I was thinking one day about the human race - if only Adam and his wife were the first two humans on the Earth, how did we become so many? In Islam brothers and sisters cannot marry each other. Were there created other human beings after Adam and his wife?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Islam forbids marriage between the brothers and the sisters. Allah Says (interpretation of meaning): {Forbidden to you (for marriage) are: your mothers, your daughters, your sisters,….} [Quran 4:23].

The above ruling is in our Shariah and every Prophet has his own Shariah. Hence, it was lawful in the Shariah of Adam that a man married a woman who was not his twin. It is reported in the Books of Tafseer like Al-Tabri, Al-Qurtubi, Ibn Katheer, Al-Bidaya Wa al-Nihayah that every time Hawa (Eve) used to give birth of twins; a boy and a girl. Adam was ordered to marry his male child to his female one who was not the male’s twin.

Allah knows best.