Darwin’s Surprise

Viruses are nothing more than protein and genetic material, yet some scientists now believe they may have played a crucial role in evolution. Retroviruses are a special category of viruses whose genetic material is RNA, not DNA. When RNA transcriptase transcribes their genetic information from RNA to DNA, that new viral DNA becomes incorporated into the DNA of the host cell. The host cell then copies the viral DNA along with its own genome during DNA synthesis, and when it divides the viral DNA is passed on to its daughter cells as well.

Darwin did not know about genes or viruses, so the mechanisms of all of this would surprise him. However, he would not be surprised by how elegantly this new information supports his understanding of common ancestors. The presence of viral DNA allows scientists to better trace the evolutionary history of species: the more viral fragments species share, the more recently they diverged. This technique can be used to investigate the relationships among species and test how closely they’re related.

Aside from being clues to ancestral lineage, these viruses have played an active role in evolution. For example, the biggest difference between the chimpanzee and human genomes is that chimpanzees have copies of a DNA sequence from a virus known as PtERV. The version of the gene TRIM5α that humans have codes for a protein that destroys the PtERV virus, protecting us from infection. But the other version of this gene, which does nothing against PtERV, completely protects against HIV. Studying these viruses and their role in evolutionary history helps explain why humans are susceptible to HIV and apes, our closest relatives, are not.

I had no idea that so much of our DNA is the remains of old endogenous retroviruses. Only 2% of our genome contains the information used to create the proteins necessary for life, while 8% is viral DNA that has been passed down from infected ancestors; I wish the article has explained where the other 90% of junk DNA comes from. I was also surprised that some retroviruses cause cancer. The article says that “experiments with mice and chickens have shown that they can block new infections by viruses with a similar genetic structure,” leading me to wonder if one reason chance of cancer is partially genetic is because endogenous viruses that protect against infection from similarly structured cancer-causing viruses would be passed from parent to offspring.

Although I understand the benefits of reconstructing viruses for research, there’s risk in creating something with an unknown function. John Coffin, a molecular biologist at Tufts University who has studied the role of endogenous retroviruses in human evolution, says “there are many more viruses that are far more dangerous than these,” but the problem is that you don’t really know how dangerous a virus is until it’s infected something. The opportunities for bioterrorism– as demonstrated by the researchers who built a polio virus and infected mice just “to prove it can be done”– worry me, but on the other hand the best way to prevent bioterrorism may be to have non-terrorist scientists researching the viruses so that we understand the risks and are better prepared to protect against potential threats.

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10 Responses to Darwin’s Surprise

  1. SanaM says:

    I was also very surprised at how important endogenous retroviruses are to our DNA. I think this article was eye opening because it gives us, as AP Biology students, a new perspective. In science: we never know if something is good or bad. There is so much undiscovered that it is not justified to claim that something like viruses are only a threat and do not have any potential benefits to us as a species. I completely agree with your thought on how these advances about viruses would have added to Darwin’s understanding of evolution and how they complement them. I think the cancer part is really interesting, because as you said, tying everything together it makes me wonder if the endogenous retroviruses have something to do with the genetic connection to cancer. I think this article is very multifaceted. It really keeps the reader on their toes because it continues to feed the reader interesting and relevant information. I think for me the most interesting part of the article, that is not mentioned here, is the development of the placenta in mammalians. The placenta has been found to be lined with syncytium tissue, which forms the barrier between mother and fetus. Researchers also found that the protein that caused these cells to fuse together to from the tissue parallels the mechanism that retroviruses employ. Lastly, I can’t stop thinking about the advancement that is mentioned about HIV. I think it’s just amazing how research has led us to figure out what makes our species susceptible to certain viruses while others are protected from it and makes me wonder where evolution will take us next.

  2. SpencerT says:

    It is confounding that only 2% of our genome codes for proteins necessary to life. That adds yet another layer of incredibility to the biological mechanism that is DNA and protein synthesis.

    When I read “Darwin’s Surprise,” I found myself wondering more about amino acids than nucleotides; given that there are only 21 types of amino acids found in eukaryotes, and we know a great deal about the function of cells, it seems feasible to chart patterns in the use of amino acids in specific aspects of cellular work. Is this something that scientists do now, and if so, how detailed are there findings? Do they use this kind of protein analysis to help in the discovery of new, extinct endogenous viruses? I like the idea of a dictionary for the words our 21 amino-acid alphabet can spell.

  3. NoraB says:

    I definitely agree with you about the dangers of resurrecting the viruses from our genetic code. The chance of it getting out of control and causing damage not only to humans, but to other organisms is huge. However I do think the benefits of doing so out weigh the costs. Deadly diseases have been worked with for years in labs and have only very rarely gotten out of control, if they have at all. We have a lot to lean from these viruses, and failing to do so out of fear is irresponsible. We could use this chance to learn about our past, and possibly protect ourselves better about viruses in the future.

