## Pagel’s Tree Transformations

This applet illustrates the effects of Pagel’s (1999) three transformations on rooted trees: lambda, delta, and kappa. A lambda value of 0.2 reduces the height of internal nodes to 20% of their original height. A delta value of 0.2 raises the height of every node (including leaf nodes) to the power 0.2. Finally, a kappa value of 0.2 raises every edge length to the power 0.2. Section 6.2 of Luke Harmon’s book provides a good explanation of these transformations in the context of comparative methods.

Use the **left/right arrow keys** to cycle among the three parameters and the **up/down arrow keys** to
increase/decrease the current parameter value. Note that the left/right arrow keys reset
the parameter value to 1.0, which is the unmodified tree. Hold down Shift when using
the arrow keys to avoid scrolling while changing parameter values. The **Simulate button** simulates
a new tree using a pure birth model scaled to have total height 100.

## Literature Cited

M Pagel. 1999. Inferring the historical patterns of biological evolution. Nature 401:877-884. DOI:10.1038/44766

## Acknowledgements

This applet makes use of the excellent d3js javascript library. Please see the GitHub site for details about licensing of other libraries that may have been used in the source code for this applet.

## Licence

Creative Commons Attribution 4.0 International. License (CC BY 4.0). To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.