His aristocratic father, Ivan Illitch Petrunkevitch, was a liberal member of the First Duma and founded the Constitutional Democratic Party.

After finishing his studies in Moscow and in Freiburg under August Weismann, Alexander settled in Yale in 1910, becoming a full professor in 1917.

Apart from describing present-day species, he was a major figure in the study of fossil arachnids, including those in amber and from the Coal Measures.

[2] He was also a skilled machinist and wrote two volumes of poetry (under the pseudonym Alexandr Jan-Ruban), and translated Pushkin into the English language, and Byron into Russian.

[3] A 1917 portrait miniature of Petrunkevitch by Margaret Foote Hawley is currently owned by the Metropolitan Museum of Art.