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On natural selection...

  1. Sep 9, 2018 #1
    In the past, natural selection selected those who are the fittest to live to pass their genes, and eliminated those who are not, but now most people pass their genes, even those who don't have the best genes to live, although now not having the best genes may affect the qualify of a person's life instead of vanishing. Based on the above, can we say that natural selection has stopped acting on humans?
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  3. Sep 9, 2018 #2


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    It is not fitness to live that determines whether genes are passed on, but fitness to generate viable offspring that can themselves generate viable offspring. Consider the many organisms that die immediately after reproducing, like salmon or some male spiders.

    Selection for that fitness may be diminished in modern human society but it has not disappeared. For instance:
    - inability to generate viable gametes ensures a human's genes are not passed on, unless cloning or other high-tech genetic manipulation is conducted
    - for most reproduction, sexual selection plays a strong part. Humans tend to select mates that have sought-after characteristics, some of which relate to ability to generate viable offspring and some of which don't ('peacock tails'). Even in the case of sperm banks, women mostly choose based on what information they can obtain about the sperm donor.
  4. Sep 9, 2018 #3

    jim mcnamara

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    @EngWiPy No. Natural selection does not have direction. It never turns off.
    Natural Selection is random - what constitutes "fit" for a short time changes, even for humans now alive - see article below

    All species suffer periodic disastrous population crashes on a local population basis or across a continent. Humans are not immune to this just because of increased longevity in first world countries. We are not exempt from going extinct either.

    Article which asserts human changes will occur due to the strong influence of climate change (Scott Solomon Rice University - pop sci version based on his book):

    Please note that you cannot predict the ways a species will or will not evolve, the article is informed guesswork.
    Last edited: Sep 9, 2018
  5. Sep 9, 2018 #4
    What is "natural selection" and is it an efficient way of strengthening the gene pool? For example, consider Type II diabetes. This form of diabetes usually develops in late middle age or the elderly. Natural selection selects out which individuals are "fit" while they are at reproductive age, decades before the onset of type II diabetes. Consequently, you cannot expect "natural selection" to be an efficient way to clean the gene pool of type II diabetes genes, and this disease does have a hereditary component. Fortunately we can treat the disease quite effectively with medical intervention that will promote the quality of life for many older members of society. And we do not have to worry about weakening the gene pool because natural selection would not have removed these genes in the first place.

    Also a better way to say natural selection selects is the environment selects which genes are passed on by influencing which individuals reach reproductive age.
    The sickle cell gene provides greater immunity to malaria, but leads to serious (I do not remember it may be fatal) illness in places where malaria is not widespread. The sickle cell gene may be advantageous in some environments and times and disadvantageous in other environments and times. This is probably why the sickle cell gene was not selected out many generations ago. A medical treatment of this disease again would not weaken the gene pool.

    Natural selection has not stopped working on humans but the definition of "natural" has certainly changed. When someone dies of "natural causes", it usually means they have lived to a ripe old age without the ravages of heart disease, cancer, diabetes, etc. In the wild kingdom, an animal dying of "natural causes" would be a most unnatural way to go. Before middle age sets in, the rabbit is torn limb from limb and eaten by the wildcat, or the wildcat, unable to catch the rabbit dies of starvation. In general the term natural causes in the animal kingdom means eating or being eaten.
  6. Sep 10, 2018 #5
    This is missing one important part: every 'fittest' has an environment where it is 'fittest'.

    All what we did is that we changed our environment: with this the meaning of 'fittest' had changed as well. I have no idea what kind of meaning has it now, but I would like to be there to see the result :smile:
  7. Sep 10, 2018 #6
    Yes, I meant natural selection selected those who can procreate, but often this doesn't cancel the fitness to live. Take humans for example, each individual cares about his/her life, while at the same time procreate and take care of their offsprings.

    The environment has changed, no doubt about that, but natural selection boils down to selecting those who are "fit" to pass their genes. In the past the not-so-healthy members, probably couldn't pass their genes, because they would be weak to live and/or females probably didn't mate with them. Now however, almost every person is capable of passing their genes because of the medical intervention, and because there are broader options to mate (in combination with the common relationship theme of sequential monogamy in humans). In the past probably an alpha male in our ancestors mated with all the females, but now this notion is no longer true, although females are still attracted to alpha males traits like being funny, confident, responsible, strong, ... etc, which are rudimentary instincts from the days past.

    But I still see that "nature" discriminates between people. For example, a person who couldn't connect with his/her group socially in the past, probably would be banished and abandoned, and die as a result. But now these socially inept people, can still live, and even pass their genes, but they won't enjoy life as those who are good in connecting socially with others.

