The Tree of Life
The Tree of Life represents descent from common ancestors. Human relationships appear within a much larger history connecting humans with other animals, plants, and other living organisms.
THE IDEA
The Tree of Life
Living organisms are connected through descent from earlier organisms. Dennett describes humans as sharing ancestors with other humans within the last hundred thousand years, with dogs and whales within the last two hundred million years, and with daisies and redwoods within the last two billion years. These broad timescales illustrate different depths of common ancestry.
The image referenced in Chapter 43 is not included here. In a tree of descent, living lineages extend to the present while extinct lineages end earlier. Non-avian dinosaurs became extinct more than 60 million years ago; birds are a surviving dinosaur lineage. At finer scales, the branches represent individual family histories, including lines that ended without descendants.
When to use it
Tracing relationships among species and comparing their evolutionary histories.
Understanding the genetic relatedness of different species for conservation efforts.
Studying the evolution of traits across different lineages.
Resolving phylogenetic relationships using DNA sequencing.
FROM THEORY TO EVERYDAY LIFE
In practice
Shared Ancestry Between Humans and Dogs
The Tree of Life shows that humans and dogs share a common ancestor that lived within the last 200 million years, highlighting our deep evolutionary connections.
Dinosaur Extinction and Bird Lineage
Non-avian dinosaurs became extinct more than 60 million years ago. Birds are surviving dinosaurs, so the dinosaur lineage has not disappeared entirely.
A MOMENT TO REFLECT
Put it to work.
How does the Tree of Life model help us understand the relationships between all living organisms?
What are the implications of the fact that all life on Earth shares a common origin?
How can we use the Tree of Life to trace the history of different species?
CONTINUE THE CONVERSATION
Source texts
- Intuition Pumps and Other Tools for Thinking