The theory [of evolution] says that things evolve over time, If that is correct then why have some species not evolved at all! Several fish have stayed the same. The crocodile has adapted and grown smaller in size but it is still a crocodile. Marine turtles have not changed according to the fossil record. Those are just a couple of examples that have been observed.I found this in the comments of this letter to the editor of a Tennessee paper in defense of evolution, written as a reply to another letter that asserted that evolution is a religion.
The argument has also recently been trampled to death by Adnan Oktar, aka Harun Yahua, who produced the now infamous Atlas of Creation. In that beautifully illustrated tome (though some pictures are of fishing lures) he similarly argued that since many species are identical to fossils that are millions of years old, these didn't evolve (as they falsely claim that the theory of evolution posits they must), and thus evolution is false.
Within evolutionary theory, the phenomenon of no phenotypic or genotypic change is known as stasis. Wikipedia does not have an article on stasis, unfortunately, so you'll have to make do with the mention of the it under the heading of punctuated equilibrium (stasis has also been called unpunctuated equilibrium, but don't let me hear that again!). Essentially, at times organisms/populations/species evolve rapidly (as is the case with Podarcis sicula), and at times hardly at all (as with the Coelacanth and other living fossils).
Why does stasis happen? Stasis occurs when
- the environment that the organism lives in doesn't change, or
- the organism is developmentally constrained so that it can't evolve.
- habitat tracking: populations whose environment changes can physically move so that they are not going to be affected by the change, and
- small populations may not be able to respond to selection because it isn't strong enough; instead, in small populations genetic drift rules.
The last two reasons could work at the same time, even in conjunction with developmental constraints.]
Developmental constraint is a little harder to explain, but I promise myself to deal with it thoroughly within very long.
On the contrary, the idea that stasis prevails when the environment doesn't change is really easy to grasp. It is the environment that determines what the fittest phenotype is, so when the environment doesn't change, neither does the organism (except for neutral evolution, in which genotypic changes that doesn't not affect the fitness of the organism can go to fixation).
In terms of fitness landscapes: If you're sitting at the top of a peak, then any phenotypic change lowers your fitness, and stasis results. This is one effect of natural selection: it weeds out the inferior phenotypes, preserving the type that produces the most offpsring (there are other effects of selection, by the way). As long as that landscape doesn't change, the peaks remains, and evolution doesn't happen.
Ahh, excellent! That should take care of that, and I suspect we won't hear that silly argument made ever again...
P.S. Yes, I love Wikipedia.