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Question about evolution

  1. Mar 11, 2012 #1
    Evolution is the passing of genetic traits from species to their offspring and the natural selection of evolution occurs because certain species die out when they are unable to cope with their environment and the surviving species continue to pass on their genetic traits, which serves as evidence that those genetic traits are more beneficial to survival. But if traits are simply being copied from one surviving generation of organisms to another, then how are new traits generated in the first place? Does the generation of new traits simply occur randomly such as when sexual species perform intercourse or when asexual bacteria receive viruses that cause them to mutate? Or does information about the environment, received by the organisms using various senses alter the genetic information contained in the DNA to make the organism more suitable to the environment?
     
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  3. Mar 11, 2012 #2

    D H

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    It's the former, more or less. Sexual reproduction is a very powerful evolutionary mechanism. Life on Earth changed very slowly until sexual reproduction appear. Shortly thereafter, kaboom, the Cambrian explosion occurred.

    Aside: Sexual reproduction is not quite random. Just look at ourselves. While some males might mate with just about anything, females are a lot more selective.
     
  4. Mar 11, 2012 #3
    well that explosion is actually thought to be over 70 to 80 million years. Agreed the time is small compared to the age of earth.

    http://en.wikipedia.org/wiki/Cambrian_explosion
     
  5. Mar 12, 2012 #4

    bobze

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    There is lots to learn for you padawan, more than anyone could probably reasonably hope to cover via forum posts.

    Fear not! There are lots of good websites with introductory biology/evolutionary biology perfunctory education available. One I often recommend to the interested novice of evolutionary biology is Evolution 101, hosted by the good folks of UC Berkeley and the California museum of Paleontology.
     
  6. Mar 12, 2012 #5
    So basically, sexual organisms can consciously select who they have intercourse with based on biological instincts that would tell the organism who initially observes its mate that this mate is more suitable and will yield better offspring to continue the species.

    But an organism must somehow have the capability to respond to the information conveyed by the stimuli of the environment so that drawing upon such information will enable the organism to evolve to better adapt to the environment because it is said that species evolved senses only to detect the presence of stimuli in a given environment and the absence of the sensory stimuli in the environment will negate the organism's need to develop the senses to detect that stimuli. That is why fish living in underground water reservoirs did not develop eyes because there is no light to be detected in such an environment, while animals that live in environments with light sources have evolved eyes. The question is how exactly does information from the environment cause DNA to change in such a way that an organism will evolve into a species with new types of traits and body parts that are more suited to the environment it is in?
     
  7. Mar 12, 2012 #6

    Ryan_m_b

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    Sort of but it's a bit more complicated than that, simply having a sexually desirable trait does not necessarily mean that said trait confers a survival advantage.
    No that's not the case. Mutation is essentially random, when an organism reproduces the offspring will possess half the genetic information of the mother and half of the father. Due to mutations of various types that offspring can have slightly different traits than that of either parent. Whether or not that trait is an advantage depends on the environment, so the trait arrives first and then is "tested" by the environment which determines whether or not it is an advantage to survival and/or reproduction or a disadvantage. The environment does not cause the trait to arrive itself.

    For example: a point mutation may result in a protein having a different sequence and therefore different chemical activity that might confer an advantage to breaking down substance X. That organism may then eat something that usually is poisonous/not-nutritious because it contains substance X but thanks to its trait it survives and gains nutrition. This puts it at an advantage over other organisms because it has a source of food that they do not (this is of particular advantage if other food is scarce). Because this organism has an advantage it will find it easier to survive meaning that it has more chance to mate and reproduce than others. Consequently the next generation will have a higher proportion of organisms with this trait and over time it will spread. Does that make sense?

    We have an introduction to evolution you might be interested in reading:
    https://www.physicsforums.com/showthread.php?t=543950
     
  8. Mar 12, 2012 #7
    So mutation is random and the environment does not directly control what traits organisms will have. The environment merely kills off the organisms that cannot cope with the environment while those that survive replicate their genes when they produce offspring. Since the mutations that cause new traits to be produced are random, the emergence of useful traits is entirely by chance, and whether they are useful or not is also dictated by chance.

    These randomized mutations are consistent with the history of evolution because if the environment directly affected the traits that organisms developed and the organisms kept on successfully adapting to changes in the environment, then there would be no mass extinctions. In conclusion, if the environment had a direct influence on evolution, then organisms will always only develop advantageous traits but this is not the case because there are many instances of neutral and deleterious mutations.
     
