A lot, but probably not as many as you might think.
The key here is the meaning of “according to their kinds” when God told Noah to take birds, animals, creeping things “male and female . . . according to their kinds.”
Does “kind” mean species? There are millions of species—somewhere between three and thirty million, a rather large range caused in part because taxonomists (biologists who figure out classifications) don’t agree on what a species is. The most common definition of a species is a group of organisms that can interbreed and produce fertile offspring.
Or does “kind” mean genus? A group of similar species is a genus. The Boa genus, for instance, includes several snakes, one of which is the Boa constrictor.
Or does “kind” mean family? A group of similar genera (the plural of genus) is a family. Canidae is a family that includes dogs, wolves, foxes, jackals, coyotes, and similar animals. Biological families number in the thousands, not the millions. Did Noah take two dachshunds, two beagles, and two grey wolves? Or did he take a pair of animals representing the Canidae family?
Many animals did not need to be on the ark for survival. Sea animals, for instance, could survive a flood. Many of the one million species of insects could probably survive without being on the ark. Interestingly, the Bible says, “Everything on the dry land in whose nostrils was the breath of life died,” but insects don’t have nostrils or lungs. They get their oxygen through their cell walls.
While God told Noah to take two of every kind of animal into the ark, He clarified his instructions so that the animals should be two of every unclean animal and “seven of each kind of clean animal” and “seven of each kind of the birds of the heavens.” People who study the Bible are equally divided on whether there were seven of each clean animal or seven pairs of each clean animal on the ark. We don’t know.
John Woodmorappe, author of the most detailed study of the ark and its animals, says if a “kind” means what we call today a genus, there would have to be just under 16,000 animals (8,000 genera). Others say that a “kind” means a family and so there would be about 2,000 animals (1,000 families).
How many animals were on the ark? There were perhaps as many as sixteen thousand. But there didn’t have to be hundreds of thousands. A lot—but not as many as you might think. Check out eight more of the most common questions about the animals on Noah’s ark in Noah: The Real Story.