From Congress, Elbridge Gerry of Massachusetts wrote to James Warren (emphasis added), “Yesterday after a long debate the question of independence was postponed until the first July, in order to give the assemblies of the middle colonies an opportunity to take off their restrictions and let their delegates unite in the measure. In the interim will go on plans for confederation and foreign alliance.
“If these slow people had hearkened to reason in time, this work would have long ere now been completed, and the disadvantage arising from the want of such measures been wholly avoided; but Providence has undoubtedly wise ends in coupling together the vigorous and the indolent; the first are retarded, but the latter are urged on, and both come together to the goal.” Smith, ed., Letters of Delegates to Congress, 4:187.
In the eighteenth century, the term "retarded" simply meant delayed or impeded in speed. Only in the nineteenth century did people begin using the term to connote developmental challenges. In modern American English, the term is a derogatory, impolite reference.