Ken Ham recently tweeted about a baby born with a “tail.” I agree with his assessment that these are not cases of bony tails, homologous to tails in almost all vertebrate species, but then I wondered, can young-earth creationists be sure that Adam and Eve did not have true bony tails as adults? After all, Ken Ham wasn’t there to see Adam and Eve and record their appearance and we have no biblical record that reveals if they had tails or not as a created kind. We do know from present day observations that all vertebrates, including humans, have tails at some point during their life and more than 99% of all vertebrate animal species have bony tails as adults so it isn’t crazy to ask the question: could the rare exceptions without adult tails simply be examples of species that once had tails but then lost them?
That led me to do a bit more reading about what we know about the genes behind tail formation and prompted me to record the YouTube video linked below.
Not long ago in my genetics course I briefly described a recent manuscript implicating mutations in a gene involved in influencing early development to primate species that lack a tail. I took another look at that manuscript and here I take a deep dive into the molecular genetics of the TBXT gene to explain the significance of this discovery and ask how young-earth creationists could potentially use it to propose that Adam initially had a bony tail and his descendants lost it as a result of alterations to their genomes via a mechanism they frequently employ in their literature called post-fall genetic entropy.
Tail or no tail originally, the mutations to the genome that may lead to the lack of tail development in adult apes is a lesson in how mobile genetic elements in genomes can dramatically affect how genes are regulated resulting in significant changes in phenotype (appearance of traits). In brief, in ape species which all lack bony tails as adults their genomes are all observed to contain an extra copy of a transposable element (a jumping gene) inserted inside a very important early development gene. I discuss how the addition of this approximately 300 bp piece of DNA to this gene alters the expression of the gene which is hypothesized to result in the lass of tails in adults. The authors of this research provide support for their hypothesis by altering the genome of a mouse mimicking the effects of this sequence in humans and showing that mice with this human-like gene expression lack or have very short tails. They also edit human cell lines showing that the gene expression is changed in the way that they predict.
Given these observations of the human TBXT gene young-earth creationists could propose that Adam and Eve were created without this inserted transposon in their genes allowing them to maintain full function of the originally created gene and then post-fall mutations inserted this new genetic element in the gene disrupting its function resulting in descendants that lost their tails. Alternatively, they would need to propose that God used the full-length gene used by all vertebrates resulting in mature tails and then added this extra bit to humans which blocks the use of part of the gene, which still maintaining the whole gene in the genome, resulting in the loss of the tail during embryonic development.
Paper discussed in the video: Xia, Bo, Weimin Zhang, Aleksandra Wudzinska, Emily Huang, Ran Brosh, Maayan Pour, Alexander Miller et al. “The genetic basis of tail-loss evolution in humans and apes.” bioRxiv (2021).https://www.biorxiv.org/content/10.1101/2021.09.14.460388v1
Ken Ham’s blog post about babies born with human tails: https://answersingenesis.org/human-body/vestigial-organs/baby-born-human-tail/