BIOSYSTEMATISTS Meeting, WEDNESDAY (DARWIN DAY), Feb 12th, 2003, at UCB

February 12th, 2003 at UC Berkeley
Benoit Dayrat of the Dept. of Invertebrate Zoology and Geology, Calif. Academy of Sciences, gave a talk entitled, "A Radical Darwinian solution to a conflict of 150 years between classification and evolution"
Host: Prof. Kipling Will, UC Berkley

BENOIT DAYRAT Department of Invertebrate Zoology and Geology, California Academy of Sciences, San Francisco

ABSTRACT: Classification, based on hierarchical subordination of groups to one another, can only express affinities between species taken on a horizontal surface, such as in the creationist pre-Darwinian paradigm. Evolution implies that species are ordered along vertical lines of descent of what Darwin called the 'great Tree of Life.' The problem is that ancestor-descendant relationships of species cannot be expressed by a horizontal classification because of a logical limitation of subordination. On one hand, Darwin suggested that the best possible illustration of natural relationships between species would be the genealogical tree itself instead of a classification. On the other hand, because his goal was to establish classifications, Hennig decided to get rid of both ancestors and ancestor-descendant relationships from his trees. The consequences of this decision will be analyzed in great detail, especially through Hennig's concept of "hierarchy" which is the fundamental basis of his Phylogenetic Systematics. Several methods have been proposed recently to reconstruct ancestor-descendant relationships between species, but have faced one of the strongest orthodoxies of cladistics according to which ancestor-descendant relationships are taboo by the rules. It is demonstrated here that, when ancestor-descendant relationships can be obtained, one has to agree with Darwin that only the genealogical tree itself illustrates the relationships between species and that evolutionary biologists no longer have to accept the constraints imposed by the horizontal hierarchical principle of classification. This also implies that, in cases where ancestor-descendant relationships can be obtained, systematists need other methods of classification that would not be based on subordination.