The “tree of life” is usually organized as a branching diagram that shows how all living things are related by evolution, starting from common ancestors and splitting into ever-finer groups.

Big picture: trunk, branches, leaves

  • Imagine a single trunk at the base: this represents the earliest common ancestors of life on Earth (for example, the last universal common ancestor of all cells).
  • Major branches coming off the trunk represent the big lineages of life (domains like Bacteria, Archaea, and Eukarya).
  • Each big branch splits into smaller limbs and twigs: these are kingdoms, phyla, classes, orders, families, genera, and species.
  • Individual leaves at the tips are actual species that exist today (or in the past, if the tree includes fossils).

So the closer two species’ leaves are on the tree (and the more of their branch they share), the more recent their common ancestor is.

How scientists organize it

Biologists build and organize the tree of life using:

  • Common ancestry
    All organisms are grouped based on shared ancestors, not just superficial similarity; this is done through evolutionary relationships (phylogeny).
  • Genetic data
    DNA and RNA sequences are compared to see how similar genomes are; more similarity usually means a closer relationship.

  • Hierarchical ranks
    Organisms are placed into nested groups:

    • Domain
    • Kingdom
    • Phylum
    • Class
    • Order
    • Family
    • Genus
    • Species
      Each level is a “branch” inside a bigger branch on the tree.
  • Clades instead of strict ranks
    Modern trees often focus on clades —groups that include an ancestor and all its descendants—rather than just the classic ranks, because clades better reflect true evolutionary history.

Modern twist: not just a simple tree

The tree of life today is not seen as a perfectly neat, symmetrical tree:

  • There are three domains at the deepest split: Bacteria, Archaea, and Eukarya, instead of a single straight line from simple to complex.
  • Microbes have a lot of horizontal gene transfer (genes moving sideways between species), which makes some parts look more like a web or network than a simple tree.
  • New DNA data constantly reshapes branches: species can be moved to different groups when genetic evidence shows a closer relationship elsewhere.

One quick example

If you follow the branch containing humans:

  • Life → Eukarya (cells with nuclei) → Animals → Vertebrates → Mammals → Primates → Great apes → Humans.

Each step is a nested branch on the tree, and every other species that shares part of that path (like chimpanzees or gorillas) shares the ancestors at those branching points.

Information gathered from public forums or data available on the internet and portrayed here.