Science in Christian Perspective

 

 

EXPERIMENTAL EVIDENCE FOR THE FORMATION OF SPECIES WITHIN THE PLANT KINGDOM
Dr. 0. J. Eigsti
Plant Geneticist, 
Funk Hybrid Seed Company, 
Bloomington, Illinois

From: JASA 3 (March 1951): 20-23

For centuries man has been aware of organic diversity among living plants and animals. The facts of such diversity are set forth in Biblical records.* Practical students of agriculture depend heavily upon that inherent diversity which is so noticeable among domesticated Animals and plants. Not only the scientist, but philosophers and artists as well., have given specific consideration to the problem of variability among populations of living things. Since such a wide interest Is attached to this problem we find ourselves engaged in discussion today dealing with organic diversity as illustrated by the various species of punts and animals that inhabit the earth about us. At the same time, man has been forced to recognize the similarity between many plants and many animals., respectively. The eases of transmission of familiar traits from one generation to another are well documented. Thus, we observe two fundamental biological principles; (1) Organic diversity or variation, and (2) organic resemblances., that is, the hereditarily transmitted characters of likeness from one generation to the next.

Every Individual plant and animal differs from any other coming before or after. This unrepeatabillity of the individual is one point upon which all of us Agree. The arguments of such a problem may be those of the artist and philosopher., however, the scientist's attention is drawn not only to unrepeatabillty but also to repeatability of certain aspects of individual characteristics. Stated in other terms; variation and heredity become the basic principles of a discipline known as GENET1CS. 1950 marked the fiftieth anniversary of this subject and any topic such as we present today falls in the scope of appropriate commemoration,

* See Genesis Chapter 1.



Geneticists constantly seek a better understanding of those phenomena basic to heredity and variations that is to say., the resemblances and differences between and among individuals. As a result of an honest search for truth., tremendous amounts of factual evidence have accumulated. Today, all educators must instruct within the sphere of these and other data., if we are to meet the need of young people eager for more knowledge about the world in which we exist.

Anyone can demonstratereadily the reality of variation among plants and animals, Such variation may be discontinuous and significant from the standpoint of phylogenetic relationship. A child at the zoo finds little difficulty distinguishing between the pet pussy cat FELIX DOMTICA and the fierce lion FEIX LWO One may say these kinds of cats represent two clusters of individuals, thus any lion is different from any pussy cat. Moreover each species forms a visibly distinct group. Finally. within each of the groups the pussy cat to a certain child may mean one particular cat not only different from lions but all other cats. The universality of these observations can be extended to living plants and animals throughout the world. We are able to estimate, with confidence in our judgement that more than a million species of plants and animals exist today as illustrated by such clusters as the lions and pussy cats.

Much argument and discussion may attend the placement of a species into biological relationship with another. Theories have been postulated to explain phylogenetie origin of species and pbylogeny generally. These theories have touched off bitter controversies. Some of the basic causes of species formation yet remain utterly mysterious. On the other hand, we have accumulated a fund of knowledge about certain groups of plants that clearly point the way toward an understanding of speciation within certain areas of the plant kingdom.

Karl Linnaeus, the great Swedish Botanist, devised our present system of naming species. His concept of the origin of species was that of a creation by a divine and direct act, After a time., he discovered that certain species of plants were definitely the offspring of two other parental species which he had previously named. Thereupon., he realized the necessity for a revision of his concept of species-origin. Linnaeus did not, at the same times discard deep religious belief in God and creation when he realized the need for revision of his earlier opinion about origin of species. The facts of hybridizations which in some cases accounts for the development of new clusters of individuals, are inescapable, if one makes any serious study of genetics and cytology.

Gregor Mendel, an Austrian monks discovered the basic laws governing variability and resemblances between parents and offspring. The rediscovery of Mendells laws in 1900 marked the beginning of our present half century which we celebrated in 1950. He followed certain characteristics of the garden peas from generation to generation and formulated genetics laws which have had a profound influence upon thinking in many of the biological s   ciences. We may illustrate the impact of Linnaeus and Mendelian concepts in the following case. Datura stramonium the Jimson weed is a good Linnaean species, well known to many as an objectionable weed in field and pasture. This species is characterized visibly by purple flowers, purple stem and spiny capsules. Another species Datura tatula, the white flowered Jimson weed, has green stems and is visibly distinct from the purple Datura. According to Linnaeus early concept the two species represented separate creations. Now the application of Mendelian laws gives us now insights because the hybrid of a yellow flowered plant., D. tatula with a purple flowered plant D. stramonium, always yields all purple-flowered plants. If we self fertilize these purple hybrids the offspring may be both yellow-flowered and purple-flowered plants. The differences are associated with different genes at certain loci on certain chromosomes. Then the basis for speciation, is found in the gene changes or mutations that occur and are transmitted from one generation to another.

