Fundamental changes to our design take hundreds of thousands of years, if not millions of years.
Smaller design changes can take shorter time frames... maybe changes in height or weight... over thousands of years. These are not fundamental changes to our digestive system though.
Modern agriculture is less than 10,000 years old... and so are it's problems.
I'm sure you're well aware of all this.
I've also heard of people eating a 100% animal food diet and doing very well. I don't have a link for it at hand but I do know that they weren't innuit.
