Map of scientific collaboration between researchers

My friend Julianne alerted me to this map (Here is a high resolution version.)

The high level of collaboration within Europe is obvious, as is that in the United States and I think Japan. There is a center of science in Brazil, another in India and one in China. The graph is not normalized for population, so that while Australia appears rather dark, the population is small and the per capita scientific collaboration is likely to be quite large. Africa appears indeed to be the Dark Continent.