I've read about that study before and I think the claim is a bit overly ambitious... There are alot more factors that should be taken into account, like race and lifestyle. For race, you have the broad groups, white, black, yellow, red whatever. But then what about going deeper i.e. a Russian vs Italian in digit length? As for life style what what did the sample pool do? Were they farmers, urbanites, some derivative of a warrior class.
here's a cutout from another study looking at race.http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2649659/Results
For the skeletons of European/Caucasian extraction (Ns = 89 males, 50 females), there were substantial sex differences for several of the metacarpal length ratios, but the pattern was not identical with the pattern previously reported for human fingers. Namely, the largest sex differences were for the three ratios involving metacarpal 5 on the left hand, while the sex difference for the ratio comparing the second and fourth metacarpals (the comparison commonly showing the largest sex difference for fingers) was small and non-significant for both hands in these European-Americans. For the skeletons of African extraction (Ns = 65 males, 55 females), no sex differences were found in any of the 20 metacarpal-length ratios. This outcome was unexpected because past research had shown sex differences in finger-length ratios for people of African extraction. For metatarsals, none of the 20 ratios exhibited a substantial sex difference for either group of skeletons.