    Maybe if a microbial epidemic strikes humanity, natural selection can be activated again. I heard that in some African countries, some people have developed immunity against HIV, because it is common, and there are no medical interventions and sexual awareness. So, those who cannot fight HIV naturally would die early before procreating, but those who developed immunity against it can live and pass their genes. But in the majority of the world, medical interventions deactivate natural selection, I think, at least momentarily.
  8. Sep 10, 2018 #7


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    But it's not been rendered inactive. Haven't you read any of the responses so far?
  9. Sep 11, 2018 #8
    Natural selection is not random. It's in response to environmental factors, including social ones, that may vary over time. Mutation is random. Natural selection acts on mutation.
  10. Sep 11, 2018 #9
    Natural selection occurs because of differential survival and reproduction. It's ongoing in every species on the planet, including humans. To know where humans are undergoing natural selection, you have to ask which populations are under the highest selection pressure where people either live or die, reproduce or not. There are 2 populations I can think of that fall under this category. First, the world's desperately poor. People living at the extreme margins, who have limited access to calories, nutrition, economic and health resources. Their bodies aren't getting enough caloric and nutritional requirements to effectively combat pathogens, so natural selection is at work here. This is why the greatest evolutionary change in our species is directed at genes governing our immune systems.

    Second, the entire world's pollution is increasing, which affects the entire human population. People who are sensitive to industrial pollution are becoming increasingly less able to survive and reproduce. So whatever genes contribute to this sensitivity is being selected out of our population.

    Because we engage in much gene flow (i.e., sex between populations), the novel mutations that are being selected for in the above groups make it into the human gene pool as a whole.

    Incidentally, the second highest rate of evolutionary change is on the genes governing the CNS. I'm not entirely sure what to make of this. It could be due to evolutionary trade offs between immune system function and CNS function in the face of extreme malnutrition or it could arise from the increase in population and whatever differential reproduction that brings about. Not quite sure on this one.
  11. Sep 11, 2018 #10
    I agree natural selection is at work in regions where there are no medical interventions, and people rely on their natural abilities to fight diseases and survive. I gave an example before about developing immunity against HIV at some regions in Africa, because those who don't have natural immunity against HIV probably dies early before procreation, because there are no medical interventions. But in our current world, this is because of political issues that these countries and regions don't have medical interventions. I mean eventually, these countries will have access to better conditions.

    Also, I am not sure how natural selection on a small groups in Africa, for example, can affect humans, say in Europe, and other part of the world? They don't live under the same conditions. In the past, homo sapiens evolved from the same ancestors as other species that were spread around the world, but scientist said it happened in Africa. Why in Africa? Probably because the conditions and the environment were more pressing than in other parts of the world. But do we have such pressing conditions now to evolve?

    Maybe some people are more sensitive to pollution, but I think most people can still make it to reproduce. Maybe the average life span will be affected, because people may not live as long as if the air is cleaner, by developing disease such as cancer.

    I think gene mutations are happening in our genes all the time, but the forces of environment are not so strong to filter these genes.
  12. Sep 11, 2018 #11

    jim mcnamara

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    @Hiding Yup Natural selection does act on mutations. And non-mutations as well. You gave one definition. Stephen Jay Gould gave another. Meoitic drive, genetic drift, epigenetics(per individual as some not all epigenetic changes across generations persist) all contribute to genetic change.

    Random change in the environment has a large effect. What you are arguing is gradualism. Which is okay up to a point.
    Random means you cannot predict the outcome. At the birth of your children can you predict their outcomes? Heredity/Environment interaction is random - the environment is random just as are the genetic changes are random. And this is an old interesting argument.
    Microclimate can be taken as random environmental change:
  13. Sep 11, 2018 #12
    I believe I can answer your questions with some relevant facts about how evolution and gene flow work. Although, we have good, but complicated answers to some of your other questions.

    First, selection pressure differs by environment, both social and natural. So evolution is differential across populations within a species, including humans. Strong localized selection pressure keeps out competing alleles, which preserves population differences across time. Malaria is an excellent example of this: there are any number of localized mutations that favor surviving malaria but are negative outside of malaria environments. So those alleles do well in environments containing malaria and badly outside of them. Alternative alleles are selected against invading these areas, so at least for malaria-specific alleles, the gene pool pushes out incoming alleles.

