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Do they exist? Yes What are they called? Marilyn Roossinck calls them viral mutualistic symbiotes. She has an excellent review here. What are some examples? My personal favorite is GB-Virus C, or Hepatitis G, which appears to slow the progression of HIV using a number of different mechanisms: Box 1. Summary of the effects of GBV-C infection in HIV-...


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During the process of selection, individuals having disadvantageous traits are weeded out. If the selection pressure isn't strong enough then mildly disadvantageous traits will continue to persist in the population. So the reasons for why a trait is not evolved even though it may be advantageous to the organism, are: There is no strong pressure against ...


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Short answer The article in particular that you reference is discussing the possibility of using a mechanism called gene drive. The concept of gene drive breaks the normal "rules" of inheritance and allows a gene to spread much more rapidly than normal in a population. Longer answer Gene drive depends on the idea of a selfish gene. There are naturally ...


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This entire answer will be long, so read the short part first, then read the rest if you (or anyone else) is curious. Citations are included in the long section. I can include additional citations in the short section if needed. Long Story Short Your question touches on some common misconceptions about how the evolutionary process. Organisms don't "want" ...


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Very intresting question. The problem is that animal intelligence is hard to measure not only for scientists, but probably also for the potential mate. Paradoxically, that is why selection for intelligence, if it occurred, may be very strong. One has to be smart in order to recognise smart behaviour, so preference and preferred feature are strongly connected....


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There's always the most obvious: Evolution is chance. Some traits allow an individual to have a higher chance to produce offspring. That doesn't mean individuals with that trait have more offspring, not even on average unless the law of large numbers applies. A randomly mutated perfect squirrel could appear, and since it's only one, it gets run over by a ...


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Mathematician/computer programmer's answer here: There is a continuum of different animals — in fact it's pretty fair to say that every animal occupies a different place on this continuum. They're just not uniformly distributed over the continuum; they're clustered around forms that are most likely to survive and reproduce, and the lowest-energy paths ...


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Another good virus would be a Bacteriophage, a virus that infects and kills illness-causing bacteria. From Wiki: A bacteriophage also known informally as a phage, is a virus that infects and replicates within Bacteria and Archaea. The term was derived from "bacteria" and the Greek φαγεῖν (phagein), "to devour". Bacteriophages are composed of proteins ...


21

To get a non-circular answer to why humans and other mammals have only two sexes, it's helpful to take a look at our evolutionary history. While mammals possess several adaptations to a terrestrial life cycle, including internal fertilization and gestation, which require substantial anatomic specialization between males and females, these are all secondary ...


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Because evolution is an effect, not a cause. That is, there's no "God of Evolution" out there deciding that this or that trait would be beneficial to a species, and deciding to add it. Evolution just works* on whatever random variations happen to come along. *And as others have pointed out, it works statistically, not deterministically.


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Short answer Why are there species rather than a long continuum? Three important reasons I could think of are sex, non-uniform adaptive landscape and ancestry. Long answer I am not sure I'll answer your question so let me know if I miss your point or if I help! To start with, you might want to read this answer on the semantic difficulties behind the ...


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Change in genetic variance From what I have been taught, Natural Selection (or even Artificial Selection) is great for panning favorable genes from a species and bringing them to the fore, however, it does not introduce new genetic changes. Yes, you are pretty much right. In a given population, directional selection will ultimately reduce genetic ...


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I would say that if any "good" viruses exist, they are already within us. Retrotransposons are genetic elements in our DNA that were likely ancient viruses and they move around from time to time either by excising themselves and moving somewhere else or by making a copy and inserting it somewhere else in the genome. Even though we are born with them, their ...


16

I looked up winglets so I had context for this answer. I'm interpreting winglets as the vertical tips at the end of airplane wings. If so, then you are correct. The spread primary feathers of soaring birds like eagles function as winglets (Tucker 1993). Airbus has a biomimicry web page devoted to some of the biological designs, including winglets, they ...


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We have engineered a few good viruses to treat certain diseases Per my comment and response: The most current example (at this time and based on my recollection) is the virus we have engineered to treat a certain type of macro degenerative eye condition: Scientists Have Reversed Age-Related Blindness by Deliberately Infecting Eyes With a Virus There are ...


