Hmmm; on the one hand, this could be taken as a kind compliment; on the other, it could be used to justify all sorts of visious anti-Semitism... :-\
In Twain's day, Jews were stateless, wandering, and rarely found to be in jobs requiring manual labor.
[Manual Labor...isn't he the Mexican Trade Unionist?]
This isn't all Twain wrote about Jews, whom he greatly admired.
As a generalization, Twain's remark does have substance and is meant more as a compliment than a slight...He knew that Jews could produce a larger GNP from a deserted swampy wasteland in just 60 years by utilizing our brainpower and intellect, whereas most other peoples would require abundant natural resources, colonies, and hundreds of years to produce wealth.
As for Twain's summation of the Negro, he also gave great credit where great credit was due, and I have done the same many times on this forum.
All things being equal, Jews don't stand a chance against a Negro sports team or against a Negro dance band.
As a stereotype, all groups of nationalities have their strong points and their weak points, and even the enemies of the Jews fear our gift of intellect and our abilities in business.
With the rebirth of Israel in 1948, the Jews have also proven our abilities in agricultural and military successes.
We are still far from adept in the fields of politics and self-governance.