    Second, some mutations will be favored in specific environments but are also useful generally, across most environments, like those that, say, increase immune system or neural efficiency. All alleles evolve locally and are subsequently distributed to the rest of the species via gene flow. So a positive mutation might arise in some specific part of Africa, say, and then move across to the greater human population via gene flow (which is just another way to say 'sexual reproduction' in humans). That takes generational time though.

    Third, populations living in areas where a species first evolves have the greatest genetic variation. Humans first evolved in Africa, so African populations have the greatest genetic variation of all populations. It's a bit more complicated than this. There were at least 2 out-migrations from Africa, the first of which eventually produced the neanderthals and devisonians. The second were anatomically modern humans who interbred with those previous populations. So nearly the entirety of human evolution happened in Africa, with some recent changes happening after. Now, with worldwide gene flow, beneficial alleles will tend to spread amongst the entire population, but very slowly, over generational time.
  14. Sep 12, 2018 #13
    No, I'm not arguing for gradualism. And, the other cases you bring up are not examples of natural selection. Yes, those are all examples of evolution. My statement is correct: natural selection is not random. In my post above, I was only correcting you on this point, not discussing other mechanisms of evolutionary change or the speed with which such change happens. You made an incorrect statement about natural selection.

    Yes, environmental change is unpredictable. That's inconsequential to the point that natural selection is not random. Adaptations are produced by natural selection in response to environmental pressure. Mutation is random, selection is the outcome of differential survivability among these. Hence not random, but directed.

    The theory of evolution by natural selection specifically addresses why species and their traits appear designed.

    No offense, but the points you raise here are all over the place. The birth of children is the result of sexual reproduction. Yes, their genetic make-up and future is unpredictable. That has very little to do with the theory of natural selection being non random.
    Last edited: Sep 12, 2018
  15. Sep 12, 2018 #14
    Here is a quote by Stephen J Gould on natural selection. Notice he does not agree with your claims here:

    "Throughout his last half-dozen books, for example, Arthur Koestler has been conducting a campaign against his own misunderstanding of Darwinism. He hopes to find some ordering force, constraining evolution to certain directions and overriding the influence of natural selection ... Darwinism is not the theory of capricious change that Koestler imagines. Random variation may be the raw material of change, but natural selection builds good design by rejecting most variants while accepting and accumulating the few that improve adaptation to local environments."

    I stole this quote from here:

    However, you can watch his lectures on youtube and he absolutely describes natural selection as non random.

    Here is a bit from the website "understanding evolution,"

    "At the opposite end of the scale, natural selection is sometimes interpreted as a random process. This is also a misconception. The genetic variation that occurs in a population because of mutation is random — but selection acts on that variation in a very non-random way: genetic variants that aid survival and reproduction are much more likely to become common than variants that don't. Natural selection is NOT random!"

  16. Sep 12, 2018 #15
    I disagree completely with your example you presented earlier that socially inept people might procreate and produce offspring that are also socially inept contributing to a large population of "unpleasant" people in the human race. Has anyone ever isolated a gene (or even several genes) for social ineptness.
    I know that researchers have tried with mixed success (perhaps no success) for isolating groups of genes for intelligence.

    I also have a tendency to dispute the premise in the original post that in your words "even those who don't have the best genes to live, pass their genes."
    How can anyone know which genes are the best to live, and which aren't

    To paraphrase Sir Peter Medawar, "the genetic goods are not always in the shop window." For example, a hereditary idiot may have genes necessary to become a concert pianist, but may never be able to avail him/herself of the ability or opportunity to demonstrate that they have these genes. Some so called "good" genes are probably linked to other so called "bad" genes, but both types may have been necessary to produce, Einstein, Bach, John Lennon, Michael Jordan, Abraham Lincoln, etc.

    As to your point, whether natural selection has stopped working on humans, it hasn't stopped but human (artificial) selection has diverted it to some extent. You can consider what this artificial selection has done in the evolution of the dog. Dog's come in shapes and sizes vastly different from their gray wolf ancestors and cohabitators. Look at what our selection has done to dairy cattle too. There are some thought in the future that humans may breed a human tailor made for long space voyages, etc.
  17. Sep 12, 2018 #16
    I didn't say that. I said that socially inept people can now procreate and pass their genes, although not being socially competent is not generally desirable. In the past, not being able to socially connect with others probably meant being banished and dead in the wilderness alone. This is because the environment has changed. Now people do not heavily rely on groups and social connections to survive. There is the state that provides protection.

