Groups inside groups

About this video

A supermarket puts thousands of products into aisles and shelves so you can find what you want. Biologists have a much bigger job: about two million kinds of living things have been named so far. Sorting them into groups is called classification.

The idea most biologists still use comes from the Swedish doctor and botanist Carl Linnaeus, who in 1735 published Systema Naturae, putting living things into groups inside bigger groups. Today the groups run from the biggest, the domain and the kingdom, through phylum, class, order and family, down to genus and species. The leopard, for example, is an animal, a mammal, a meat-eater or carnivore, a member of the cat family and one of the big cats, the genus Panthera.

The more groups two living things share, the more closely related they are. A leopard and a lion share the big cats; a leopard and a house cat share only the cat family.

At the very top, Carl Woese and two colleagues proposed in 1990, from comparing the chemical instructions inside cells, that all life falls into three domains: Bacteria; Archaea, tiny single cells that look like bacteria but are very different inside, many living in hot springs or salty lakes; and Eukarya, everything whose cells have a nucleus, including animals, plants and fungi. So you, an oak tree and a mushroom share one domain but belong to different kingdoms. The Catalogue of Life now counts over two million named species, with tens of thousands added every year. This video goes with the lesson Sorting Life in Biology Level 1 on Knaph.

Transcript

1. 0:00A supermarket sorts thousands of products into aisles and shelves. Biologists must sort about two million named kinds of living things.
2. 0:09They sort living things into groups inside bigger groups. Carl Linnaeus started it in 1735.
3. 0:16Take the leopard. An animal, a mammal, a meat-eater, in the cat family, among the big cats.
4. 0:24Today the groups run from domain and kingdom down to genus and species.
5. 0:31The more groups two living things share, the closer relatives they are.
6. 0:37A leopard and a lion share the big cats. A leopard and a house cat share only the cat family.
7. 0:45In 1990, Carl Woese and colleagues proposed three domains, by comparing the chemical instructions in cells.
8. 0:52Bacteria. Archaea, which look like bacteria but are very different inside. And Eukarya, whose cells have a nucleus.
9. 0:59You, an oak tree and a mushroom are all in one domain, but in different kingdoms.
10. 1:06Over two million species have been named so far, and tens of thousands more are added every year.
11. 1:18Groups inside groups. The more two living things share, the closer their family ties.