Science in Christian Perspective



Irving W. Knobloch, Ph.D.

From JASA 8 (September 1956): 20-21.

Phylogenetic Trees

Most general biology books grace one of their pages with a diagram bringing together our present knowledge on the time of origin of the major groups of organisms and the relationships that may exist between these major groups. The one in Pauli's "The World of Life" is called "The Tree of Life". This one starts with the viruses, bacteria, blue-green algae and others and derives, by implication, all of the "higher" plants and animals from the more "simple" forms. The diagram shows a branching "tree". The tree effect is obtained by employing several assumptions among which are (1) the fossil record is reasonably complete and (2) that phyla are connected by ancestral forms with other phyla. The trees in some books show less an anastomosing than others, so much so that the ancestral trunk has been eliminated and only the tips of the branches remain.

If the biblical account is to be taken literally, it would seem that God created creatures capable of living on land, in the air and in the sea. If one furthermore assumes that this is fiat creation, then there is no room for the derivation of all living things from simpler forms of life, as taught in the theory of evolution. One solution to this dilemma has been proposed by the writer in a series of articles in this magazine. Briefly, the thesis given was that certain types were created by fiat and from these our present forms have evolved by the various means known to science. This thesis can neither be proved nor disproved by evidence of a conclusive nature but the same is true of organic evolution per se.

The purpose of this article is to examine certain facets of the phylogenetic tree concept. It is not planned to exhaust this topic but only to mention such evidence as bears upon it in a general fashion.

Something needs to be said briefly at the outset upon the dating of the rocks. The basis of rock dating still depends largely upon the use of index fossils. Certain fossil species are characteristic of certain periods and were not found before or after that time in history. A case in point would be the now extinct passenger pigeon. Should any of these have become buried and fossilized and later dug up, future scientists would say that these were one of the characteristic forms of the life of the quartenary period. They must be careful not to push this too far however. We know that the passenger pigeon would only be characteristic of such quartenary deposits laid down in parts of this hemisphere.

Similarly, paleontologists dealing with more commonly known fossils, must beware of assuming that plant and animal life of the past was uniformly distributed over the face of the earth. This may have been so, but it is quite hard to prove in all cases.

If rocks are dated by fossils, how do we know the order of evolution; how do we know which fossils are older than others? It is quite logical to assume that rock layers underneath other layers are older than those above. No fault can be found with this reasoning except in these cases where the strata have obvious been overturned. (Lewis overthrust).

It is only fair to state that at no place on the earth is there a series of rocks running from the archaeozoic up to and including the most recent rocks of the cenozoic era. We cannot therefore see the entire story at any one place. It is necessary to "bring in" strata from various places (dated by the fossils) and superimpose one series upon the other. The need for cautious interpretation on this procedure has been indicated. Dr. Kulp, of our own organization, has kindly written me telling of two series of deposits where the series are extensive enough to be helpful. In the gulf coast region there are deposits (he writes) at least 30,000 feet thick "going" from the Pleistocene (ice age) down to the Cretaceous (of the Mesozoic era). A larger series is that in the Appalachian syncline where the rocks encompass be period between the Cambrian and the Mississippian periods.

A method superior to datinz of rocks by fossils is the radioactivity method. If and when enough dates can be established ' we will have.a fairly reliable time table for the pre-historic development of 'life on the earth.

Another aspect of the problem is the completeness of the fossil record. Opinion among sound scholars is divided on this point. Undoubtedly there were many soft-bodied creatures living in the past, of which we have no record. The rocks probably have faithfully preserved most of the shelled creatures and others capable of being preserved but, as it has been said, the record is very incomplete with respect to all the kinds of organisms living at any one time. Our estimates, therefore, as to when a phylum or class first made its appearance cannot be based with complete assurance on the fossil record. G. G. Simpson, in his book "Major Features of Evolution" says that paleontologists do not always seem to realize how exceedingly spotty is the geographic sampling of most of the fossil record.

With these points in mind, we turn to a cursory study of the fossil record itself, for after all, a phylogenetic tree 'is constructed largely on the basis of fossil remains.

Fossils are found in pre-Cambrian rocks but their remains belong to smaller, relatively unspecialized organisms.

In the Cambrian rocks are found remains of all the animal phyla except too-soft bodied ones and the chordates. One writer ventures the guess that over 5,000 species are found in the Cambrian rocks. I would welcome confirmation or refutation of this figure from some reader. All fossil species fall into the major existing groups, according to Austin Clark. Our "tree" therefore must have most of its animal phyla lines going back to the Cambrian. There has been no evolution of phyla since the Cambrian except for the Chordates,- and it is very unlikely that the Chordates arose full blown and suddenly in the next period (Ordovician). It must also be emphasized that very complicated creatures shared the Cambrian seas with their simpler neighbors.

The sudden appearance of abundant fossils in the Cambrian is remarkable and is not easily explained, according to Schuckert and Dunbar ("Outlines of Historical Geology")

Ostracoderm fishes are found in Ordovician rocks and probably arose from simpier, as yet undiscovered fishes, of the Cambrian period or-they were created. There does not seem to be any- creature in either PreCambrian or Cambrian times which might have given rise to such a creature as a fish.

The oldest known amphibia,have been, found in the upper Devonian of East Greenland, according to
Gregory (Evolution Emerging). Very few amphibia have been fossilized, due possibly to their skeletal composition.

(To Be Continued)