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.