In researching raw food diets (my mom is into it) in the archives and on the
beyond veg. site:

http://www.beyondveg.com/nicholson-w/hb/hb-interview2c.shtml

came across some interesting ideas about the rate at which we can evolve-
here is a bit:

 >>But again, and importantly, the key point here is that genetic changes in
response to diet can be more rapid than perhaps once thought. The difference
in time since the advent of Neolithic agriculture between countries with the
highest and lowest incidences of these two genes is something on the order
of 3,000-5,000 years,[126] showing again that genetic changes due to
cultural selection pressures for diet can force more rapid changes than
might occur otherwise.


I admit to not questioning the idea that humans are not able to evolve
quickly enough to adapt to the advent of agriculture.

Help,
Bronwen