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A few questions

  1. Jan 24, 2005 #1
    I'm guessing that our history class is (in the next couple of days) going to break out into a huge debate about evolution. In order to quell the usual outburst of completely illogical and factually incorrect arguments that will come up, I want to learn a few basic things about chemistry, mainly adaptation...so at least we have some facts to argue around.

    1. When a big creature like a human adapts, what causes that? Would I be correct in saying "The brain sees the room for change, and sends chemical messages to the body to develop different." Also, for changes that might be made at birth, does an organism change its own DNA, thus automatically changing its child's? Or, does it keep its own the way it is, then change the kid's in the time when it's born? I'm assuming that adaptation occurs because of DNA changes, if thats wrong then please inform me.

    2. Also, we have of course witnessed small evolution, like those butterflies changing colors in europe. Assuming that evolution would occur because of chemical signals, would it be impossible for a single-cell organism to adapt/evolve?

    3. Have biologists ever (in a scientific environment, of course) witnessed a single-cell organism change into a multi-cell organism?

    4. Does the theory of a very complex organism like an ape being formed from a single-cell organism have any gaping holes as for as biology is concerned?

    5. If a complex organism like an ape was formed from a single cell, shouldn't we have fossils of those "in between" stages?
     
  2. jcsd
  3. Jan 24, 2005 #2

    Phobos

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    There is variation (already present) in every population. When conditions change (or some of the population moves into a new area), then the variations that are best suited to that new condition are favored.

    Also, new variations arise over time (mutation, gene mixing, etc.) & are tested by the ecological conditions of that time.

    So, adaptation is not an intentional reaction. Instead, adaptation is a shift in which part of the existing population does better.

    See above. The genes (DNA) is set at birth. There's no evolution in an individual. Evolution occurs to an entire population over time kind of a statistical summary of the overall gene pool....i.e., which variations (genes) do better.

    Some bacteria can be proded to adapt/evolve at a faster rate due to external stimuli. For example, under stressful situations (such as a new environment that is not ideal) some bacteria can swap genes with others and, if I recall correctly, reduce their DNA-repair such that more mutations are passed through to the next generation.

    I don't think so.

    The Theory of Evolution has two main parts....(1) how evolution works (mechanisms) and (2) the history of it.

    There is always some level of uncertainty in science. For this theory, part (1) (mechanisms) is pretty well understood although you can still find much scientific debate about the details. For item (2) (history), that relies a lot on the fossil record, for which there are many "gaps". It's impossible to get a step-by-step progression from single-cell to ape from the fossil record (not only because fossils are rare, but also because evolution does not proceed in a linear fashion). However, the existing fossils do build a picture that supports such a development. Plus, importantly, there is further confirmation of this picture from the study of genetic relationships. Each new fossil that is found & genetic test that is run further fills out the details of the history of evolution.

    We do have "transitional" fossils. (many examples)

    As I mentioned above, it's impossible to get every single transitional step. So, people who argue against evolution will always have that debate point.

    Watch out for attempts to debate evolution in a linear fashion....it's not a simple step by step ladder-like progression. Evolution is a result of many variations & branching/zig-zagging pathways.

    Good luck in class! Keep asking questions here! :smile:
     
  4. Jan 24, 2005 #3

    Moonbear

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    To further expand on this, adaptation can also include loss of some variation. As a simple example that doesn't really apply on large evolutionary scales, but is easier to understand - Your house has been overrun by mice. You observe some variation in the colors of the mice as they scurry across your kitchen floor, some are very light color, nearly white, and others are a darker tan. Your kitchen floor is a very nice, white tile, and the light-colored mice blend in pretty well.

    You're fed up with mice in the house, so adopt a few cats from the local animal shelter with reputations as good mousers (introduction of a predator). The cats preferentially catch the darker tan mice (perhaps they are easier to see against your white floor, maybe they run a little slower than the white mice, or maybe cats just prefer tan mice) and while they can catch the white mice, just aren't efficient enough at it to ever catch every mouse. Since mice are very quick to breed, in just a matter of months, you notice that while you still have mice in the house, they are all white now, you never see a tan one.

    Now, these white mice living in isolation in your house continue breeding for generations, and small things continue to select for various traits. Mice normally breed during the night, but there have always been a few that breed during the day. This is a rare trait, and in the past their frequency in the population has remained low. Now that there is a nocturnal predator present (cats), those who breed during the day are becoming more successful and having more litters than those breeding at night because they don't get eaten while in pursuit of a mate.

