...the test subject read in Courier New, a fixed-width font similar to the old typewriters, and rarely used on modern computers.

That kind of defeats the purpose of the test, no?

Reading speed only improved marginally, the paper found, and only for the 21 "two-spacers," who naturally typed with two spaces between sentences. The majority of one-spacers, on the other hand, read at pretty much the same speed either way.

Translation: One-spacers are smarter than two-spacers.

Conclusion: If you want to be smart and get lots of ladies, use only one space.