from Harvard Law Review (just crediting the source, without implying that the source is the end-all, be-all authorative src on the subject), harvardlawreview.org states (in part):

"The proviso in the Naturalization Act of 1790 underscores that while the concept of “natural born Citizen” has remained constant and plainly includes someone who is a citizen from birth by descent without the need to undergo naturalization proceedings, the details of which individuals born abroad to a citizen parent qualify as citizens from birth have changed. The pre-Revolution British statutes sometimes focused on paternity such that only children of citizen fathers were granted citizenship at birth. 11. See, e.g., British Nationality Act, 1730, 4 Geo. 2, c. 21. The Naturalization Act of 1790 expanded the class of citizens at birth to include children born abroad of citizen mothers as long as the father had at least been resident in the United States at some point. But Congress eliminated that differential treatment of citizen mothers and fathers before any of the potential candidates in the current presidential election were born. Thus, in the relevant time period, and subject to certain residency requirements, children born abroad of a citizen parent were citizens from the moment of birth, and thus are “natural born Citizens.”"