Ye, this isn't really true. Lets take, for example, 18th century Naval officers from the UK:

* Captain Cook - discovered Australia, mapped the Pacific etc. Father was a farmer

* Horatio Nelson - Defeated the French, considered greatest Naval commander of all time. Father was a minister

* Arthur Philip - Commander during American Revolution, lead colonization of Australia. Father was a teacher.

It is a very common misconception that in old society it was impossible to move from the lower classes into the upper classes. The British Empire, the prototypical aristocracy, was largely shaped and developed by people who were raised in the lower classes. This is because the military, navy, their universities (eg. Isaac Newton), and many other parts of government and private societies were strict meritocracies.

The upper classes actually produced a very small number of notable people, outside of royalty (Charles Darwin, Churchill, Brunel (although his grandfather was a French farmer)

(Edit: "America became the first large-scale experiment of a society that could be called a meritocracy." - Citation needed. See above.)