An Old But Valid Complaint

So, here's a methodological issue that impacts on both discrete and continuous character reconstruction, one not raised by the papers we read. When an active directional trend exists in the true character evolution, ancestral state reconstruction will often be highly misleading (see references below). With some knowledge of taxa closer to the base node, we can control for this (such as fossil taxa). But obviously we don't have such taxa for many groups and for many of the characters we wish to understand better.

So, in those later cases, could we test for whether a trend may or may not be present in our character history of interest? How pervasive do we believe character trends to be, and should we be concerned if we cannot actually control for them?

Food for thought.

Refs:
Finarelli, J. A., and J. J. Flynn. 2006. Ancestral State Reconstruction of Body Size in the Caniformia (Carnivora, Mammalia): The Effects of Incorporating Data from the Fossil Record. Systematic Biology 55(2):301-313.

Oakley, T. H., and C. W. Cunningham. 2000. Independent Contrasts Succeed Where Ancestor Reconstruction Fails in a Known Bacteriophage Phylogeny. Evolution 54(2):397-405.

Webster, A. J., and A. Purvis. 2002. Testing the accuracy of methods for reconstructing ancestral states of continuous characters. Proceedings of the Royal Society of London. Series B: Biological Sciences 269(1487):143-149.