'Those who cannot remember the past are condemned to repeat it."
Something now matters more than who first wrote/uttered the statement.  Both Marx and Santayana were most quotable within the first decade or so of the 20th century.  This is important, because during those years (and for a few decades beyond), history was a mainstream subject.  It was taught to virtually anybody who went beyond grade 6.  

Today, that's not the case, and so the statement is moot. Nobody can "forget" something they never heard of.  THAT is one of the fatal flaws undermining today's western society.  People haven't forgotten history (even mid-20th century history.)  They never knew it to begin with.