• some of the research that went into the modern synthesis looked at races of insects (subspecies)
• what is a species?
• previously an ideal type
• now a new biological definition: a set of interbreeding subpopulations (traditionally called races)
  
• if a subpopulation is isolated it can become a new species, unable to breed with the other subpopulations
  
• in the case of the fruit fly that Theodosius Dobzhansky studied, he declared a subpopulation to be a new species even though it looked identical because when bred with the other subpopulation the resulting males were infertile (the females were not, but apparently males counted more than females to him)

A. Essentialist concept--entirely a social idea, not a biological idea
B. Population--this could be what population biology tells you, depending on what characteristic you focus on (but skin color does not tell you much about how closely related population groups are)
C. If you look at genetic diversity, there is no separation of what we call races

Dobzhansky argued that races could be defined only by gene frequencies, not by appearance, and were always shifting and mixing

• races would divide differently depending on what genes you chose to look at
• he didn't support using ethnic groups instead--thought this would have the same issues
  

A present-day way of visualizing this (more on African ancestry--in this system it only shows up if less than about 200 years ago):

23andme also tells me my overall DNA is a bit less than 4% Neanderthal (putting me in the 91st percentile for Neanderthal variants)
Note that we are learning what we thought were different species were not so separate--humans and Neanderthals interbred--though one scientific theory is that they differences were enough that male hybrids were infertile while females were fertile

Dobzhansky saw it as theoretically possible that races would be different enough that interbreeding would lead to disharmonies, but he saw no credible evidence of that (note footnote 9 on pages 64-65)

• he argued that comparing means (averages) was meaningless because there were was so much variation between individuals
• comparing means only made sense if each race had an ideal type, which was now an unscientific notion

A different way of thinking about race mixing

• race is a characteristic of a subpopulation, it doesn't biologically make sense to talk about the race of an individual
• races always mix, otherwise they would be different species
• empirical evidence shows no pattern of infertility or disharmonies as a result of race mixing

Dobzhansky argued (in opposition to Montagu) that the term race should still be used, but the public should be educated on its scientific meaning

• Coon argued that the different races of humans had evolved separately (polycentrism)
• Homo erectus evolved into Homo sapiens separately at different times in different places
• but how could separate evolutions result in the same species?
  
• Dobzhansky wrote against this and other attempts to use science to support segregation, arguing they were bad science