One cause (of many) delaying the completion of On Common Descent, my monograph examining the theory of the universal common ancestry of life on Earth — Darwin’s monophyletic Tree of Life, rooted in LUCA (the last universal common ancestor) — has been the explosion of publication on the topic. In 1998, when I submitted my dissertation, only a handful of researchers openly doubted monophyly, and only generally-known-to-be-crazy philosophers of science, like me, cared much about it.
Now an international workshop series on the question has been organized, to culminate in a major meeting in London in July 2010. The first workshop in the series was held on November 7th, 2008, at the Philosophy of Science Association biennial conference, in Pittsburgh. Massimo Pigliucci provides a helpful summary of much of the discussion.
For those who like to think about all this, here’s a thought experiment to try. Imagine two, or more, places on the early Earth where life is coming to be, contemporaneously [i.e., at the same slice in time]. Suppose, in addition, that those places are distant from each other: in the northern and southern hemispheres, let’s say. The physical distance between the locations ensures no direct causal interactions between them.
Now — will the biomolecules being formed in these independent settings be ‘the same,’ or ‘different’? How would you know? What does your answer, either way, do to the post-Darwinian understanding of “homology” as meaning “descended from a common ancestor?”