@Marvin the Martian

Oh I don't agree with that... the Galapagos Islands are not "un-competitive" but rather allows biologists to study evolution within a self contained ecosystem with relatively little influx of external pressures and so it can be assumed that evolution there happens to specifically gain an advantage over a rival species or over rivals in the same species at a certain point in time. This is one of the tenets of Darwinism that I find few folk actually get. Namely, that evolution happens in response to a condition that the organism is exposed to that leads to said evolution showing a marked advantage for that condition, and which is only advantageous whilst that condition exists. Once that condition passes, then the evolutionary step may become redundant and either be evolved away from and replaced, or vestigial, like the appendix in the current state of modern humans. Note that the sea, which is very stable in terms of environment for evolution, has very low speciation but rather a large number of genus, which is due to it being such a stable environment. The same effect can be seen up at higher altitudes, where the conditions are less variable and so the number of organisms that can thrive there are reduced.

I think the closest thing you can call an "evolutionary cul-de-sac" is when the process of evolution produces a species that is so overly specialised that is fails to adapt to a new set of conditions and then dies out, much like Australopithicus did - apologies if the spelling is wrong as it has been several beers and over a decade since I studied this.