Rabbi Levitas, a man of Jamnia, said: He separated the males from the females of all which came to the ark when they came into the ark, as it is said, "And Noah went in, and his sons, and his wife, and his sons' wives" (Gen. 7:7). Verily the males were on one side. When they went forth from the ark, He caused the males to be joined with the females, as it is said, "Go forth of the ark, thou, and thy wife, and thy sons, and thy sons' wives with thee" (Gen. 8:16).
Verily a man with his wife (went forth), "Thy sons, and thy sons' wives with thee" (ibid.) || He blessed them, that they might increase and multiply on the earth, as it is said, "And God blessed Noah and his sons, and said unto them, Be fruitful, and multiply, and replenish the earth" (Gen. 9:1). The sons of Noah were fruitful and multiplied, and they begat sons with their twins with them.