    Last edited: Mar 12, 2012
  9. Mar 12, 2012 #8

    Ryan_m_b

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    You're getting there but not quite. You're absolutely right that mutations are (essentially) random but whether or not they are useful, or to put it a better way advantageous, deleterious or neutral, is not random or by chance. It's determined non-randomly by the environment.
    I'm not so sure. Mass extinctions tend to occur because a (relatively) sudden change disrupts the ecological network. This is more of a problem if the majority of species are highly specialised e.g. a volcanic eruption reduces global temperatures causing the killing off of a plant that is the only food source of several species who are the pollinators/prey of several other species etc.
    If, somehow, the environment directly influenced mutation so as to make an animal more adapted then yes it is more likely that mutations will be advantageous but as you say this is not the case.
     
  10. Mar 12, 2012 #9
    Of course the usefulness of the trait will be tested by the environment, but whether the organism will coincidentally be in the right environment at the time a mutation randomly takes place that happens to be advantageous in that environment or not is out of the organism's control so chance still plays a part in this process. Though the organism may keep on exploring different types of ecosystems and arrive at the one most suitable to the traits that it possesses entirely by process of trial and error.

    So in conclusion, after millions of years of natural selection and random mutations, trial and error will eventually give rise to species which will combine many advantageous traits once held separately by many different species. Though evolution is not entirely linear because the environment can also make some random changes, genetic drift may be caused by random accidents, disasters, or extreme environmental changes that are too destructive for any species to cope with and cause what could be potentially be good traits to not be replicated because a large percentage of a certain species can be wiped out by such events, and of course, the replication of DNA during reproduction is not perfect and random deleterious traits that may kill offspring can emerge.
     
  11. Mar 12, 2012 #10
    There are many examples of phenotypes that could be considered comparatively detrimental. Such as peacock, with such a large tail, limits it's survivability comparatively. Raising this example to point out that the "resources" for sustenance & "resources" for reproduction both effect genetics & sometimes they are not complimentary. (birds seem to get away with odd phenotype mutations more so than other species)

    For the bolded part, tweak the reasoning just little bit. You're right that eyes didn't develop because there is no light, but from an evolution perspective, it is because being able to see light gives no comparative advantage in that environment. Said different, if we imagine the species used to have eyes and could see light, but changed environment to the deep dark sea due to too much competition in the visible light waters, the species would only lose the eye sight from mutation(s), and not because there is no need for eyes.

    To say it differently, that species may have developed eyes, but didn't becomse a succesful trait due to lack of competitive advantage.
     
  12. Mar 12, 2012 #11

    Ryan_m_b

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    No this is incorrect. Different species cannot interbreed, it's part of the definition of what makes two organisms different species.
     
  13. Mar 12, 2012 #12
    No, the new species possessing the combination of advantageous traits may simply evolve traits that are coincidentally similar to other species through random mutations and natural selection. The statement did not imply that different species would breed with one another. It simply stated that a specie may evolve by chance to contain a combination of beneficial traits possessed separately by many different species.
     
  14. Mar 12, 2012 #13

    Ryan_m_b

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    Yes this is known as convergent evolution and is common when certain traits are extremely advantageous.
     
  15. Mar 12, 2012 #14
    I think the mistake we do is we always think of evolution in terms of individual organism of a species. Problem is nature does not work with only a particular individual or organism. Nature works with population of different species.

    Consider random mutations occurring within a particular population. Now, some of those mutations are so random they can be advantageous or detrimental to individuals of the population. But if individuals within that population have slight advantageous mutations ( over long time ) which increases their chances of reproduction then those traits get passed on. But, on short time periods all those variation within the population remain stable (meaning it may not offer particular advantage over short time periods).
     
  16. Mar 12, 2012 #15

    bobze

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    No organisms don't choose to mate to propagate the species. You're at the wrong level of thinking here. The point of reproduction is propagation of genes, not species.


    Wrong level again. Organisms don't evolve, populations do however. Organisms pass on genes, the collected assemblage of genes: a population, we think of as the gene pool. The genes being spatially fixed entities in the gene pool (research: locus), existing of different "flavors" we call alleles. Alleles are the substance of variation that are recombined through sex and changed through mutation to provide new variation in an environment. The frequency that alleles exist in the gene pool is what is determined by selection in a non-random fashion.

