In Genesis, clean animals received seven pairs for Noah’s Ark, while unclean animals received one pair.
Genesis 7:2 instructs Noah to take seven pairs of every clean animal and one pair of every animal that is not clean. The wording is translated differently across English versions: some say “seven pairs,” while others say “seven of each kind” or “seven male and female.” The central contrast is between clean and unclean animals.
The distinction is connected to biblical categories of ritual suitability, although Genesis does not provide a complete classification list in this passage. Genesis 8:20 later says Noah built an altar and offered burnt offerings from every clean animal and clean bird, which helps explain why extra clean animals were present.
A common simplified retelling says that every species entered as only one male-and-female pair. That summary misses the special provision for clean animals in Genesis 7.