    As for how to know the best genes is by the manifestation of the genes, and how that fits in the surrounding environment. Good and bad genes are relative to the environment, and I think they are measured by who can pass their genes by natural selection. There is no absolute good, and absolute bad. Having an infection now isn't necessarily a death sentence, although it might have been 100 years ago. Where is natural selection here?

    Can you give us some examples in humans?
    Last edited: Sep 12, 2018
  18. Sep 12, 2018 #17
    This is speculation on my part, but I have heard from many circles (although I can't quote the source), that obesity in our time may be the result of selection for metabolic processes that provided a selective advantage against starvation. The obesity problem is a consequence that at least in Western society there is ample (possibly) too much food. That is we developed nations have changed our local environment (i.e, efficient production of food) to lead to a obesity crisis. (But this is probably a good problem to have; it beats starvation)

    If we start custom designing space-men, this will be another example.
  19. Sep 19, 2018 #18
    Its a common fallacy to believe that what we believe to be valuable traits has any influence on natural selection. Its worth remembering that things like intelligence seem to reduce fitness and I doubt that obesity stage 1 has any significant adverse effect on fitness.
  20. Sep 19, 2018 #19


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    Humans have never had alpha males. Ever. The last time in our lineage that such a classification scheme might have been useful was probably before the genus Homo had even evolved. Also note that trying to take certain personality traits and using them to invent a human analogue to an alpha male in other animals is utterly wrong, as human behavior is far too complex for such a simple classification scheme. Anything you read that talks about alpha males and human societies is absolute rubbish and should be thrown away, burned, and/or deleted.

    Humans have, for almost the entirety of our existence, lived in small communities consisting of interrelated members. These are your family and your friends. People that would have known you since you were born or they were born. Being 'sociable' back then is not the same as it is nowadays, where most people live in towns and cities of hundreds, thousands, or even millions of people, the vast majority of whom are strangers to each other. Imagine growing up and living your entire life surrounded by your parents, siblings, perhaps your aunts/uncles, your cousins, and their children. And that's it. Occasionally you might meet a neighboring tribe and trade food, arrange marriages, and do other neighborly things, but for the most part you're just living with your immediate family. As long as someone wasn't stealing things or murdering people, I see no reason why they would have been shunned and kicked out of their tribe. No reason to get rid of a useful person who they knew and loved and who wasn't causing trouble. Would you kick your brother out of your tribe because he only spoke a few times a day? No, not if he's also helping gather food, make shelter and clothing, raise the children of the tribe, etc.

    It would only affect the rest of the world if their genes are passed on by their offspring to the rest of the world. You are correct in that without a similar environmental pressure to the one in Africa it would be very difficult for these genes to spread to the point that a large point of people in the world have them. You would have to rely on genetic drift instead of natural selection, and genetic drift is far less effective with large populations than it is with small populations.

    Why in Africa? Likely there is no reason other than sheer luck. That is, the right mutations happened, in the right order, at the right time, with the right environmental pressures, to make us evolve into what we are today. Changing any one of those things would likely drastically alter the course of our evolutionary history.

    Pretty much.
  21. Sep 19, 2018 #20
    I said alpha males in our ancestors. We humans are the descendants of those ancestors that had alpha males, and thus human females inherited the tendency to be attracted to alpha male like traits. I am not inventing anything. I said alpha male traits in purpose, because I don't believe in alpha males in humans, at least nowadays. I am not sure in the age of hunters-gatherers. I read that some scientist say that we were a combination of hierarchical and egalitarian, like bonobos. In any case, we cannot deny that old species in our lineage had an alpha male, and if we don't have an alpha male, we cannot just erase the genes that were evolved in conditions where there was an alpha male.

    The second point I want to comment on, is that sociable indicates collaboration. In one of his books (maybe Shadows of Forgotten Ancestors), Carl Sagan said that a baby who didn't smile to his/her parents probably was left and abandoned. This was a sign that the baby is not sociable and cannot relate to others. Being collaborative was very important. Nowadays we know this maybe a sign of autism. But people don't abandon their kids now because they are autistic. Also, note that this was an example. What I wanted to say is that many conditions in the past prevented the less fit people (maybe with some inherited diseases, or physical disabilities) from procreating. But now most people live long enough to procreate, even those who are not the "best" fit.

    Now we have a control over our environment, and thus the forces of nature are no longer strong to make natural selection effective, except probably in small parts of the world, where there is no medical intervention, where more immune people have advantage over the less immune in face of infections. But in most parts of the World, most people have the same immunity against many diseases because of vaccination. So, nature plays a less important role here.
    Last edited: Sep 19, 2018
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