May 17 2013
This is the fourth is a series of posts analyzing the claims of Don McLeroy, former chairman of the Texas School Board of Education and young Earth creationist. I recently interviewed Don on the SGU about his successful insertion into the Texas science textbook standards language requiring books to address stasis and suddenness in the fossil record and the complexity of the cell.
In parts 2 and 3 I addressed Don’s stasis and suddenness arguments. They are classic denialist fallacies – focusing on lower order details as if they call into question higher order patterns (they don’t). In this case, Don is arguing that the fact that many (not all) species display relative morphological stability in the fossil record, with episodes of (geologically) rapid speciation events, calls into question the bigger picture of the change of species over time in an exquisitely evolutionary pattern.
The former is a reflection of the tempo of evolutionary change and an artifact of the fossil record, while the latter is home-run unequivocal evidence for common descent and evolutionary change. Don has not provided any explanation for why the pattern of change we see in the fossil record presents any problems for evolutionary theory.
In this post I will address Don’ other main point, which he feels is the greatest weakness of evolutionary theory – the complexity of the cell. His premise seems to be that, if evolution were true, then evolutionary biologists should be able to provide detailed evidence for the specific evolutionary history of many biochemical pathways and cell structures. He argues that they cannot, and therefore the evidence for evolution is weak.
Before I get into what the current evidence for the evolution of cellular complexity is, let me address the logic of Don’s position. First – his major premise is false, and therefore his argument is not sound. Evolution can be true even if we are currently unable to provide robust evidence for the evolution of biochemical pathways.
His false premise reflects a misunderstanding of how science operates. Science operates by posing testable hypotheses. Often the greatest challenge for scientists is to figure out a practical method for testing their ideas. They generally start by picking the low-hanging fruit – looking where the evidence is robust and accessible.
In other words, biologists ask – if evolution is true, then what should the evidence we do have look like? They then see if the evidence matches the predictions of evolution.
If the theory makes predictions about evidence that we are unable to obtain, for practical reasons, this is not a weakness of the theory or evidence that it is wrong, it is simply a reflection of practicality.
Life on Earth is at least 3.4 billion years old. Multicellular creatures first appear in the fossil record about 540 million years ago. That means that most of the history of life on Earth, about 3 billion years, was nothing but single-celled creatures. That is a very long time in which to evolve biochemical pathways and cellular complexity – more that 5 times as long as it took to get from a single cell to a person.
Cells, proteins, RNA, organelles, and biochemical pathways do not fossilize. They are scantly preserved at all. We are therefore limited in our ability to reconstruct the evolutionary history of billions of years of evolution on this scale.
Scientists only have a few methods available from which to infer the evolutionary history of cell structures and biochemical pathways. The main method is to look for patterns in living organisms. By analyzing thousands of species they can partially reconstruct the evolutionary tree.
Perhaps the best method available is genetic analysis. Genes are a sort of fossil – they do record to some degree their evolutionary past. We can see when genes duplicated and then evolved to take on new functions. We can sometimes see inactivated genes, truly fossil genes, and infer past function from them.
Scientists can also investigate plausible pathways – they can demonstrate the functionality of possible antecedents to current biochemical pathways or structures. This is not the same as evidence for the actual evolutionary pathway to current complexity, it just shows possible pathways.
In short scientists are doing the best they can unraveling an extremely complex picture with the relatively little evidence available to them.
An unbiased way to approach this evidence is to ask – does the evidence we do have support evolutionary theory? Is any biochemical evidence incompatible with evolution? The answers are yes and no – what evidence we have supports evolution, and there is nothing that is incompatible with evolution.
Don is not asking those questions, however. He is not really asking any cogent question. He is simply asserting that the paucity of evidence for cellular and biochemical complexity is evidence of the weakness of evolutionary theory. It clearly isn’t.
