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Possible Problem With Evolution ?

  1. May 31, 2003 #1
    First off, I do believe in evolution.

    But I was thinking, Evolution is based on natural selection, the survival of the fittest. Insects are extremely strong, fierce, and capable for their sizes. Why would it just happen that insects are so small? It almost seems as if this situation was set up for the benefit of mammals. If, for example, some insect eating insect was the size of a horse, it would absolutely dominate other animals. Why then, would evolution not have made sure by now that insects get bigger? Ones that could survive on the flesh of other animals atleast.
  2. jcsd
  3. May 31, 2003 #2
    Welcome to the PFs, BasketDaN! :smile:

    The flaw in your question is the assumption that there is something that chooses what does and doesn't evolve. You see, there is nothing that causes animals to mutate, just to meet some necessity. If there were, there would be no extinct species. Animals just evolve, and if they happen to evolve in a beneficial way, they were just lucky.

    This means that insects are not small for a reason, but just happen to not have mutated to be any larger.
  4. May 31, 2003 #3


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    Insects have an exoskeleton, a configuration which cannot support its own weight above a certain limit.
  5. May 31, 2003 #4
    There are several reasons

    why insects are relatively small. The almost all fly, which is easier for smaller things. That have an inefficient system for conveying oxygen to their cells which wouldn't work well for a large insect. Their exoskelton limits the rate at which they can grow because they have to shed it and make a new one for any size increase.
  6. May 31, 2003 #5


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    Re: There are several reasons

    It has recently been discovered that insects have a respiratory system comperable in efficiency to that of mammals. A new X-ray machine was able to watch them breathe, and revealed that they do not just passively allow air to pass through, but actively respire.
  7. Jun 1, 2003 #6


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    Remember the old adage? Size matters, but it's what you do with it that counts?

    Consider this... What would happen if mosquitoes were the size of, say a dog. Consider how easy they would be to swat. See... Size != always good.

    Insects are in fact phenomenally successful creatures. They are more populous than almost all other types of animal life. They were the first to perfect flying, group societies, communication, and they live in all parts of the world. They are one of the few creatures that BENEFITS from human activity.

    Why? Because insects didn't pick the size route. They picked the numbers route. There's their niche and after so long, leaving it would lead to greater competition. The size of insects is in many ways a local high in survivability, which is what evolution is about.

    Consider this. If insects increased in size a little bit as a result of random mutation, their food consumption would greatly increase. With continued reproduction at the current rate, they would run out of food within a couple of generations. Add to that the fact they would be a much bigger target to any predators. And the fact that due to all that moulting, it would take longer to get to their full mature size and insects don't live all that long. Result: a small increase in size would lead to a drop in survivability until it gets to a gain, and bigger insects would be descriminated against. Big jumps in characteristics are quite rare, so insects are pretty stuck at being small.

    Of course, this doesn't mean insects have to be small. Some insects are actually quite big. And evidence exists that dragonflies were once MUCH bigger than today. Perhaps a change in food supplies made it more advantageous to be small, and now insects are just starting to recover?
  8. Jun 1, 2003 #7


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    Well, there's your answer. They are already highly successful.

    Like others said, insect anatomy does not allow for enormous sizes. Their form would have to change in order to support the heavier weight. That form change may make them less insect-like.

    But consider this...if bigger was always better and every creature had a trend toward bigger size, then there would be overcrowding (lots of competition) at the upper end of the size range and a wide open niche (easy living) at the lower end of the size range. Smaller creatures may do quite well in a world of giants.
  9. Jun 1, 2003 #8
    What if bacteria were the size of footballs?

    Then they would not be able to work in the same way.

    There is that thing about ants being really strong for their size due to the fact that strength scales to the power of 2 where as weight scales roughly to the power of three.
  10. Jun 2, 2003 #9
    Your initial mistake is in believing that evolution is based on natural selection. There are multiple selection factors that work on a species, such as genetic drift, which many scientists see as more important that natural selection.
  11. Jun 3, 2003 #10


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    You are correct that there are many evolutionary "forces" at work...mutation, natural selection, sexual selection, genetic drift, recombination, gene flow. Some scientific short-hand is to lump these together and say evolution is essentially mutation plus natural selection. Anyway, your point is correct. Darwin himself...the guy who made natural selection famous...gave several arguments that other aspects of evolution are at work (often debated Wallace, who held to a strict nat. sel.-only version of the theory).
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