To clarify, I'm almost positive it was Herbert Spencer, speaking of "social Darwinism", who first coined the term "survival of the fittest". It's a connotation thing, I know, but in the case of evolution it's more like...
Survival of the traits of those best able to adapt to their environment.
So it's not necessarily that the whole world is some bloodthirsty, dog-eat-dog place where all but the strong will die, as the term inplies; just that the fittest are going to survive long enough to reproduce
more often than those less able to avoid predators and catch prey.
Oh, and I think the world could use a few more jars.
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As far as the original topic, well, I don't think I have more to say beyond what others have contributed... yes, teach the flaws; I was really actually encouraged by learning theories' flaws in my chemistry class when I was younger (as an example), as it showed me that there definitely *is* still much to learn out there. But, (since this cannot be repeated too often) make sure that the flaws taught are real flaws.