Further, Don’s assessment of the current state of the evidence is extremely flawed. He is using popular books and high-school level textbooks as if they were an accurate reflection of the current state of the evidence. The evolution of cellular and biochemical complexity is a very advanced area of biology. I would argue it is not suitable for a high-school level textbook. Any treatment of it at that level, and in popular writing, is by necessity superficial. Don is taking this superficiality as evidence for weakness of evidence.
This also gets to another flaw in Don’s reasoning – his belief that he, as a dentist and engineer, can reasonably challenge the conclusions of the broad scientific community. Many scientists have dedicated their careers to studying evolution, and even tiny areas of the evolution of certain biochemical pathways. They are steeped in a highly technical literature. It is a fatal mistake to confuse familiarity with popular writings with deep knowledge of the technical literature.
Of course, scientists can be wrong, and the consensus does at times change. But there are many scientific consensuses that have not changed in decades and will probably never be overturned. DNA is the substrate of inheritance, for example. The brain is the organ of the mind. The Earth and Sun revolve about their center of gravity. Stars are fueled by nuclear fusion. None of these conclusions are going anywhere. New knowledge about the details of genetics or star mechanics do not threaten the more basic conclusions.
Likewise – all life on Earth is related through common descent. Life changes over geological time in an evolutionary pattern. These scientific conclusions are as solid as any in science, and are not going anywhere. The details of what evolved from what and how are another layer to evolutionary history, but don’t address the higher order conclusions.
What is the current evidence base for the evolution of biochemical pathways? Well, I am no expert, and so I am in no position to give a definitive answer to this question. But as a familiar lay person, I am aware of much more evidence than Don claims exists.
Here, for example, is an interesting technical review – Biochemical Pathways in Procaryotes can be Traced Backwards through Evolution Time. The paper reviews current knowledge about aromatic biosynthesis, DAHP synthase, PABA synthase, and many others.
Here is an overview and list of technical papers on the evolution of eukaryotic pathways by endosymbiosiss of prokaryotes.
Here is another paper, the main conclusion of which is that as biochemical pathways evolved, cells became less dependent on exogenous material and more independent.
This brings up another major premise implied by many of Don’s statements, and typical of creationist arguments. Essentially he echoes the “irreducible complexity” arguments of Michael Behe – how could the cell have functioned prior to developing critical complexity? This is addressed by the plausibility research, as with the paper above, showing that simpler pathways and structures were perfectly functional, just inefficient. RNA can replicate itself without ribosomes, just slowly. As complexity developed, cell metabolism became faster, more efficient, and less dependent on specific nutrients from the environment (although, of course, not completely).
The final pillar of Don’s argument, reflected in his proposed changes to science textbooks, has now collapsed. His premises are faulty, his logic is not valid, and therefore his arguments are not sound. He neither understands or accurately represents the process of science or the current findings of evolutionary biology. He further uses popular writing and high-school level textbooks as if they represent the technical literature.
Don also gives away a major flaw in his approach – during the interview I accused him of criticizing one of the weaker legs of support for evolutionary theory, and he essentially responded that of course he is. This is not a scientific approach, however.
The relevant question is – how robust is the scientific evidence for common descent and evolutionary change, and how solid are our current conclusions? In order to answer this question you have to look at all the evidence. When you look at evidence from fossils, geology, genetics, developmental biology, the morphology of living organisms, and laboratory experiments on short term evolutionary change, the picture that emerges is one of highly robust evidence all firmly pointing to evolution as the conclusion. Further, there is no alternative scientific theory that is even compatible with evidence, let alone predicts the evidence.
Evolutionary theory is a solid scientific conclusion, without rival.
The robustness of the different types of evidence reflects only our practical ability to get at the evidence – not the predictive power of evolutionary theory.
As a research paradigm, evolution has proven to be very powerful and successful. It shows no signs of ever being overturned – no more so than any foundational scientific theory.
Don’s arguments, which are those of the creationist/ID mainstream, reflect pure pseudoscientific denialism.
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