Furthermore there is the complication caused by ambiguous problem statements. In your example, how we define the first human that got to North America? Which im

Furthermore there is the complication caused by ambiguous problem statements. In your example, how we define the first human that got to North America? Which immigration wave? What if there were immigration waves that were completely wiped out without leaving any effects of the subsequent populations? What is the 20th birthday? According to which calendar? (Leap days etc)? What is lunch? Not every people subdivide their meals in a predictable way that you can pinpoint to what "lunch" is Etc etc EDIT: forgot the most obvious: define what counts for human. It's not clear cut to distinguish boundaries between species