Within the last 25 years we have demonstrated that gene and chromosome-diversity (mutations) can be induced by physical and chemical agents, i.e. x-ray and colchicine, respectively. The consequences of these studies have direct bearing on our present knowledge of species formation.

In the spring of 1937, experiments conducted at the Carnegie Institution Department of Genetics, Cold Spring Harbor) Long Island., New York, proved that a drug called to accumulate within individual cells. New tissues arose from the treatment wherein cells carried a duplicated number of chromosomes. Onion root tips regularly have 16 chromosomes'per cell, but the colchicine-treated root tips showed cell conditions with 32 and 64 chromosomes, and in some cases, cells bad 500 chromosomes per nucleus. When the drug is applied to young seedlings, a new type of plant with double the number of chromosomes may be obtained, These behave differently from the original untreated plants. These are called polyploid plants. Among flowering plant species over 50% known for chromosome number belong to the category of polyploids and undoubtedly arose tn nature by some kind of doubling of the chromosomes before or after specific hybridizations.

Further experimenting with colchicine revealed that a sterile species-hybrid when doubled became fertile and as such became a reproducing unit or population that ad not previously exist. We may illustrate these principles by the following actual experiment carried out by two different scientists,, independently two species of cotton, asiatic diploid, G-arboreum, a 26 chromosome species crossed by another American diploid, G.-thurbegri,also with 26 chromosomes, yields a sterile hybrid (G. arboreum x G. thurberi) cells of the hybrid have 26 chromosomes and no flowers of such plants set seed. When colchicine it applied to growing stem tips, new tissues develop that have cells with 52 chromosomes. Now, these new tissues produce flowers that set seed. Furthermore., one may also use these fertile flowers for crosses with standard varieties of American cultivated cotton G-hirsutum., a 52 chromosome species, The species-hybrid (G. arboreum and G. thurberi polyploid). and American cultivated cotton may be crossed without difficulty. We may say that a synthetic species G.-hirsutum synthetic is thus created. Hence we may obtain by experimental procedures a synthetic species that simulates a Linnaean species and theoretically recognized by Botanists as a reproduction of that found in nature. Time does not permit to review many other documented cases of genetic experiments which have led to the production of synthetic species very similar to those formed in nature. Such origin of species in nature is postulated as the "cataclysmic origin" of new species. Many crop plants of economic importance are ploypolid, and fit a similar pattern as for cotton. Not all speciation has occurred-in this manner but these illustrations are excellent and are scientifically documented. We may go a step farther and hybridize a radish with a cabbage. The hybrid is, as to be expected, sterile, but by duplication of the chromosomes with colchicine, a fertile radish-cabbage plant may be obtained. We must assign the name Raphano-brassica to this creation. Agan (wheat X rye) hybrids can be doubled and from such experiment arises the Triticale or a new wheat-rye hybrid different from either wheat or rye. Numerous additional cases are being studied so that hybrids made fertile with colchicine are of common occurrence. To date, 165 synthetic species have been made with cololdoine.

The mechanisms which operate in nature to establish species are complex and outside the sphere of our limited time. Nevertheless geographic isolation, ecological, and physiological factors play a very fundamental role in speciation in nature.

Our problem now becomes one of orientation of this newer knowledge with Biblical records that describe the origin of living plants and animals. When we use the word creation we are not replacing the Scriptural teaching by present scientific laws. The basic genetic mechanism and the gene complex or origin of genes remain as that which was created. We have merely enlarged our concept of how different plants or individuals come into being once the basic gene system was derived.

Summarizing the area covered in this discussion, we have shown how new species of plants may arise by hybridization and subsequent doubling of chromosomes to form new reproductive units. These fit the status of a new species. Our interpretation of Biblical accounts of the origin of plants and animals must take into consideration the accumulated factu4l evidence provided by genetic investigation., if we are to make effective presentations to students entering the field of biology.

There is no conflict between the genetic evidence at hand and Biblical records. Organic diversity is clearly stated in the Bible and organic diversity is observable. Organic similarities are outlined in the text of Scriptures and these are explained from careful genetic investigation. The explanation of speciation appears sound as viewed from the vantage points of science and religion. I trust that this brief survey can be used for better understanding by those earnestly seeking to continue sincere religious belief and also pursue scientific investigations dealing with the controversial biological materials of phylogeny and phylogenetic relationships.