Biology 105 Evolution and Selection
"Nothing in biology makes sense except in the light of evolution" -- T. Dobzhanski, 1973
Definition of evolution: A gradual process in which something changes into a different and usually more
complex or better form.
) The theory that.
.. species change with time so that descendants differ morphologically and
physiologically from their ancestors (Am. Heritage Dictionary)
A. Some ancient thinkers, such as the Greek Anaximander and the Roman Lucretius, believed that living
things were related to one another and had changed over time. They developed evolutionary ideas based
on their observations and inspiration from various sources.
1. Aristotle, for example,
wrote of a ladder of transition from inanimate matter up to the most perfect
beings (Greek men).
2. However, the Greeks did not develop or explain their observations, and their ideas were later
overshadowed by biblical interpretations of nature.
B. Until the 18th century, most Western scientists believed in special creation of life by God, which
included the following ideas:
1. Life is organized into a fixed number of species.
2. Species arose during the Creation and did not change thereafter.
3. Although special creation is not a scientific hypothesis, it does provide testable predictions.
a. All species and the Earth itself are the same age, which was considered to be less than 10,000
b. The species composition of the Earth has not changed over time.
C. By the late 1700's, is began to be clear that these predictions were not correct.
The Earth was found
to be much older than 10,000 years, and organisms were found that had lived in the past but were now
1. The theory of gradualism was proposed, which stated that geological processes in the past operated
the same way they do today.
a. Geologists showed that if processes such as erosion, mountain building, cave formation, etc.
occurred in the past at the rate they do now, the Earth must be billions of years old.
2. Biologists realized that fossils are the remnants of ancient organisms, and that in general, the farther
down a fossil was found, the older it was, so that the order of fossils in the rock reflected when they existed
3. Most scientists in the 1800’s began to accept that there had been changes in the diversity of life on
earth, or evolution; however they could not organize the known facts nor explain the changes in diversity.
4. Jean Baptiste Lamarck offered an early explanation of evolution: inheritance of acquired
characteristics. He proposed that organisms change as they get adaptations that they need through
interaction with the environment, and that their offspring inherit these changes.
a. For example, Lamarck hypothesized that giraffes stretched their necks to reach higher leaves, and