As an aside, after writing the evolution post earlier I heard a very good, concise of reproductive fitness: fitness is the ability to pass on your genes to offspring that can pass on their genes. The example is that producing a mule doesn't contribute to reproductive fitness because mules don't reproduce.
The thing that I'm really thinking about, though, is about defining evolution as a change in a population's allele frequencies over time. I'll get in trouble with some evolutionary biologists for cutting it down that far since there is a whole field that is devoted to understanding how the generational change in a population's allele frequencies can result in speciation, or the formation of new species. But making a distinction between evolution proper and speciation is an important thing for evolution's apologists to do (and, in my opinion, something that many seem unwilling to do at least in part for the reasons I stated in my earlier post on the matter) because: a) you can't argue that a change in allele frequencies happens over time since we can see it; b) it refocuses the debate about evolution onto evolutions core principles rather than its predictions.
So for evolution to take place, you need two have multiple alleles for a given gene, you need to have an external pressure that causes having a particular allele to not be neutral (i.e. there is a benefit or cost to having the allele), and you need to have reproduction. If we use eye color, let's say that there are only two alleles for eye color - blue and brown. Let's also say that Debbie Gibson has blue eyes, and so all of the boys in the 1980s grew up with crushes on her and decided that they would only marry women who have blue eyes. All of the sudden, blue eyed girls all get to reproduce while some brown eyed girls don't get to. There will be more blue-eye alleles in the next generation, and presumably all of those blue-eyed children will be able to reproduce. Evolution just happened. Of course, the same thing could happen the following generation with Debbie Gibson's daughter, who has brown eyes, and the pendulum could swing back towards an increase in brown-eyed alleles the following generation. The most interesting changes will be permanent shifts in allele frequencies, and these will usually result from continuous or very strong pressures.
The problem, of course, is that a change in the blue-eye color allele in the human population is less interesting than gamma-radiation from a special effects show at a Debbie Gibson concert causing everyone at the show to produce children that are actually a new species of Homo (called Homo gibsonii, this new species is actually born with eyes that are shaped like Ray-Bans and skin that looks like a jean jacket). The likelihood that a child will be born as a different species than its parent is extremely small (i doubt it could ever happen but never say never, right?), and so the question that arises is: how can a new species evolve? A more problematic, but related, question people like to ask is, "Why don't we ever see chimp-human hybrids if evolution is an ongoing process?" The former question is entirely appropriate but the latter is fundamentally flawed (another time...). At least one way that new species evolve is by isolation of individuals of that species by external barriers - such as geographic, social, or reproduction barriers between individuals in a population.
Can you see people who believe that the earth and all earth life was created by God being less resistant to teaching evolution if it focused on this?
As an aside, I thought it would be informative to check on a few definitions for evolution in online dictionaries. I was really surprised. Dictionary.com hit it on the head, but webster's is a bit off the mark, focusing not on the definition, but on the implications of the definition. I'm quick to add that I'm not aware of any evidence that contradicts Webster's definitions, but I think that defining evolution by its predictions and implications rather than by its underlying principles is flawed and causes a lot of unnecessary contention.
Dictionary.com : change in the gene pool of a population from generation to generation by such processes as mutation,natural selection, and genetic drift.
Webster's: a theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations; also : the process described by this theory
Future points:
"can" vs. "do" pass on genes
speciation vs. evolution
geographical isolation
undirectional evolution
long term evolutionary vision
a problematic species definition
possible speciation mechanisms (egg and sperm mutations)
alleles arise by mutation
define "allele", "locus", etc
