An artist’s impression of prehistoric animals from the early Cretaceous period.
Credit: Mark P Witton/Science Photo Library
Fossils come in many forms, not just the mineralised remains embedded in ancient rocks or animal and plant remains preserved in amber. They can take the form of vestigial structures, deactivated atavistic genes which used to code for structures no longer used, ancient retroviruses which got inserted in the genome in ancient times and, as has been discovered by two Oxford University, UK, researchers, the remains of 'Maverick' viruses which infected our remote ancestors and, like ancient retroviruses, have been replicated in our genome, for no good reason.
Because these got inserted in the genome of our ancient ancestors, they also appear in the genomes of all the descendants of that remote ancestor and, as such are conclusive evidence of common descent. It's almost like some ancient scientist inserted a marker in the genome so we could work out the phylogenetic relationship between all mammals. The two Mavericks discovered by Jose Gabriel Nino Barreat and Aris Katzourakis of Oxford University's Department of Biology were inserted in the genome of the small early mammals that were around with dinosaurs. The first around 106 million years ago and the second about 2 million years later.
Maverick viruses belong to a rare form of DNA virus. Unlike retroviruses which are RNA viruses that use the enzyme reverse transcriptase to insert the DNA template of their genome into the host cell's DNA, Mavericks become incorporated accidentally. If these viruses get incorporated into the DNA of cells in the germ lines that give rise to eggs or sperm, then will be passed on to a descendant and will be replicated in every cell in that offspring and all its descendants.
Copyright: © 2022 The authors. Published by BioRxivOpen access
In the abstract to their open access paper published open access in bioΧriv, the authors say:
AbstractHere then we have conclusive evidence of common descent from early mammals that would have co-existed with dinosaurs, in the form of two fossil viruses that, by occasional mutation, can be used to map the phylogenetic relationships of almost all mammals which can be traced back to that early common ancestor.
The genomes of eukaryotes preserve a striking diversity of ancient viruses in the form of endogenous viral elements (EVEs). Study of this genomic fossil record provides insights into the diversity, origin and evolution of viruses across geological timescales. In particular, Mavericks have emerged as one of the oldest groups of viruses infecting vertebrates (≥419 My). They have been found in the genomes of fish, amphibians and non-avian reptiles but had been overlooked in mammals. Thus, their evolutionary history and the causes of their demise in mammals remain puzzling questions. Here, we conduct a detailed evolutionary study of two Maverick-like integrations found on human chromosomes 7 and 8. We performed a comparative analysis of the integrations and determined their orthology across placental mammals (Eutheria) via the syntenic arrangement of neighbouring genes. The integrations were absent at the orthologous sites in the genomes of marsupials and monotremes. These observations allowed us to reconstruct a time-calibrated phylogeny and infer the age of their most recent common ancestor at 268.61 (199.70–344.54) My. In addition, we estimate the age of the individual integrations at ~105 My which represent the oldest non-retroviral EVEs found in the human genome. Our findings suggest that active Mavericks existed in the ancestors of modern mammals ~172 My ago (Jurassic Period) and potentially to the end of the Early Cretaceous. We hypothesise Mavericks could have gone extinct in mammals from the evolution of an antiviral defence system or from reduced opportunities for transmission in terrestrial hosts.
Importance The genomes of vertebrates preserve an enormous diversity of endogenous viral elements (remnants of ancient viruses that accumulate in host genomes over evolutionary time). Although retroviruses account for the vast majority of these elements, diverse DNA viruses have also been found and novel lineages are being described. Here we analyse two elements found in the human genome belonging to an ancient group of DNA viruses called Mavericks. We study their evolutionary history, finding that the elements are shared between humans and many different species of placental mammals. These observations suggest the elements inserted at least ~105 Mya in the most recent common ancestor of placentals. We further estimate the age of the viral ancestor around 268 My. Our results provide evidence for some of the oldest viral integrations in the human genome and insights into the ancient interactions of viruses with the ancestors of modern-day mammals.
Barreat, Jose Gabriel Nino; Katzourakis, Aris
An ancient endogenous DNA virus in the human genome
bioRxiv 2022.02.01.478760; doi: https://doi.org/10.1101/2022.02.01.478760
Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
We also have yet another example of the massive redundancy, prolific waste and needless complexity that distinguishes the 'design' produced by a mindless natural process in which no intelligent plan was involved, and what would reasonably be expected to be the result of design by a competent, intelligent designer.
No wonder it is next to impossible to have an adult debate with Creationists about these genetic fossils that exist in every cell in our bodies and the bodies of all our relative species.
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