## 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.

## 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.