“Darwin’s Surprise” – Can Viruses Make Us Human?

“Darwin’s Surprise” by Michael Specter focuses on the significant role of retroviruses in human evolution. Scientists are investigating and resurrecting ancient viruses in hopes of gaining information that will help address “the medical complexities that we confront today.” This has led to the creation of a new discipline, paleovirology, which studies the genetic history of ancient viruses. The article was very fascinating as it looks at viruses from a more positive perspective.

The article is titled “Darwin’s Surprise” because Charles Darwin would have been surprised to learn that humans descended from viruses. In addition, his revolutionary idea that humans and apes share a common ancestor is supported by evidence that we share retroviral DNA with chimpanzees and monkeys and “the only way that humans, in thousands of seemingly random locations, could possess the exact retroviral DNA found in another specie is by inheriting it from a common ancestor”. This suggests that humans and chimpanzees endured identical viral infections in the course of millions of years.

It was not until 2003, when the sequence of the human genome was fully mapped that researchers discovered fragments of retroviruses in our bodies. This took place only 13 years ago! I was surprised to learn that 8% of our DNA is composed of “broken and disabled retroviruses” which were able to embed themselves into the DNA of our ancestors, hence the name endogenous retrovirus, while two percent of our genome is made up of DNA that codes for proteins. Since the retroviruses are broken and disabled, they no longer serve a purpose or cause harm, the remnants are referred to as “junk DNA.” Since endogenous viruses are old and reproduce at a high speeds, they makes a lot of errors when they reproduce. As a result, they are unable to kill us. Thierry Heidmann and his colleagues pieced back together the broken parts of a virus, placed it in human cells, and noticed that the virus was able to insert itself into the cell’s DNA. The virus also infected hamster and cat cells. In the article, this idea is often referred to as bringing the dead back to life. Scientists however do not consider viruses to be alive since they lack the properties associated with living organisms such as the ability to reproduce without a host cell and the ability to metabolize or respond to environmental stimuli. Heidmann named the virus after the mythical bird, Phoenix, in order to gain attention.

Years ago, Heidmann’s words, “We would have not survived as a species without them [viruses],” would have sounded like something unbelievable to me, especially since I had always seen viruses as harmful, agreeing with Joshua Lederberg that the “single biggest threat to man’s continued dominance on this planet is the virus.” However, endogenous retroviruses have helped mammals develop a placenta, leading to live births, and the development of large brains. The impact of viruses has been so significant in our function that without them, we would have been born from an egg and years later, lay eggs. Syncytin is a protein that causes placental cells to fuse together using the same mechanism that allows retroviruses to fix themselves onto the cells they infect. In trying to understand the inability of the AIDS virus to make infected chimpanzees sick, Harmit Malik and Michael Emerman have found a remarkable difference between the human and chimp genomes. Chimpanzees have about 130 copies of the virus Pan troglodytes or PtERV, gorillas have 8 copies, and while humans have none. Humans have the gene TRIM5a that manufactures a protein that binds to and destroys PtERV, protecting us against PtERV, while leaving us vulnerable to H.I.V.

As the article mentions, the act of bringing back deadly extinct viruses could conjure images of Jurassic Park or be linked to bioterrorism. The benefits outweigh the disadvantages as further research in palevirology could lead a greater understanding of harmful diseases and the development of vaccines.

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