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- But reading between the lines, his reasons for staying a Christian were shaky. He acknowledged poignantly: “My
- So why did he stay a Christian? “As a purely practical matter, I have compelling reasons to believe in God. My parents are deeply committed Christians and would be devastated were I to reject my faith. My wife and children believe in God, and we regularly attend church. Most of my friends are believers. I have a job I love at a Christian college that would be forced to dismiss me if I were to reject the faith that underpins the mission of the college. Abandoning belief in God would be disruptive, sending my life completely off the rails.” Note that Dr. Giberson’s “compelling reasons” to believe in God were sociological. They weren’t about whether Christianity is true.
- Within a few years of writing Saving Darwin, Giberson resigned his post at the Christian university where he taught. In a book following his departure, Saving the Original Sinner (2015), Giberson made clear that he now regards the Bible as a mishmash of divergent stories from
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- Investigators examine traits in different species, such as a specific protein.
- They assume that the different versions of the trait evolved from a common ancestor and attempt to envision the ancestral version, such as an ancestral protein’s amino acid sequence.
- They imagine what steps could have transformed the ancestral version into the modern versions, such as the series of amino acid changes in an evolving protein.
- Researchers often rely on circular reasoning, a pattern demonstrated in a recent article in PNAS, “Order of amino acid recruitment into the genetic code resolved by the last universal common ancestor’s protein domains.” The article, which claims to elucidate the origin and evolution of the genetic code, is entirely based on this flawed reasoning. It rarely attempts to demonstrate the plausibility of the proposed steps, instead focusing on crafting an engaging narrative.
- Enigma of the Genetic Code
- The origin of the genetic code is one of the most challenging and intractable problems in the field of the origin of life research. Even the most primitive biological information storage and retrieval system
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- The sequence of nucleotides in DNA must encode the sequences of amino acids corresponding to all essential cellular proteins.
- A complex protein must separate the two DNA strands to allow genetic information to be accessed. The protein in modern cells is called helicase.
- As the strands separate, DNA starts to coil. A protein must uncoil the DNA by breaking it, passing one section of the DNA through the break, and then mending the DNA fragments. The protein in modern cells is called topoisomerase.
- A suite of proteins must transfer the information from DNA to RNA in transcription.
- Another suite of proteins must translate the information in RNA into the amino acid sequences corresponding to proteins.
- Origins researchers assume that the original system was more straightforward than today. The modern genetic code encodes 20+ amino acids (e.g., valine) into sets of three nucleotides known as codons (e.g., GTA). The first autonomous cell is believed to have used only around half of the amino acids today. Trifonov (2000) proposes that the original set includes the following nine:
- The other amino acids are believed to have been added to the code sequentially. The last ones to be added could not have formed through natural processes in non-trace quantities, so cells are believed to have evolved the chemical pathways to manufacture them before they were incorporated into the genetic code. The amino acids that must have initially been manufactured in cells include those with the more complicated atomic structures, such as histidine (His, H) and tyrosine (Tyr, Y).
- Previous studies postulated the order of amino acid incorporation based on such factors as the ease with which the amino acids could have formed on the early Earth through simple chemistry, the complexity of the amino acids’ structure, and their biosynthetic pathways in modern cells. In contrast, the PNAS study compared the sequences of closely related proteins in modern organisms to reconstruct the sequences of ancestral proteins believed to reside in the last universal common ancestor (LUCA) of life today. The investigators also reconstructed sequences of proteins thought to reside in even earlier cells. They compared the sequences in ancient proteins to those today to postulate the amino acids’ order of incorporation.
- To determine the likely time of recruitment of a specific amino acid into the genetic code, the researchers meticulously employed statistical data analysis tools to compare the enrichment of each amino acid in protein sequences dating back to LUCA and even further back in time. An amino acid that appeared preferentially in ancient sequences was likely incorporated early. Conversely, LUCA’s sequences are depleted for later recruits of amino acids but became available when the timeless ancient protein sequences emerged.
- The study still concludes that the simplest amino acids comprised the original code, but it proposes an order of incorporation of later amino acids that differs from previous proposals:
- Neither the PNAS study nor earlier studies present substantive details about how the genetic code originated or how amino acids were later added. They assume that everything transpired through undirected natural processes and then, based on circumstantial evidence, construct the order in which they were incorporated. When serious questions are raised about the details of what would have been required to engineer the genetic systems or significantly modify them, the entire narrative collapses.
