Now there are examples of speciation, I believe. However, they are a lot fewer and further between than most evolutionists have liked to admit and as a younger fellow, I've spent months asking for honest speciation examples before somebody finally comes up with something, usually obscure, usually from the insect family. I accept that these are legitimate instances but this is the sort of thing that should be in the FAQs and on the tip of the tongue of most evolutionist arguments and not the "you're religious" ad homenim that bedevils so much of the conversation.
Hmm, I both agree and disagree with this. I agree that a lot of people ought to be better informed about what speciation events we *have* observed, and that this information should be better collated and more easily available. [files mental note for project, in my oh-so-copious spare time]
I disagree that we see fewer than we should have expected. As I noted in a previous post, speciation is observable most easily where it happens fast -- fast breeding populations with short generation times. Yes, that largely does limit it to prokaryotes, plants, and the smaller invertebrates. But that is not unexpected, or unreasonable. Most speciation events are expected to take place over, at a minimum, hundreds to thousands of years, as new genetic organisations spread through a population. Why should we expect to catch most of these "in the act", so to speak, when we've only really been looking for a century and a half?
I also agree that the "you're only saying that because you're religious" ad hominem is not a good argument at all. *sigh* however...it is hard to stay away from saying it someone who holds the religious position that the literal inerrancy of the Bible as trumping all physical evidence, because there you are trying to get them to think outside the entire frame of reference.
On the creationist side of the argument, there are certain "species" that can interbreed and produce fertile offspring. Polar bears are an example (hybrids with brown bears and even grizzlies have been verified) which goes to show that, at the very least, there should be some cleanup in the present system to describe reality better.
Oh, believe me, you have no idea.
Terry Pratchett actually wrote very well about the problem of defining boundaries in his first "Science of Discworld" book. Humans look for neat, clean classifications for things; we like clear delineation. Unfortunately, nature has no reason to be interested in that. Very few things in nature have exact, clean, clear delineations -- individuals squarely in the center of a classification we have invented are clear and distinct from individuals squarely in the center of a different classification. However, individuals at the very edges of a population, or classification, tend to merge on sort of a spectrum with individuals from the edge of the next classification over.
"Reproductive isolation" is the core concept behind species, but it is far from being absolute. Often the best we can manage is to tack on "under normal circumstances" at the end of that.
That said, there is some interesting research going on at the minute about gene flow through hybrid zones. Where polar bears breed with brown bears is a good example of a hybrid zone, actually. One thing that distinguishes hybrid zones is that generally, the hybrids are weaker or weedier or in some way not as well adapted as full individuals of either parental population, so the hybrid zone does not spread and the population "even out"; there's generally a narrow area where hybrids are found, and that's it. However, if a particularly beneficial gene crops up in one population and finds its way into a hybrid zone, it seems that this particular gene will spread far and rapidly out of the hybrid zone again into both parent populations -- possibly carrying with some neutral genetic variation as well -- because it has a fitness advantage. This kind of mixing keeps the two species more closely related than they would otherwise be. Reality isn't
Reality can actually be very well described indeed by way of mathematics. For example,
dPi /dt = Wi Pi - <W> Pi - S j uji Pi + S j uij Pj , i =
is time, <W> = S ij Wij Pij
is the mean fitness in a population; uij
is the mutation rate of the transition Aj --> Ai, uii =0 (i, j = 1,..., K)
...but now, just try translating that into English
. Believe me, it ends up a lot messier, and if you are trying to put into a simple sentence, you sacrifice exactness.
<i>Forte est vinu. Fortier est rex. Fortiores sunt mulieres: sup om vincit veritas.</i>