We updated the section on classification in our Biology, 3rd Edition, textbook, which was released in 2020. This edition teaches a history of the classification system, including the 5-kingdom structure so that students can be familiar with it since many biologists use it in the UK. It also mentions the 1993 8-kingdom system, the 2015 7-kingdom system, and a newer not-fully-developed creation-based, baraminology system. The text then teaches the three-domain and four-eukaryotic kingdom classification system. You can find this discussion in Module 9.