crashfrog responds to
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Science is OBSERVABLE. Evolution isn't!
Sure it is. Rrhain has an experiment you can do in your own biology lab (I love when he says that)
Ooh...then perhaps I should say it more often. Though, that runs the risk of it becoming a stock phrase and thus losing its effectiveness. Drat these difficult decisions!
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where bacteria evolve resistance to disease, and then the disease evolves new ways to atack the bacteria. You can watch it happen and observe evolution.
And the best thing, it doesn't cost a lot of money.
Take a single E. coli bacterium of the wild, K-type. This type of bacteria is susceptible to a type of virus called T4 phage. So you take this single bacterium and let it reproduce to form a lawn. Then, infect the lawn with T4 phage.
What should we expect to happen?
That's right, plaques of dead bacteria start to form. The phage is infecting them and, since they are susceptible to T4 phage, they start to die.
But we also see some colonies within the plaques merrily living without a care in the world, surrounded by live, active phage.
How can this be? Remember, all the bacteria are descended from a single ancestor whom we knew to be susceptible.
That's right...the bacteria evolved. In fact, they are now called K4-type because they are resistant to T4 phage.
But wait. Let's continue. Take one of the K4 bacteria and again, let it reproduce to form a lawn. Now, infect the lawn with T4 phage.
What should we expect to happen?
That's right: Absolutely nothing. These bacteria are resistant to T4 phage and thus, the phage should have no way to establish itself.
But what do we actually see? Instead, we see plaques starting to form again. How can this be? Remember, all the bacteria are descended from a single ancestor that was resistant to T4 phage. So how could any of them be dying?
We now have to figure out which one evolved. A little thought will show that it has to be the phage that evolved, not the bacteria. See, if a bacterium experienced a reversion mutation such that it would be susceptible to T4 phage, it would immediately be infected and killed, leaving it surrounded by K4 bacteria which would immediately take over the space just vacated. In short, K-type bacteria could never take hold.
Instead, it necessarily must be the phage that evolved. And, in fact, we call these phage T4h because they have experienced a "host" shift.
So there you go. Evolution right before your eyes. And it doesn't take that long to do. Many high schools do this experiment.
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Rrhain
WWJD? JWRTFM!