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Natural Selection, why not even better?

  1. Aug 13, 2014 #1
    I'l start by saying that I'm not a creationist or something like that, I fully support evolutionism and the scientific approach.

    However, while natural selection can powerfully explain the traits of all current species, it can be hard to understand why if this is the mechanism driving evolution, it has not produced even better organisms.

    I mean, surely we would be better off if we had eyes also in our back, multiple eyes have evolved in other organisms so why not in us or in many other animals? Or, we would be better off if we could dive in the water for a long time as cetaceans do. Or if we had echolocation. Or if we could see well in the dark as other animals do. Or if we had the smell of dogs. Or if we could survive under a wider range of ambient temperatures as many other animals do. And so on (I will not go to the extreme of "and if we could fly").

    I am putting these examples from a human perspective to be more clear but the argument is general, given that many advantageous traits have evolved in many animals, it is somehow strange that these have not evolved in many other species, when they would surely mean also a benefit to them.

    It seems that organisms have evolved just a few advantageous traits, and that "few" is a different set for each species. It seems strange that no organism has harnessed most (or a lot) of the best mutations but each species has only a few of them.

    Humans have developed intelligence and the ability to manipulate things with our hands but have not developed many of the advantageous traits found in other species. If mutations are really random, it is hard to understand why a mutation for, say, being able to see a wider spectrum of electromagnetic radiation than our visible light spectrum has never happened to the human ancestors as it did in other species. Because if it ever did, it should have provided a survival advantage to its possessor and should have therefore stayed in time.
    Last edited: Aug 13, 2014
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  3. Aug 13, 2014 #2


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    Evolution relates to mutations that improve a species' survival in their environment. For example, humans don't live in the water so there is no survival advantage to having gills.
    In fact, species can often lose capabilities that they no longer need based on their environment such as fish that live in caves. Over time, several species of fish that originally had eyes, no longer have them. In a completely dark environment, eyes provide no advantage so fish without them have the same survival chances as a fish that does.
  4. Aug 13, 2014 #3
    As Borg pointed out, animals typically only retain traits that are essential to their survival and reproduction. It's a basically a trade-off between the usefulness of the trait and the energy cost of retaining the trait. If the trait isn't absolutely necessary, the energy investment typically isn't worth retaining or developing the trait.

    As far as your example above, there really isn't a compelling survival advantage to expanding the capacities of the eye-brain network in humans to process ultraviolet light signals. The neural resources are better spent elsewhere. However, for a bee, there is a clear survival advantage, so they have developed the capacity to see into the UV range:

  5. Aug 13, 2014 #4
    ^ mmm, I can't see why being able to see UV or infrared should not provide any advantage compared to individuals able to see only visible light. Whatever the amount of "advantage", it can never be negative, seeing more is better than seeing less. And I don't see why this should mean a sensibly higher energy expenditure, many animals detect a wider electromagnetic spectrum than humans and I don't think they have that much more energy expenditure, I believe that humans have energy enough to cope with that without any significant loss in any other areas. Sorry but I don't buy that argument.
  6. Aug 13, 2014 #5


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    What makes you think that humans would ever acquire this ability in the first place? It's not like one day the human body goes "oooh, let's add *this*".
  7. Aug 13, 2014 #6
    Of course not. But there are so many useful features found in "lower" animals which have not gotten their place in humans or other "higher" animals. It is hard to understand why mutations which helped other species to see better, to hear better, to smell better, to breath better, to echolocate themselves, to survive in a wider range of temperatures etc, none of them ever happened to the ancestors of humans. I guess the academical answer is just "well, it certainly could have happened but it just didn't", but the fact that they did for many other species still leaves an open question as to why similar mutations did not happen in many other organisms such as the human ancestors.
  8. Aug 13, 2014 #7


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    The problem with your logic is that the useful features that you give as examples aren't simple mutations. They are the combined result of mutations that occurred over a very long time due to environmental conditions for that species.

