Now the 'Shrub of Life'!

2: Reading the Map of Life

Learn how to read the Tree of Life as a biological timeline. Explore the three domains—Bacteria, Archaea, and Eukarya—and discover the Last Universal Common Ancestor (LUCA).

While early scientists saw life as a ladder, modern science views the Tree of Life as a phylogenetic tree—a diagram showing how every living organism evolved from a common ancestor.

The Roots: Where it All Began

At the very base of this tree is the Root, representing the LUCA (Last Universal Common Ancestor)

Who was LUCA? A single-celled organism.
When? Roughly 3.5 to 3.8 billion years ago.
Modern Goal: Projects like the Darwin Tree of Life are currently sequencing genomes to fill in the "missing leaves" on this ancient map.

The Three Domains of Life

Today, we divide the "main branches" of life into three massive groups called Domains:

Bacteria: The nutrient recyclers of our planet.
Archaea: Specialist organisms famous for living in "impossible" places like deep-sea vents.
Eukarya: This includes complex life like plants, animals, and humans.

The Big Picture: Supergroups and Skills

In modern science, we often look at "Supergroups" to understand how life functions:

Supergroup Familiar Examples Main "Skill"

Amorphea Humans, Dogs, Yeast, Mushrooms Hunting or Decomposing

Archaeplastida Oak Trees, Grass, Seaweed Photosynthesis

SAR Kelp forests, Algae blooms Ocean oxygen production

Bacteria E. coli, Cyanobacteria Recycling nutrients

Archaea Deep-sea vent dwellers Extreme survival

From Filing System to Timeline

The most important thing to remember is that the biological hierarchy is not just a filing system; it is a timeline of innovation. To remember the order, use the mnemonic: "

Dear King Philip Came Over For Good Soup".

Domain/Kingdom (3.8+ Billion Years Ago): The invention of the nucleus.
Phylum (500 Million Years Ago): The invention of backbones or exoskeletons.
Class (200 Million Years Ago): The invention of milk or feathers.
Order/Family (60–20$ Million Years Ago): The rise of primates or specialised flowers.
Genus/Species (Last few Million Years): The rise of modern humans or specific roses.

A Shift in Perspective: In the "old days," humans were drawn at the top of the tree. Today, we draw life as a circular bush. In this view, a Great White Shark or a mushroom is just as "evolved" as a human; we have all been surviving and changing for the same 3.8 billion years

Before you go

"The Timeline Challenge"

Pick a common animal (like a cat or a hawk). Using the "Timeline" section above, list which "innovation" that animal belongs to. For example:

Does it have a Backbone? (If yes, it joined the tree 500 million years ago) .
Does it produce Milk or Feathers? (If yes, its branch became distinct 200 million years ago)

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