The Changing Classifications of Life
It wasn't that long ago that scientists only had two groups in which to toss living creatures - Animal or Plant. That was it, and everything alive was one or the other. They called this major classification a "Kingdom".
However, life has changed and grown for billions of years, and it has not followed neat rules about "all plants are green" and "all animals have four legs". There are plants that move, plants that eat meat, animals that are stationary, animals that are green. There are animals that live in water for some of their life and live in air for other parts. How can you make a "set system" that tries to categorize all of these various things?
The answer is that as we learn more about each creature, and what makes it unique and special, we adapt and change our categories to meet our new information. In the 1800s, scientists began to realize that not all living creatures WERE animal or plant. THey began to realize that there were fungus and bacteria - and these were not like animals NOR like plants. They suggested making a new kingdom just for fungus ... and then a new kingdom just for bacteria.
But as scientists learn more and more about these smaller forms of life, they realize that even at that level, there are VAST differences between types of bacteria, and types of fungus. There are virusses, which are considered to be very different than the other kingdoms. Scientists are still working on agreeing on just how life should be broken out in a way that makes sense.
For now, consensus seems to be with four kingdoms: Viruses, Archaea, Bacteria, and Eukaryotes. Read More about the Four Kingdoms. But as science learns even more about life and the various living creatures around us, expect even more information to expand our knowledge!
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