    Think about this. How do you think that eyes formed? Did they just suddenly appear on some creature one day? Why don't plants have eyes?
  9. Aug 13, 2014 #8


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    As others have pointed out traits to not simply mutate fully formed (at least of the sort you are describing). Whilst the end product might confer a survival/reproductive advantage the steps required to get there clearly do not. In other organisms though these individual steps did. The difference is one of environment (at various times in their evolutionary history their environment favoured those mutations) and lineage (their evolutionary history itself made it possible for these mutations to occur).
  10. Aug 13, 2014 #9
    If the information we need is in the visible spectrum, adapting our optics to include infrared or uv will comprises what we need for something we don't need.

    Just as an example of what we don't need, take a look at the bands collected by the Thematic Mapper (a general purpose imaging satellite):
    http://igett.delmar.edu/Resources/Remote Sensing Technology Training/Landsat_bands-sm.pdf
    It has 8 bands, including visible and infrared - but no ultraviolet.
    There are modern advantages to look in the infrared. But if you review Landsat imagery, I think you can see that there would be nothing of critical use to our ancestors.
    Last edited: Aug 13, 2014
  11. Aug 13, 2014 #10


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    We have the capability to make cars that drive extremely fast (>250 mph/400 kmph), so why can't the typical car you see around town reach these speeds?

    The answer to this question and the question you ask is the same: cost. Many traits come with a cost, for example, in terms of the resources required to form and develop new organs or structures. If these traits confer only marginal fitness benefits to a particular organism, organisms lacking that trait would likely be able to outcompete those with that trait just because they use their resources more efficiently.

    In another thread, I discuss and link to a news piece from Science that talks about the evolutionary trade-offs associated with increased intelligence that explains why some animals have not evolved increased intelligence.
  12. Aug 13, 2014 #11


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    Not if the cost of seeing these wavelengths results in a situation that lowers the fitness of an individual. For example, the human eye can see UV in a limited manner, but only if you remove the lens. However, removing the lens would lead to a loss of fine focus and would be very detrimental to our fitness, so it will not happen.

    It's not always about energy expenditure. Changing the structure of the eye could mean it is more susceptible to injury, which would lower our fitness. You also have to consider that even if there is a way to alter our eyes without making them more fragile, there may be no way to get from our current eye to the new one without going through steps in between that reduce our fitness. A good example is the recurrent laryngeal nerve (RLN), the nerve that controls your larynx. You would expect that the nerve would split off from the main vagus nerve around the level of the larynx and run directly to it. But this isn't the case. The two branches of the RLN run all the way down into your chest before splitting off and running back up to your larynx. The left RLN in particular takes a very indirect approach, looping under your aortic arch before running all the way up to your larynx.

    You would think that evolution would change this nerve, as it is susceptible to damage from blows to the chest and moving it would shorten and protect it. But evolution can't. To do so would require several major changes during the development of the embryo, and each of these changes would affect the fitness of the person. There's simply no intermediate stage that works, so evolution leaves it as it is.
  13. Aug 14, 2014 #12
    This reminded me of an old paper I read by Terrence Sejnowski where he draws an anology between brain evolution and the upgrading of an old power plant that couldn't afford to be taken "offline."

    It took me a few minutes here to find the reference, and it was actually in a review article by Sejnowski on John Allman's book, Evolving brains. I actually read that book too and own it, but remember the passage from Sejnowski's review. In any case, here it is:

    https://papers.cnl.salk.edu/PDFs/A High Point for Evolution 1999-2940.pdf

    The article and Allman's book also go into some discussion on the evolution of the visual system and the tradeoffs in development vs energy concerns discussed in this thread in case the OP is interested.
    Last edited: Aug 14, 2014
  14. Aug 14, 2014 #13


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    Couldn't resist. :tongue2:

  15. Aug 14, 2014 #14


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    Evolution is more "lazy" than you presume. It need only do the minimum required to sustain a genetic lineage. It needn't go further.

    The selection process uses death to weed out the unfit, not hearing amd seeing tests. If you can survive (and reproduce) without hearing or seeing, you pass.
  16. Aug 16, 2014 #15
    I think it depends on your definition of 'better', as far as humans go, most things seem to be worse that other animals, or our past selves.

