Tree of life (biology)

The tree of life or universal tree of life is a metaphor, conceptual model, and research tool used to explore the evolution of life, and to describe the relationships between organisms, both living and extinct.

"The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth." (Charles Darwin, On the Origin of Species)

Quotes

• The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. … As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.
  • Charles Darwin: The Origin of Species by Means of Natural Selection (Sixth Edition), ch. 4, "Natural Selection", pp. 104–105. John Murray (1876). Republished by Cambridge University Press (2009). ISBN: 1-108-00548-9.

• For evolutionary biologists there is something very special about the classification of living organisms, something that is not true of any other kind of taxonomy. It follows from the idea of evolution that there is one uniquely correct branching family tree of all living things, and we can base our taxonomy upon it.
  • Richard Dawkins: The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe without Design, ch. 10, "The One True Tree of Life", p. 256. W. W. Norton & Company (1986). ISBN: 0-393-30448-5.