And of every living thing of all flesh, two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female. Of fowls after their kind, and of cattle after their kind, of every creeping thing of the earth after his kind, two of every sort shall come unto thee, to keep them alive. (Genesis 6:19-20)
Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female. Of fowls also of the air by sevens, the male and the female; to keep seed alive upon the face of all the earth. (Genesis 7:2-3)
Of clean beasts, and of beasts that are not clean, and of fowls, and of every thing that creepeth upon the earth, there went in two and two unto Noah into the ark, the male and the female, as God had commanded Noah. (Genesis 7:8-9)
And they that went in, went in male and female of all flesh, as God had commanded him: and the LORD shut him in. (Genesis 7:16)
The question of the number of animals of each kind that were saved in the ark has puzzled many, and many unsatisfactory theories have been tried; but the truth may be found by assembling all the relevant texts and testing the various hypotheses against the information given in all of them. The only coherent view that is in harmony with all the statements can be summed up in four points, as follows:
1. The first biblical text relative to our question, Genesis 6:19-20, gives the general rule: "two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female." The animals were to be brought into the ark in pairs, a male and a female of each kind of every living thing of all flesh." This latter expression is universal and emphatic, and shows that all the animals were thus to be paired. Verse 20 elaborates further, "of fowls after their kind, and of cattle after their kind, of every creeping thing of the earth after his kind." The purpose stated is, "to keep them alive with thee [with Noah]." This is not merely to keep these particular individual animals alive, but to ensure the survival of each kind in perpetuity by saving breeding pairs. 
2. The last two texts confirm this basic fact. The phrase, "two and two" in 7:8-9 applies to all the animal kinds, "...of clean beasts, and of beasts that are not clean, and of fowls, and of everything that creepeth upon the earth." And in 7:16, the fact is restated that there was a male for every female of all flesh. The male and female pair is thus the basic unit.
3. When the difference of clean and unclean beasts is later addressed, the expression, "by sevens" must be understood of seven pairs; otherwise there would be a male without a female, or a female without a male, in violation of the general rule already given. In 7:3, "Of fowls also of the air by sevens, the male and the female" surely can only mean seven males and seven females! Especially when it is added as a reason, "to keep seed alive upon the face of all the earth."
There is a view that there were just seven of each clean animal, rather than seven pairs. On this view, there were three breeding pairs; and the extra, unpaired animal was for sacrifice. The language of verse 3, "by sevens, the male and the female" precludes this possibility. Nothing is said to suggest three pairs plus one.
And nothing is said anywhere, in the flood account or after, about how many would be used as sacrifices. Sometimes, in the case of birds, the Mosaic law called for two at a time, as in Leviticus 5:7, "And if he be not able to bring a lamb, then he shall bring for his trespass, which he hath committed, two turtledoves, or two young pigeons, unto the LORD; one for a sin offering, and the other for a burnt offering." Noah may have sacrificed pairs of these, for all we know.
4. Thus the number of clean animals of each kind would be fourteen, and of unclean, just two. God would take care of the rest, by His providence guaranteeing that the numbers would be sufficient to secure the re-population of the earth.
There were good reasons why the clean animals were to be saved in larger numbers. First, some were to be used as sacrifices, as we find in Genesis 8:20, "And Noah builded an altar unto the LORD; and took of every clean beast, and of every clean fowl, and offered burnt offerings on the altar." Second, assuming that the categories were the same then as in the later Mosaic legislation, the clean category would include the cattle that men had cultivated for milk, leather, wool and such things from the earliest times; as well as animals for labor and for transportation. Third, many of the unclean animals were predators. For ecological balance, large numbers of peaceful animals are required to sustain just a few predators. 
1 Great stress is laid on the purpose of replenishing the stock of animals in the earth, in the record of Noah's debarking from the ark:
Bring forth with thee every living thing that is with thee, of all flesh, both of fowl, and of cattle, and of every creeping thing that creepeth upon the earth; that they may breed abundantly in the earth, and be fruitful, and multiply upon the earth. (Genesis 8:17)
2 Some have proposed a fourth reason-- the permission, revealed after the flood, for man to eat meat. They assume that more clean animals would be needed for food. But the law was very broad in scope: "Every moving thing that liveth shall be meat for you; even as the green herb have I given you all things." (Genesis 9:3) It gives no credence to a distinction of animals that might be lawfully consumed, versus animals that might not. The "cleanness" of certain animals in pre-Mosaic times therefore does not seem to relate to dietary uses; but to their fitness for sacrificial use.
It was only when God wanted to erect a barrier between the chosen people and the rest of the nations, in Moses' time, that the distinction of clean and unclean was applied to diet. This law constituted a severe hindrance to social intercourse between the Hebrews and the Gentiles; not to mention its tendency to promote prejudice and resentment on the part of both. The removal of the barrier was therefore necessary to the propagation of the gospel from the Jews to the Gentiles.
Howard Douglas King
March 10, 2015
Revised March 26, 2015