Hmmmmm. I just took a flip through the book. A couple of things....
First, IMHO, this is a) questionable anthropology and b) mediocre science. There's a way to approach these types of questions with respect to populations (actuarialists attempt this all the time), but this doesn't seem to be the way. That, or the presentation is just poor. Any actuarial scientists feel like commenting? I'd love to hear the input. This book just seems to be a sensational look at numbers with little consideration of the actual variables that make the populations and their environments unique.
Also, I'm a deputy medical examiner. Just out of curiosity I did a little casual case review of motorcycle deaths in the county and a neighboring county in the last few years. The bottom line is, don't drink and ride. Just don't. There is an interesting series of studies by University of Notre Dame that is paraphrased here:
that has some good information about absorption rates and muscular response to ethanol. Fast-forwarding to the nudity, your eyes, hands and ears begin to go first, quite early, which affects your hearing and equilibrium just a little bit early on. Sketchy.