    Now, reintroduce these white, exclusively daytime breeding mice to another population of mice that lived in a house with a dog that preferentially caught white mice only during daytime, and the two populations no longer interbreed because they breed at opposite times of day.

    As I said, this is a simplified example, but I hope it serves to highlight how adaptation arises from traits already present, not from some miraculous development of new traits on demand.


    Oh, and the "butterflies" were actually peppered moths. That's a good example of natural selection and adaptation, but not of speciation. There was no new species, just a shift in the trait frequency from the lighter to darker colored moths.
     
  5. Jan 24, 2005 #4
    Ah, thanks a lot for the info. So what I think your saying is that: Adapting to surroundings is not something the body does consciously or unconsciously, rather there are variations in the body taking place all over. And basically that the people with the 'best' variations survive and pass down those variations, and the ones with bad variations for the surrounding don't pass them down. Is this correct?

    A few more questions:

    Wouldn't this mean that, for example, the sort of 'extra' eye lid that makes oriental people have (usually linked to dust storms or something in very early history or prehistory) is something that a small population had and that a very large amount of non-oreintal-eyed people must have died in order to make those eyes very consistent in that region?

    Also, it just in general seems like a lot of death must happen for that, so I think I'm misinterpreting something in thinking that what you mean is that 'the even not-great variations in the populations die'...

    I know gaining muscle by lifting weights is your body's way of adapting to the new amount of work required of it. Is this something totally different than an adaptation such as an extra eye lid or extra body hair? Or in the case of the butterflies, color?

    Is there a major difference in 'evolution' and 'adaptation'? Currently I hold the belief that evolution is just adaptation on a much larger time scale. Is this false?
     
  6. Jan 24, 2005 #5

    iansmith

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    Bacteria will not necessarly swap genes (conjugation) during stressfull situation. Bacterial conjugation requires alot nutrients. Bacteria are more likely to pick up genetic material from the environment. DNA can serve as food and if the nuclease such as restriction enzyme does not degrade the DNA before it recombine. There is also something called adaptive mutation which is the increase of mutation rate under stress which may lead to beneficial/advantegous trait.

    Some bacterial are also capable of phase and/or antigenic variation. These mutation events are reversible and pass to the next generation. These events increase the variation within a bacteria population and increase the chance of survival.

    http://en.wikipedia.org/wiki/Bacterial_conjugation
    http://en.wikipedia.org/wiki/Nuclease
    http://en.wikipedia.org/wiki/Restriction_enzyme
    http://www.ncbi.nlm.nih.gov/entrez/...ve&db=pubmed&dopt=Abstract&list_uids=15258095
     
  7. Jan 24, 2005 #6

    iansmith

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    That would be a reasonable assumption and this could be an example of evolution.

    It is not necessary for death to happen. Reduce offspring will have also an effect on the diversity of the population. For example in the animal kingdom, several colors and organs are there for courting and mating purposes. It might be flashy but if 100 baby of flashy father vs 25 of the non flashy are born, guess what happen.

    It's something different. Your increase muscle mass will not be pass to your offspring. The extra body hair due to genetic, the extra eye lid, the moth color will be pass to the next generation and events will either select for or against these traits

    Adaptation is part of evolution. Evolution is much more than adaptation, evolution includes changes of genetic baggage, non-adaptive selection such as the founder effect or the bottle neck effect.
     
  8. Jan 24, 2005 #7

    iansmith

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    In addition, if you can get a book on comparative zoology, compartive embryology and/or comparative botany, you will be able to see several transitional species/group that are present nowadays, or at least will be capable of seeing evolution and common descendant.
     
  9. Jan 24, 2005 #8
    I see. It's really great to hear from more knowledgeable people here.

    Can we take the oriental eyes example one step further? (By the way, sorry if I am missing a politically correct term, I'm really just probing for the facts here.)

    Say there is a population of people in a surrounding that has recently started having huge dust storms. Eventually all of the people still in this area have oriental eyes (with an extra eye lid)...and people elsewhere have occidental eyes (no extra eye lid. I originally thought that in this example something revolutionary would have to happen:

    The people with occidental eyes would have to have many survive, and the people with oriental eyes would have to not survive at all, i.e., all die.

