This textbook discusses evolution, a controversial theory some scientists present as a
scientific explanation for the origin of living things, such as plants, animals and
humans.
No one was present when life first appeared on earth. Therefore, any statement about
life's origins should be considered as theory, not fact.
The word "evolution" may refer to many types of change. Evolution describes
changes that occur within a species. (White moths, for example, may "evolve"
into gray moths.) This process is microevolution, which can be observed and described as
fact. Evolution may also refer to the change of one living thing to another, such as
reptiles into birds. This process, called macroevolution, has never been observed and
should be considered a theory. Evolution also refers to the unproven belief that random,
undirected forces produced a world of living things.
There are many unanswered questions about the origin of life which are not mentioned in
your textbooks, including:
- Why did the major groups of animals suddenly appear in the fossil record (known as the
Cambrian Explosion)?
- Why have no new major groups of living things appeared in the fossil record in a long
time?
- Why do major groups of plants and animals have no transitional forms in the fossil
record?
- How did you and all living things come to possess such a complete and complex set of
"instructions" for building a living body?
Study hard and keep an open mind. Someday you may contribute to the theories of how
living things appeared on earth.
