both are needed for a fuller understanding. Revelation points to the who and why; science elucidates the how. Neither is sufficient alone. I find it interesting that, as much as we know of life, its complexity and origins still baffle and astound us.
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Randall D. Isaac says...
Posted Sunday, April 15, 2018
Tony, I appreciate your comment and the opportunity to clarify some of the key issues. First, I should point out that I think the title of my post is somewhat misleading. By saying “Common Descent or Common Designer” I erroneously give the impression that these are mutually exclusive. They aren’t. As Christians, we all believe that God created everything and that he is the common creator/designer of all life and all matter. The issue is how God created life and whether or not he used evolution as the means of creation. Perhaps the title should more appropriately have been “Common Descent or not” implying that the question is whether or not God used a method other than evolutionary common descent to carry out his creative intent.
On one level, the analogy you offer of an engineering design or a computer program seems relevant but I would suggest that a different analogy would be closer more accurate. We all have a lot of experience with human design activity but what is our experience with biological design activity? We have no experience at all of any intelligent being creating any synthetic life, notwithstanding all the incredible progress on biotechnology today. Rather, our ubiquitous experience is that of observing biological reproduction with variation. We observe it in every species in the world. We know much, though we still have more to learn, about the types and rates of changes that occur in both the genetic and the epigenetic composition of life. The overwhelming evidence of the vast majority of genes is that the similarities and differences between genes of related species are consistent with this pattern of reproduction having continued ever since the origin of life.
Why then is there such a compulsion to reject common descent and to insist that our creator used a different method? Indeed, no alternative method has yet been offered other than to speculate on a sudden appearance of a new species. Or perhaps reproduction with divine variation instead of natural variation. No evidence that I am aware of has ever been offered for an alternative path. Instead, the argument appears to be that common descent doesn’t explain all the data. This suffers from the problem that Robert Bishop highlighted in his December 12, 2017 comment on this blog. His analysis would also apply to this situation: “There are at least two problems with this response. First, it's a reasoning fallacy known as unobtainable perfection: Increase the evidential demands beyond what can reasonably be met; proclaim victory when the demands cannot be met. Second, the demand would prove too much. We have relatively few explanations in the sciences that have every detailed step filled in. The implication is that there few acceptable explanations in any of the sciences. A conclusion that serves as a reductio of the demand.”
In other words, while there are many situations that are not yet understood, these do not constitute refutation of common descent. The point I was trying to make in my post is that no evidence has yet been offered that conceivably falsifies common descent. Some examples of hybridization, orphan genes, remarkably rapid development, etc., may not be fully explained but not a single one has been shown to contradict the possibility of common descent. Meanwhile, the existence of a common designer is not a denial of common descent nor is it an alternative explanation.
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