    Now I see it differently, like this:
    The mixed population wouldn't have to undergo any sudden change in their eyes. Instead, if occidental-eyed people survived only 90% as well as oriental-eyed people, that could cause their population to decline relative to oriental-eyeds. So the occidental-eyed people's population could very very slowly exponentially decay and over a long period of time and eventually be or equal nothing, especially considering that interbreeding of the two types would result in a 50/50 chance either way. In short, even if the oriental-eyeds survive even a tiny bit better, the way populations proliferate could eventually cause them to be extremely prominent.

    Is this correct?

    EDIT: Also, I don't really have time to read any books. Sorry, I would if I had more time. Can you guys give me just one example of a transitional fossil, just in case anyone claims there are none?
     
    Last edited: Jan 24, 2005
  10. Jan 24, 2005 #9
    whats this? an extra eyelid? last time i checked, i had one eyelid...
     
  11. Jan 24, 2005 #10

    DocToxyn

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    One of the examples of this that I like are the cichlid fishes of the great lakes of Africa- Malawi, Tanganyika, Victoria, etc. The myriad forms of the fish which have filled in all the ecological niches in these lakes through adaptive radiation induced by isolation is truly beautiful. The interesting thing about this topic is that amateur fish hobbyists have taken many of these species to heart and contributed to our scientific understanding of this unique group of fishes.
     
  12. Jan 24, 2005 #11
    I think it might actually be called an epicanthic fold.
     
  13. Jan 25, 2005 #12

    iansmith

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    I meant to answer this last night by my computer crash because my CPU fan is not working properly. I had a nice long answer. I try again but crashed again.

    Here a brief answer.

    Amphibian might be seen as a transitional form between water and terrestrial animals. Amphibian need water to complete their life cycle. Yet, it can surive on land for a long time. An example would be also the salamander-like amphibian that has lung stinking out of sides. I just don't remember the name of the specie.

    Dinosaures have some mammal-like carateristics. Their bone is more like mammal than reptilian (as far as I remember). It has also been hypothesised that some dinosaure were warm-blooded.

    In mammals, you seen the evolution from egg laying (Monotremes; http://www.ucmp.berkeley.edu/mammal/monotreme.html) to placental mammals. The marsupial would be the transitional form.

    In plants, you see different reproductive stratedy. You start with the lower plant that release sperm and egg, to a more advance that release only sperm but do not produce seed but a spore (ferns), to a more advance that release sperm and produce a naked seed or a seed within a fruit-like complex (gymnosperm; the ginko produce a fruit like thing), and to the most advance that release only sperm and produce a seed within a fruit (angiosperm).
    You also have the non-vascular to the vascular plant.
     
  14. Jan 25, 2005 #13

    DocToxyn

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    I believe you are looking for Axolotl, Ambystoma mexicanum. It's a relative of the tiger salamander but retains its neotenous state throughout adulthood.

    See http://www.axolotl.org/ for pics and more info.
     
  15. Jan 26, 2005 #14

    iansmith

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    Yeah that the group i was taking about
     
  16. Jan 26, 2005 #15

    DaveC426913

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    The PC term is 'Asian'. As I've heard from some Asian friends, 'Oriental' is a rug.

    Spread that process over tens of thousands of years. That's hundreds and hundreds of generations.
     
  17. Jan 27, 2005 #16

    Phobos

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    couple famous examples...

    Archaeopteryx - example of a species from the time of the transition from dinosaurs to birds

    Ambulocetus natans – example of a transitional form from land mammal to whale

    other examples...

    Sphecomyrma freyi - - transitional form between modern ants and their wasp ancestors

    Acanthostega – part fish, part amphibian

    When you have time to read...
    http://www.talkorigins.org/faqs/faq-transitional.html

    And of course there's examples like the human ancestors, H. erectus, H. habilis, the australopithecines, etc.....but usually people are asking about bigger changes like "fins-to-feet". People may also ask about a "missing link"...but there is no single link in these transitions....instead, it's a lot of diversifying populations over time.
     
  18. Jan 27, 2005 #17

    Phobos

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    Or, more to the point, "reproduced" (instead of survived).
    The ecosystem change need not kill...it could just reduce one group's chances at making more babies than the other group.
     
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