Question

When the Linnaean system of classification was first developed in the early 1700s, it had three kingdoms. By the mid-1900s, it had five kingdoms. Which of the following best explains why the number of kingdoms increased?

Answer 1

Many new animal species were discovered during that time which meant the animal kingdom needed to be divided.
More kingdoms were needed once non-living things, such as viruses, were included in the classification system.
New kingdoms were needed that reflected our growing knowledge of the differences between living organisms.
The original three kingdoms soon filled up with newly discovered species which created a need for additional kingdoms.