Geology Reference
In-Depth Information
began. What they have documented through observations and experiments, and with
the help of the geologic record, is how living organisms transition from one species to
another over long periods of time.
The theory of evolution explains the mechanism of biological change, or
how
this change occurs, not why it happens. The mechanism for biological change in
organisms is what I describe in this chapter.
The Evolution of a Theory
Like all scientific theories, including the theory of plate tectonics described in Chapter
9, the theory of evolution began with ideas that have since been proven wrong or expan-
ded and improved upon. In this section I briefly describe the development of the mod-
ern theory of evolution.
Acquiring traits doesn't do it
When scientists first began to explore ideas about the inheritance of physical character-
istics, or
traits,
some suggested that an organism could change a physical trait during its
lifetime and then pass this modified trait on to its offspring.
A naturalist named Jean-Baptiste Lamarck observed giraffes and proposed the following
scenario to explain their long necks. He suggested that a giraffe that needs to reach
leaves at the top of a tree will stretch its neck. After its neck is stretched, the offspring of
this giraffe will be born with longer necks and, therefore, the ability to reach leaves on
the tallest trees. He called this idea the
inheritance of acquired traits.
Lamarck was cor-
rect in his inference that traits are inherited, but he was incorrect about how the traits
are acquired.
As an example, consider the modern science of laser eye surgery. Perhaps for many gen-
erations, everyone in your family has needed to wear glasses. You decide to correct this
problem once and for all by getting corrective laser eye surgery. You no longer need
glasses, but it is still very likely that your children will need glasses. Your corrective eye
surgery, a trait acquired during your lifetime, does not transfer to your children.
Naturally, selecting for survival