    Evolution does not have a direction, I also think it should be "nature selection" not 'natural', artificial or 'unnatural' don't really apply (again IMO).

    Apart from a big brain, we have lost most anything else that is considered 'advancement', we are weak, slow, don't see or smell well, we cant run fast or that far.

    As for our intelligence, it gets us by and is sufficient to give us the required edge to survive as a species, but does that mean MORE intelligence would give us more advantage? Is there any real selective pressure based on a persons level of intelligence now?

    In the past being a skilled hunter meant that you were also a able provider for a family, but once you have the level of intelligence to skilfully hunt and provide does more intelligence help you much?

    Height is one thing that seems influenced by evolution, people see (generally) tall people to be more successful and potentially more able to be a good provider, so tall people get all the nice looking tall girls, (not me, I am short), the tall gene is then more favoured that shorter, so over time we evolve to be taller, (but not too tall).
  17. Aug 17, 2014 #16
    ^ I think not even that is relevant anymore for humans, now (in developed countries at least) everybody has basically the same chance of survival and reproduction, tall or short, clever or dumb, physically strong or weak. Of the relatively few people who die without any offspring, I don't think for many of them the cause was a weak genetic profile (except for those few who die very young due to some severe health issue). And it's not the case anymore either that the 'fittest' have more offspring than the average person.
    In the developed world natural selection is not present anymore. Will this have any long-term effects in the quality of the human gene pool? who knows...
  18. Aug 17, 2014 #17
    BTW, what is the proposed explanation for the persistence of genetic disorders which affect the chances of reaching adulthood or of reproduction in the gene pool? Such as cystic fibrosis, which causes infertility (in 97% of the males and 20% of the females according to Wiki). A simplistic Darwinian interpretation would suggest that such a disorder should have long been eliminated from the human gene pool but the fact is that it is still relatively common in Caucasians. This is another form of the question "why not even better?". Why not having eliminated such genetic disorders altogether?
  19. Aug 17, 2014 #18


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    Evolution is a crap shoot. For every successful mutation, there are innumerable failed mutations. Furthermore, there are a number of genetic disorders that are just a matter of bad luck. For example, it has been shown that acquiring one copy of the gene responsible for sickle cell anemia confers protection from malaria. Acquiring this gene from both parents results in sickle cell anemia.
  20. Aug 17, 2014 #19


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    There is no such thing as a "weak genetic profile". Whether or not a gene is advantageous, neutral or deleterious is almost always entirely contextual. A gene granting resistance to a certain disease is of no benefit in a society with adequate hygiene and healthcare. In fact it might be a disadvantage if there are side effects to resistance (e.g. sickle cell trait and malaria).

    You seem to be leaning towards a way of thinking that "fitness" in an evolutionary sense is equivalent to everyday human usage implying that with strong selective pressure we would all be strong, smart, healthy individuals. Aside from the fact that being strong, smart etc isn't always the best survival strategy when it comes to health you need to consider the evolutionary arms race between predator/prey and host/disease. Essentially whilst natural selection might lead to a species developing resistance towards a certain disease it can also lead to the disease adapting to work around said resistance. Most of the time this means that no species comes out dominant but rather there is a constant too-and-fro, this is called the red queen effect.

    If you apply this to the way of thinking that using technology to keep people alive makes us weaker you realise that this isn't the case. Without technology we would have a situation in which generations adapt to fight disease but disease keeps up ensuring a constant threat.

    Cystic fibrosis is caused by a recessive mutation. You can carry a copy of a damaged CFTR gene and be absolutely normal if your second copy works fine. You can only have cystic fibrosis if both your parents are carriers and through chance (a 1/4 chance) passed on two faulty copies to you. Thus whilst a person with CF is unlikely to reproduce due to infertility and reduced life expectancy genes leading to CF persist in the population due to carriers.
    Last edited: Aug 17, 2014
  21. Aug 19, 2014 #20
    Why haven't any animals evolved wheels? Surely that would be an improvement for speed.
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