Science in Christian Perspective




From JASA 8 (December 1956): 17-18.

(Continued from September 1956)

Phylogenetic Trees

Reptiles are first found in the coal measures of the Pennsylvania (Paleozoic era) and birds from the Jurrasic (Mesozoic era), according to E. 0. Dodson (Textbook of Evolution). As commonly stated in textbooks, the reptiles and birds "arose" in these periods. This, of course, may well be, but it is seemingly naive to be dogmatic about it. We know that many groups appear so suddenly in the record that it seems logical to assume that the group in question has had a longer history than evidenced by its fossils.

Dodson takes the mammals back to the Permian or to the Pennsylvanian. William D. Mathew (Climate and Evolution, 2nd Ed. 1939) points to the fragmentary knowledge of the origin of the mammals as deduced from the fossil record. The record from the Mesozoic era rocks shows two jaws and a few teeth (Triassic), a number of more or less fragmentary jaws (Jurassic) and various teeth and jaws from the Cretaceous. Thus, of the earliest mammals, we do not have either a complete skull or a complete skeleton (according to Mathew). Rock pressures, unfavorable burial conditions, and the very nature of mammalian bones, have deprived us of a more complete picture of these animals.

Turning now to plant evolution, we find bacteria and algae going back to Cambrian or even Pre-Cambrian rocks. It is interesting to point out that these same groups are still with us, changed possibly as to species or kinds but still recognizable as bacteria and algae. Mosses have been found in the Pennsylvanian (late Paleozoic) but no doubt they existed long before this.

Vascular plants (ferns and some seed plants) trace their origin at least, as far as the Silurian period (Paleozoic era). According to Ralph Chaney, one of the foremost paleobotanists, the first vascular tissue comes from the Silurian and the first seeds from the Devonian. Incidentally, Darrah (Textboo k of Palo botany) disposes of the old idea that Rhynia (Devonian) is the first stage in the evolution of the land plants, pointing to earlier fossils from the Silurian deposits of Australia. Gymnosperms (seeds in cones) are found earlier as fossils than the angiosperms (seed plants with flowers).

The oldest evidence of angiosperms (pollen) comes from the Jurassic rocks, according to W. B. Turrill (Bot. Rev. 8(8):1942). The pollen belonged, possibly, to members of the water lily, magnolia and butternut families. Since these are complex organisms, it would be very naive to assume that the angiosperms (larose" or "originated" in the Jurassic. In the rocks of the next period, the Cretaceous, we find fossil leaves and seeds of numerous present day forms. Indeed, the sudden (apparent) rise of the angiosperms is one of the great mysteries of evolutionary study. Without doubt, fossil finds of the next few centuries, will help to clarify this mystery.

We cannot claim that all plant phyla go back to the Cambrian. It is surprising, however, to note that some seed plants (the so-called highest group) go back to the Devonian period. It is not likely that these developed from the ferns. In many ways, our knowledge of plant-fossils is inferior to that of animal fossils. Our knowledge here is woefully incomplete.

Julian Huxley (The New Systematics, p. 19) said that-

in lower taxonomic categories such as species and subspecies, parallel mutation may make a phylogenetic interpretation an almost impossible ideal, of little practical help or even theoretical significance. Even in larger groups, such as those of the higher plants, phylogeny may be almost hopelessly obscured by paral lel or convergent evolution, added to the lack of fossil material in early evolutionary stages.

The opinion of C. R. Metcalf and L. Chalk (Anatomy of the Dicotyledons) has been quoted elsewhere. Briefly they hold that views on phylogenetic interrelationships in plants is a matter of personal opinion. They consider it "fundamentally misleading" to arrange plant families in a single, linear, phylogenetic tree.

One of England's great botainsts is W. B. Turrill.  He writes (Bot. Rev. 8(8), P. 508)-

it is usually not difficult to arrange living organisms in series such a manner that differences in the struc ture of or more organs appear as graded steps. Such series are frequently interpreted as phylogenetic or, if the study be concerned with only one organ, as morphogenetic or organogenetic. When the evidence is carefully stated and fully established, evolution nay well be the most rational explanation of such a series. The great diversity of opinion in published accounts of plant phylogeny suggests, however, that the avail able data are still too few for the construction of a
valid general phylogenetic scheme. There is no doubt that the paucity of relevant pateobotanical data in most
groups of plants (partial exceptions are the Pterido phyta and the Gymnospermae) is a major cause of un certainty as to whether or not proposed series are phylogenetic, and if they be, in which direction they should be read.

In monographic treatments or longer papers, one frequ ently finds intraphyletic trees. In these, the authors attempt to trace species relationships as influenced by genetic changes and recombinations. This is a commendable pursuit because it is on surer ground, attacking the problem on an inductive basis rather than on a theoretical or deductive basis. Deduction and theory have an important role to play in science but one must, necessarily, be less dogmatic about such approaches than those placed on an inductive basis.

In conclusion, therefore, it seems to be more consistent 'with one of the scientific attitudes (withhold judgment until all the data is in) to figure a phylogenetic tree with thephyla trunks (for the most part) deeply imbedded in the Cambrian period. Whatever evolution has occurred, has been confined to changes within the phyla and classes. The phylogenetic tree becomes, in fact, a series of trees each one confined to a phylum, a class, order or even smaller category. This is as far as the evidence, it seems to me permits one to go at the present time.

Virus Reconstitution Achieved

This is the title of an article in the California Monthly for January 1956. Briefly it tells of the achievements of Drs. Fraenkel-Conrat and Williams in putting together inert fragments of tobacco mosaic virus to produce disease-producing viruses, A virus had been found earlier by Dr. Stanley to be composed of a core of nucleic acid surrounded by protein. The two California scientists warmed a virus preparation in a detergent. This technique remove the enveloping protein, leaving the nuclei acid. After much empirical trial and error it was possible to obtain pure samples of both the protein and the nucleic acid. Both of these were found to be inert. By careful mixing of the two inert portions, the two united in their respective and correct position, to produce an active and infectious
virus when placed on tobacco leaves.

This research leads us to believe that at some time in the f uture other viruses can be torn down and rebuilt, thus furthering our knowledge of living matter.

It is not claimed that this is an example of spon taneous generation despite the apparent mixing of two lifeless materials to produce a living virus. Scientists have learned caution through a study of the his of science. It will be interesting to see if someone obtain both the protein and the acid in a relative large quantity, sterilize and mix them, and obtain fectious viruses.