Jorge Fernandez Diaz made the comments after Spain's highest court held that same-sex marriages were constitutionally valid, thinkSpain reported Sunday.
While defending the "public presence" of religion in Spanish society, Diaz said his beliefs were not based on religion.
"There are rational arguments which say marriage of this type should not have the same social protection by public powers as normal and natural marriage," he said. "The survival of the species, for example, is not guaranteed."
Gay rights groups were incensed by Diaz' comments, saying many children have been born to gay or lesbian parents through the use of sperm donors or surrogates.