442 Brian K. Hall
similar features resulting from independent evolution (homoplasy). Category 1,
similarity due to common descent, is homogeny as proposed by Lankester. Cate-
gory 2, similarity arising by independent evolution, is very close to homoplasy as
proposed by Lankester to include analogy, parallelism and convergence. Remove
parallelism from Lankester’s homoplasy and you have homoplasy as I construe it.
This realignment of the categories of homologous and homoplastic features pro-
vides a way to bridge phylogenetic and developmental approaches to homology
and homoplasy. Seeing reversals, rudiments, vestiges, atavisms and parallelism as
closer to homology than to homoplasy should frame our agenda when searching
for commonalities underlying these features. Regarded them as homoplastic sets
our mind to independent evolution and directs us to search for different develop-
mental and genetical mechanisms underlying homoplasy than underlie homology,
an approach that is essentially pre-Darwinian and neglects the century and a half
of evidence for a single evolutionary history of life on the planet. There is but one
set of historically contingent phylogenetic and mechanistic relationships of fea-
tures and taxa. Homology and homoplasy represent a continuum. Understanding
that continuum is at the very foundation of empirical, historical and philosophical
approaches to biology.
ACKNOWLEDGEMENTSI came to these views on homology and homoplasy over the years following a
workshop (held in Columbus. Ohio in 1999) on “Homoplasy in Primate and Human
Evolution”, organized by Charles Lockwood and John Fleagle and sponsored by
the Wenner-Gren Foundation for Anthropological Research, and by the Institute
of Human origins at Arizona State University. My thanks Charles and John for
providing such a creative workshop environment. I thank Matt Vickaryous for
comments on a draft manuscript and for his attempts (resisted by me more than
he would like) to keep me on the cladistic straight and narrow. The research
underlying this paper has been supported, most recently, by the Natural Sciences
and Engineering Research Council (NSERC) of Canada, the Killam Fellowship
programme of the Canada Council for the Arts, and through funds associated
with the University Research Professorship and Campbell Chair in Biology of
Dalhousie University.