Table of Contents

• 1: The case of the resistant hoppers
• 2: Hoppers evolve resistance
• 3: Variability
• 4: Inheritance
• 5: Selection pressure
• 6: Quick review
• 7: Evolution and immunity
• 8: Immunity in prokaryotes and eukaryotes

Quick review

People naturally think of selection pressure and evolution as meaning the same thing. Its important to remember, however, that selection pressure is only the FINAL PART of a 3-part process: without variability and inheritance, selection pressure wouldn't make any difference in the long run.

So here are the 3 pre-requisites of evolution again:

 

Make sure you can list and define all three pre-reqs.

So, how do these pre-reqs apply to organisms that aren't bugs? Like, maybe, humans? Let's pose another evolutionary question: Could humans evolve blue hair? Essentially, do humans have the pre-requisites? Because if they do, evolution will follow naturally.

Let's assume that blue hair will help humans survive ... maybe Earth has been taken over by aliens who like blue hair, or maybe blue hair is so trendy that people with other hair colors can't get a date. In any case, we'll assume that blue hair has real advantages. So what do you think?

Variability	Heritability	Selection Pressure	Conclusion: Will blue hair evolve???
or ?	or ?	or ?	or ?
Make a choice above... It's true that there are people now that dye their hair blue, so I guess you could say that there is variability. That's right, there are no humans that we know of that have naturally blue hair.	Make a choice above... Sorry, the only way that humans can get blue hair is by dyeing it. It's like the Schwarzenegger effect -- not something you can pass on to your children. That's right, the only way that humans can get blue hair is by dyeing it. It's like the Schwarzenegger effect -- not something you can pass on to your children.	Make a choice above... That's right, we started out by assuming that there's a good reason that people with blue hair would survive or reproduce better. Sorry, we started out by assuming that there's a good reason that people with blue hair would survive or reproduce better.	Make a choice above... Sorry, that's wrong, blue hair cannot evolve because at least one of the prerequisites is missing. That's right, blue hair cannot evolve because at least one of the prerequisites is missing.

 

Usually when we say "variability", we mean "genetic variability" -- that is, some members of the species have a gene that gives them a particular trait. And (as you can verify above) even if there is non-genetic variability, it doesn't help from an evolutionary point of view, because it doesn't get inherited.