I found this interesting. Recent research suggests less fit intermediates can and do occur.

It appears, therefore that this particular evolutionary two-step often passes through an intermediate with significantly lower fitness than either its ancestor or its compensated descendant.

more info here: http://blog.lib.umn.edu/denis036/thiswe ... death.html

I just stumbled upon that article too, but I see it posted already.
I think this is one of the most important questions that need to be answered by evolutionary theory.

http://blog.lib.umn.edu/denis036/thisweekinevolution/2010/03/crossing_the_ridge_of_death.html#more

It's fairly easy to get from A to Z, provided that B is at least as fit as A, while C is at least as fit as B, and so on. This can be the case, as shown by experiments on the five-step evolution of antibiotic resistance, discussed in a previous post. But is this the only way a population can evolve a superior genotype? Or does evolution sometimes reach new heights (faster-flying birds, scummier pond scum, etc.) through intermediates that are significantly less fit?

It doesn't actually present a problem for evolution. It should be noted that evolutionary theory doesn't predict improvements in fitness at every stage, nor should it. The only thing that matters is meeting or approaching mean fitness. Remember that fitness isn't binary, but works more like a high-pass filter, and an imperfect one at that. So representative alleles that actually constitute a reduction in mean fitness can still survive to reproduction, providing a basis for future mutations. The reduction in mean fitness doesn't represent extinction, just a reduced average representation in following generations.

hackenslash wrote:It doesn't actually present a problem for evolution. It should be noted that evolutionary theory doesn't predict improvements in fitness at every stage, nor should it. The only thing that matters is meeting or approaching mean fitness. Remember that fitness isn't binary, but works more like a high-pass filter, and an imperfect one at that. So representative alleles that actually constitute a reduction in mean fitness can still survive to reproduction, providing a basis for future mutations. The reduction in mean fitness doesn't represent extinction, just a reduced average representation in following generations.

Perhaps you should email him and tell him there is no need to continue working on his upcoming book, as you have so easily already answered the question

What question? It still constitutes interesting research.