  4. MayaH says:

    Although it is scary to think that college undergraduates with proper lab equipment are able to revive a dead virus, the ability to do so could potentially lead us to answering some important questions in the medical field. With the correct precautions, there should be a very low risk of a threat to humanity. As you stated, the best way to protect against bioterrorism is to research the viruses that pose a threat to better understand them and lower the risk of the spread of infection. As of right now, the only way we know to avoid a virus is to create a vaccine for it; if we shy away from reviving unknown viruses for research, we would be at a greater risk for potential threats.

  5. arsyed says:

    You bring up an interesting point with the potential for bio-terrorism through the revival and manipulation of viruses. The fact that we cannot know how dangerous a virus is until it has infected something worries me as well. If it does turn out to be a very dangerous and very infectious virus, then exposing it to the opportunity to infect something might not be the greatest idea. However, I understand that this research would allow for a better understanding of viruses and stop potential pandemics from lethal viruses. After reading this article, I thought hard about where I stand on this point. In the end, I realized that this research could end up being the difference between suppression and release of a virus that would cause the next “Spanish Flu” or a similar pandemic. In that case, understanding viruses is an important field in biology and must not be disregarded. However, this information and creation of viruses must be kept in the right hands to avoid the potential for bio-terrorism. Under proper management and regulation, this research is then very beneficial to our survival, for it could prevent future pandemics from affecting humans.

  6. EmilyD says:

    I was also really surprised by the fact that so much of our DNA is just remnants of endogenous viruses, especially in comparison to the amount of DNA that actually codes for proteins we need. Honestly, it almost felt like the article included those statistics just to catch the readers’ attention – knowing that our DNA contains viral remnants is important for an understanding of the article, but the way in which they pointed it out, it almost read more like “omg guess what guys 8% of our DNA is from viruses” than “we are presenting valuable scientific context for what we are about to tell you”. It definitely made me really curious about that other 90% as well; obviously it wasn’t necessarily relevant to the rest of the article, but I think in general the concept of junk DNA (as well as the fact that apparently 98% of our DNA is non-coding) is just fascinating and I’d like to know more about the make-up of DNA in general.

  7. PaulineE says:

    Hi Eleanor! Your blog post was really great to read! I definitely agree with you on the fact that resurrecting viruses comes with a risk. That is also something that worried me while reading the article. The scientific community seems to have such a limited amount of knowledge about viruses, that there could be some serious unintended consequence to current procedures. For example, if until recently, we thought the oldest lentivirus was one million years old and that “almost no one thought a lentivirus could become endogenous”—something that was disproven by scientists at Stanford University and the Imperial College London– what is to say that the rest of our information is not faulty in similarly jarring ways? It seems like scientists should spend a reasonable amount of time developing safety standards, or at least weighing the consequences before doing the things that you mentioned, like recreating the polio virus.

    Additionally, I have some comments about your observations on cancer. I thought you had a really interesting way of looking at it—I , too, was surprised that retroviruses were such a major contributing factor to cancer. However, I have had to do some research on cancer for my senior project and a lot of the genetic components have to do with things such as tumor suppressors and mutations in cell cycle checkpoints that induce apoptosis in mutated cells. That said, there is a host of genetic factors, including information for the immune system, expression of apoptotic resistance, etc. So, retroviruses could definitely be one of them! I just thought you might find that information useful.

    Great blog post!

  8. IsabellaC says:

    I think your response very accurately and eloquently addresses the focal questions. I really like how you first introduced the subject itself, and then began answering the prompts. When tying it together to Darwin, I like how you mentioned that despite his lack of knowledge of DNA he would not have been surprised by “how elegantly this new information supports his understanding of common ancestors.” Your response also has the most elaboration, and synthesizing information about specific viruses works really well in your writing. Like you, I was also intrigued as to what the rest of DNA is, since the function of only 10% was explained in the article. Overall, you answered the questions while maintaining a flow and articulation that was autonomous from said questions- it was my favorite response to read!

  9. RyanB says:

    It is definitely tough to weigh out the risks of reconstructing potentially dangerous viruses, especially with the possibility of bio-terrorism or accidental infections displaying just how dangerous a virus can be. Still, I have to contend that education and information are the best forms of protection. The further we understand our own origins and viruses in general through paleovirology, the better we can predict patterns and combat the harmful effects of such viruses. Still, this research would have to be conducted with great care and under strict scrutiny to ensure safety. In a controlled environment, with responsible research, we can conduct experiments with significantly less danger. I think the potential for discovery outweighs the risk.

  10. dbhuang says:

    The idea of bioterrorism is a looming threat when it comes to reconstructing these viruses. Like Eleanor, I agree that the means may not justify the results. Despite there being many viruses that could still be worse, I feel that it is irresponsible to assume that just because things could be worse, justifies the dangers that come with the process. On the other hand, the benefits that have come from reconstructing these ancient viruses are undeniably helpful. The knowledge gained from studying the evolution of viruses has lead to a revolutionized AIDs treatment. The reason many viruses are incorporated into our DNA is because millions and millions of years have passed rendering them harmless. Now, scientists are developing drugs that can increase the reproductive rate of viruses in order to render them extinct. Because there are so many things to consider in terms of costs and benefits, I am still on the fence as to whether or not I support this cause, but the advancements that the field has currently shown has definitely piqued my interest.

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