Some Pharisees came to Jesus, testing Him and asking, "Is it lawful for a man to divorce his wife for any reason at all?"And He answered and said, "Have you not read that He who created them from the beginning made them male and female, and said, 'for this reason a man shall leave his father and mother and be joined to his wife, ad the two shall become one flesh'?" So they are no longer two, but one flesh. What therefore God has joined together, let no man separate." They said to Him, "Why then did Moses command to give her a certificate of divorce and sender her away?" He said to them, "Because of your hardness of heart Moses permitted you to divorce your wives; but from the beginning it has not been this way. (3-8 NASB)
Jesus is saying nothing new regarding gender except quoting Genesis. See Objection: Genesis 1:27.