The Wellcome Trust's interactive Tree of Life illustrates an idea that Darwin and his contemporaries used to explain the evolutionary links between living things.
This is an extract from Darwin's On the Origin of Species, in which he invoked the idea of the 'tree of life', a way to describe the evolutionary relationships between all living things on Earth.
"The affinities of all the beings of the same class have sometimes been represented by a great tree...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."
The theory of evolution by natural selection, and with it the concept of the evolutionary Tree of Life, have since been thoroughly tested and verified by a wide range of evidence and especially by the discoveries of genetics. The universality of the genetic code - the DNA instructions that specify the make-up of the proteins from which organisms' bodies are built - confirms a common ancestry for all life on Earth today.
About 150 years on from Darwin's famous book, we know today that the concept of a 'Tree of Life' has its limitations and that the relationships between organisms may be more accurately represented by web than a tree. Nevertheless the concept of the 'Tree of Life' remains a valid metaphor for much of the historical process of evolution.
If you're ready to get started and to explore the links between living things, go to the interactive now.
If you want ideas on what to do with interactive, find out how you can use the interactive.
Sources: Charles Darwin's On the Origins of Species, Wellcome Trust, Open University. Darwin's Tree of Life sketch reproduced by kind permission of the Syndics of Cambridge University Library.