God made them male and female

Jesus came into the district of Judea and across the Jordan.
Again crowds gathered around him and, as was his custom,
he again taught them.
The Pharisees approached him and asked,
"Is it lawful for a husband to divorce his wife?"
They were testing him.
He said to them in reply, "What did Moses command you?"
They replied,
"Moses permitted a husband to write a bill of divorce
and dismiss her."
But Jesus told them,
"Because of the hardness of your hearts
he wrote you this commandment.
But from the beginning of creation, God made them male and female.
For this reason a man shall leave his father and mother
and be joined to his wife,
and the two shall become one flesh.
So they are no longer two but one flesh.
Therefore what God has joined together,
no human being must separate."
In the house the disciples again questioned Jesus about this.
He said to them,
"Whoever divorces his wife and marries another
commits adultery against her;
and if she divorces her husband and marries another,
she commits adultery."
(Mk 10:1-12)