If Adam wrote the words of Genesis 1-3, he wrote them by divine inspiration from the Holy Spirit of God. There are more words in existence today available to man than ever in the history, and people read very little. We can now understand why a man who had no father or mother, that is, why Adam would say that a man should leave his father and mother for his wife. He was prophesying what would be the universal law for marriage. Both Jesus the Son of God, and Matthew, a divinely inspired writer of Scripture confirmed that what was written in Genesis was the divinely inspired Word of God, whether Adam wrote it, or whether Moses wrote it.
Many animals mate for life.
Somehow we seem to have a special esteem for animals that mate for life. It seems so right, even for animals, to come together as a pair loyal and faithful to each other for life. There is a sense of maturity about being mated for life. There is an unselfishness about being mated for life. To be mated for life is so important that God said a man must leave his father and mother, to cleave to his wife.