Polygenism is the idea that human beings arose from many "first parents" via Evolution, 11 and that Adam and Eve are symbolic representations of mankind. On November 30, 1941, in an address to the Pontifical Academy of Sciences, Pope Pius XII identified three elements that must be retained as certainly attested by the Sacred Author of Genesis, without any possibility of allegorical interpretation:
The essential superiority of man in relation to other animals, by reason of his spiritual soul.
Derivation in some way of the first woman from the first man.
The impossibility that the immediate father or progenitor of man could have been other than a human being, that is, the impossibility that the first man could have been the son of an animal, generated by the latter in the proper sense of the term. 12
As Fr. John Hardon, S.J. pointed out, in context this statement of Pope Pius XII reads,
"Only from a man can another man descend, whom he can call father and progenitor."
Even if the Pope had primarily intended in this address to stress the great gap in kind which exists between animals and human beings, nevertheless, as Cardinal Ruffini also pointed out, the possibility that human beings could have been born of animal parents is untenable.
11 The idea of multiple pairs of first parents in one locality is known as monophyletism; in various places and times is known as polyphyletism.
12 See Fr. John A. Hardon S.J., The Catholic Catechism (London: A Geoffrey Chaptman book published by Cassell Ltd., 1977), p. 92.