Before this analysis goes too far, lets make sure that we have all our facts straight, and the facts, of course, are those laid out for us in the inerrant words of genesis. First, as to the number of birds, Gen 7:03 tells us "Of fowls of the air by sevens...", not just two pair for all the birds. It would seem that all birds are considered to be like clean beasts. But the real kicker is that Noah was commanded, according to Gen 7:08 & Gen 7:14 to gather pairs of "...every creeping thing that creepeth upon the earth..." (For some reason, that phrase always reminds me of a blind date I once had.) And since Noah "found grace in the eyes of the lord" - (Gen 6:08) he would certainly have followed that command. So, now we have all the kinds of insects, worms, reptiles, amphibians, etc. that creepeth upon the earth.
Some bible apologists who believe not the words of the holy scriptures make up a story that many of these kinds were not brought to the ark, but survived by finding refuge on floating rafts of logs, flotsam, or other floating debris. But then Noah would have been disobeying the words of the lord by not gathering all those critters to the arc. But Gen 6:09 tells us: "Noah was a just man and perfect in his generations, and Noah walked with God. " and would never disobey god. Besides, Gen 7:05 says: "And Noah did according unto all that the LORD commanded him.". Also, Gen 7:04 lays any doubt to rest when god tells Noah: "every living substance that I have made will I destroy from off the face of the earth"; and Gen 7:21 & :22 "And all flesh died that moved upon the earth, both of fowl, and of cattle, and of beast, and of every creeping thing that creepeth upon the earth, and every man. All in whose nostrils was the breath of life, of all that was in the dry land, died." So there can be no doubt, unless we are to reject the stories of the bible as silly mythes, that all "kinds" that are alive on the earth today had pairs of ancestors on the ark. There are over 80,000 species of nematode worms. But Noah and his family would have had a rather easy time with 15,000 of these species since they are parasitic and would have come aboard on other animals. Noah would just have to have been careful to select infected animals to start with. Insects presented an even greater labor of love for Noah and his family.
The real question that the Noatic flood presents is: If "God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually. And it repented the LORD that he had made man on the earth, and it grieved him at his heart. " (Gen 6:05 & :06), why did he take it out on all the ignorant beasts and creepy-crawly things? Why did he kill off all those cute little bunny rabbits, kitty cats, and puppy dogs? What does this tell us about the most benevolent and merciful lord? The bible lays out god's modus operandi very clearly when it comes to his preference for killing things: He likes asphyxiation, whether it be through smoke inhalation (fire and brimstone, i. e., sulphur fumes), slow strangulation (as in crucifixion), or drowning. So, perhaps god was just staying in character with this flood extravaganza.
The final fact worth noting is that the oldest generation of ancestors of all living humans was of course Noah and his wife. The next generation of our ancestors were Noah's three sons and their wives. But the generation after that, the third generation of all our ancestors, were people who married and had children by their first cousins. This probably goes a long way in explaining the current human condition.
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