Forms of Life part 2: Cladistic Tree of Life

In the first part of this series, I discussed taxonomic terminology such as clades and kingdoms, but didn't go into the actual groups and the lifeforms within them. This article will provide a top-down phylogenetic overview of all lifeforms, with focus on how the traditional "kingdoms" of categorizing lifeforms relates, and some frequently miscategorized groups.


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The graph above is my attempt to show the tree of life in a cladistic/phylogenetic way (i.e. showing the actual evolutionary origins of new forms of life, usually determined by their DNA). Part 1 of this series covered the differences between cladistic categorization and morphogenic categorization (observations of the form, such as number of legs or structure of branches).

  • "Domains" are shown as squares (note Bacteria and Archea are also kingdoms as well as domains).
  • "Kingdoms" are shown as hexagons (except Bacteria, Archea and Algae)
  • Clades which are not a domain or traditional Kingdom are shown as ellipses.
  • Solid lines indicate direct genetic ancestry.
  • Dotted lines indicate an unusual genetic relationship, expanded upon in more detail below.

The rest of this article will explain these relationships in more detail.


The "last universal common ancestor" (or "last universal ancestor", as the word universal implies commonality) @@@@

Not the First Lifeform Ever

The LUCA is probably not the first lifeform that ever evolved. However, it is the first lifeform which all other known lifeforms descended from @@@@

The Three "Domains"

The Traditional "Kingdoms"

xxx@@@@ historic discussion, 2 or 3 para

xx@@@ original kingdoms, xx@@@ 20 century changes

xx@@@ now deprecated

Prokyarotes: Bacteria and Archea

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xxx@@@@ originall included algae and fungi; fungi are now known to be closer to animals @@@@ algae are polyphyletic protists



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Protists - the Miscellaneous Kingdom

There are a few conflicting definitions of protist, but generally it is accepted as

xx@@@ note polyphyletic but most amoebae are in one clade @@@ slime molds

A protist (/ˈproʊtɪst/) is any eukaryotic organism (one with cells containing a nucleus) that is not an animal, plant, or fungus. The protists do not form a natural group, or clade, since they exclude certain eukaryotes with whom they share a common ancestor[a] i.e. some protists are more closely related to plants or animals than they are to other protists.


xx@@@ deprecated term

Amoebae and Slime Molds

Examples 0f: @@@@@@@ Amoeba diseases @@@@ TODO Plasmodium (causes malaria) Phytophthora (cause of the Irish potato famine) Slime molds