Dobzhansky first used the title statement, in a slight variation, in a 1964 presidential address to the American Society of Zoologists, "Biology, Molecular and Organismic", to assert the importance of organismic biology in response to the challenge of the rising field of molecular biology.[2] The term "light of evolution"—or sub specie evolutionis—had been used earlier by the Jesuit priest and paleontologist Pierre Teilhard de Chardin and then by the biologist Julian Huxley.[3]
As he had said in his earlier presidential address, "If the living world has not arisen from common ancestors by means of an evolutionary process, then the fundamental unity of living things is a hoax and their diversity is a joke."[2] The unity and diversity of life provide central themes for his essay.
Overview
Dobzhansky opens with a critique of Shaikh Abdul Aziz bin Baz, who later became Grand Mufti of Saudi Arabia, for holding the geocentric view that the Sun revolves around the Earth. Dobzhansky asserts that "it is ludicrous to mistake the Bible and the Koran for primers of natural science. They treat of matters even more important: the meaning of man and his relations to God." He criticizes the early English antievolutionist Philip Henry Gosse—who had proposed that fossils were created to mislead people—for blasphemously implying that God is deceitful.[1]
Addressing the diversity of life on Earth, Dobzhansky asks whether God was joking when he created different species for different environments. This diversity becomes reasonable and understandable, however, if Creation takes place not by the whim of the Creator "but by evolution propelled by natural selection."[1] He further illustrates this diversity from his own investigation of the widely diverse range of species of fruit flies in Hawaii. Either the Creator, "in a fit of absent mindedness," created many species of fruit flies in Hawaii, or the fruit flies that arrived on the islands diversified to fill a wide range of vacant ecological niches.[1]
He turns to the unity of life: "From viruses to man, heredity is coded in just two, chemically related substances: DNA and RNA. The genetic code is as simple as it is universal. There are only four genetic 'letters' in DNA: adenine, guanine, thymine, and cytosine. Uracil replaces thymine in RNA. The entire evolutionary development of the living world has taken place not by invention of new 'letters' in the genetic 'alphabet' but by elaboration of ever-new combinations of these letters.
Not only is the DNA-RNA genetic code universal, but so is the method of translation of the sequences of the 'letters' in DNA-RNA into sequences of amino acids in proteins. The same 20 amino acids compose countless different proteins in all, or at least in most, organisms. Different amino acids are coded by one to six nucleotide triplets in DNA and RNA. And the biochemical universals extend beyond the genetic code and its translation into proteins: striking uniformities prevail in the cellular metabolism of the most diverse living beings."[1] He notes the similarity of proteins in different species: "the so-called alpha chains of hemoglobin have identical sequences of amino acids in man and the chimpanzee, but they differ in a single amino acid (out of 141) in the gorilla. Alpha chains of human hemoglobin differ from cattle hemoglobin in 17 amino acid substitutions, 18 from horse, 20 from donkey, 25 from rabbit, and 71 from fish (carp)."[1]
Another example of the unity of living things using the molecular sequence of cytochrome C, which Emanuel Margoliash and Walter M. Fitch had shown to be similar in a wide range of species, including monkeys, tuna, kangaroos, and yeast.[1] This unity is further illustrated by the similarity of the embryos of different species. Either God deliberately arranged things "to mislead sincere seekers of truth"[1] or these similarities are the result of evolution.
Dobzhansky concludes that scripture and science are two different things: "It is a blunder to mistake the Holy Scriptures for elementary textbooks of astronomy, geology, biology, and anthropology."[1] He argues that the choice between science and religion is false: "It is wrong to hold creation and evolution as mutually exclusive alternatives. I am a creationist and an evolutionist. Evolution is God's, or Nature's method of creation. Creation is not an event that happened in 4004 BC; it is a process that began some 10 billion years ago and is still under way." He argues that evolution provides an organizing principle for biology: "Seen in the light of evolution, biology is, perhaps, intellectually the most satisfying and inspiring science. Without that light it becomes a pile of sundry facts—some of them interesting or curious but making no meaningful picture as a whole."[1]
The underlying theme
The underlying theme of the essay is the need to teach biological evolution in the context of debate about creation and evolution in public education in the United States.[4] The fact that evolution occurs explains the interrelatedness of the various facts of biology, and so makes biology make sense.[5] The concept has become firmly established as a unifying idea in biology education.[6]
The phrase
The notion of the "light of evolution" came originally from the vitalistJesuit priest Pierre Teilhard de Chardin, whom Dobzhansky much admired. In the last paragraph of the article, Dobzhansky quotes from de Chardin's 1955 The Phenomenon of Man:
(Evolution) general condition to which all theories, all hypotheses, all systems must bow and which they must satisfy henceforward if they are to be thinkable and true. Evolution is a light which illuminates all facts, a curve that all lines must follow. (p. 219 of The Phenomenon of Man)
The phrase "nothing in biology makes sense except in the light of evolution" has come into common use by those opposing creationism or its variant called intelligent design.[4][7] While the essay argues (following de Chardin) that Christianity and evolutionary biology are compatible, a position described as evolutionary creation or theistic evolution, the phrase is also used by those who consider a creator to be unnecessary, such as Richard Dawkins, who published The Selfish Gene just three years later.
↑ Huxley, Julian (1953), Evolution in Action, New York: Harper & Brothers, p.152, Medieval theology urged men to think of human life in the light of eternity—sub specie aeternitatis: I am attempting to rethink it sub specie evolutionis—in the light of evolution.
↑ David L. Haury (1996). "CSMEE Digest 96-4". Teaching Evolution in School Science Classes. The Educational Resources Information Center. Archived from the original on 2007-09-23. Retrieved 2007-12-13.
PDF as published by The American Biology Teacher, Vol. 35, No. 3 (Mar., 1973)
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