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Below are the reasons I can think of. The list is not exhaustive and there are some conceptual overlaps. The trait seems advantageous but it is not, maybe due to its effect on another component of fitness (trade-off). It sounds to me to be the most likely explanation whenever you are wondering why a given species does not carry a given trait. In other words,...


14

Cowpox and smallpox viruses structurally similar, and catching one confers immunity to both by immune system response, but one was a deadly disease and the other almost harmless. Once this was discovered, the days of smallpox were numbered. We had the means and the motivation to stamp it out. On my last check a few years ago, we are deliberately keeping ...


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Official definition Is there an official definition of natural selection that is adopted by biologists nowadays? and what is that definition exactly? I don't think there is such a concept as an "official definition" of any concept in science. There are common definitions though. The definitions you cite Let's go through your three definitions ...


13

Charles Darwin formulated his theory after travelling the world aboard the Beagle, here's the route. He found the Galapagos Islands particularly inspiring, 'The natural history of this archipelago is very remarkable: it seems to be a little world within itself.' This is a more detailed account of his relationship with the Galapagos islands, and there ...


13

I agree with you that the question is ambiguous, and also that the most sensible answer would be C. However, one could make a more or less reasonable argument in favor of several other answers, too. a. The common ancestor of whales and fish possessed genes for fins. Technically, this statement is true. At least some of the fins of whales and fish are ...


12

Nothing happens to them. Organisms exist. They breed with other organisms who are genetically compatible. We humans might try to categorize them according to certain traits, but our labels are just labels, biology isn't governed by them. Over time, we might see that a population used to have one trait, and its descendants no longer have it, they look ...


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About your question This kind of very basic question has the drawback to need a very long answer. In consequence, your question might get some close vote. I'll do my best to help but you might want to look at some source of information as an introduction to evolutionary biology. A book eventually or Khan academy maybe. Darwin's evolution theory The ...


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I accidentally wrote a lot! I first discuss the term Darwinian evolution. I then describe the main evolutionary processes insisting on the two elements of interest in your question, that is mutations and natural selection. In the end, I directly address your two statements and bring a few more complications into the subjects. Did you say Darwinian ...


11

The evolution to the current state of life on earth has occurred through some 3.8 billion years. During this time it has gone from the most basic forms of life, simple self-replicating units, to the complex beings we see today. Evolution, the process of change within a collection of units, is caused by 4 factors, mutation, selection, drift, and gene flow. So ...


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More specifically, the lack of observable gradual change between species. Most significant phenotype differences occur over several thousand generations, which means several thousand years on up. While we certainly can create experiments where a controlled form of evolution occurs within a very small time-frame, I'm going to assume that you're not ...


11

The logical assertion "winglets have not happened in a long time, therefore they are not advantageous" is incorrect. It is possible for an advantageous trait not to evolve even when advantageous, if there is no "path" to it. The trait only occurs gradually, in small incremental steps. If intermediary steps are harmful, the trait will not occur, even if the ...


11

Evolution occurs by a change in gene frequencies, with gene frequencies potentially affected by four mechanisms (mutation, migration, drift, and selection). The answer to the question Why does the seemingly advantageous trait X not evolve? could be: The mutations for a trait have never occurred within a population, or such genes have never migrated into ...


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You're right that the mutation must be in a germ cell in order to be passed on. Most errors are introduced during DNA replication (at a rate of around 10-10), which occurs a number of times between the zygote stage and mature gametes. This book estimates that there are 24 divisions between zygote and egg and 23n+34 divisions between zygote and sperm, where n ...


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The statement individuals do not evolve, populations do is rooted in the (classical population genetic) definition of evolution. Here is this definition: Evolution is a change of allele frequency through time in a population Evolution is defined for a population, it is not defined for an individual. And it makes intuitive sense once you get more used to ...


10

Typically when both new and old species still exist it is because evolution pushed the new one into a different habitat or role. As a hypothetical example reef fish vs. deep water fish and their relative size. Let's say deep water fish evolved into reef fish, but we still have deep water fish. So there were deep water fish that were a little smaller ...


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