【Ancestor】 , 【progenitor】 , 【forefather】 and forebear mean a person from whom one is descended.
【Ancestor】 , especially in genealogical and in historical use, implies lineal descent through one's father or mother, but it is seldom applied to a grandparent.
he had three ancestors who were judges
In more general use, 【ancestor】 (especially in the plural) may imply kinship through collaterals or through race.
the gentleman will please remember that when his half-civilized ancestors were hunting the wild boar in Silesia, mine were princes of the earth —Benjamin
【Ancestor】 often suggests knowledge of identities and family pride in them as persons.
【ancestor】 worship
they had plenty of money, but apparently no ancestors
【Progenitor】 differs from 【ancestor】 chiefly in its connotations rather than in its implications. It does not exclude parents or grandparents; it usually carries no hint of family or racial feeling, and it often suggests a reference to heredity or the transmission of characters.
do as your great progenitors have done, and, by their virtues, prove yourself their son —Dryden
men resemble their contemporaries even more than their progenitors —Emerson
Whenever an evolution is suggested, 【ancestor】 and 【progenitor】 may be used of living things or of nonliving things (as races, social castes, or literary or artistic forms) that are subject to development; they then often denote one or a kind or group from which a later or a presently existing kind or group has been derived.
the wild ancestors of our domestic animals
Fielding was . . . the 【progenitor】 of the modern realistic novel —New Yorker
【Progenitor】 , even more than 【ancestor】 , names the ultimate source or root.
he sang of the nuptials of Janus and Comesena, progenitors of the Italian people —Quiller-Couch
【Forefather】 is used less often than 【ancestor】 in historical writing but is probably more common in poetic and in general use, especially when simplicity of life, strength of family feeling, or persistence of a family in one locality is connoted,
each in his narrow cell forever laid, the rude forefathers of the hamlet sleep —Gray
think of your forefathers! Think of your posterity! —J. Q. Adams
Forebear is not only less rich in its implications than 【forefather】 , but it is also less connotative of sentiment.
the land had been owned by his forebears for generations
