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Natural selection: What do they mean by average individual?

  1. Apr 11, 2012 #1
    Natural selection: What do they mean by "average" individual?

    You know how they say stabilizing selection favors the "average" individual - i.e, it is centered around the mean?

    I have a question. How do they calculate this "mean"? I'm confused. All I know is that if pure-white rats mate with pure-black rats and stabilizing selection occurs, assuming white & black are codominant alleles, the descendants will become increasingly gray.
  2. jcsd
  3. Apr 11, 2012 #2
    Re: Natural selection: What do they mean by "average" individual?

    The mean DOES NOT have to be calculated. No one goes around calculating the mean for every characteristic there is. It might be done for a few characteristics, but not a lot. We know that they exist, intuitively, and the few tests confirm it. Suppose you have a large muscular man, an average man, and a skinny man. Suppose the population relies on food sources that are found in small places and running quickly to get to food sources. Ready, set, go! The bulk of the large person makes it difficult for him to get around cracks and holes, even though he has swift muscular legs (you can't run fast if you can't fit). The small guy on the other hand, can easily fit through places, but he is too slow. The average guy balances being able to fit and speed (Not too large and not too slow). He gets food relatively quickly and he's over there hitting it up some chicks. His time is less devoted to finding food and more devoted to getting chicks than the other guys. At the end of the day, he contributes two children and the other two each contribute one child. Now, repeat the same things for this generation. But this time, you got two average babies. They multiply at an increasing rate, drowning out the other two extremes.
  4. Apr 12, 2012 #3
    Re: Natural selection: What do they mean by "average" individual?

    I see that now. So I guess they usually only calculate the mean when they want to use a mathematical model to predict exactly what an organism might look like in the future For example, if a small giraffe manages to collect food from high-hanging branches, a new species of giraffes with claws would likely evolve. Then scientists would measure the claw lengths and width of each generation or something and use that data to predict the length and width of the giraffes in 2,200.
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