Naked Science Forum
General Science => Question of the Week => Topic started by: evan_au on 06/05/2023 03:43:41
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On today's podcast, a listener asked how long does it take a mutation to spread through a population?
In summary, the answer was: Evolution can be very fast or very slow.
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One aspect that was not really addressed in the podcast response was the impact of pathogens.
A contagious disease can significantly change the frequency of a gene in a population in a very short time, by killing everyone with susceptible variants of a gene. In this case, it is not a matter of how quickly a beneficial gene can spread through a population, but how quickly a novel pathogen can spread through the population.
In more general terms, it is said that there is a continual genetic arms race between hosts and parasites, as the host tries over many generations to fight off the parasite, and the parasite tries (over shorter generations) to evade the host's immune system. This causes continual evolutionary pressure on immune system genes.
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I've always argued against creationists that evolution occurs with every generation that reproduces sexually. If you don't look exactly like both of your parents, you have evolved - that's all the word means.
Selection is another matter. Pathogen resistance will be one factor favoring a particular genetic line, but there other environmental influences and adaptations may be important. One instance seems to be the evolution of the Caucasian strain of homo sapiens, which can tolerate ethanol and digest milk into adulthood, thus favoring long sea voyages (beer and wine don't spoil or support parasites that survive in barrels of fresh water) and life in northern Europe (getting winter fat and protein from cattle). The only mystery is what happened to the Neanderthals who preceded us
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I believe pathogens have played a critical role in our evolution. Suppose, for example, aids had arrived on the scene 150years ago before the understanding of the cause such diseases and methods of control. Given man's sexual proclivities it would have spread throughout the population, eventually leading to massive casualties. The only survivors would be that small cohort that we know now are immune to hiv.
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& the ones who followed Chastity or observed Abstinence.
Even Children & Adult asexuals.
(Vampires...no chance!)
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& the ones who followed Chastity or observed Abstinence.
Even Children & Adult asexuals.
(Vampires...no chance!)
They might survive as individuals, but if they're not reproducing they won't survive as a lineage.
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Given man's sexual proclivities it [AIDS] would have spread throughout the population, eventually leading to massive casualties.
Probably not. Many diseases are transmitted through sexual activity and/or the exchange of body fluids, but animals with low reproductive rates tend to mate for life and/or fight (including competitive display) for the privilege of copulation, thus ensuring that STDs are restricted and the fittest get to reproduce more frequently.
Interestingly I heard of two professionals who were diagnosed with sudden deterioration of their peripheral vision, to the extent that they could not detect rapid movement - an essential part of their work. It turned out that (a) something had destroyed most of the rods in their retinas and (b) both had recovered spontaneously from HIV. Seems that some folk can fight back, but I have now lost contact with the cases.
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Alancalverd, I disagree. Many bird species mate for life yet have offspring at least once a year, some with several broods. Not as fecund as mice but still quite active in reproduction. Man in contrast, with a low reproductive rate may mate for life but still have a "bit on the side", effectively nullifying the monogamous state. Most creatures mate at oestrus only while man is not limited by such inconvenient barriers. I am not a biologist but I reckon no other creature comes close to man in terms of sexual activity.
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I reckon no other creature comes close to man in terms of sexual activity.
You clearly have not studied bonobos or sparrows - God knows how they find time to eat!
You could calculate the R factor for any STD, but you need two measures: the "known source" factor - how many people will be infected from a single source, and the "source density" factor - what proportion of the sexually active population is actually infectious at any time. The success of the COVID virus is in its long pre-symptomatic infectious period, meaning that the second factor was several times the preponderance of symptoms, but most STDs express themselves before the carrier has infected many others. Problem with AIDS is, I think, the subtlety of its early symptoms.
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Hiv beats them all, it can be asymptomatic and yet infectious for 10years or more. What's a bonobo?, you'll have to excuse my ignorance. Despite living in a remote rural location we have had a large and growing family of sparrows, probably started around 10-12years ago. I do not analyse their behaviour to check for "hanky panky" but if it was that obvious I thought I should be aware of it. If asked I would have suggested wood pigeons to be the most active. Anyway i'll take your word on this important matter.
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https://www.britannica.com/animal/bonobo
The more I learn about these chaps, the closer they seem to humans than any other ape species. On film, they seem to walk far more upright than others, and swim very much like us. But "uninhibited" is a fair description of their attitude to sex and friendship - as Benjamin Braddock put it: "like shaking hands". My neighbor is a primatologist.
AFAIK nobody knows why the sparrow population has declined in England, but it certainly isn't due to any reticence on the part of the females, who dosey-do and change partners quicker than a square dancer. My pianist is an ornithologist.
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Problem with AIDS is, I think, the subtlety of its early symptoms.
From the point of view of teh virus, that's not a problem; it's a great asset.
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When it comes to growing another limb or developing another sensory apparatus, evolution definitely takes a long time. Millenia.
I mean we still have vestiges like the appendix(I don't) or the coccyx bone, these are parts of the body that serve no purpose except they sometimes lead to injury. Sometime in the very distant future human beings will no longer have them, they will however posses other vestiges that we have no idea about.
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It really depends on various factors like the mutation's impact, population size, and selection pressures. Some mutations can spread quickly, while others may take generations to become widespread.
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Re-reading the first post, it doesn't make sense! Mutations do not spread through a population, but populations evolve as successful mutants out-breed or out-eat the others. So the rate at which a population evolves depends on how you define the population (there is no rigid definition of species), at what point you consider the average to have changed, and how quickly they die.
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The rate a species changes or diverges into new species depends on reproduction rate and on how stable an environment is.
Bacteria, like the ones that evolve drug resistant strains, evolve relatively quickly because they reproduce quickly. The antibiotics are the selective pressure that helps things along by making the environment less stable.
A contrasting example is the molluscs. These have remained relatively unchanged in form, especially the bivalves, since they appeared; the environment for these critters hasn't altered very much for hundreds of millions of years.
Note: the above rule applies to the viruses, although they aren't respiring forms of life they are evolving.