The most basic classification of living things is kingdoms. Currently there are five kingdoms. Living things are placed into certain kingdoms based on how they obtain their food, the types of cells that make up their body, and the number of cells they contain. Species are as specific as you can get. It is the lowest and most strict level of classification of living things. The main criterion for an organism to be placed in a particular species is the ability to breed with other organisms of that same species. Generally similarities between the members of each species are so much more than the similarities between members of a kingdom. The natural world contains about 8.7 million species and by using validate model the researchers predicted the approximate number of species in each kingdom to be: 7.77 million species of animals so there are much more organisms in kingdoms in contrast to species.