Geology Reference
In-Depth Information
produce is unlikely. For example, mutations that lead to disease or physical de-
fects may shorten the life of an organism, not providing it a chance to reproduce.
Therefore, the mutation will not be passed on to future generations.
The neutral:
Some mutations are neither good nor bad; they simply occur, having
no direct effect — positive or negative — on the organism's survival. These are
called
neutral mutations.
For example, some domestic cats have six toes, which
neither helps nor hinders their survival.
Speciating right and left
As chromosomes accumulate random and spontaneous mutations, the organism sur-
vives and reproduces according to how beneficial those mutations turn out to be. Over a
long period of time, this accumulation of beneficial mutations may change an organism's
physical characteristics so much that a new species is created. The development of new
species from existing ones through mutation and natural selection is called
speciation.
A
species
is defined in biology as a population of individuals that breed in
nature and produce fertile offspring. This definition rules out animals such as the
liger,
a combination tiger and lion that is bred in captivity but is sterile. Ligers do
not compose a new species.
Two competing explanations exist for how quickly new species develop through the pro-
cess of natural selection:
Punctuated equilibrium:
The
punctuated equilibrium
explanation proposes that
very little change takes place until a sudden surge of changes occur, creating new
species over a relatively short time, such as a few thousand years.
Phyletic gradualism:
Phyletic gradualism
suggests that a gradual accumulation of
minor genetic changes occurs continually through time, slowly creating new spe-
cies.
Modern understanding of evolution is informed by scientists from many different fields.
Together, through testing and experimentation, they build strong support for the theory
of evolution as a mechanism for biological change.
