I just listened to the audiobook version of The Sports Gene by David Epstein. I highly recommend it to anyone that is in the fitness industry or is interested in athleticism.
What I really enjoyed is that Epstein discussed not only genetic predispositions to athletic traits, but also gave weight to the necessity of training as well as technology in the development of athletes.
This TED Talk is a great overview. I had heard of the book, but this video got me to pull the trigger in downloading the book.
One of the best take-aways from this book is that there are genetic differences that make people respond to training differently. Apparently, most people are effected positively by exercise (although some are not). Some people respond much better to explosive anaerobic training and others respond better to slower aerobic training. Unfortunately, Epstein and many coaches feel that individualized training programs is what is needed. However, instincts tell me that constantly varied CrossFit programming is what works for the majority of people by having a broad range of stimuli. Imagine if you had 100 athletes and you wanted to maximize their fitness, if you trained them all anaerobically, you would see a disparity of results based partly on their genetics disposition to anaerobic training. Conversely, you would probably see a similar disparity if they were all trained aerobically. However, if you trained them in a mixed modality manner such as CrossFit you would probably see less of disparity between the athletes. Although, those most sensitive to a particular training modality might not be optimized and have less gains than if they were to specialize.
The other side of this is that really we can’t know the genetic predispositions of all our athletes and absent such knowledge a program based on constantly varied functional movements executed at high intensity is the best way to maximize the results to the greatest number of people.