DEVELOPMENT OF EVOLUTIONARY THEORY
Table of Contents
Pre-Renissance Thought | The Age of the Earth | Evolutionary Thought During
the 1770's
Evolution by Natural Selection | Natural Selection and Genetics | Links
Pre-Renissance Thought | Back to Top
The Ancient Greek philosopher Anaxiamander (611-547 B.C.) and the Roman
philosopher Lucretius (99-55 B.C.) coined the concept that all living things were
related and that they had changed over time. The classical science of their time was
observational rather than experimental. Another ancient Greek
philosopher, Aristotle developed his Scala Naturae, or Ladder of Life, to explain his
concept of the advancement of living things from inanimate matter to plants, then
animals and finally man. This concept of man as the "crown of creation" still plagues
modern evolutionary biologists (See Gould, S.J., Wonderful Life, 1989, for a more
detailed discussion).
Post-Aristotlean "scientists" were constrained by the prevailing thought patterns of the
Middle Ages -- the inerrancy of the biblical book of Genesis and the special creation
of the world in a literal six days of the 24-hour variety. Archbishop James Ussher of
Ireland, in the mid 1600's, calculated the age of the earth based on the geneologies
from Adam and Eve listed in the biblical book of Genesis, working backward from the
crucificxion. According to Ussher's calculations, the earth was formed on October 22,
4004 B.C. These calculations were part of Ussher's History of the World, and the
chronology he developed was taken as factual, even being printed in the front pages of
bibles. Ussher's ideas were readily accepted, in part because they posed no threat to
the social order of the times; comfortable ideas that would not upset the linked
applecarts of church and state.
Geologists had for some time doubted the "truth" of a 5,000 year old earth. Leonardo
da Vinci (painter of the Last Supper, and the Mona Lisa, architect and engineer)
calculated the sedimentation rates in the Po River of Italy, and concluded it took
200,000 years to form some nearby rock deposits. Galileo, convicted heretic for his
contention that the earth was not the center of the Universe, studied fossils (evidence
of past life) and concluded that they were real and not inanimate artifacts. James
Hutton, regarded as the Father of modern Geology, developed (in 1795) the Theory
of Uniformitarianism, the basis of modern geology and paleontology. According to
Hutton's work, certain geological processes operated in the past in much the same
fashion as they do today, with minor exceptions of rates, etc. Thus many geological
structures and processes cannot be explained if the earth is only 5000 years old.
British geologist Charles Lyell refined Hutton's ideas during the 1800s to include slow
change over long periods of time; his book Principles of Geology had profound
effects on Charles Darwin and Alfred Wallace.
The Age of the Earth | Back to Top
Radiometric age assignments based on the rates of decay of radioactive isotopes, not
discovered until the late 19th century, suggest the earth is over 4.5 billion years old.
The Earth is thought older than 4.5 billion years, with the oldest known rocks being
3.96 billion years old. Geologic time divides into eons, eroas, and smaller units. An
overview of geologic time may be obtained