Research Seminar - October 23, 1998

Abstract

In this study, the evolution of species is modelled by starting with a single ancestral species with a particular suite of morphological "characters", that is then evolved in discrete steps. The characters are of two distinct types - hereditary characters that are passed on from the parent species (apart from the effects of random mutations), and functionally adaptive characters (produced during ontogeny by interaction with the home environment of each species). At each step, a small number of these characters may change. Random extinction, migration, and fossilisation are also included.

Living and fossil forms alone are then used to reconstruct a phylogeny and migration history, and the results compared against the known true phylogeny from the simulation. Two techniques of reconstruction are employed. The first technique involves matching existing species and fossils to the most closely (morphologically) related earlier fossil. The other involves a phylogenetic reconstruction based on the discrete morphological characters of the existing species only.

Initial results show that, even at artificially high fossilisation rates, the number of fossils leading to living species is rather small - most fossils being on extinct lines, and the most recent common ancestor is close to the stem of the model, and is usually not a fossil. This contrasts with the reconstructions, where most fossils seem to lead to living species, and the most recent common ancestor is usually a very recent fossil.