Because this question does specify that what is evolving is a population, my reaction to this question is that yes, the population of the US is evolving. One way this may not seem completely obvious is that evolution is occurring at the gene level, and we simply cannot see genotypes; evolution is a change in the genetic constitution of a population. Also, I think that the average generation time of a human plays largely into not being able to see changes in a population. If you had a population of fruit flies, on the other hand, who have a life expectancy in terms of weeks to a month or so (and have to be born, reproduce, and then die in that time frame), it's easy to observe changes in the population, just because genetic information is being passed on at a faster rate than it is in human populations. Bottom-line, I do think the population of the US is evolving, it may just not be that evident and as easily observed.
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Making cladograms...
We spent most of lab just trying to shift through different characteristics, so we never came close to writing a somewhat complete cladogram and phylogenetic tree. However, we ended lab by putting Orrorin and Sahelanthropus branching out of two separate branches, as well as having a third branch (with a separate origin) that diverges to produce Ar. ramidus and Ar. Kadabba (neither one leading to the other).
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