    Genes, those spatially fixed entities, can be "created" as well through other genetic processes (research: gene duplications); where then new and novel alleles for the new genes will be added to the pool.

    When we talk about evolution this is the meat of it--at the level of the population, specifically the population's gene pool that is changing through time. In any one generation the horizontal variation (between distantly related individuals of a population) is far greater than the vertical transmission of variation between parent and offspring. The ensures that members of a population will be reproductively active with each other within the population. It answers the often asked question "who was the first of X species...."

    The environment acts as the arbitrator of variation; in a way you can think of it as "feeding" on variation. Where certain variation will be culled out because of either a penalty to survival OR a penalty to reproduction. While those members of the population left will out produce those with penalties to survival OR reproduction. This is, in essence what we call natural selection. So the 4 postulates which support this theory to explain how those allele frequencies change are; variation, heritability, finite environments and differential survival and reproduction.

    There are other ways to explain how allele frequencies in a population change over time, but none of them posses the ability to build adaptable variations. For example, as has already been broached, sexual selection: which again delves into differential representation in subsequent generations; specifically in this regard we are talking about differential reproductive output because of some novel, mate driven, feature. My favorite example is the widowbird and their tails.

    347761432_143e5ccb3c.jpg

    Sexual selection "works" because alleles which are selected for by choosy mates are maladaptive traits. The payoff for the choosy mate is that mate partners with such a maladaptive trait must have a compliment of "good" traits to overcome the penalty to survival the sexually selected trait imparts. Its a way for the trait-bearer to say "look at me see how good my genes are, they can over come this large survival disadvantage".

    The balancing force to sexual selection will always be natural selection, because there will be some limit to which maladaptive sexually selected traits will be pushed--beyond that limit then the penalty imparted to survival will be so high, that it cannot be overcome: Thus extinction.

    Which is the last piece of the puzzle. Traits too maladaptive get culled by selection, when this happens across large swaths of a population--you get extinction of a lineage. And we think about the greatest driver for extinction as "fast" (geologically speaking) environmental change (read here an environment is the sum of biotic and abiotic interactions a population exists in).



    Like someone above pointed out, you are thinking about it backwards. Fish didn't choose to evolve no eyes. Fish which lived in an environment where there was no or little visual stimuli, and so members of the population with eyes failed to match the reproductive output of members without eyes.

    Note: this is dangerously simplistic here. Eyes are a very complex biological trait, its not like there is a "gene to make eyes" and then different alleles of that gene. Eye genetics has to span thousands of genes and even more alleles for those genes. So bear that in mind when reducing something so complex to such a simple description.


    It doesn't. Don't put the cart before the horse, this is something that people (even ones with lots of biology under their belts) get tripped up on.

    Remember this is very important: Evolution has no end goal in "mind". An adaptation is not the point of evolution, it is the BYPRODUCT of selection. Likewise speciation is not the point of evolution, it is the BYPRODUCT of reproductive isolation.

    Environments don't cause change. Variation, new and novel, is only introduced through mutation (caveat, mutation is a vague term here there are many types of mutation and they are all not equally the same). For the novice of biology then, its probably best to think of mutation as "random". And the environment selects from the pool of variation created by mutation and sex--not that selects here refers to differential survival and reproduction.

    (Another caveat here; while it wise to think of mutations as "random", the true story is its not that simple either. Mutations are underconstraints by the topology of DNA. For instance a certain base substitution maybe less likely in a given local because of the associated sterochemistry of the DNA. Likewise how DNA is packed alters how mutation can happen. Any spot in the genome does not have an equiprobable chance of having a mutation, because of how DNA is "stored". Which leads to some areas being more prone to mutation than others; we call mutational hotspots (searchable term)).
     
  17. Mar 12, 2012 #16

    jmm

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    I haven't read all of the replies so this has probably been covered by someone, but I wanted to briefly say your definitions of evolution and natural selection are kind of shaky. Evolution is not merely the passing on of genes, but a change in gene frequencies between generations. Natural selection does not act on a species, it acts on individuals. The selection of one phenotype over another can lead to evolution, but it also often doesn't for a number of reasons. Also keep in mind that natural selection is dependant on the particular environment an individual is in and thus is a major contributor to speciation. These are gross oversimplifications, but hopefully it clears some things up.
     
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