It's race denialism bullshit. Among other things, it relies on the conception that cognitive effects of evolution must have happened before migration rather than after, for which there is no evidence at all other than some supposition made by the author. Furthermore, it denies the differences existing between groups of people that find themselves in different conditions (i.e. perhaps cooperation is good in a winter if you live on average 1 km away from anyone, but not at the equator if you live with 40 people around you all the time who may have increased violent tendencies). It then commits the error of thinking that genetic diversity as measured on a per-letter-of-DNA basis is a good quantification to affirm or deny the presence of distinct evolutionary pressures applying to different groups. It doesn't. We could have less variation than chimpanzees in number of letters, yet stronger natural selection pressures could be at play in shaping the different frequencies between groups. Finally, it strawmans the race realist position by stating that races are "genetically homogeneous groups," which is not the position and which should always raise a red flag in the reader, since setting such an impossible standard is clearly evidence that the author wanted to reach the conclusion that races don't exist.
