Evolution: how viruses might fit in (Introduction)

by David Turell , Sunday, April 25, 2021, 17:17 (1090 days ago) @ David Turell

Lots of unproven theory:

https://nautil.us/issue/99/universality/the-vast-viral-world-what-we-know-and-dont-know...

"Simple in structure but advanced in function, viruses exist in a category that lies between the inert and the living. Some biologists think of them as quasi-alive, while others refer to them as inanimate tiny particles or arrangements of matter. But experts agree they are like vines wrapping around the tree of life; their existence involves symbiosis, an intimate association between two forms of life. Viruses can reproduce only inside living cells. Even at our healthiest, our bodies are home to trillions of viruses, maybe more. There, they are most “alive,” as their genetic material penetrates into their host’s cells and turns them into virus-making factories.

“'Think of a virus and a cell together as a microscopic copy machine,” explains Sarah Olson, a disease ecologist with the Wildlife Conservation Society’s Health Program. “The virus uses existing entry points to get into the cell—and when it enters, it’s carrying instructions to take over the cell’s machinery and make copies of itself. Then off it goes to the next.”

"A virus replicates through a series of steps, first attaching to a host cell and injecting its genetic material, then incorporating itself into the cell’s genetic material as the cell churns out more viruses. Once the viral information becomes integrated into a host’s genome, that information becomes part of the host and can be passed across generations. Indeed, approximately 8 percent of the human genome comes from viral genes, which means we’ve evolved along with viruses and will continue doing so. In fact, without viruses, humans and other mammals might still be laying eggs. At some point during evolution, the protein syncytin, which is essential for the formation of the placenta, came from a retrovirus infection. We also know that viruses can keep bacteria from invading our gut and causing infections.

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“'You’d like to have a single explanation for the origins of all current viruses,” says Julia Durzyńska, a biologist at Adam Mickiewicz University in Poznań, Poland, who has written about viral evolution. “Instead, there are three dominant models that seem to complete each other.”

"The so-called “virus-first” model suggests that at the dawn of life, very simple forms of viruses existed before cells. The ancient ancestors of modern viruses may have provided raw material for the development of cellular life. If this model were true for all viruses in the world today, it would mean that they all evolved from a few viral ancestors. In some ways, that would make identifying new viruses and developing vaccines or treatments easier—scientists could take what they know about one virus and use it as a starting point to understand its relatives.

"The second so-called “escape” or progressive model of viral origins suggests that viruses arise from genetic elements that escape from the genes of larger organisms. Bacteriophages (viruses that infect bacteria), for example, would come from bits of bacterial genetic material. So according to this model, not all viruses come from deep time—that is, early in the immense arc of the earth’s history, before any multicellular life existed.

"The third model, known as the “reduction” model, is based on a hypothesis that viruses were once larger, free-living organisms. Over time, it is believed that they lost their genetic information and ended up smaller and unable to reproduce alone. But they managed to sustain their existence by replicating in the cells of other organisms. The discovery most commonly interpreted as evidence for this model is that of the mimivirus—the first “giant virus,” which was initially isolated in 2003."

Comment: Viruses had to come after independent life appeared. so I don't accept possibility first. That viruses contributed to evolution has been discussed in the past. Since I think God designed life, I must accept God also designed viruses and used them in advancing evolution.