davoid

Pascher, influenced by Haeckel's phylogenetic speculations, constructed a hypothetical ancestor of the Protista. It was a unicellular, photosynthetic cell with two flagella--a phytoflagellate. It had one plastid and a cell wall. From such an ancestor, Pascher believed there could be derived all the algae and from them the higher plants, fungi, and protozoa. In other words, this was the start of eukaryotic evolution. This hypothetical ancestral phytoflagellate of Pascher illustrates the weakness of this kind of phylogenetic speculation. No experiments can be done with it, since it does not exist. Rigorous comparisons for homology are impossible, since it does not exist. The only thing in its favor is that it alerts us to the phylogenetic problems in this area by saying that a biflagellate, unicellular eukaryotic producer is the kind of cell we are looking for. But the worst effect of this kind of thinking is that it is prejudicial to any other theory. The implication is that there was a unitary origin of the Protista. But was there? What is the evidence? It suggests that a certain moneran species evolved into this type of protistan. Did it? We will see shortly that some people favor a startlingly different point of view. In summary, Pascher's suggestion and others like it must be held at arm's length to avoid the distortions they can introduce. Perhaps better, we should ignore them altogether and simply work from plesiomorphs.

Working from plesiomorphs, we immediately face the situation already described, namely, there are many plesiomorphs and there is a huge gap between the plesiomorphs and the prokaryotes. The next step is to look for homologies, which, as we have also noted, will probably have to be molecular. Are there any? The growing answer is yes, there seem to be some, but the story is not yet entirely convincing.