CAN WE SEE EVOLUTION OCCURRING?
experiments and similar ones on other organisms is given in the author’s book “Life and Death, Heredity and Evolution in Unicellular Organisms” (R. Badger, Boston, 1920). An account of racial changes observed in the fruit-fly is given in T. H. Morgan’s “Evolution and Genetics.” (Princeton Univ. Press, 1925.)
The evidence of evolution has been read in the rocks and the structures of plants and animals, but under the miscroscope Dr. Jennings is able to follow evolution not as a theory but as a thing that is actually taking place.
Intensified study reveals that the hereditary characteristics do become changed by external conditions. Through such diversities, continuing for great numbers of generations, single stocks, uniform in their hereditary characteristics, gradually differentiate into many faintly differing hereditary features.
In higher organisms the state of knowledge of this point appears less satisfactory. But the evidence, so far as it goes, indicates that processes here are in agreement with those in lower organisms.
“The organisms whose bodies are condensed into a single cell have, too, a life condensed into a few hours. They present a wonderful opportunity for solving in a brief period some of the deeper problems of life.
“In a watch glass on our table we may in a week see generations come and go. We may follow in successive generations the struggle for existence and the results of natural selection.
“In a few days we may see the birth, babyhood, youth, and age of individuals and their replacement by descendants. We may study the inheritance of parental traits by the new generation or the appearance of new traits. We may observe how the population changes with the passage of ages—all while we wait for one of the changes of the moon.
“What have the simple organisms to teach us on youth and age, death and rejuvenescence, heredity, variation, evolution?”—Dr. Jennings.
“In scientific deductions one single divergency suffices to demolish the structure on which they are based.”
Evolution is not a force, but a process; not a cause, but a law.—Lord Morley.
[ 33 ]
